++
A bite is inflicted by mouthparts, however a sting is inflicted by a posterior, tapered, needle-like structure intentionally designed to inject venom. Ants, bees, wasps, and scorpions have stingers while spiders inject their venom through oral fangs. Ants are unique in that they may inflict damage via either a venomous sting or through a noxious bite. Bite wounds remain a significant problem worldwide and over 90% of these wounds are bites from dogs, cats or other humans. An estimate of the incidence of all bites wounds sustained is very difficult to establish since many victims of minor bites do not seek medical care. Fortunately most bite wounds require very little specialized care, can be managed with soap and water, and do not need antimicrobial coverage; however, the very young, elderly, diabetics and those who are chronically immunecompromised are at higher risk of infection. Hand and face bites, however, do pose particular challenges with respect to diagnosing the extent of injury, the risk of infection and loss of function or disfigurement.
++
Bites inflicted from other humans span the spectrum from pleasure to abuse. Human bites that occur in association with intoxication or assault/abuse typically present in a delayed fashion which may complicate their care. Sexual assault, domestic or child abuse must be considered when reviewing a human bite; however, other etiologies such as sporting activities or self-inflicted biting are also in the differential. Although there is a male predominance in bites to the clenched fist, other wounds do not show a gender discrepancy. Bites to the upper extremity are the most common human inflicted bite, and are associated with both the greatest loss of function as well as the highest risk of infection, particularly bites to the hand.
++
Victims of animal bites tend to be predominantly children and adolescents, with a large male predominance. When children are victims of animal bites, it tends to more frequently occur on the face, whereas extremities are more likely injured in adults. Most cases of animal bites, especially dog and cat bites involve an animal known to the victim which is helpful in assessing for potential rabies exposure. There remains a demographic discrepancy with respect to victims of dog versus cat bites. Dog bites victims are more likely male, whereas females are more likely to be victims of cat bites. Approximately two-thirds of dog bite victims are children or adolescents, whereas the majority of cat bite victims are adults or elderly individuals.
++
Estimates of the incidence of animal bites vary considerably, it has been reported that as many as 4.5 million dog bites occur annually65 and approximately 500,000 cat bites66 occurring in the United States. The severity of the injury is often related to size of the dog, with the jaws of larger dogs being capable of generating up to 300 lb of pressure. These high pressures can result in considerable crush injuries with soft tissue avulsions, fractures, and devitalized tissue. Dog bites have markedly lower rates of infection when compared with bites from cats or humans; however, all dog bites require copious irrigation. Facial dog bites may be loosely approximated and carefully observed after irrigation, whereas it is generally recommended to treat dog bites in other anatomic locations with either delayed primary closure or closure by secondary intention. When an infection does occur, expeditious treatment with excision of necrotic tissue and irrigation is indicated. In extreme cases, excision of infected bone or amputation of digits may be necessary and any reconstructive interventions should be delayed until the infection has resolved.
++
Bites from cats do not carry as much force as seen in dog bites and thus are not associated with the same degree of crush and tissue injury. Due to their sharp and narrow teeth, cat bites tend to present as small but deep puncture wounds that often penetrate a joint capsule or disturb the periosteum of the underlying bone. Cat bites are more likely to present in a delayed fashion and tend to have a higher rate of becoming infected, although the exact incidence of infected cat bites is not known due to underreporting. In one paper it was suggested that up to 30% of cat bites will require hospital admission; however, this rate is likely overinflated since the true denominator of those sustaining cat bites and not seeking treatment remains unknown. Other literature has estimated that the true rate of patients requiring admission following cat bit is around 6%.
++
The optimal closure of bite wounds remains controversial, with equal bodies of literature advocating for primary closure versus healing by secondary intention.67,68 Concerning among this literature is the heavy emphasis on cosmetic outcomes but it is clear that not all bite wounds are the same with respect to functional detriment, infectious risk and/or patient satisfaction. It is widely accepted that all bite wounds need thorough washout and debridement of devitalized or necrotic tissue in order to minimize complications and maximize good outcomes. Obviously, primary closure is ill advised if the wound is infected or inadequately debrided. Much of the data on management of facial wounds is focused on cosmetic outcomes, as the physical wounds to the face may carry an associated long term psychological burden, accordingly a preponderance of these studies advocate for primary closure. The evidence pertaining to hand wounds notes the very high rates of infection with devastating consequences including amputation of digits, especially with cat,69 snake, and certain insect bites thus these wounds should not be closed in primary fashion.
++
Irrespective of the etiology, bites to the hand may have profound immediate and long lasting effects given the central role the hand plays in many daily work and life activities. Injuries to the hand may have dramatic socioeconomic consequences for both the victim and their family since these wounds tend to be underappreciated, carry relatively high rates of infection, and can have devastating consequence when management is delayed. “Fight bites” are bite wounds that occur during a fight and are due to either the impact of the closed and clenched fist with teeth during a fight, or from deliberate occlusive bite injuries to the hand or fingers. These injuries especially bite wounds to the clenched fist, have extremely high rates of becoming infected and the majority of these injuries occur in male patients and involve the dominant hand occurring at the metacarpophalangeal joints. Occlusive bites occurring in women should give rise to concern for the possibility of domestic or sexual abuse. Occlusive bites in children are often related to other children but may also be associated with abuse. Features such as the intercanine distance noted on the bite can assist in distinguishing between bites delivered by adults or children. Given the relatively minor degree of soft tissue coverage of the extensor portion of the hand, penetration into the underlying extensor tendon mechanism, a joint capsule, or into the deep connective tissue is noted to occur in 75% of “fight bites” to the hand.70 This critical finding may often be overlooked by health care personnel so providers should be alert for joint violation.
++
In hand bites of any etiology it is critical to perform a complete assessment of extension and flexion of the hand and fingers since the acute presentation of the wound may have minimal findings. Further when the hand is examined in the relaxed unclenched position the extensor tendon retracts and/or the capsular tear is covered over hiding the injured portion from direct view. Recreating the clenched fist to adequately examine the wound and potential underlying tissue injury is often limited due to the pain from the acute injury but it is indicated since a missed injury creates a closed environment encouraging bacterial growth and complications. Infection may subsequently spread and progress along the subaponeurotic region with development of palmar or flexor tendon sheath infection. Occlusive bites, due to animals or humans, especially to the fingers tend to penetrate both the dorsal and volar surfaces with high rates of tendon and capsule involvement.
++
There is no clear or accepted management whether all human hand bites should be managed in the operating room versus careful exploration and washout in the emergency department; however, it is clear that all human bites to the hand require irrigation. Some authors contend that all human inflicted hand wound skin defects should be extended to facilitate adequate exploration and some have even advocated for performing an arthrotomy to achieve adequate exploration, washout, and repair but there is no consensus regarding these practices.71,72 Empiric wound cultures should not be taken upon initial presentation of a noninfected hand bite, since such cultures neither predict whether the wound will become infected nor do they predict the organism, should the wound become infected. In cases where the hand bite is associated with an underlying fracture the wound should be considered an open fracture and treated as such with operative washout and administration of antimicrobial agents. Complications can be minimized if the exploration and washout is early since delayed exploration or inadequate debridement is associated with poor outcomes. Delayed presentation beyond 8 days from the bite is associated with an 18% rate of amputation73 and the rate of amputation is highest in the most distal wounds, including fingers, with lower risk in more proximal wounds.
+++
Infections Following Bites to the Hand
++
In general, prophylactic antibiotics for bite wounds do not reduce the rate of subsequent infection74 but the exception to this are bite wounds to the hand.75 While large randomized controlled studies are lacking, multiple reviews have advocated for routine prophylactic antimicrobial coverage in cases of bite wounds to the hand.67,74,76 Antimicrobial prophylaxis for bite wounds to the hand were shown to reduce infection rates from 28% to 2%.74 Broad spectrum antimicrobial agents, especially with the addition of a β-lactamase inhibitor, are recommended to address the polymicrobial nature of mouth flora. Amoxicillin-clavulanate is an excellent oral agent for human or animal coverage since it is effective against most of the bacteria found in the oral cavity including anaerobes. Wounds may be closed primarily following washout and debridement but it should be noted that leaving a wound open does not supplant the need for antimicrobial prophylaxis.
+++
Infections in Human Bites
++
Human bites are a challenging problem, especially given the variety and numbers or organisms found in the oral cavity, on the plaque on teeth and in human saliva which may contain up to 1011 bacteria per milliliter. When infections do occur, they tend to be polymicrobial and common infecting organisms include Streptococcus viridans, Staphylococcus spp, Eikenella corrodens, Bacteroides spp, and microaerophilic streptococci. Staphylococcus aureus accounts for 30% of infections from human bites to the hand, and is noted to cause some of the most difficult to treat infections. A combination of staphylococcal and Streptococcal organisms are commonly found in “fight bites” and although viral transmission is theoretically possible, the incidence of HIV or hepatitis transmission from a human bites is rare.77,78 If the saliva is significantly bloody then the risk of HIV transmission increases and postexposure antiviral prophylaxis is recommended.77 Rates of transmission of hepatitis B virus are higher, and administration of the accelerated course of HBV vaccine is recommended79 but there is little data about the rate of hepatitis C transmission.
+++
Infections in Dog and Cat Bites
++
Cat bites to the hand are 10 times more likely than dog bites to become infected but fortunately the rate of dog hand bites that become infected is only 1%. Surprisingly, the timing of infection following the bite is short with nearly 50% of cat bite infections occurring within the first 24 hours following the bite. The high incidence of Pasteurella organisms when infections occur related to cat and dog related bites makes these bites particularly difficult to treat. Pasteurealla is a gram-negative facultative anaerobic, nonspore forming coccobacillus that resides in the normal oral flora of cats and dogs and is notable for the profound inflammatory response it elicits. Pasteurella strains predominate in cat bites as noted by rates approaching 80% of infected cat bites80 while Pasteurella canis is often specifically related to dogs. Pasteurella multocida infections of the hand, commonly found after cat bites, have been reported to lead to sepsis and disseminated infections such as pneumonia.
++
Rarer organisms, such as Capnocytophaga canimorsus, present mainly in cat but also in dog oral flora, are particularly problematic in immunecompromised patients such as the elderly or those with diabetes. Infections with Capnocytophaga have high rates of progression to sepsis and may lead to disseminated intravascular coagulopathy, multiorgan failure and death.81 Since Capnocytophaga has such a long incubation period from the time of bite to time of the infection, the inciting bite can be over looked.
++
Although relatively rare in the United States, rabies remains a significant problem worldwide, with the most common etiology due to dog bites. Approximately 40% of individuals affected are children and given that most cases occur in underdeveloped parts of the world, many go unreported so it is estimated that actual cases and deaths maybe 10-fold higher. Stray dogs are the most common vector of human rabies infections but other mammals such as bats or skunks maybe also harbor the virus. In either case, in regions with high rates of stray dogs or bites from wild animals, rabies must be assumed and postexposure prophylaxis should be administered. Rabies is a viral disease caused by 12 strains of lyssaviruses, which belong to the Rhabdoviridae family, which induces a rapidly progressive encephalitis that is often fatal if not treated.
++
Rabies replication occurs rather slowly leading to prolonged incubation periods, with reports ranging from 7 days up to 7 years. The virus undergoes replication in an infected muscle or nerve, a process that is so slow it allows for immune system evasion. The virus then travels along the peripheral nerve, often replicating in the motor neuron, ultimately reaching the brain. Since the central nervous system (CNS) is a privileged immunologic site, rabies can continue to evade immunological detection and attack. Once in the CNS, the rabies virus undergoes rapid replication and eventually travels back outward via the peripheral nerves to the salivary glands. In the salivary gland, the virus promotes saliva production leading to the characteristic picture of the rabid dog or person “foaming at the mouth.” Salivary production is believed to be an evolutionary adaptation to facilitate transmission to the next host enhancing viral propagation. There is no component of hematogenous spread of the virus. It is at the point of salivary infection and foaming, that the patient also exhibits extreme hydrophobia marked by fear of liquids, pain, and difficulty with swallowing and extreme thirst. Transmission of the virus is predicated upon large volumes of infected saliva ready to be transmitted with the next bite, thus the induction of pain from spasms of the laryngeal musculature induced by the virus prevents viral load reduction from the host swallowing the viral-laden saliva.
++
The early symptoms of rabies infection are subtle and vague, manifesting as mild fatigue or minor behavioral changes. At approximately 7 days from the initial bite, overt symptoms develop such as painful and excessive muscle movements or muscle flaccidity and somnolence and it is at this stage that dysautonomia develops. The neurological deterioration continues until the patient lapses into coma and progressive motor paralysis with death ensuing within 3 days of the onset of these overt symptoms in most individuals. Rabies infection in humans is uniformly fatal thus post-bite prophylaxis for rabies is critical.
++
The main stay of therapy for a potential rabies associated bite is to maintain a high index of suspicion and to administer postexposure rabies prophylaxis. Given the very slow replicating nature of the virus, many victims, even in confirmed rabies associated bites, have low or undetectable viral levels and a diminished or absent immune response. The first rabies vaccine was created by Louis Pasteur in 1885 from the infected spinal cord of rabbits. Considerable advances have increased the effectiveness of rabies vaccine as well as reducing significant side effects. Although rabies prophylaxis is costly, it is a testament to the work undertaken in this field that there has been no recorded failure of the cell-based postexposure prophylaxis (PEP) for rabies since 1970 if promptly administered (Table 47-5).82,83
++
++
Rabies infections induces aberrant behavior in animals thus a bite form a normally timid or reclusive animal should prompt a high index of suspicion for rabies exposure and PEP is warranted. Wound care should consist of immediate and extensive cleaning of the wound followed by the administration of multiple doses of rabies vaccine to establish active immunization as well as the administration around the wound and intramuscularly of human rabies immune globulin to establish passive immunization. Fortunately the very slow nature of the virus’ replication allows for postexposure prophylaxis with a vaccine in order to establish immunecompetence against the virus. Rabies vaccination is atypical and unlike many other vaccines which need to be given prior to viral exposure for them to actually prevent viral infection since it is effective well after viral inoculation but once overt symptoms develop, the infection has progressed to the later neurological stages and PEP has little benefit in these patients. There are a few rare case reports of patients who presented late after extensive neurological symptoms who have survived despite not receiving rabies directed PEP. Overt rabies infection is treated via an experimental therapy, called the Milwaukee Protocol,84 which involves critical care support, induction of a coma to minimize central nervous system excitatory function and the administration of antivirals85 including ribavirin but this therapy is somewhat controversial.82,86
++
Approximately 15% of all bite wounds occur to the face and the majority of these are dog bites. Approximately 44,000 children sustain dog inflicted face bites per year in the United States, some of whom will require hospitalization and many will be left with life-long scars. The predominant anatomic areas injured in the face are the lip, nose, and cheeks which differ from human inflicted facial bites that primarily affect the ear or lower lip. The larger the animal or dog, or the smaller the victim, particularly young children, the greater the likelihood that a life threatening injury will occur from bleeding, airway collapse or associated intracranial hemorrhage.
++
Despite the presence of huge numbers of bacteria in the oral cavity, bites to the face have a very low rate of developing a subsequent infection largely due to the excellent blood supply to the face as well as the fact that most patients with facial bite wounds will present early following an attack, unlike other anatomic regions. Dog wounds that present early usually contain low bacterial loads, and can be usually minimized with thorough washout of the wound. Of the multitude of washout techniques available, sustained high-pressure irrigation should never be undertaken because such pressure is likely to further injury delicate underlying soft tissue exacerbating the tissue injury. Bacterial culture of the wound is not indicated but antibiotic prophylaxis is. Akin to cat bites to the hand, facial cat bites increase the risk of a subsequent infection when compared to dog bites since the deep slender penetration of feline bites typically involves deeper structures and may extend down to bone. Delay in seeking medical attention, and/or delay in initiating care for wounds such as washing out the wound allows for low bacterial contamination of the wound to grow. Underlying ischemic or crushed tissue, often seen with larger animal attacks, establishes an environment conducive to bacterial growth thus debridement of devitalized tissues is an important therapeutic intervention. Bites to the nose or ear with associated cartilage exposure, especially if induced by human bites, have the highest risk of developing an infection due to the relatively avascular nature of cartilage. As with animal hand bite wounds, early onset of infection in a facial bite usually indicates P. multocida infection, thus antibiotic prophylaxis should be active against this organism.
++
Surgical debridement is indicated for ischemic or devitalized tissue however this may be impractical for bites involving the face, especially the vermillion border of the lips, the eyebrows and eyelids or the nasolabial folds. Another area of concern is the buccal fat pad which is relatively avascular and if involved in a bite wound it is highly susceptible to infection thus cheek bite wounds should be thoroughly cleansed, explored, and gently debrided. In children, these activities are best carried out in the operating room. Given the very low rate of infections, as well as cosmetically detrimental effect of facial scars, primary wound closure is indicated. Exceptions to this are for wounds that are infected or present in a delayed fashion. Following washout and debridement, primary closure of the skin with a fine monofilament suture should be accomplished but deep subcutaneous sutures should be avoided since these may serve as a nidus for infection. Avulsion injuries rarely respond to attempted reattachment so delayed grafting or reconstructive flaps may be required in these situations.
++
The care of facial bite wounds that present in a delayed fashion is controversial with authors supporting both primary closure versus other delayed options. Although the preponderance of the literature advocates for primary closure of delayed bite wounds if the wound is not infected, acknowledgment is made of the increased risk of developing an infection with this approach. Most authors cite the worse cosmetic appearance of delaying primary closure for up to 4–5 days thus most argue for prompt primary repair. Caution must be exercised and very close follow-up arranged given the often devastating nature of facial infections, particularly in children. Unlike adults, children are at increased risk for associated nonsoft tissue injuries.87 Injuries to the periorbital, nasal, and cheek region in young children have increased risk of having an associated underlying facial bone fractures and these need to be treated as any other open fractures with washout, debridement, and prophylactic antibiotics. Penetration of the globe or damage to the lacrimal system must be considered in cases of periorbital wounds and eyelid lacerations. Facial nerve injury is relatively infrequent in young children, but may be very difficult to assess in an uncooperative child, especially if the wound is large and swelling has begun.
++
There are approximately 120 known snake species which are indigenous in the United States but only 40 of these species are believed to be venomous to humans, all of which belong to the Viperidae and Elapidae families. The Elapidae family displays a considerable range with respect to size and includes the king cobra, the world’s longest venomous snake measuring up to 18 ft in length. Elapids possess a pair of fangs through which they can inject their venom, a potent neurotoxin that induces paralysis making Elapid bites potentially lethal. The venom of the Viperidae, commonly known as vipers, often induces tissue necrosis as the venom possess over 50 active components, including considerable amounts of metalloproteinases,88 phospholipases and inflammatory mediators. An envenomation may induce considerable pain, swelling and tissue necrosis as well as disruption of the clotting cascade. The cause of death from viper envenomation is commonly from cardiovascular collapse. Despite this general distinction, there appears to be a degree of cross over wherein some viperids may produce neurotoxic effects and some envenomation from elapids may induce tissue necrosis. The degree of tissue destruction and severity of clinical consequences induced by a viperid bite may vary considerable, and is dependent on numerous factors including duration from bite to treatment, subfamily and species of viperid snake, dose of venom in the wound, anatomic location of the wound, as well as the victims immunologic response to either the venom or the antivenin. Greater consideration for possible extensive tissue necrosis must be given when the victim of the snake bite is a child, given the smaller volume of distribution in children for the same volume of injected venom (Table 47-6).
++
++
The Crotalinae are a subfamily of the Viperidae and the Copperhead (Agkistrodon contortrix), a member of the Crotalinae subfamily, account for over 40% of the reported snakebites occurring in the United States annually.89 The three most frequently encountered genera of Crotalidae for which medical assistance is sought are Crotalus, Sistrurus (rattlesnakes) and Agkistrodon (copperheads and water moccasins). Although copperheads are reported to have the lowest potency for their venom, it is important not to dismiss the potential for serious tissue damage resulting from a bite. Characteristic features of these snakes include a broad triangular head with a thick body and facial pits. Rattlesnakes possess the characteristic rattles, often heard before an attack, and, if heard may aid in distinguishing a rattlesnake attack. The other commonly encountered snake attack for which medical care is sought is from coral snakes. Coral snakes are members of the Elapidae family and these snakes are relatively small and are known for their bright distinctive coloration forming rings around the body of the snake. The venomous coral snakes may be distinguished from a similarly appearing benign snake by the sequence of the coloration. If a red band is adjacent to a yellow band, then this is a venomous snake, whereas if the red band touches a black band, then the snake is lacking venom. This has led to the oft-stated idiom of “Red on yellow, kill a fellow, red on black, venom lack.” However, this association of coloration and presence of venom only applies to coral snakes found in North America, as venomous coral snakes from other parts of the world have other characteristic color patterns. Coral snakes have short fangs which may have difficulty penetrating thick clothing and bites from these snakes are relatively rare due to their rather reclusive, burrowing and nonaggressive nature. Despite their timid behavior and limited fangs, coral snakes possess some of the most potent venom among snakes in North America thus they should not be taken lightly or else significant morbidity and mortality may ensue (Fig. 47-1).
++
++
All patient snake bite assessments begin with consideration of whether an envenomation has occurred. Examining for the presence of fang marks is very helpful, as the lack of fang marks effectively rules out a possible envenomation but even if fang marks are identified, envenomation will have occurred in only 25% of bite victims. Even when envenomation occurs it has been estimated that about half of victims have only very mild reactions. Symptoms of viperidae envenomation include pain, especially with movement, swelling, erythema, and nausea. Moderate to severe envenomation is associated with tissue destruction from the enzymes present in the venom, vomiting, and bleeding with resultant tachycardia. Tissue destruction is related to MMPs, phospholipases and the inflammatory mediators inducing vascular endothelial damage as well as activation of platelets and complement. The MMPs in snake venom have been shown to be diverse and have a variety of adverse effects upon the coagulation/fibrinolytic pathways in humans88 and may progress to a severe consumptive coagulopathy.90 The degree of local destruction is considered a marker of the degree and nature of the envenomation. Symptoms of elapidae envenomation rarely occur immediately but as the neurotoxins circulate the effects manifest as tingling and numbness in the extremities, dysarthria, lethargy and shallow respirations. Patients with suspected elapidae envenomation and who present with neurological symptoms should be transported to a center of care capable of offering critical care, since these neurotoxic effects may be progressive to respiratory failure and the need for intubation and mechanical ventilation. Given the fact that the effects of envenomation, whether neurotoxic or tissue destructive, have relatively fast onset of actions, it is reasonable to assume that a lack of symptoms upon arrival at a care center is highly associated with a lack of envenomation, and thus practitioners may withhold antivenin treatment or other advanced treatment options, and follow with close clinical examination. Despite the common occurrence of snakebites, severe injuries including fulminant respiratory failure and/or sever tissue necrosis are relatively rare and most can be managed with non-ICU and nonoperative therapy.
++
The initial response to a snake bite, whether prehospital or following arrival to a definitive care center, should be focused on minimizing further harm from “therapeutic maneuvers.” A spectrum of commonly employed measures undertaken at the scene may worsen the clinical situation thus field management of snake bites now focuses on rapid and expedient transport to a medical facility rather than attempting care in the field.91,92 The most common “helpful” field maneuvers include incision of the potential bite area and attempted sucking the venom from the wound, electrical shock or stun gun therapy, immersion of the affected limb into ice, or the application of a tourniquet. Incision and attempted aspiration of possible venom is fraught with potential harm, as this is likely occurring prehospital outdoors with nonsterile hunting equipment by an individual with very limited knowledge of anatomy. Given the fact that 25% of snake bites will result in little or no envenomation, the risk of creating a potentially serious soft tissue infection far outweighs any potential theoretical benefit. Commercially available suction devices for potential extraction of the venom through the puncture wound have also proven to be ineffective and may contribute to delays in definitive care. Electric shock therapy administered from a stun gun, largely advocated by investigators from Ecuador has also been proven to be ineffective as both clinical data and animal studies have demonstrated no benefit of electric shock therapy in snakebite wounds. Placing the affected limb into ice was considered a potential therapeutic option based on decreasing the temperature and diminishing the activity of the enzymes contained within the venom but not only has this been shown to be ineffective, it has also led to considerable numbers of snake bite victims having the whole extremity immersed in ice with significant ice-related tissue loss and destruction with no evidence of actual envenomation. Tourniquet application has been advocated and employed by many first responders but the application of an arterial tourniquet for greater than 2 hours may result in severe ischemic damage to the extremity with potential limb loss from the tourniquet. Venous tourniquets, loosely applied, have the potential theoretical benefit of impairing venom outflow while allowing arterial inflow to perfuse the extremity however these are often difficult to correctly apply in the field due to lack of knowledge or experience. The proper application of a tourniquet in this situation is loose enough to allow the passage of one to two fingers while also being tight enough to impede venous return but it should be noted that animal models showing a theoretical benefit have not been proven in clinical studies. Furthermore, it is postulated that containing the venom in a restricted region may increase the potential for local tissue destruction therefore the application of a tourniquet is best avoided in all cases of snake bites. Pressure immobilization (PI), originally described in 1979 for neurotoxic envenomation in Australia, remains controversial.93 PI it has failed to show a benefit in other regions of the world including in the United States calling into question the Australian experience. PI involves wrapping a moderate pressure dressing around the entire affected extremity to generate a pressure of approximately 40–70 mm Hg in the upper extremity and a pressure of 55–70 mm Hg in the lower extremity, and then immobilizing the extremity. In Australia where travel to definitive care is over vast areas, and the rate of neurotoxin envenomation is considerably higher, this may theoretically work, it has been discouraged in the United States where the predominance of true envenomation is tissue destructive rather than neurotoxic. Furthermore, application of the PI to ensure the correct pressure is exceedingly difficult to achieve. When incorrectly applied with elevated pressures, the PI becomes effectively an arterial tourniquet thus the use of a PI is greatly discouraged.
++
Although a substantive body of evidence-based literature remains lacking for the management of snakebites, several well detailed guidelines have emerged regarding issues such as use of antivenin and the role of surgical debridement.94,95 Once the patient arrives at the site of definitive care, care should commence with supportive measures such as gaining IV access, fluid resuscitation, pain control and a clinical assessment and good documentation of the presence and/or extent of tissue injury which will aid in following for progression of tissue loss. The ubiquitous nature of cell phone cameras and widespread use of electronic medical records and media is helpful in documenting and following tissue destruction. It must be recognized that the majority of snakebites that occur in the United States are nonvenomous, and given the potential for adverse reactions to antivenin, an attempt should be made to identify the snake, preferably by an individual trained in herpetology. Since considerable numbers of snakebite victims are snake handlers, it is not infrequent that the patient will offer the best description and knowledge of the snake. In a 2011 guideline for management of bites from the crotaline subfamily the following indications for antivenin administration were outlined, “swelling that is progressive and associated with signs of tissue necrosis such as bleb formation; abnormalities in coagulation studies including elevated prothrombin time, decreased fibrinogen or platelets; systemic manifestations including distal site bleeding, hypotension, or vomiting.”95
++
It must be stressed that poison control centers should be contacted as they can offer real-time advice based on extensive and ongoing clinical experience.89 Overall the use of antivenin has increased over the past 15 years, but this may change as stocks of antivenin expire and are not being reproduced. Despite increasing awareness of the potential benefit of antivenin, many institutions do not stock, or are unaware of the availability of the appropriate antivenin. A fivefold variation exists between high- and low-use institutions but even when used correctly, many of the existing antivenins are associated with considerable allergic side effects that, on occasion, may induce severe organ failure. Even with milder cases of allergic reactions to antivenin the adverse effects may last up to several months.
++
Considerable limitations have developed over the past 10 years with respect to coral antivenin since its production has ceased in the United States due to the rare incidence of coral snake envenomations. Production of coral antivenin in the United States ceased in 2003 and most stocks of coral antivenin in the United States expired roughly 5 years later. Although licensing and expiration dates have been amended several times, there is no longer any coral snake antivenin available. Originally created in 1954, commercial Crotalinae antivenin has undergone extensive modifications over the years to minimize its side effects. The original antivenin contained whole immunoglobulin G including the Fc fragment which led to severe hypersensitivity reactions including bronchospasm and cardiovascular collapse. Anaphylactic reactions were reported to occur as frequently as 50% of administrations and much higher rates of serum sickness were also noted. This early product was also limited in its ability to work against the rapidly spreading neurotoxin or in controlling the coagulopathic and hemorrhagic components of the envenomation. Modifications in antivenin design allowed for cleavage of the Fc and the Fab segments, isolating the Fab preparations for the final antivenin which minimized its side effects, with serum sickness being reported in about 15% of patients. Although randomized control trials for Fab fragment antivenin are lacking, animal data suggests both significant mortality improvement and salvage of muscle and soft tissue from the bitten extremities in major envenomations.
++
The use of antivenin is discouraged in cases of mild envenomation with few symptoms95 nor should antivenin be administered to individuals with a history of allergic reactions to antivenin or in settings where a severe life-threatening allergic reaction cannot be managed. Administration should be through slow infusion while watching for an allergic reaction and stopping immediately upon detecting any hypersensitivity. Antivenin treatment, although ideally administered pre-injury, remains effective if given up to 6 hours following the envenomation but there have been anecdotal reports of effective antivenin therapy when administered later. In life-threatening envenomation antivenin has been administered up to 24 hours following the bite with variable benefit. The dose of antivenin administered remains empiric and is based on a clinical judgment of the amount of venom delivered from the bite thus adults and children are dosed based upon the amount of venom from the bite and is not patient-weight based. Multiple administrations may be necessary, with 10 vials or more potentially required for patients with large exposures and severe envenomation. In patients with progressive clinical manifestations repeat doses may be required.
++
Ongoing supportive care should encompass fluid resuscitation, pain control, administration of tetanus prophylaxis and correction of coagulopathy. Although the mouth of a snake is colonized with bacteria like all animals, infection following a snake bite is rare. In a placebo controlled trial, there was no difference in infectious outcomes with routine administration of an antimicrobial agents following snakebites96 thus routine prophylactic antimicrobial agents are not indicated. Secondary bacterial infections are much more likely to occur in patients who had their wound manipulated in the field in an attempt to “extract” the venom. Coagulopathy is a more frequent complication of envenomation and should be corrected based on laboratory values of clotting times and blood products levels as well in response to evidence of bleeding. Given the potential degree of physiological derangement associated with progressive and severe envenomation, consideration of early transfer to a definitive care center should always be considered when dealing with any envenomation.
++
The surgical management of envenomation has changed over the past 20 years as excising the region of the bite attempting to remove the venom laden fangs combined with empiric fasciotomy has fallen out of favor. Now, surgical intervention is indicated is limited to debridement of necrotic or devitalized tissue and wound care. The rationale for early aggressive operative intervention lay in the postulation that the tissue destruction was a local effect amenable to locally excising the infused venom with the surrounding necrotic muscle and decompressing the adjacent healthy tissues pending resolution of the inflammation. However, it has been clearly demonstrated that empiric operative intervention or empiric fasciotomy is not indicated for all envenomations and that muscle necrosis is more likely the result of the ongoing venom rather than the presence of compartment syndrome. Although the risk of compartment syndrome is unusual it still occurs. There is a wide range in the literature on the rate of rattlesnake envenomation progressing to requiring fasciotomy and decompression, ranging from 0% to 15%94,97 but it is estimated that the incidence of true compartment syndrome needing fasciotomy rather than just “prophylactic fasciotomy” is considerably lower at approximately 1–2%. Compartment syndrome is more likely to occur in the anterior leg, fingers or in the hand, and is usually associated with deeper bites. The concern for a possible compartment syndrome must be at the forefront of clinical thought to avoid a potential delay since delayed recognition leads to disastrous complications. The diagnosis of compartment syndrome may be difficult given the overlap in clinical findings such as pain with passive motion, pain out of proportion to findings, swelling and firmness to exam, between severe local tissue inflammation and true compartment syndrome. Thus it is highly recommended to base the decision to intervene surgically on objective measures of the compartment pressures rather than exclusively on physical examination.94 With fasciotomy, acute debridement is to be discouraged, as injured muscle may improve with the concomitant administration of antivenin and supportive care. Despite the infrequency of progression to fulminant tissue necrosis and/or compartment syndrome, snake bites should still be considered a potential surgical disease and early surgical consultation is critical given the consequences of missing progression to compartment syndrome (Fig. 47-2).98
++
++
All spiders are noted to have a venomous component to their bite which is essential for neutralizing and killing their prey but due to the small biting mechanism and the low toxicity of the venom to humans, most human spider bites are rather harmless. Indeed the incidence of “spider bites” is exaggerated and overreported, since many wounds reported as spider bites are indeed due to other ticks, bites or infected minor traumatic lesions. Most true spider bites require only local wound care, mild analgesics and a tetanus booster but the two most concerning spider bites with respect to the potential for tissue necrosis or loss of life are the brown recluse (Loxosceles reclusa) and the black widow (Lactrodectus macrotans).
++
In the United States, the brown recluse is responsible for the majority of spider bites that present with a necrotic component to the wound.99 A similar spider which produces a necrotic component to the wound is the Chilean brown spider but to date no reported injuries have occurred in the United States due to this organism. The brown recluse measures approximately 10 mm long and is dull, dark yellow to dirty brown in coloration with a dark brown pattern noted on its dorsum. It is a nocturnal spider which seeks hot dry spaces and it hibernates during fall and winter thus most reported brown recluse bites occur indoors, which is in sharp distinction to the black widow wherein most bites occur outdoors. The venom produced by the brown recluse is comprised of proteases, lipases, and hyaluronidase activity among others and there is no antivenin available to date in the United States. The primary toxin in the venom is sphingomyelinase-D, which is noted to affect the endothelium, erythrocytes, and platelets, causing endothelial swelling and injury leading to capillary plugging causing tissue necrosis. Initial symptoms of a brown recluse bite are often very mild with minimal pain; however, as the local tissue ischemia progresses, symptoms worsen and a very painful necrotic wound may develop in up to 40% of cases. Rarely the skin necrosis may progress to a degree requiring skin grafting. Aggressive initial surgical management in an attempt to “cut out the wound” or limit potential necrosis spread is contraindicated and it is best to wait for the wound to demarcate before excising in order to minimize wound size and tissue loss.
++
Bites from black widow spiders (L. macrotans) usually manifest as an extensive systemic toxic reaction rather than local tissue destruction. Most serious bites are inflicted by the female, who typically display the characteristic shiny black body with a red hourglass on the underside of the abdomen. Symptoms of a black widow bite usually occur rapidly, within 1 hour, of the bite and are due to α-latrotoxin which induces a large presynaptic release of acetylcholine. This release leads to muscle pain and rigidity, altered mental status and seizures. Although the pain is often intense it typically resolves within 72 hours and the treatment is mainly supportive; however, an antivenin is available and dantrolene has been used in cases of severe muscle rigidity. Serious cases are defined by severe and prolonged pain associated with systemic manifestations such as hypertension (systolic blood pressure >140 mm Hg or diastolic blood pressure >90 mm Hg) or tachycardia greater than 100 beats per minute.100 The reported mortality from black widow bites is low, usually less than 5%.
++
The seas and oceans contain several potential stinging or biting hazards to humans. These include jellyfish, sea snakes, and stingrays. Marine envenomations may induce a spectrum of manifestations including allergic reactions, neurotoxic effects such as paralysis and cardiac depression due to cardiotoxins. Stingrays are flat cartilaginous fish with a long tapered tail that has bilateral serrated edges. This tail is noted to contain multiple barbs containing venom and this venom is noted to be cardiotoxic. It also contains proteolytic and hyaluronidase activities which may contribute to tissue necrosis and skin loss around the site of the sting. The flat shaped nature of the stingray body allows it to easily bury under a shallow layer of sand, and thus remain unexposed and difficult to visualize leading to stings; however, gentle agitation of the sand will disturb the stingrays prompting them to move away as stingrays are not aggressive by nature. Most stingrays possess one or more barbed stingers located on the tail that are loaded with venom and are used by the stingray as a defense mechanism thus these animals should be left alone in order to minimize the likelihood of a sting. Most stings usually occur from accidentally stepping on a stingray and while most stingray stings are not fatal, they do induce considerable pain from both the site of the sting as well as from venom induced muscle cramps.
++
Imaging is undertaken to assess for possible remaining fragments of the barb, and wound exploration should be strongly considered as the barb from the tail may break off and remain lodged in the stung extremity. Stingray wounds should be left open to heal by secondary intention and surgical debridement may be indicated in cases of significant necrosis. Prophylactic antimicrobial agents are administered given the relatively high rate of infection, especially if there is a multitude of lacerations from the sting. Tetanus prophylaxis should be updates, but currently there is no available stingray antivenin.
++
There are two families of venomous spiny fish, the Scorpaenidae include stonefish and lionfish, and the Trachinidae contains the weeverfish. Lionfish are often kept as part of home aquariums which increases the incidence of stings due to this tropical fish and stings from lionfish are the most common marine related sting called to poison centers in the United States. Most patients experience moderate to severe pain at the sting site and stings from lionfish may induce significant skin necrosis. Stonefish toxins may induce local tissue necrosis, severe muscle contracture, neurotoxicity and may even induce cardiotoxicity with severe cardiac depression and death. The weeverfish inhabits the waters of Europe and the Mediterranean and can inflict a painful sting typically to the foot or ankle due to humans stepping on them at low tide. These stings require local wound care only and there are no confirmed fatalities due to this fish.
++
The Jellyfish (Cnidaria) comprise four different classes including Cubozoa (box jellyfish) Scyphozoa (true jellyfish), Anthozoa (anemone) and Hydrozoa (Portuguese man-o-war). All species of Cnidaria have hollow sharp pointed coiled thread tubes surrounded by venom called cnidae. Most jellyfish stings induce an acute dermatitis and are self-limiting; however, box jellyfish, residing mainly off the coast of Australia, are the most deadly of jellyfish and some have contended that box jellyfish may be the world’s most venomous creature. Most reported cases of box jellyfish stings involve painful lesions which may progress to skin necrosis within 12–18 hours. Although the exact mechanism of action of the venom is largely unknown in humans it is postulated that the venom causes cellular pore-formation leading to massive and swift sodium and calcium fluxes into cells with rapid cellular compromise. This venom leads to rapid hypotension, cardiovascular collapse and death which has been reported to occur in as little as 60 seconds after the sting.
++
Fire ants, both red (Solenopsis invicta) and black (Solenopsis richteri) were originally imported into the southern United States in the 1920s but these insects continue to march forward and colonization has extended across vast areas of the United States. Approximately 5% of victims of fire ant bites will require medical attention and of those, approximately a fifth will have systemic allergic reactions.101 The fire ant is capable of multiple stings during one attack leading to a characteristic pattern of bites in a circular or a linear pattern of pustules on the victim. The multiple stings in succession give the feeling of “fire” along the site and the majority of the fire ant venom is composed of nonprotein piperidine alkaloids which lead to the characteristic pustules following the stings. Following a fire ant sting, immediate washing of the stung area will help to reduce the venom load. Akin to other stings, the effects can be classified as local, local large, or systemic with about 2% of patients presenting after a fire ant sting with a severe systemic reaction. Patients manifesting systemic symptoms require prompt medical attention since these reactions may progress to full blown anaphylaxis. If a patient develops a severe local reaction to the bite or survives a systemic reaction to the venom then referral to an immunologist for possible immunotherapy to minimize the response to repeat exposure to fire ant venom is warranted.
++
Stings from bees and wasps are relatively common during the warmer months of the year and the vast majority of these remain unreported requiring only local wound care or topical analgesics. Ten percent of individuals who sustain wasp or bee sting develop a large local reaction and approximately 1–3% of individuals who are stung will display a life-threatening allergic reaction. Honey bees differ from wasps in that the stinging mechanism of the bee is strongly barbed and is designed to remain in the flesh, whereas wasp stings are not intended to remain in the victim which facilitates multiple stings. The presence of a retained stinger distinguishes bee and wasp sting aiding in identifying those will benefit from allergic reaction therapies.102 The incidence of anaphylactic reaction and deaths from bee stings is exceedingly rare yet constitutes more deaths per year than from all other venomous animals. The European honeybee was introduced to the United States in the 1600s while the subspecies of honey bee Apis mellifera scutellata was introduced into Brazil from Africa in 1956 in order to improve honey production. Escaped swarms of the Apis mellifera scutellata spread north and hybridized with the already present European honey bee to create the “Africanized Honey Bee.” When compared to the European honey bee, the Africanized honey bee is smaller, more irritable, more likely to swarm and defend their hives more vehemently often inflicting repeated stings if provoked. The venom of the Africanized bees is not substantially more toxic; however, the cumulative dosing from the collective amounts of stings ensuing from the swarming hive contributes to the deadly nature of these bees. The median lethal dose for an average adult is estimated between 500 and 1000 stings. Whereas a sting from a European Honey bee may be from a single bee, an assault involving Africanized honey bees may involve hundreds of individual bees. It is this behavior along with the capacity for multiple bites that has led to the popular term “killer bees” to refer to these insects.
++
Stings from bees can be categorized as minor local, major local or systemic. Local symptoms include pain and erythema but the presence of symptoms distal to the site of the sting, defines a systemic response. These symptoms include nausea, vomiting, bronchospasm, and ultimately may progress to anaphylaxis and cardiovascular collapse. The reported deaths from bee stings are usually related to anaphylaxis and a delay in seeking medical care once the symptoms start. Small children are especially at risk of larger allergic reactions since the venom load is consistent among the bee population and is not based on the weight of the victim. When a bee sting victim presents for medical care, the offending bee should be submitted for examination if possible since the report of the offending insect is frequently incorrect. Immunoprophylaxis is available, but there are several limitations for its use. Any person who has exhibited bee sting anaphylaxis should be equipped with an emergency allergy kit and should be referred for consideration of immunoprophylaxis (Table 47-7).
++