Animal bites, stings and envenomation

• Animal bites are usually caused by dogs, cats or humans, and most can be cared for with wound cleaning, careful early assessment and selective closure and antibiotics.
• Dog bites make up roughly 60 to 80 percent of reported animal bites, cat bites 20 to 30 percent, and human bites up to 20 percent in some urban series. ^[9]
• In general 10 to 20 percent of bite wounds become infected, with higher rates for cat bites (30 to 50 percent), human bites (15 to 25 percent) and hand wounds (18 to 36 percent). ^[9]
• Every bite needs a tetanus decision and, where rabies is endemic, an immediate rabies risk assessment: wound washing, then vaccine, human rabies immune globulin, animal observation or testing as indicated. ^[2][3]
• Antivenom is treatment for significant North American crotaline, coral snake, bark scorpion, black widow and certain marine envenomations, but faces and hands need surgical judgement and many snakebites are dry. ^[5]
• Necrotising soft-tissue infection after shellfish or seawater exposure is usually Vibrio vulnificus; it needs rapid combination antibiotics and urgent surgery. ^[7]

By the end of this page you should be able to:

1. Assess a mammalian bite for tetanus and rabies risk and manage the wound without increasing infection.
2. Decide when to close an animal bite and when prophylactic amoxicillin-clavulanate is reasonable.
3. Anticipate the main organisms in dog, cat, human and rodent bites.
4. Run the rabies and tetanus post-exposure flowcharts in the acute setting.
5. Distinguish common envenomations by features and give appropriate first-line treatment.
6. Recognise delayed presentation or a high-risk wound and refer appropriately.

A bite is a wound produced by teeth or claws and contaminated with saliva. A sting is an envenomation by a venom apparatus, most often an insect, sometimes a fish, stingray or other marine animal. The clinically useful split is between bites, which are mainly infection problems, and stings or bites by venomous animals, which are mainly toxidrome problems.

Useful categories:

• Mammalian bites: dog, cat, human, rodent, wild and exotic animals. Infection is the main risk.
• Insect stings: Hymenoptera (bees, wasps, hornets, ants), with the added risk of IgE-mediated anaphylaxis.
• Arthropod envenomation: spiders and scorpions.
• Snake envenomation: pit vipers, coral snakes and (globally) other elapids and vipers.
• Marine envenomation: jellyfish, stonefish, scorpionfish, stingrays, catfish, sea snakes and sea urchins.
• Tick bites: a skin bite plus a tick-borne disease risk.
• Any bite can lead to a secondary necrotising infection when water or marine organisms are involved.

Bite injuries are common in industrialised and low-resource settings alike. In the United States the incidence of animal bites is estimated at 200 per 100,000 persons per year, with about 1 to 2 million dog bites and 0.4 million cat bites annually among roughly 100 million dogs and cats. ^[9] In Germany 30,000 to 50,000 bite injuries occur each year. ^[9]

• About half of people in industrialised countries are bitten at some point, and animals live in more than one third of German households. ^[9]
• Approximately 1 percent of emergency department visits are for animal bites, and more than 50 million US dollars in annual healthcare costs in the United States are attributed to bites. ^[1]
• Bite injuries are not evenly distributed: roughly 70 to 80 percent occur on the limbs, 10 to 30 percent on the head and neck, and up to 90 percent of bites in children under five years occur on the face and anterior neck. ^[9]
• Children are bitten more often than adults. About a quarter of bite victims are under six years, 34 percent are 6 to 17, and 25 percent of all bite victims are under six. ^[9]
• Dogs account for roughly 60 to 80 percent of animal bites, cats 20 to 30 percent, and human bites up to 20 percent in some urban series. ^[9]
• Most dog bites are by a known dog: 90 percent by the victim's own dog or one known to the victim; male dogs cause about three quarters of dog bites. ^[9]
• Cats more often bite females and young adults; dogs more often bite males and children. ^[9]
• Snake envenomations are less common but measurable: more than 35,000 snake envenomations were reported to the National Poison Data System in the United States between 2009 and 2013. ^[5]
• Human bites are a minor wound type overall but cause frequent infection and present forensic issues (tooth-distance measurements, DNA sampling). A distance greater than 3 cm between canine teeth indicates an adult biter. ^[9]

The most useful epidemiological question is not how common bites are, but which bites get infected. Risk rises with:

• Location: hands, feet, face, genitals, joints and periosteum, and any bite crossing a flexor surface. ^[9]
• Depth: puncture wounds and cat bites inoculate deeply and are difficult to clean. ^[9]
• Delay in presentation (more than 8 to 10 hours), foreign body, heavy contamination. ^[1]
• Wound with oedema, poor perfusion, marked tissue destruction or crush. ^[9]
• Host: extremes of age, asplenia, cirrhosis, diabetes, immune suppression, HIV, neutropenia, prosthetic valve or joint. ^[9][1]
• Animal species: cat and human bites carry higher infection rates than dog bites. ^[9]
• Environment: seawater, brackish water or raw shellfish exposure raises the risk of Vibrio vulnificus necrotising infection. ^[7]
• Endemic rabies area, or a wild animal reservoir (bats, raccoons, foxes, skunks in the Americas). ^[2]
• Tick habitat and Ixodes attachment for 36 hours or more in a Lyme-endemic region. ^[8]

Teeth crush and tear tissue, creating devitalised tissue, possible foreign material and a deep inoculum of oral flora. Anaerobic pockets form. Infection develops in 12 to 24 hours with Pasteurella multocida, often somewhat later with other organisms. ^[9] Capnocytophaga canimorsus can present after 5 to 8 days. ^[9]

Soft-tissue infection can extend to tenosynovitis, septic arthritis, osteomyelitis, meningitis, endocarditis and abscess. Capnocytophaga canimorsus is the pathogen most likely to cause acute sepsis, especially in predisposed patients, and may lead to disseminated intravascular coagulation, gangrene and renal failure. ^[9]

Take a structured bite history:

• Which animal and whose. Rabies and tetanus status if known.
• Time, place and circumstances, including provocation. ^[9]
• Wound type: crush, tear, puncture, avulsion, degloving. Hand, face, genital or joint involvement.
• Whether the patient swam in seawater or ate raw shellfish (Vibrio risk). ^[7]
• Host factors: diabetes, splenectomy, cirrhosis, immune status, medications, allergies.
• Immunisation history for tetanus and rabies.
• A bite in a child or any human bite mark must raise safeguarding considerations; assessment of supervision is part of good care.

Redness, swelling, discharge, pain and fever appear with infection; signs of deeper involvement include tenosynovitis (pain on passive extension), joint effusion or instability, and reduced range of movement. ^[9] Always remove rings and constricting items early.

Recorded observations: temperature and haemodynamic status. Examine for compartment syndrome when swelling is marked and progressive. Compartment syndrome is treated first with antivenom when snake bite is plausible. ^[5]

Look specifically for:

• dog or cat teeth on plain radiographs if a fang may have broken off, or in clenched-fist injuries, but routine radiography is not required in uncomplicated bites. ^[5]
• joint involvement and tendon integrity; in hand bites, bones, joints and tendons can be penetrated. ^[9]

Most bite presentations are straightforward. Consider:

• Cellulitis from another portal: ask about breaks in the skin and animal contact.
• Sporotrichosis or atypical mycobacterial infection in a chronic ulcero-nodular lesion after soil or plant contact.
• Necrotising infection: pain out of proportion early, systemic upset, rapidly spreading skin changes, bullae.
• Tetanus if a dirty wound and a neurological picture.
• Rabies if an animal exposure followed by encephalitis, hydrophobia or aerophobia; once symptomatic rabies is almost always fatal, so prevention is the whole topic. ^[2]
• Anaphylaxis after an insect sting can mimic chest pain, angio-oedema and shock.

Most bites need none.

• Swabs for aerobic and anaerobic culture in purulent or deep infections, plus blood cultures if septic. Tell the laboratory that anaerobes and unusual pathogens are expected; allow 7 to 10 days incubation and adequate transport media. ^[9]
• Blood tests if systemic illness: full blood count, C-reactive protein, creatine kinase, renal function, coagulation.
• Radiographs in hand bites, deep scalp bites, clenched-fist injuries, and suspected foreign body or fracture. ^[9]
• Ultrasound for suspected abscess.
• In snake bite: full blood count, renal function, creatine kinase, venous blood gas, prothrombin time, D-dimer and fibrinogen for coagulopathy; urine testing. ^[5]
• In all suspected envenomation: troponin, creatine kinase, potassium and urinalysis as clinically indicated, and pregnancy status where relevant.

Wash first and do not delay.

1. Irrigate under pressure through a large syringe and 19-gauge needle or cannula, with normal saline after a brief povidone-iodine or plain water wash. High-pressure irrigation is especially important when primary closure will follow. ^[1]
2. Debride devitalised tissue and remove foreign material. ^[9]
3. Retained fangs or foreign bodies are removed with appropriate protection; rarely are fangs broken off. ^[5]
4. Do not incise, suck or use extraction devices in snake bite. Do not use tourniquets. ^[5]
5. Mark the leading edge of swelling and measure its circumference at intervals. ^[5]
6. Immobilise an affected hand or limb where appropriate; elevate.

Closure is not automatic. Most open wounds need thorough cleaning first; drainage and dressing come before stitches. ^[1]

• Face (and paediatric scalp and face): wounds in the face are closed primarily even if several days old, usually with local anaesthesia or sedation. ^[9]
• Hands: primary closure of bites on the hands is generally contraindicated because of infection risk; irrigate, debride and leave open, or use delayed primary closure once clean. ^[9]
• Puncture wounds with deep inoculation, especially cat bites, are left open. ^[9]
• Human bites: primary closure is contraindicated except on the face. ^[9]
• Deep, contaminated or hand wounds are left to heal by secondary intention or delayed primary closure once clean and after 3 to 5 days of observation if required. ^[9]
• Deep irrigation under pressure through a catheter or cannula is helpful for cleaning; pressurised irrigation with a syringe has been recommended for prevention of infection. ^[1]

A common error is to close a wound in the first hour and create an abscess in the second. If there is any doubt and the wound is not on the face, clean thoroughly and review.

Dog and cat wounds commonly carry mixed flora. The main aerobic and anaerobic species are shown in the tables in the original reviews; the clinically useful points are these:

• Pasteurella multocida is the most common isolate in cat and dog bites and often causes rapid infection within 12 to 24 hours. ^[9]
• Capnocytophaga canimorsus is carried by dogs and causes severe sepsis in predisposed patients. ^[9]
• Eikenella corrodens is the organism most commonly isolated from human bite wounds (around 30 percent), is gram-negative and microaerophilic, and is resistant to clindamycin, metronidazole and first-generation cephalosporins. ^[9]
• Streptococci are found in about 50 percent and Staphylococcus aureus in about 40 percent of human bite wounds. ^[9]
• Mixed aerobic-anaerobic infection occurs in 30 to 60 percent of infected bite wounds. ^[9]
• Rodent bites rarely infect, but when they do P. multocida is the usual organism; tularemia, rat-bite fever and rabies are less common associations. ^[9]
• Monkey bites can transmit macaque (herpes B) virus and need specialist advice beyond this page.

Prophylactic antibiotics are not universally required; they are indicated for high-risk wounds and high-risk patients:

• hand bites, deep puncture wounds, crush injury, delay beyond 8 to 10 hours, wounds needing closure, bones or joints involved, patients with diabetes, splenectomy, cirrhosis or immune suppression, and prosthetic valves or joints. ^[1]
• Amoxicillin-clavulanate is the usual choice, because penicillin alone misses beta-lactamase producers, Eikenella and (in envenomation) some marine organisms. ^[9][1]
• Duration for prophylaxis is typically 3 to 5 days for fresh deep wounds, hand wounds, face or genital wounds, and high-risk patients. ^[9]
• In manifest infection, aminopenicillin with a beta-lactamase inhibitor is first line; deeper infection may need intravenous cefotaxime or piperacillin-tazobactam. ^[9]
• Duration in treatment: 1 to 2 weeks for cellulitis or abscess, 2 to 3 weeks for tenosynovitis, and 3 to 4 weeks for osteomyelitis or septic arthritis. ^[9]
• If the patient presents at least 24 hours after the bite without clinical infection, antibiotics are usually unnecessary. ^[9]
• Cefoxitin or a beta-lactam/beta-lactamase inhibitor is recommended for first-line empirical therapy in human bites because of Eikenella resistance. ^[9]
• Where penicillin is contraindicated, co-trimoxazole with clindamycin is an alternative, though clindamycin alone should not be used if Pasteurella, Eikenella or anaerobes are likely. ^[9]

Animal and human bites are dirty wounds: animal or human bites are listed as examples of dirty or major wounds because the wound contains saliva. ^[3] The tetanus flowchart integrates wound type, immunisation status and TIG.

Notes from the guidance: ^[3]

• TIG is never indicated for clean, minor wounds, but is indicated for dirty or major wounds in unknown, unvaccinated, incompletely vaccinated, HIV-positive or severely immunodeficient patients. ^[3]
• TIG does not neutralise toxin already bound to nerve endings. ^[3]
• Antibiotics should not be used to try to prevent tetanus. ^[3]
• In bite patients without adequate immunisation, many services give tetanus toxoid plus TIG; follow the local immunisation schedule. ^[9]

Rabies is a practical problem for any bite in a rabies-endemic area, and for travel history. Post-exposure prophylaxis is a package: wound washing, passive immunity (HRIG) and active vaccination, with risk graded by exposure and animal. ^[2] The category-of-exposure framework used by STIKO and DGPI is also clinically useful, where category I is skin contact, II is non-bleeding scratch or abrasion, and III is bite, scratch or mucous membrane contact; the implication is active plus passive immunisation for category III. ^[9]

Key operational points: ^[2]

• HRIG provides passive immunity until the vaccine takes effect and is given only once, at the start. ^[2]
• For patients previously vaccinated or receiving pre-exposure prophylaxis, do not give HRIG; give vaccine only on days 0 and 3. ^[2]
• Wash first: wound cleansing alone markedly reduces rabies likelihood in animal models. ^[2]
• If the animal can be captured safely, 10 days of veterinary observation is the standard for a dog or cat. ^[9]
• Decisions should be made with public health and veterinary services; they localise epidemiology and can locate animal carcases for testing. ^[2]
• There is no contraindication to PEP by pregnancy or age; all ages are eligible. ^[2]
• Sutures may delay cleaning; wash first and keep the wound open wherever practical. ^[9]

Local and large local reactions are common; anaphylaxis is uncommon but dangerous. Bees leave a barbed stinger; scrape it off rather than pinch it. Wash the area and apply cold. Fire ants, wasps and hornets cause most systemic stings in temperate regions.

Anaphylaxis to Hymenoptera venom is treated as any anaphylaxis: ^[4]

• Remove the trigger and assess airway, breathing and circulation.
• Intramuscular adrenaline 0.01 mg per kilogram of body weight to a maximum total of 0.5 mg, given as 0.5 mL of 1 mg per mL solution, in the mid-anterolateral thigh. Repeat every 5 to 15 minutes if needed. ^[4]
• Large doses by inappropriate routes (intravenous boluses or endotracheal dosing) are associated with serious harm; intramuscular is first line. ^[4]
• Adjuncts include intravenous fluids, nebulised adrenaline for airway oedema, and inhaled bronchodilators; antihistamines and corticosteroids are secondary and do not replace adrenaline. ^[4]
• Venom immunotherapy for sensitised patients is offered after specialist assessment and markedly reduces future systemic reaction; patients should carry an adrenaline autoinjector if prescribed. ^[4]

Tickling in the mouth, tongue or throat after a bee sting suggests airway involvement; any hypotension, syncope or widespread urticaria should be treated as anaphylaxis. ^[4]

Large local reactions peak at 24 to 48 hours, in contrast with infection, and should not prompt antibiotics. ^[1]

North American dangerous envenomations are dominated by pit vipers, with smaller numbers of coral snakes, bark scorpions and two spiders. ^[5] More than 35,000 snake envenomations were reported to the National Poison Data System from 2009 to 2013. ^[5] Recognition rests on the syndrome more than on identifying the animal. ^[5]

Pit viper antivenom (CroFab) carries immediate hypersensitivity in about 8 percent of administrations, so monitor closely during infusion and afterward for serum sickness and recurrent coagulopathy. ^[5] Cobra or other elapids are not covered above and need regional advice.

Marine injuries include surface stings and puncture wounds. Emergency care for most stings is washing and removing tentacles or spines with protection; hot water immersion is the main analgesic treatment for many fish and scorpionfish stings. ^[6]

• Jellyfish (box jellyfish, Portuguese man o' war): remove tentacles, wash with seawater; vinegar for specific species only; analgesia; box jellyfish antivenom in Australasian waters.
• Stingrays, stonefish, scorpionfish, catfish: hot water immersion at 42 to 45 degrees Celsius for 30 to 90 minutes (or until pain eases) is effective and safe. ^[6]
• Stonefish and scorpion fish antivenom is available for severe cases, usually unnecessary for milder stings. ^[9]
• Sea urchins: soak, remove spines carefully; debridement as needed. ^[6]
• Sea snakes: neurotoxicity; antivenom where indicated with region-specific advice.
• Stonefish, scorpion fish and stingray wounds may be complicated by secondary bacterial infection, including Vibrio and Pseudomonas species; debride and inspect. ^[6][7]

Marine envenomation can activate complement and release toxins that are inactivated by heat; this is the rationale for hot water rather than ice. ^[6]

Remove the tick promptly with fine-tipped tweezers, grasping close to the skin and pulling straight up; avoid burning, twisting or chemicals. ^[8] Test the tick itself and test asymptomatic patients are not recommended. ^[8]

Prophylaxis against Lyme disease is for high-risk bites only: ^[8]

• Single oral doxycycline 200 mg in adults, 4.4 mg per kilogram to a maximum of 200 mg in children, given within 72 hours of tick removal. ^[8]
• High risk requires all of: an identified Ixodes species, a highly endemic region, attachment for 36 hours or more. ^[8]
• Not for equivocal, low-risk or beyond-72-hour situations. ^[8]

Tick-bite fever, anaplasmosis, babesiosis, RMSF, tick paralysis and Powassan virus require clinical follow-up and local epidemiology, not routine antibiotics. Prompt removal remains the most effective prevention; repellents, permethrin-treated clothing and tick checks reduce exposure. ^[8]

Vibrio vulnificus is a gram-negative halophile that thrives in warm, brackish water. ^[7] Infection occurs from eating raw (especially oysters) or undercooked shellfish, or from exposing an open wound to seawater or brackish water. ^[7] Mortality exceeds 50 percent in high-risk individuals. ^[7] People with cirrhosis, haemochromatosis, diabetes or immune suppression are at markedly increased risk. ^[7]

• Presentation: gastroenteritis, primary sepsis after seafood, or necrotising fasciitis after wound exposure, often within 12 to 72 hours. ^[7]
• A delay of 24 hours in antibiotic treatment is associated with about 33 percent fatality, rising to 100 percent after 72 hours, so treat before culture confirmation. ^[7]
• Blood, blister or wound specimens should be sent for culture and Gram stain; necrotising soft tissue infection needs urgent surgical debridement or fasciotomy, sometimes amputation. ^[7]
• Standard regimen: doxycycline 100 mg orally or intravenously twice daily for 7 to 14 days plus a third-generation cephalosporin such as ceftazidime 1 to 2 g intravenously or intramuscularly every 8 hours. ^[7]
• Alternatives include a third-generation cephalosporin with ciprofloxacin, or other regimens supported by susceptibility testing. ^[7]
• In children, alternatives to doxycycline and fluoroquinolones (contraindicated in children) have been recommended: co-trimoxazole plus an aminoglycoside; exact paediatric regimens should follow local guidance. ^[7]

Aseptic, rapidly progressive, exquisitely painful skin lesions after seawater exposure should raise this diagnosis even before culture results return. ^[7]

• Children. Most dog bite victims are children. Cat bites to the hand have high infection rates; observe carefully. ^[9]
• Older adults with fragile skin. Minor bites can produce large tears and deep inoculation. ^[9]
• Pregnancy. Rabies PEP, tetanus toxoid and TIG are not contraindicated in pregnancy; adrenaline and antivenom decisions follow maternal severity. ^[2][3]
• Immunocompromised patients. Lower threshold for intravenous antibiotics, TIG, and full rabies PEP with five doses; check serological response if immunodeficiency. ^[2][3]
• Chronic liver disease or haemochromatosis. Markedly increased Vibrio vulnificus mortality; avoid raw shellfish and be cautious with seawater wounds. ^[7]

• Wash wounds early with soap and water or dilute antiseptic, then clean water; irrigation is inexpensive and effective. ^[1]
• Delayed presentation is expected; risk stratify for high-risk wounds. ^[1]
• If rabies PEP products are unavailable, wound washing remains highly protective; immunoglobulin can be given up to 7 days; contact national authorities for immunoglobulin and vaccination. ^[2]
• Tetanus TIG 250 IU intramuscularly is a low-cost intervention for dirty wounds in non-immunised or incompletely immunised patients. ^[3]
• Antivenoms in many regions are scarce; poison control, public health laboratories and zoos can be sources, and severe management rests on supportive care. ^[5]
• Vibrio treatment can be given empirically with available agents while awaiting cultures; always include a cephalosporin-based approach if possible. ^[7]
• Capnocytophaga sepsis after minor dog bites is a particular danger in asplenic or cirrhotic patients. ^[9]

• Most bites heal without infection if cleaned early; infection rates are higher for cat, hand and human bites.
• Dog bites are the most common source; cats cause smaller but deeper wounds; human bites carry Eikenella and blood-borne virus risks.
• Primary closure on the face is accepted; most hand, puncture and human bites should be left open.
• Amoxicillin-clavulanate is the usual prophylactic antibiotic for high-risk wounds for 3 to 5 days; deeper infection needs longer targeted therapy. ^[9]
• Tetanus prophylaxis after a bite uses the dirty-wound rule: vaccinate if at least 5 years since the last dose, or 10 years for clean minor wounds; give TIG 250 IU for unknown or incomplete immunisation. ^[3]
• Rabies PEP is wash, then 20 IU/kg HRIG infiltrated into the wound plus vaccine 1.0 mL on days 0, 3, 7 and 14; no HRIG if previously vaccinated. ^[2]
• Animal observation for 10 days is the standard for dogs and cats when rabies risk is uncertain. ^[9]
• Many snakebites are dry; treatment and antivenom depend on the toxidrome and progression, not on the snake's appearance. ^[5]
• Hot water immersion at 42 to 45 degrees Celsius for 30 to 90 minutes is the primary treatment for many marine stings. ^[6]
• Vibrio vulnificus infection needs combination antibiotics and urgent surgery; suspected cases are treated before culture. ^[7]
• Tick-bite Lyme prophylaxis is a single 200 mg dose of doxycycline only after high-risk Ixodes bites. ^[8]

• Lyme disease (tick bite prophylaxis and diagnosis)
• Anaphylaxis
• Tetanus
• Antimicrobial stewardship
• Necrotising soft tissue infection
• Travel medicine and rabies prevention