Zoonotic Exposures: Bites, Scratches, and Other Hazards

Introduction

International travelers may not be aware of the risks that certain animal species pose, particularly when encountering animals that are not native to the traveler's country of origin. For example, people coming from areas where dangerous reptiles are not present may not recognize the risk posed when they visit places where reptiles are venomous. Animals around the world have adopted a wide variety of mechanisms to protect themselves, including bites, toxins, and venoms. Additionally, animals like birds, reptiles, ruminants (e.g., cattle, goats, sheep), rodents, bats, and non-human primates can be asymptomatic carriers (reservoirs) of pathogens that can cause illness in people, ranging from mild to life-threatening. Zoonotic transmission between animals and humans can occur in several ways: through contact with infected animals, their body fluids (e.g., blood, saliva, urine, or feces), or animal products (e.g., hides or horns); through contact with contaminated surfaces or animal habitats; through foodborne or waterborne routes; or by bites of infected arthropod vectors (e.g., ticks, mosquitoes, fleas, mites) that have fed on infected animals. Animal bites and scratches are common sources of serious infections. Any animal (domestic or wild) can bite or scratch if it feels threatened, is protecting its young or territory (including food), or is injured or ill. Travelers should be aware that attacks by domestic animals (e.g., stray dogs and cats) are far more common than attacks by wildlife. Infections caused by bite or scratch wounds can result in serious illness or death in humans. Table 3.7.1 highlights groups of animals and arthropod vectors that are common reservoirs and routes of transmission of zoonotic diseases.

Table 3.7.1: Animal hosts and routes of human exposure to selected zoonotic pathogens that may pose a risk to travelers^1,2

Bites and scratches

Bites and scratches from certain animals, including bats, cats, dogs, non-human primates, and rodents, present a risk for serious illness. Also, certain reptiles and amphibians may be venomous, and their bites require immediate medical attention. Human exposure to saliva and other body fluids of infected animals can occur through bites, scratches, cuts in the skin, or other contact between mucous membranes like the eyes or mouth.

Prevention

Animal adoption

Travelers should avoid the temptation to adopt a stray animal from abroad because the animal's medical history often is unknown, behavioral screening is often incomplete or inaccurate, and the animal might be infected or incubating a disease not found in the United States. In addition, animal importation restrictions may complicate or prohibit bringing an animal back (see Traveling with Pets and Service Animals chapter).

Animal avoidance

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, often have unpredictable behavior, and may associate humans with food. Travelers should exercise caution to avoid bites, scratches, and exposure to body fluids like blood, saliva, urine, and feces of animals while traveling.

Animals in some areas have learned that plastic or paper lunch bags, often placed in backpacks, are a food source. Non-human primates 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, Indonesia, Gibraltar, and Thailand, 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 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.

It is also important to advise travelers to wash hands or use hand sanitizer after being in areas around animals, even if they did not touch the animals, to prevent indirect transmission of zoonotic diseases.

Pre-travel vaccines

Before departure, travelers should have a current tetanus vaccination or documentation of a booster vaccination in the previous 10 years. Travel medicine specialists also should assess a traveler's need for pre-exposure rabies vaccine (see Rabies chapter).

Management

High-risk exposures

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.

B Virus

If bitten or scratched by a monkey, travelers should be evaluated for B virus post-exposure prophylaxis (PEP). B virus is enzootic in macaque monkeys (e.g., crab-eating macaques, rhesus macaques) found in North Africa, Gibraltar, and 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. Antiviral post-exposure prophylaxis with oral valacyclovir may be indicated in the case of an exposure to broken skin or mucus membranes. In addition, rapid laboratory diagnosis and early initiation of antiviral treatment can help to prevent development of severe disease or death.

Capnocytophaga infection

Capnocytophaga spp. are bacteria that live in the mouths of dogs and cats. Most people who have contact with a dog or cat do not become sick with Capnocytophaga infection. Rarely, Capnocytophaga spp. can spread to people through bites, scratches, or close contact from a dog or cat (especially contact with their saliva) and may cause serious illness, including sepsis. People with weakened immune systems who have difficulty fighting off infections (e.g., people with cancer, who have had their spleens removed, or those taking certain medications such as steroids) are at greater risk of becoming seriously ill.

In people, Capnocytophaga infection can have a range of signs and symptom, including blisters around the bite wound within hours of the bite; redness, swelling, draining pus, or pain at the bite wound; and systemic symptoms including abdominal pain, confusion, diarrhea, fever, headache, muscle or joint pain, or vomiting. After being bitten, most people who become ill will show symptoms within 1–14 days. Some infections can lead to death.

Rabies

A healthcare professional should evaluate travelers bitten or scratched by any animal to assess the need for rabies PEP (see Rabies chapter). If a suspected rabies exposure has occurred, travelers should stop their journey and seek care at a reliable place where they can obtain appropriate PEP; this could require traveling to another country. During the pre-travel consultation, suggest countries where PEP is available and most accessible.

Rabies exposures are relatively common among travelers. 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. With very rare exception, rodent exposures should not constitute a rabies exposure.

Tetanus

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.

Wound care

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 reduce the risk of infections like B virus or rabies. Where possible, healthcare 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.

Inhalation, ingestion, or contact with body fluids of infected animals

The normal flora in the saliva, urine, and feces of many animals can be pathogenic for humans, although exposure to animal body fluids is not always obvious or recognized. For example, water contaminated with animal urine or feces might be used to wash food items.

Prevention

In 2008, Marburg virus infection 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 inhabited by bats also have other inhalation and ingestion hazards, such as fungi.

To help prevent inadvertent exposure to animal body fluids (e.g., blood, saliva, urine, or feces), travelers should be advised to avoid areas with dense populations of animals (e.g., caves, corrals, mines, livestock markets). Travelers planning to enter areas with dense populations of animals or planning to have contact with blood or body fluids of animals (e.g., participating in animal slaughter) should wear appropriate protective equipment (e.g., face shield, respirator, gloves) and clothing. Upon leaving the area, travelers should safely and appropriately remove dirty equipment and clothing and wash or bathe as soon as possible. Travelers should also avoid bringing food and drink into areas with dense populations of animals or areas that may be contaminated by body fluids of animals.

Crimean-Congo hemorrhagic fever (CCHF), another example of an important zoonotic viral disease, is found globally, with most human cases occurring in Europe, Central Asia, the Middle East, and Africa. CCHF virus is most commonly transmitted to humans by bites of infected ticks or contact with blood or body fluids of infected domestic ruminants such as cattle, goats, and sheep. Human-to-human transmission, including healthcare-associated infections, through contact with infectious blood, body fluids, or contaminated medical equipment, is possible. Up to 40% of CCHF cases are fatal. To prevent exposures to CCHF virus in endemic areas, travelers should avoid contact with blood and body fluids of domestic ruminants, avoid known tick habitats such as wooded and brushy areas with high grass, wear protective clothing, and use insect repellent on exposed skin and clothing. Insect repellants containing DEET (N, N-diethyl-m-toluamide) are the most effective in warding off ticks (see Mosquitoes, Ticks, and Other Arthropods chapter).

Management

Illnesses might not appear for hours or even weeks after exposure, depending on the pathogen, route of exposure, or other factors. When evaluating an ill traveler, healthcare professionals should take highly detailed travel histories that include all activities that could result in exposure to or contact with animals and their habitats.

Acknowledgements

The following authors contributed to the previous version of this chapter: G. Gale Galland, Nina Marano, and Kendra Stauffer.