In the U.S., an estimated 2.5 million children are bitten by dogs annually. Bites occur more frequently in males and are more common in the younger ages, with 5–9 years of age being the most highly affected age group. ^, The increased incidence in children has been attributed to their smaller size, lack of awareness, underdeveloped motor skills, and playful manner when interacting with the animals. Bites more frequently occur in the summer months and are most commonly from animals that are familiar to the child. ^{, ,} Half of the annual deaths attributed to dog bites occurred in patients less than 10 years old. Additionally, children less than 10 are three times more likely to be admitted for dog bite injuries than ages 11 and up. This likely can be attributed to the distribution of injuries, with children under 10 years of age more frequently suffering from bites of the head and neck while older children are more frequently bitten on their distal extremities ( Fig. 11.1 ). There have been multiple analyses attempting to define the breeds that are most frequently associated with aggressive behavior, but these studies have been limited due to changing prevalence, incomplete registration and reporting, as well as inaccurate description of breeds. However, larger breeds are associated with more severe presentations and injuries.

This 2-month-old child sustained bilateral complete traumatic amputation to the level of metatarsal shafts after a dog attack. Following negative pressure therapy, skin grafting was performed.

A dog’s bite functions to crush and tear prey, so the most common presenting injuries are lacerations and abrasions with some component of crush injury. Deaths typically occur from bites to the head and neck, involve multiple injuries, and have associated hemorrhage and intracranial trauma. ^, About 60% of presenting cases involve only superficial wounds, with about 40% involving some component of full-thickness wound and 33% with puncture-type wounds ( Fig. 11.2 ). The outcome of greatest concern is wound infection due to the contaminated nature of bites. Predictors of developing an infection include deep/puncture wounds, bites to hands, feet, or joints, delay in presentation greater than 24 hours, female sex, wounds in immunocompromised patients, and wounds requiring debridement. ^, Historically, primary closure of wounds was considered contraindicated due to concern for increased infection rate, though more recent data have failed to show consistent evidence supporting a statistically significant increase in wound infection risk with closure after thorough cleaning of the bite wound. A meta-analysis of randomized controlled trials covering a total of 1071 patients demonstrated no difference in the incidence of wound infection between primary closure and nonclosure or delayed closure (7.0% vs. 7.6% infection rate). Though this study did not specifically analyze the data in terms of use of prophylactic antibiotics, 69.8% of participants were given no antibiotics, with 12% receiving 3 days of amoxicillin-clavulanate, and the remaining 18.2% receiving 5 days of amoxicillin-clavulanate. Across the literature, amoxicillin-clavulanate is the most widely used and recommended choice for prophylactic antibiotics.

This 2-year-old child sustained a left eyelid laceration and a nondisplaced fracture of the left orbital floor after an attack by a dog. An injury to the globe was ruled out, and the eyelid laceration was repaired. He developed a post-discharge lacrimal duct infection.

Dog bites involve a diverse spectrum of organisms, with microbiome studies on bite injuries revealing a median number of five isolates, including both aerobic and anaerobic bacteria. Pasteurella was isolated in 50% of the bites studied. Because of this, wound infection is a much-feared complication of dog bites. Prospective studies have suggested that prophylactic antibiotics may not be necessary for superficial wounds, as they have an overall low infection incidence (approximately 2.1%–3.6%), following irrigation and standard wound care. ^,

Cats are the second most common source of bites, with an estimated incidence of 400,000 per year, but less than 1000 cat bites reported annually in the U.S. Of those, approximately 1/3 are in children. Females are twice as likely to suffer from a cat bite compared with males, and the most common bite location is to the upper extremity, particularly the fingers and hand. One retrospective review found that 65% of cat bite wounds occurred on the upper extremities, 20% on the head and neck, 10% on the lower extremities, and fewer than 5% on the trunk. The majority of incidents (>90%) involve cats that are owned by the family and are considered provoked. ^, This is significantly higher than dog bite injuries, of which 67% are reported as provoked.

Cats have long, narrow teeth that cause puncture-type injuries that are more likely to penetrate bones and joints, leading to deep abscesses and osteomyelitis. Feline bites have a six times higher infection rate compared with dog bites, though they are far less likely to have associated crush wounds. In one large, retrospective study of 1592 patients presenting after mammalian bites, the infection rate for dog bites was found to be 15%, compared with 37% after cat bites, although this incidence is as high as 50% in other reviews. ^, Additionally, cat bites manifest signs of infection more rapidly when compared with dog bites (12 vs. 24 hours). This can likely be attributed to the puncture nature of the wound, which inoculates bacteria deep into the tissue but allows rapid healing of the relatively small break in skin, thus trapping bacteria. There is also a higher likelihood of Pasteurella species being present in feline flora, and the increased incidence of bites to the hand makes the proportion of high-risk wounds higher overall. The common pathogens isolated from infected cat bite wounds are similar to those found in dog bites, and amoxicillin-clavulanate is the recommended first line for prophylaxis.

The incidence of human bites is difficult to determine because many patients do not seek medical care; however, human bites represent 2%–3% of bite injuries treated in the U.S. Human bites generally compress tissue but rarely avulse the skin and soft tissue like animal bites. Human bites are most commonly due to acts of aggression and have the highest incidence in males 10–34 years old. A fight bite occurs when a fist hits a tooth. The injury is often dismissed by patients. These occur from clenched fists and frequently involve the distal phalanx of the long or index finger of the dominant hand. However, these injuries can cause significant morbidity due to infection from mouth flora. Human bites have a higher complication and infection rate compared with animal bites. Infections occur in 5%–50% of human bite wounds, with closed fist injuries being at highest risk. The wounds frequently contain both aerobic and anaerobic bacteria, and antibiotics need to be broad. Coverage for Staphylococcus , Streptococcus , and Eikenella as well as anaerobic organisms such as Fusobacterium , Prevotella , and Veillonella is needed. ^, In a multicenter, prospective study of 50 patients with infected human bites, the median number of bacteria isolated per wound culture was four (three aerobes and one anaerobe), with Streptococcus anginosus being the most common (52%). Bites to the hands are often deep and are more likely to become infected compared with bites to other areas. ^,

Data have consistently proven the usefulness of prophylactic antibiotics in human bite wounds that penetrate deeper than the epidermis. Ideally, prophylactic antibiotics should be initiated within 4 hours of the bite and continued for 5 days. It is also important to note that human bites can transmit diseases such as human immunodeficiency virus (HIV) and hepatitis B and C, especially if blood is present in the mouth at time of bite injury. Risk should always be assessed and postexposure prophylaxis given when appropriate. Closed fist wounds additionally should be evaluated for injury to the extensor tendons, which occurs in up to 20% of cases. There also is a risk of retained tooth fragments, which should be removed if discovered on wound exploration.

In the pediatric population, it is uncommon that bites from other children are severe enough to break skin and necessitate medical attention. When assessed, however, the size of the bite is important to note. An intercanine distance greater than 3 cm is indicative of an adult-sized mouth, which should raise concern for abuse.

Key factors to assess include type of animal, anatomy affected, depth of the wound, and infection risk. Overall, the goals in wound management are to achieve hemostasis, prevent infection, and promote healing of the involved tissues ^, ( Box 11.1 ). The first step in achieving hemostasis for actively bleeding wounds is direct pressure. Temporary suture or hemostatic dressings (e.g., Surgicel or QuikClot) can also be used. The wound should ideally be assessed in a clean, bloodless field to allow adequate visualization of all structures and potential foreign bodies. A blood pressure cuff can be placed and inflated above the patient’s systolic blood pressure for up to 20 minutes to assist in assessment if hemostasis is otherwise unable to be achieved. Distal neurovascular assessment is essential for all bites to extremities. Adequate analgesia is an important factor to consider allowing for patient tolerance of full wound evaluation.

Further management of these wounds involves the basic tenets of wound care, including irrigation and debridement of any necrotic tissue. A large-bore blunt needle connected to a syringe can provide adequate pressure to clean these wounds. High-pressure irrigation should be avoided as this can drive bacteria deeper into tissues and increase infection risk. For grossly soiled wounds, 1% povidone-iodine or 1% benzalkonium chloride solution should be used to further clean the site. Wound cultures are not routinely necessary for fresh wounds without signs of infection but should be taken for any wounds that appear infected or if presentation was delayed greater than 8–12 hours.

Radiographic studies should be obtained when there is a concern for bone or joint penetration, if fracture or exposed bone are suspected, or to assess for suspected foreign bodies. Tetanus immunization status should be investigated for all bite victims and vaccine given if not up to date. Risk for rabies should be assessed, and prompt initiation of prophylaxis is important when indicated. Tetanus and rabies prophylaxis is discussed in more detail in subsequent sections.

Primary closure of bite wounds remains controversial but can be considered once wounds are thoroughly cleaned if presentation was prompt and there are no concerning features of infection. Primary closure should be avoided in cases of crush or puncture wounds; bites to hands, feet, or joints; cat or human bites (except to face and scalp); and in immunocompromised patients. If left open, wounds can be reevaluated in 2–3 days for consideration of delayed primary closure, if there continues to be no sign of infection. ^, Multiple prospective and randomized controlled trials comparing primary closure to nonclosure have demonstrated no difference in infection rates of the wounds. ^, The benefit of primary closure is improved cosmesis and reduced healing times. However, because wounds to the distal extremities and puncture wounds have been shown to have a higher rate of infection, it is recommended to avoid closure. Wounds that have been open for more than 6 – 12 hours before washout also are at high risk and should not be primarily closed. Additionally, consideration should be given to not closing wounds that are visibly infected or have delayed time to irrigation unless closing them loosely over a Penrose drain or vessel loop to allow ongoing drainage. Facial and scalp wounds have a low rate of infection due to the rich blood supply and increased likelihood of prompt presentation for medical attention, and these lacerations typically heal well if closed after proper irrigation and debridement.

Admission should be considered for patients with multiple or severe injuries, wounds requiring surgical intervention, bites to hand or cranium, or those at high risk for infection. High risk includes those due to cats, humans, or primates, wounds to hands and feet, those involving crush injuries or devitalized tissues, or delayed presentation (>6 hours). Patient factors can also increase risk for developing infections, such as immunocompromised status, diabetes, liver disease or renal failure, malnutrition, or corticosteroid use. It is also important to consider social issues that may limit compliance with proper wound care.

No clinical trials have reliably demonstrated increased efficacy of any specific antibiotic regimen when prophylactic antibiotics are indicated. When choosing an antibiotic regimen, it is important to consider the polymicrobial nature of bite wound infections and include coverage of Pasteurella species. The widely accepted oral drug of choice is amoxicillin-clavulanate. For penicillin-allergic patients, azithromycin or trimethoprim-sulfamethoxazole plus clindamycin can be used. A prophylactic course of 3–5 days may be sufficient, though therapeutic treatment of an infected wound usually involves a minimum course of 5–7 days, guided by clinical assessment. Development of septic arthritis or osteomyelitis warrants several weeks of antibiotic treatment, and the infectious disease team should be consulted to help guide management.

It should be noted that the treatment guidelines discussed here can be extended to apply to mammalian bites from other commonly kept pets (e.g., ferrets, rabbits), although they should not be applied to other more exotic pets (e.g., birds, farm animals, lizards) as mouth flora may be different for these animals. Specialist advice should be sought in these cases. Rodent bites have a low risk for local wound infection and have not been known to transmit rabies, so generally, they only require local wound care, and antibiotic prophylaxis is not recommended. Primate bites, while uncommon, are high risk and should be managed similarly to human bites.

Loxoscelism is a form of cutaneous-visceral (necrotic-systemic) arachnidism found throughout the world, with a predilection for North and South America. There are four species of brown spiders within the U.S. known to cause necrotic skin lesions ( Loxosceles deserta , L. arizonica , L. rufescens , and L. reclusa ). L. deserta and L. arizonica can be found in the southwestern U.S. L. reclusa , known as the brown recluse spider, is the most common species associated with human bites. It is usually found in the south-central U.S., especially Missouri, Kansas, Oklahoma, Arkansas, Tennessee, and Kentucky. Spiders can be transported out of their natural habitat but rarely cause arachnidism (poisoning caused by the bite or sting of an arachnid such as a spider, tick, or scorpion) in nonendemic areas. L. reclusa is tan to brown with a characteristic dark, violin-shaped marking on its dorsal cephalothorax, giving it the nickname “fiddleback” or “violin” spider ( Fig. 11.3 ). The spider can measure up to 1 cm in total body length with a 3-cm or longer leg span. These spiders have only three pairs of eyes, unlike most spiders, which have four pairs.

Loxosceles reclusa (brown recluse, “fiddleback”) spider showing the classic violin-shaped marking on the back (dorsal side) of the cephalothorax. Note the long, slender legs and oval body segment with short hairs. The arrow is pointing toward the classic violin marking.

From Ford M, Delaney K, Ling L, et al. Clinical Toxicology . Elsevier; 2001.

L. reclusa bites predominantly occur between April and October in the U.S. The venom of the brown recluse spider contains at least 11 protein components, most of which are enzymes with cytotoxic activity. Sphingomyelinase D is believed to be the enzyme responsible for necrosis and activity on red blood cell membranes. In addition to the local effects, the venom has activity against neutrophils and the complement pathway that induces an immunologic response. The result is a necrotic dermal lesion with the potential for a hemotoxic and systemic response that can be life-threatening.

The prevalence of brown recluse spider envenomation is unknown. It is common for the victim to not feel the bite or to feel only a mild pinprick sensation, and most victims do not see the spider at the time of the bite. Many are bitten while they sleep and may be unaware of the envenomation until a wound develops. Many bites remain asymptomatic or are associated with only a mild skin reaction, though they can be associated with significant underlying necrosis. Systemic loxoscelism is less common, though it can involve hemolytic anemia, disseminated intravascular coagulation, and even death. Smaller children are at the highest risk of severe loxoscelism.

The course typically begins with progressive itching and tingling at the site, which then becomes ecchymotic, indurated, and edematous over the course of several hours. During this period a characteristic bleb or bullae will commonly form. The tissue under the blister is likely to become necrotic, but the extent of necrosis is not predictable from the superficial appearance. As the ischemia and inflammation progress, the wound becomes painful and may blanch or become erythematous. Inflammation, ischemia, and pain increase over the first few days after the bite, and as the toxic enzymes spread over hours to weeks, an eschar forms at the site of the bite ( Fig. 11.4 ). Eventually, this eschar sloughs, revealing an underlying ulcer that may require months to heal, usually by secondary intention. On rare occasions, the ulcer does not heal and requires surgical intervention.

Brown recluse bite, approximately 1 week after bite. The central portion of the wound becomes dark and gangrenous with surrounding zones of erythema and ischemia.

James WD, Elston DM, Treat, JR, et al. Parasitic infections, stings and bites. In: Andrews’ Diseases of the Skin . Published December 31, 2019; pp. 421–452.e3. © 2020.

Development of systemic symptoms requires hospitalization. The true incidence of systemic loxoscelism is unknown due to the low rate of spider identification. Thus, there is often insufficient proof that the symptoms are related to the spider bite. Other common systemic symptoms include a maculopapular rash, nausea and vomiting, headache, malaise, muscle and joint pain, hepatitis, pancreatitis, and other organ toxicity. Life-threatening systemic effects include hemolysis (intravascular and/or extravascular), coagulopathy, and multiple organ system failure. Secondary effects include sepsis, necrotizing fasciitis, and shock. ^, Hemolysis usually manifests within the first 96 hours. However, late presentations can also occur. When hemolysis does develop, it can take 4–7 days (or longer) to resolve ( Fig. 11.5 ). Complications such as cardiac dysrhythmias, coma, respiratory compromise, pulmonary edema, congestive heart failure, renal failure, and seizures can occur.

(A) A 3-year-old girl hospitalized on the third day after a brown recluse spider bite for severe hemolytic anemia, hemoglobinuria, and ecchymosis (note the vast expansion of the ecchymosis secondary to hyaluronidase “spreading factor” in the venom). There is no necrosis or ischemia, but a small bleb/blister is present over the right clavicle that, although not pathognomonic, is often present early in lesion progression. Also note that the cutaneous lesion is mild compared with this patient’s systemic presentation. (B) On the 15th day after envenomation, the lesion measures 5 × 2 cm. Multiple small areas of necrosis have become apparent in the past week. The largest area indicates the original bite size. The lesion’s edges have begun to involute with healing, and the ischemia is fading. (C) Nine months after the bite, the necrotic wound has healed.

The diagnosis of a brown recluse spider envenomation is largely one of exclusion. Although the wound can appear classic for an envenomation, other causes must be considered in the differential diagnosis ( Box 11.2 ). Certain laboratory findings can be consistent with a brown recluse spider envenomation but are not specific in making the diagnosis ( Box 11.3 ). There has been some evidence that an enzyme-linked immunosorbent assay can be used to confirm the presence of Loxosceles venom and provide a definitive diagnosis in suspected loxoscelism, though this has not been extensively studied.

The mainstay of care is supportive with expectant observation recommended for both dermatologic and systemic symptoms. Medications such as dapsone, nitroglycerin, and tetracycline have been proposed as part of management, but none have proved effective in treating or preventing the development of an ulcer. In South America, an antivenom has been developed and used in the treatment of Loxosceles envenomation that has shown efficacy in reducing necrosis with early administration. Unfortunately, the usual long delay in seeking medical care often leads to ineffective use of this antivenom. An antivenom is not available in North America. In addition, hyperbaric oxygen (HBO) therapy has been used in cases of rapidly deteriorating wounds, though evidence for its efficacy is conflicting.

Dapsone (a leukocyte inhibitor) has been advocated in case reports and animal studies. However, other animal studies have shown conflicting data demonstrating no reduction in necrosis with use of dapsone, HBO, nor the combination treatment, compared with controls. In addition, the risks of dapsone may outweigh the benefits as hypersensitivity reactions can occur, and at therapeutic doses, dapsone has been associated with hemolytic anemia, methemoglobinemia, and other hematologic effects in patients both with and without glucose-6-phosphate dehydrogenase deficiency.

HBO has been advocated for treatment to slow necrosis of a rapidly progressive wound, based on the belief that tissue hypoxia was partially responsible for the subsequent necrosis that occurred after a bite. As mentioned previously, no statistical differences were noted in animal studies that compared dapsone and HBO. ^, Similar results have been seen in animal studies assessing the effect of HBO alone. ^, A randomized, controlled trial of HBO in a rabbit model in which standard HBO was used showed a significantly reduced wound diameter at 10 days. However, there was no significant change in blood flow at the center or 1–2 cm from the wound center. Notably, HBO is expensive and can lead to complications of lung damage and vision changes. Data are contradictory regarding the benefit of HBO for brown recluse spider envenomation. Thus, it is not currently recommended, though it may be helpful in a subset of patients with underlying or preexisting vascular compromise, such as sickle cell anemia or diabetes.

Early surgical intervention also has not been proven to be helpful due to rapid diffusion of venom throughout the soft tissues surrounding the bite. In addition, patients may be more at risk for delayed wound healing and excessive scarring if the operation occurs within the first 72 hours of the bite. ^, Debridement of enlarging blebs has been proposed, with the theory that toxins exist within the blister fluid, but it is advised against as necrosis almost always occurs beneath the blisters. Surgical intervention should only be approached after the limits of necrosis are clearly defined, at least 2 weeks from the time of the bite. The wound from the brown recluse spider may take 2–3 months to heal. Thus, skin grafting of a nonhealing necrotic area should be delayed up to 12 weeks to allow for neovascularization of the demarcated area.

Supportive care should focus on managing both the symptoms and the skin lesion as well as minimizing hemolysis. Tetanus prophylaxis is recommended for all spider bite victims. Systemic corticosteroids are commonly used in the management of cutaneous-hemolytic loxoscelism, but there is no consensus on the efficacy in experimental studies, and no clinical trials have been done to evaluate their use. However, when given, a 5–10-day course with a subsequent tapering dose is generally used. Methylprednisolone can be administered as a 1- to 2-mg/kg intravenous loading dose (no maximum) followed by a 0.5- to 1-mg/kg maintenance dose every 6 hours. Supportive therapy for hemolysis is primarily focused on hydration to maintain urine output of 1–2 mL/kg/hr to prevent acute renal tubular necrosis. If acute kidney injury develops, the patient should be assessed for renal replacement therapy. If severe anemia develops, packed red blood cells should be transfused. Consumptive coagulopathy is uncommon, and other blood products are rarely necessary.

Antibiotics are not generally required early in the care of these patients because the spider does not inoculate humans with bacteria, and infection is unlikely at presentation. However, secondary infections can occur in the eschar phase (typically more than 2 weeks after the bite) and can lead to sepsis, toxic shock syndrome, and necrotizing fasciitis. These complications require close observation and antibiotic therapy to cover anaerobic, staphylococcal, and streptococcal infections.

Black widow spiders ( Latrodectus mactans ) are found throughout North America. They can usually be found outdoors in warm, dark places, as well as in garages or basements. They are web-making spiders and usually strike when their web is disturbed. The female spider is readily recognized as a black spider with a red hourglass-shaped marking on her ventral abdomen ( Fig. 11.6 ). Widow spiders have a neurotoxic venom, α-latrotoxin, that acts on the neuromuscular junction. It causes depletion of acetylcholine at the motor endings and of catecholamines at the postganglionic sympathetic synaptic sites, followed by subsequent complete blockade of the neuromodulator release.

Female black widow ( Latrodectus spp.), with characteristic red hourglass-shaped marking on ventral abdomen.

From iStock.com/Mark Kostich

More than 2600 black widow bites are reported annually in the U.S. In most cases, a pinprick sensation is felt at the time of a bite. A “halo” lesion may develop, but this tends to disappear within 12 hours of envenomation ( Fig. 11.7 ). Within a few hours, patients may develop tenderness of the regional lymph nodes and affected extremity. Depending on the location of the bite, pain usually migrates to the large muscle groups in the thigh, buttock, abdomen, or chest. The most common presenting complaint is intractable abdominal, chest, back, or leg pain, corresponding to the site of the bite. The pain generally peaks at 2–3 hours, but it can last up to 72 hours. Board-like rigidity of the abdomen, shoulders, and back can develop that may lead to the misdiagnosis of a surgical abdomen or other etiology.

Black widow bite. Note the “halo” with central induration surrounded by area of blanching and outer redness. Puncture wounds may or may not be seen.

Courtesy Sean Bush, MD; Orloff, K, Zimmerman, K. Bites and stings. In: Fuhrman and Zimmerman’s Pediatric Critical Care . Published December 31, 2021; pp. 1317–1326. E3. © 2022.

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