Zoonotic Exposures: Bites, Stings, Scratches & Other Hazards
CDC Yellow Book 2024Environmental Hazards & Risks
International travelers might encounter familiar animals (e.g., dogs and cats) that demonstrate unfamiliar behavior, and unfamiliar animals that can be venomous, toxic, or aggressive. People coming from areas where dangerous reptiles do not exist, for example, do not necessarily recognize the risk posed when they visit places where reptiles can threaten human health.
Animals do not have to be sick to be a risk to humans. The normal flora of poultry, reptiles, and ruminants can cause serious infections in humans, and rodents, bats, and nonhuman primates can be carriers of disease. Any animal (domestic or wild) can attack if it feels threatened, is protecting its young or territory, or is injured or ill. Free-roaming (stray) dogs are also common in many destinations and do not behave like pet dogs. Travelers should be aware that attacks by domestic animals are far more common than attacks by wildlife, and secondary infections of wounds can result in serious illness or death. Table 4-07 highlights groups of animals that are common reservoirs and routes of transmission of zoonotic diseases.
Table 4-07 Animal reservoirs & mechanisms / routes of human exposure to zoonotic diseases & pathogens1
|ANIMAL RESERVOIR||BITES & SCRATCHES||INHALATION & INGESTION|
|Rabies||>200 bat-associated viruses (almost all RNA)
Hemorrhagic fever viruses
Paramyxoviruses (parainfluenza type 2 virus, Mapuera, Menangle, Nipah, Hendra)
Coronaviruses (SARS-CoV-1, SARS-CoV-2, MERS)
|Avian influenza (highly pathogenic) in humans|
|Cats & dogs||BACTERIAL|
|Lymphocytic choriomeningitis virus
Viral hemorrhagic fevers
Hemorrhagic fever with renal syndrome2
Lymphocytic choriomeningitis virus2
Viral hemorrhagic fevers2
|Rodent fleas, ticks & mites||BACTERIAL|
Abbreviations: : FEV1, forced expiratory volume in 1 second
1See Healthy Pets, Healthy People: Diseases That Can Spread Between Animals and People.
2Transmitted through inhalation or ingestion of rodent feces or urine.
3Transmitted through direct rodent contact.
Bites & Scratches
Bites from certain mammals encountered during foreign travel (bats, cats, dogs, monkeys, and rodents) present a risk for serious infection. Saliva from these animals can be contaminated so heavily with pathogens that a bite might not be required to cause human infection, and exposures can occur through cuts, scratches, or mucous membranes. For example, a 60-year-old man visiting Morocco was scratched on the face by a dog, became sick with rabies, and died.
Travelers should avoid the temptation to adopt stray animals from abroad, because the animals’ medical history often is unknown, behavioral screening is incomplete or inaccurate, and the animal might be infected or incubating a disease not found in the United States. See Sec. 4, Ch. 9, Bringing Animals & Animal Products into the United States, for more details.
Advise travelers to never pet, handle, or feed unfamiliar animals, domestic or wild, even in captive settings (e.g., game ranches, petting zoos), particularly in areas where rabies is enzootic. Safaris and ecotours may encourage up-close contact with animals; these animals are wild, however, often have unpredictable behavior, and associate humans with food. Travelers should exercise caution to avoid bites, scratches, and exposure to infectious materials.
Animals in some areas have learned that plastic or paper lunch bags, often placed in backpacks, are a food source. Monkeys are notorious for climbing into vehicles and opening backpacks to get food. Remind travelers to keep food items separated from personal effects in the vehicle. Travelers also should remove shiny or flashy jewelry, because these can attract attention from monkeys. Monkey bites are common in India, Thailand, Indonesia, and Bali, and most injuries occur when people try to touch or feed these animals.
When navigating cities, travelers should move wide around corners or blind spots, and check under restaurant tables, food stalls, and parked vehicles, because cats, dogs, and monkeys tend to rest in these places. Startling one of these animals might result in a bite or scratch. Advise parents traveling with young children to watch them carefully around unfamiliar animals, because children are more likely to be bitten or scratched and to sustain more severe injuries.
Before departure, travelers should have a current tetanus vaccination or documentation of a booster vaccination in the previous 10 years (see Sec. 5, Part 1, Ch. 21, Tetanus). Travel health providers also should assess a traveler’s need for preexposure rabies vaccine (see Sec. 5, Part 2, Ch. 18, Rabies).
A high-risk exposure is an animal bite or scratch that was unprovoked or that came from an animal that appeared ill. Provoked bites and scratches are often inflicted when a person attempts to feed or handle an otherwise healthy-appearing animal. Unprovoked bites and scratches increase the likelihood that the animal might be sick and possibly infectious for certain zoonotic diseases (e.g., rabies). Travelers with high-risk exposures should seek professional medical care immediately, and not wait until they return to their home country.
If bitten or scratched by a monkey, travelers should be evaluated for B virus postexposure prophylaxis (PEP; see Sec. 5, Part 2, Ch. 1, B Virus). B virus is enzootic in macaque monkeys (e.g., crab-eating macaques, rhesus macaques) found in North Africa and Gibraltar, and in Asia. Although B virus infections in humans are rare, and no reports of infection in travelers have been documented, the death rate in infected humans is high. Travelers should properly clean the wound after being bitten; prophylactic antiviral treatment with acyclovir or ganciclovir might be indicated in some cases.
A health care professional should evaluate travelers bitten or scratched by any animal to assess the need for rabies PEP (see Sec. 5, Part 2, Ch. 18, Rabies). If a suspected rabies exposure has occurred, travelers should stop their journey and travel to a reliable place where they can obtain appropriate PEP; this could require traveling to another country. During the pretravel consultation, suggest countries where PEP is available and most accessible.
Rabies exposures are relatively common among travelers and are positively correlated with length of stay. One study estimated travelers’ rabies exposure incidence at 0.4% per month of stay, and other studies have shown that most exposures occur within the first 2 weeks of travel, indicating that even short-term travel can pose a risk for exposure.
Bats, a reservoir for rabies and rabies-related viruses globally, have very small, sharp teeth that might not leave discernable bite marks; travelers might not recognize or might trivialize bat exposure and not seek care. In many countries, bats, cats, dogs, and terrestrial carnivores are the most commonly reported rabid animals. Rabies is comparatively rare in primates and rodents. Rodent exposures should not constitute a rabies exposure with very rare exceptions.
Travelers with high-risk exposures, including animal bites and scratches, who were not recently vaccinated for tetanus will require a dose of tetanus toxoid–containing vaccine (Tdap, Td, or DTaP). This applies to people who received their most recent tetanus toxoid–containing vaccine >5 years before their exposure and to people who have not received ≥3 doses of tetanus toxoid–containing vaccines (see Sec. 5, Part 1, Ch. 21, Tetanus).
If a traveler receives a bite or scratch wound, they should clean the wound as soon as possible by washing with soap and running water for ≥20 minutes to prevent infections (e.g., B virus, rabies). Where possible, health care professionals should promptly clean and debride wounds contaminated with necrotic tissue, dirt, or other foreign materials. Often, a course of antibiotics is appropriate after animal bites or scratches because such wounds can lead to local or systemic infections. Some bite or scratch wounds might need to be left open to heal by secondary intention.
Stings & Envenomations
Snakes, insects, marine fish, and invertebrates are hazards to humans in many locations. Snakebites usually occur in areas where human populations coexist with dense snake populations (e.g., Southeast Asia, sub-Saharan Africa, Australia, tropical areas in the Americas). Of the 3,000 species of snakes, 600 species are venomous, and only 200 species can kill or significantly wound a human. One study showed that 25%–40% of venomous snakebites result in negligible or trivial envenomation.
Bites and stings from spiders and scorpions can be painful and can result in illness and death, particularly among infants and children. Other insects and arthropods (e.g., mosquitoes, ticks) can transmit infections (see Sec 4, Ch. 6, Mosquitoes, Ticks & Other Arthropods).
Most injuries from marine fish and invertebrates occur from chance encounters or defensive maneuvers. Resulting wounds have many common characteristics: bacterial contamination, foreign bodies, and occasionally venom. The incidence of venomous injuries from marine fish and invertebrates is rising as the popularity of surfing, scuba diving, and snorkeling increases. Most species responsible for human injuries, including jellyfish, scorpionfish, stingrays, stonefish, and sea urchins, live in tropical coastal waters.
Most stings and envenomation result from startling, stepping on, handling, attempting to feed, or otherwise harassing an animal. Before engaging in recreational activities, travelers should try to learn about the animals they might encounter, including their characteristics and habitats. Travelers should be especially aware of their surroundings at night and during warm weather, when snakes tend to be more active. The same caveat (awareness of surroundings) applies when conditions involve poor visibility, rough water, or confined areas.
Travelers planning hikes in outdoor areas possibly inhabited by venomous snakes or biting insects should wear heavy, ankle-high or taller boots, and long sleeves and pants (see Sec. 4, Ch. 6, Mosquitoes, Ticks & Other Arthropods, for information on proper insect repellent use). Advise travelers going surfing, diving, or snorkeling to wear rash guards and swim boots, or other protective footwear.
Instruct travelers to seek immediate medical attention any time a sting or envenomation occurs. Lifeguard stations at beaches or local clinics might have treatment kits for common stings or envenomations. In case of injury, species identification can help direct the best course of treatment. If possible, travelers or their companions should provide photographs of the animal to aid medical personnel. Travelers or their companions can immobilize an affected limb and apply a pressure bandage that does not restrict blood flow as first aid measures during transport to a medical facility.
Victims or their companions should not make incisions at bite sites or use tourniquets to restrict blood flow to affected extremities. Snakebite care is controversial and is best left to local emergency medical personnel. Specific antivenoms are available for some snakes in some areas; knowing the species of snake involved might prove critical to management. Consultation with a herpetologist can be beneficial.
If the traveler does not see or recognize the animal, health care providers will need to base treatment on the nature of the injury and the clinical effects. Bear in mind that—in some cases, at least—signs and symptoms might not appear for hours after contact. Symptoms can range from localized mild swelling and redness to more severe clinical findings (e.g., difficulty breathing or swallowing, chest pain, intense pain at the sting or bite site). Medical management will vary according to the severity of symptoms; therapy could include diphenhydramine, steroids, pain medication, and antibiotics.
Inhalation & Ingestion
The normal flora in the saliva, urine, and feces of many animals are pathogenic for humans. Exposure to animal body fluids is not always obvious or recognized, however. For example, water contaminated with animal urine or feces might be used to wash food items. In 2008, an indirect (inhalation) exposure to Marburg virus occurred in 2 tourists who visited a cave inhabited by bats, Python Cave in western Uganda. One case was fatal, and neither person reported a bite or scratch from a bat. Caves and mines also have other inhalation and ingestion hazards, such as fungi (see Sec. 5, Part 4, Ch. 2, Histoplasmosis).
To help prevent inhalation of aerosolized urine or feces, discourage travelers from going into densely populated animal habitats (e.g., caves, corrals, mines, tunnels) housing large populations of animals. Travelers planning to enter densely populated animal habitats (e.g., bat caves) should don protective equipment (e.g., face shield, respirator, gloves) and clothing. Upon leaving the area, travelers should appropriately doff dirty equipment and clothing and wash or bathe as soon as possible. Travelers also should plan to remove all food and drink from their backpacks before entering populated animal habitats.
Illness related to animal excreta might not appear for hours or even weeks after exposure. Health care providers must take highly detailed travel histories that include all activities that could result in exposure to or contact with animals and their habitats.
The following authors contributed to the previous version of this chapter: Kendra Stauffer, Ryan M. Wallace, G. Gale Galland, Nina Marano
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