Animal bites and stings

A wide variety of animals, both wild and domestic, will bite or sting to ward off enemies or kill prey, posing a common cause for visits to the emergency department. Arthropod, reptile, fish, jellyfish, and mollusk stings and bites generally cause little mechanical trauma to humans, but they can cause potentially severe local and/or systemic damage if they deliver venom. Clinically significant venomous animals include various species of spiders (e.g., black widow and recluse spiders), scorpions (e.g., Arizona bark scorpion), hymenoptera (esp. bees and wasps), snakes (e.g., rattlesnakes), fish (e.g., scorpionfish, stonefish), mollusks (e.g., blue-ringed octopus, cone snails), and jellyfish (box jellyfish). While venomous mammals exist (e.g., shrews, slow lorises, platypuses), attacks on humans are rare. Mammal bites are instead clinically relevant for the mechanical trauma they cause (esp. with larger mammals, such as dogs) and the risk of infection (e.g., rabies, rat-bite fever). Diagnosis involves wound assessment, ruling out hypersensitivity reactions, and identifying the animal responsible to determine the risk of infection and/or envenomation. Symptoms of envenomation depend on the species of animal and may involve local pain, swelling, and paresthesia; hypersensitivity reactions up to anaphylaxis; nonspecific symptoms (e.g., nausea and vomiting); and, in severe cases, neurotoxicity, autonomic dysfunction, and shock. Treatment depends on the severity of the bite or sting and the animal responsible, potentially involving trauma care up to surgery, hypersensitivity management up to epinephrine, care with antibiotics, and the administration of antivenom.

For the general management of animal bites, see ”Bite wounds.” and “Rabies risk assessment.”

• Epidemiology
  • Account for 1% of injury-related emergency department visits in the United States ^[1]
  • Account for 60–90% of animal bites ^[2]
  • Children are more likely to be attacked and their injuries will be more severe than in adults ^[3]
• Clinical features
  • Erythema, swelling, and possibly pus in the case of infection
  • Depending on the size of the dog, injuries include puncture wounds, superficial abrasions, lacerations, and/or crush injuries.
  • In adults, the extremities are most commonly affected, and in children < 5 years of age, head and neck injuries are more common.
• Diagnostics
  • Wound exploration for tendon or bone involvement and foreign bodies (e.g., broken off tooth)
  • Radiography in the case of bone involvement
• Treatment ^[3]
  • Clean wound and irrigate with water, normal saline, or dilute povidone-iodine solution
  • Dog bite wounds should generally be left open to prevent infection, if feasible.
    • Wounds with a low risk of infection may be closed after cleaning if the patient wishes (e.g., for cosmetic reasons).
    • Wounds with a high risk of infection (e.g., hand wounds, delayed presentation, puncture wounds) should always be left open.
  • Antibiotic treatment and prophylaxis
    • Should be used for high-risk bite wounds (e.g., wounds to the hand, delayed presentation, puncture wounds) and for wounds requiring closure
    • First-line therapy is amoxicillin/clavulanate
  • Prophylactic vaccination
    • Rabies: indicated if there is suspicion or evidence of animal infection (see “Rabies post-exposure prophylaxis”)
    • Tetanus: recommended if the last vaccination was ≥ 5 years ago (see “Tetanus prophylaxis” for more details)
• Complications ^[4]
  • Wound infection (risk is higher for deep and destructive bites)
  • Arterial/neurological damage
  • Arthritis, osteomyelitis, sepsis
  • Cat scratch disease
• Reporting ^[3]
  • The reporting of dog bites is mandatory in most states.
  • Rabies in animals as well as in humans is a notifiable disease.

• Epidemiology: : account for 5–20% of animal bites ^[2]
• Clinical features
  • Usually manifest as a single puncture;
    Most commonly on the hand or arm
  • Erythema, swelling, lymphangitis, and possibly pus in the case of infection
• Diagnostics: wound exploration to estimate depth and extend of injury and for foreign bodies (e.g., broken off tooth)
• Treatment ^[3]
  • Clean wound and irrigate with water, normal saline, or dilute povidone-iodine solution
  • Wound closure: All cat bites are considered high risk for infection and should be left open to prevent secondary infection.
  • Antibiotic prophylaxis: amoxicillin/clavulanate is first-line
  • Vaccination: Tetanus vaccination is recommended if the last vaccination was ≥ 5 years ago (see “Tetanus prophylaxis” for more details).
  • Rabies: See “Rabies post-exposure prophylaxis.”
• Complications ^[4]
  • Wound infection (risk is higher for deeper and more destructive bites)
  • Arthritis, osteomyelitis, sepsis
• Reporting: Rabies in animals as well as in humans is a notifiable disease.

• Examples: rats, mice, squirrels
• Clinical features: Rodent bites generally carry a low risk of infection.
  • Local inflammation: cardinal signs of inflammation
  • Local and systemic infection: purulent secretion, fever, and arthritis
  • May cause:
    • Leptospirosis
    • Lassa fever
    • Rat-bite fever
      • Transmitted by Streptobacillus moniliformis
      • Characterized by fever, rigors, and polyarthralgia
      • Can cause severe organ damage (e.g., hepatosplenomegaly, interstitial pneumonia, endocarditis).
    • Small rodents have not been known to transmit rabies to humans.
• Treatment
  • General: dirty wound treatment
  • Leptospirosis: aminopenicillins, doxycycline, penicillin G
  • Rat-bite fever: penicillin G

References:^[5]

• Epidemiology ^[6]
  • ∼ 5000 venomous snakebites per year in the US
  • Crotaline snakes (pit vipers, e.g., rattlesnakes, copperheads, cottonmouths) are responsible for the majority of snakebites in the US.
• Clinical features
  • “Dry bites” (bites without envenomation): minor local symptoms
  • Envenomation leads to varying degrees of local and systemic symptoms that depend on the amount and toxicity of the venom (see table below).

• Diagnostics: usually based on history (description of possible identifying features of the snake) and clinical features

• Management ^[7]
  • Antivenom administration
    • Can slow or halt the progression of toxicity and is most effective when administered within 4–6 hours of the snakebite ^[9]
    • Should only be given to patients with clear symptoms of envenomation and in whom the benefits are likely to exceed the risks of adverse reaction to antivenom
    • For pit viper bites: crotalidae polyvalent immune fab
    • Adverse effects: hypersensitivity, serum sickness
  • Pressure immobilization and/or tourniquets are not recommended as part of routine management in the US. ^[11]
  • Patients must be monitored closely for signs of cardiovascular instability and respiratory compromise.

• General treatment includes cleaning of the wound, cooling, and analgesia.
• They rarely require specific medical treatment.

Bark scorpion sting

• Distribution: southwestern US
• Pathophysiology: venom contains a neurotoxin that inhibits the inactivation of the sodium channels → prolonged depolarization → neuronal membrane hyperexcitability
• Clinical features
  • Mild: local pain, swelling, and paresthesia at the sting site
  • Severe: cranial nerve dysfunction, autonomic dysfunction, neuromuscular toxicity (e.g., fasciculations, muscle jerks), rarely acute pancreatitis
• Diagnostics: based on history and clinical features
• Treatment: antivenom administration for severe cases

• Examples: bees, wasps, yellow jackets, hornets, fire ants
• Distribution: worldwide
• Pathophysiology: Insects from the Hymenoptera order release venom into tissue when stinging, triggering a local skin reaction and potentially life-threatening systemic reactions.
• Clinical features
  • Local skin reaction at the site of the sting
    • Initial pain
    • Swelling and redness appear within minutes of the sting event.
    • Usually resolves within hours
    • Large local reactions (LLR): gradually extending area of swelling and redness (typically > 10 cm) that lasts for days ^[12]
  • Systemic allergic reactions, anaphylaxis are possible
• Diagnostics: primarily a clinical diagnosis
• Treatment
  • Removal of the stinger if it is still lodged in the skin
  • Cold compresses
  • Analgesia (NSAIDs)
  • Observation of patients with multiple stings or a history of systemic reactions or other allergies
  • Severe cases
    • Oral prednisone for LLR to reduce significant swelling
    • Systemic reactions (anaphylaxis): See ”Management of anaphylaxis.”

• Example: oysters
• Distribution: worldwide in warm coastal waters
• Epidemiology: increased risk in individuals with immunodeficiency, diabetes, or liver disease (e.g, hemochromatosis)
• Pathophysiology
  • Consuming raw or undercooked shellfish → infection with Vibrio vulnificus
  • Dermal injury exposed to contaminated marine water. Necrotizing wound infections can occur.
• Clinical features
  • Dermatologic
    • Hemorrhagic bullous lesions
    • Severe necrotizing fasciitis
  • Gastrointestinal
    • Diarrhea
    • Vomiting
  • Primary septicemia ^[13]
• Diagnostics
  • Laboratory: blood cultures
  • Imaging methods of affected tissues (e.g., CT, MRI)
• Treatment
  • Emergent surgical debridement
  • Antibiotics: IV doxycycline and ceftriaxone

References:^[13]

The following sections cover the venomous aquatic animals most commonly responsible for hospital visits in the US. Included here are not only animals native to US waters, but also animals popular among aquarists. Wounds caused by aquatic animals are particularly susceptible to infection with Vibrio species, due to contaminated seawater (see “Noncholera Vibrio infection” for more information).

• Distribution: Box jellyfish are most commonly found in Hawaii, Northern Australia, and the tropical Atlantic.
• Pathophysiology: Jellyfish have tentacles with specialized capsules (nematocysts) that attach to the skin and release venom. The toxicity of the venom depends on the species.
• Clinical features
  • Local envenomation
    • Initial pain
    • Sting develops into a linear urticarial lesion.
    • Severe stings can be complicated by skin necrosis.
  • Systemic envenomation: anaphylaxis, cardiac arrest
• Diagnostics: based on history and clinical features
• Treatment: Routine management depends on the jellyfish species and the geographic location. ^[14]
  • Apply topical vinegar: recommended only for some jellyfish species (e.g., box jellyfish)
  • Remove attached tentacles and rinse the sting site with seawater.
  • Immerse in hot water for pain relief.
  • Administer antivenom in the case of severe stings (e.g., stings affecting large areas, systemic symptoms).

• Distribution: freshwater and coastal regions
• Epidemiology: 750–2000 stings reported annually in the US ^[15]
• Clinical features
  • Local: laceration or puncture wound, with severe pain that is disproportionate to the injury
  • Systemic:
    • Headache, seizures, syncope
    • Dyspnea
    • Muscle cramps
    • Hyperhidrosis
    • Abdominal pain, nausea, vomiting
  • Potential allergic reaction or anaphylaxis
• Diagnostics
  • Imaging: x-ray to check for retained barb
  • Laboratory studies: swab sample for culture if signs of secondary infection
• Differential diagnosis: stonefish sting
• Treatment
  • Immerse injury in hot water (42–45°C) for 30–90 minutes (provides analgesia and denatures the venom).
  • Administer NSAIDs or opioids if analgesia from hot water immersion is insufficient.
  • Wound treatment
    • Clean puncture site.
    • Check for retained barb under local anesthetic.
    • Do not suture wound (due to risk of infection).
  • Administer prophylactic antibiotics.
  • Tetanus: recommended if the last vaccination was ≥ 5 years ago (for further information see “Tetanus prophylaxis”)
• Complications
  • Infection or necrosis (due to retained barb)
  • Potentially lethal systemic toxicity in the event of penetrating trauma to abdomen, chest, or neck

• Distribution
  • Worldwide, mainly Indian and Pacific Oceans
  • Injuries not limited to coastal areas, due to inland aquarium trade
• Pathophysiology: Venom causes vasodilation, hypotension, neuromuscular paralysis, arrhythmias, and myocardial ischemia.
• Clinical features ^[16]
  • Local: intense burning sensation at the puncture site, which radiates proximally
  • Systemic:
    • Headache, syncope, weakness
    • Chest pain, dyspnea (due to pulmonary edema)
    • Hyperhidrosis
    • Abdominal pain, nausea, vomiting
  • Potential hypersensitivity reaction including anaphylaxis
• Diagnostics
  • Primarily a clinical diagnosis
  • Imaging: x-ray to exclude retained spines and foreign bodies
  • Laboratory studies: swab sample for culture if there are signs of secondary infection
• Differential diagnosis
  • Sea urchin sting: dark discoloration around the puncture site (due to pigment in the spines)
  • Stingray sting
• Treatment
  • Immerse the affected area in hot water at 42–45°C for 30–90 minutes (provides analgesia and denatures the fish venom).
  • Administer NSAIDs or opioids if analgesia from hot water immersion is insufficient.
  • Wound treatment
    • Clean puncture site.
    • Check for retained spines under local anesthetic.
    • Drain blisters, as they may contain venom.
  • Administer antivenom if systemic symptoms occur.
• Complications: wound infection, necrotic ulcers, compartment syndrome, chronic neuropathy

• Epidemiology: the leading cause of rabies transmission in the US (70% of cases) ^[17]
• Pathophysiology: Bats transmit rabies through infected saliva, but their bites can be very small, painless, and difficult to identify.
• Treatment
  • Clean wound.
  • Irrigate wound with water, normal saline, or dilute povidone-iodine solution.
  • Rabies prophylaxis should be administered:
    • In the case of any bite or scratch, even if through clothing
    • If a child is left unattended in a room where a bat is found
    • If an individual wakes up to find a bat in their room
    • For further information, see “Rabies post-exposure prophylaxis.”
  • Tetanus: recommended if the last vaccination was ≥ 5 years ago (for further information see “Tetanus prophylaxis”)

• Examples: great white shark, tiger shark, bull shark
• Epidemiology
  • Despite posing a relatively low public health risk, shark-related injuries often generate a disproportionate amount of public and media attention.
  • Annually, 70–80 unprovoked shark attacks occur worldwide ^[18]
• Management
  • In the rare event of a patient being admitted with shark-related injuries:
    • Prioritize hemorrhage control
    • Clean wounds thoroughly to prevent infection
  • For more information, see 'Management of trauma patients'

Approx. 7% of shark attacks are fatal. ^[19]