Zoonotic diseases (also known as zoonoses) are caused by germs that spread between animals and people.

Animals provide many benefits to people. Many people interact with animals in their daily lives, both at home and away from home. Animals provide food, fiber, livelihoods, travel, sport, companionship, and education for people across the globe. Millions of households in the United States have one or more pets. We might come into contact with animals in either urban or rural settings, during travel, while visiting animal exhibits, or while enjoying outdoor activities.

However, animals can sometimes carry harmful germs that can spread to people and cause illness – these are known as zoonotic diseases or zoonoses. Zoonotic diseases are caused by harmful germs like viruses, bacterial, parasites, and fungi. These germs can cause many different types of illnesses in people and animals, ranging from mild to serious illness and even death. Animals can sometimes appear healthy even when they are carrying germs that can make people sick, depending on the zoonotic disease.

Zoonotic diseases are very common, both in the United States and around the world. Scientists estimate that more than 6 out of every 10 known infectious diseases in people can be spread from animals, and 3 out of every 4 new or emerging infectious diseases in people come from animals. Because of this, CDC works 24/7 to protect people from zoonotic diseases in the United States and around the world.

Because of the close connection between people and animals, it’s important to be aware of the common ways people can get infected with germs that can cause zoonotic diseases. These can include:

• Direct contact: Coming into contact with the saliva, blood, urine, mucous, feces, or other body fluids of an infected animal. Examples include petting or touching animals, and bites or scratches.
• Indirect contact: Coming into contact with areas where animals live and roam, or objects or surfaces that have been contaminated with germs. Examples include aquarium tank water, pet habitats, chicken coops, plants, and soil, as well as pet food and water dishes.
• Vector-borne: Being bitten by a tick, or an insect like a mosquito or a flea.
• Foodborne: Each year, 1 in 6 Americans get sick from eating contaminated food. Eating or drinking something unsafe, such as unpasteurized (raw) milk, undercooked meat or eggs, or raw fruits and vegetables that are contaminated with feces from an infected animal. Contaminated food can cause illness in people and animals, including pets.
• Waterborne: Drinking or coming in contact with water that has been contaminated with feces from an infected animal.

INJURY & ILLNESS

Animals do not have to be sick to be a risk to humans. Animals such as poultry, reptiles, and goats, carry human pathogens as normal flora. Other animals, such as rodents, bats, and nonhuman primates, can be subclinical carriers of pathogens. Animals, even those in close association with humans, such as dogs or animals in petting zoos, can attack if they feel threatened, are protecting their young or territory, or are injured or ill.

Travelers should be aware that attacks by domestic animals are far more common than attacks by wildlife, and secondary infections of wounds may result in serious illness or death. This section will cover the most common routes of transmission of illness and injury from animals and will highlight those animals that are common reservoirs of zoonotic diseases.

ROUTES OF TRANSMISSION

Bites and Scratches

Bites from certain mammals encountered during foreign travel (monkeys, dogs, bats, and rodents) present a risk for serious infection. Saliva from these animals can be contaminated so heavily with pathogens that a bite may not be required to cause human infection; contact with a preexisting cut or scratch or mucous membrane can represent sufficient exposure.

PREVENTION

Before departure, travelers should have a current tetanus vaccination or documentation of a booster vaccination in the previous 5–10 years. Travel health providers should also assess a traveler’s need for preexposure rabies immunization. During travel, people should never try to pet, handle, or feed unfamiliar animals (domestic or wild, even in captive settings such as game ranches or petting zoos), particularly in areas where rabies is enzootic. Avoiding unfamiliar animals can help mitigate the risk of exposure to rabies, and travelers should avoid the temptation to adopt stray animals from abroad. Advise parents traveling with young children to watch them carefully around unfamiliar animals, as they are more likely to be bitten or scratched and to sustain more severe injuries.

MANAGEMENT

Travelers should clean all bite and scratch wounds quickly with soap and water to prevent infection. Wounds contaminated by necrotic tissue, dirt, or other foreign materials should be debrided promptly by health care professionals, if present. Often, a course of antibiotics is appropriate after dog or cat bites or scratches, as these can lead to local or systemic infections.

Wound care is especially important for exposures where rabies or tetanus is a concern. Health care professionals should evaluate travelers bitten or scratched by any animal, but particularly if the attack was unprovoked, to assess the need for rabies postexposure prophylaxis (PEP). In many countries dogs, terrestrial carnivores, and bats are the most commonly reported rabid animals; a health care professional should treat high-risk exposure immediately.

Rabies is comparatively rare in primates and rodents. Nevertheless, travelers should seek evaluation from a health care professional, especially if an attack was unprovoked or the animal appeared ill. Additionally, if bitten or scratched by a monkey, travelers should be evaluated for B virus PEP.

Travelers with high-risk exposures (including animal bites and scratches) not vaccinated for tetanus will require a dose of tetanus toxoid–containing vaccine (Tdap, Td, or DTaP). This applies to those who received their most recent tetanus toxoid–containing vaccine >5 years before their exposure and those who have not received ≥3 doses of tetanus toxoid–containing vaccines.

Stings and Envenomations

Snakes, insects, and marine fish and invertebrates are hazards in many locations. Snakebites usually occur in areas where dense human populations coexist with dense snake populations, such as Southeast Asia, sub-Saharan Africa, and tropical areas in the Americas; 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, such as mosquitoes and ticks, can transmit infections.

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 stingrays, jellyfish, stonefish, sea urchins, and scorpionfish, live in tropical coastal waters.

PREVENTION

Avoiding stinging and venomous animals is a traveler’s best precaution. Most stings and envenomation result from startling, stepping on, handling, attempting to feed, or otherwise harassing the animal.

• Before engaging in recreational activities, travelers should try to learn about the animals they may encounter, including their characteristics and habitats.
• Travelers should be aware of their surroundings:
  • Especially at night and during warm weather when snakes tend to be more active
  • When water conditions create poor visibility, rough water, currents, or confined areas
• Travelers should wear protective clothing:
  • Heavy, ankle-high or higher boots and long sleeves and pants when walking outdoors in areas possibly inhabited by venomous snakes and biting insects
  • Rash guards, swim boots, or other protective footwear in water where these animals are present

MANAGEMENT

Advise travelers to seek immediate medical attention any time a sting or envenomation occurs. In case of injury, species identification can help direct the best course of treatment. Photographs of the animal can aid medical personnel. Immobilization of affected limbs and application of pressure bandages that do not restrict blood flow are recommended first aid measures during victim transport to a medical facility.

Incision at bite sites and use of tourniquets to restrict blood flow to affected extremities should not be used as therapeutic options. Snakebite care is controversial and should be left to local emergency medical personnel. Specific antivenoms are available for some snakes in some areas; knowing the species of snake involved may 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 may not appear for hours after contact. Symptoms can range from localized mild swelling and redness to more severe findings, such as difficulty breathing or swallowing, chest pain, or intense pain at the sting or bite site. Management will vary according to the severity of symptoms; therapy may include diphenhydramine, steroids, pain medication, and antibiotics.

Inhalation and Ingestion

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

PREVENTION

Discourage travelers from going into caves, tunnels, or mines housing large populations of animals. Travelers planning to enter densely populated animal habitats (such as bat caves) should don protective equipment (face shield, respirator, gloves) and clothing. Upon leaving, they should then doff dirty equipment and clothing and wash or bathe as soon as possible. Travelers should not eat or drink anything potentially contaminated by animal feces or urine. Avoiding dusty animal enclosures or housing can help prevent the inhaling of aerosolized urine and/or feces.

MANAGEMENT

Illness related to animal excreta may not appear for hours or even weeks after exposure. Health care providers must take highly detailed travel histories that include all activities resulting in exposure to or contact with animals and their habitats. Base treatment of illness on signs, symptoms, and the specific pathogen.

Common reservoirs of zoonotic diseases and mechanisms/routes of human infection

A recent example of an indirect exposure is an imported case of Marburg fever in a tourist who had visited a cave inhabited by bats (Python Cave in western Uganda). This case illustrates the risk of acquiring diseases from indirect contact with cave- dwelling bats. This same cave was the source of a fatal case of Marburg hemorrhagic fever in a Dutch tourist in 2008.

The viruses we study are zoonotic, meaning they naturally occur in animal or insect populations in the environment. People become infected with these viruses when they encounter an infected animal or insect, or their body fluids. After infecting one person, many of these viruses can continue to spread from person-to-person.

Most high-consequence viral pathogens are classified as Biosafety Level 4 (BSL-4) pathogens, meaning they must be worked on in special laboratory facilities with the highest level of safety measures. We operate a BSL-4 laboratory which is designed with specific precautions and controls to contain dangerous BSL-4 pathogens.

Viral Hemorrhagic Fevers

Viral hemorrhagic fevers (VHFs) are a group of diseases caused by several distinct families of viruses. Some VHFs cause relatively mild illness, while many others cause severe, life-threatening disease with no known cure, like Ebola. Most of the diseases we study are VHFs that are classified as BSL-4 pathogens. These are listed below, grouped by virus family. Find information on other VHFs on the VHF website.

Arenaviridae

• Chapare Hemorrhagic Fever (CHHF)
• Lassa Fever
• Lujo Hemorrhagic Fever (LUHF)
• Lymphocytic Choriomeningitis (LCM)

Nairoviridae

• Crimean-Congo Hemorrhagic Fever (CCHF)

Hantaviridae

• Hantavirus
  • Hantavirus Pulmonary Syndrome (HPS)
  • Hemorrhagic Fever with Renal Syndrome (HFRS)

Phenuiviridae

• Rift Valley Fever (RVF)

Filoviridae

• Ebola Virus Disease (EVD)
• Marburg Hemorrhagic Fever (Marburg HF)

Flaviviridae

• Alkhurma Hemorrhagic Fever (AHF)
• Kyasanur Forest Disease (KFD)
• Omsk Hemorrhagic Fever (OHF)

Paramyxoviruses

Paramyxoviruses cause sudden onset of respiratory diseases and usually spread through the air. While there are many more viruses included within the Paramyxoviridae family, we study these two viruses because they require a BSL-4 lab and they are highly pathogenic, zoonotic, and have no vaccine or treatment currently available.

• Hendra Virus Disease (HeV)
• Nipah Virus (NiV)

Anyone can get sick from a zoonotic disease, including healthy people. However, some people are more at risk than others and should take steps to protect themselves or family members. These people are more likely than others to get really sick, and even die, from infection with certain diseases. These groups of people include:

• Children younger than 5
• Adults older than 65
• People with weakened immune systems
• Pregnant women

Animal diseases that people can catch are called zoonoses. Many diseases affecting humans can be traced to animals or animal products. You can get a disease directly from an animal, or indirectly, through the environment.

Farm animals can carry diseases. If you touch them or things they have touched, like fencing or buckets, wash your hands thoroughly. Adults should make sure children who visit farms or petting zoos wash up as well.

Though they may be cute and cuddly, wild animals may carry germs, viruses, and parasites. Deer and deer mice carry ticks that cause Lyme disease. Some wild animals may carry rabies. Enjoy wildlife from a distance.

Pets can also make you sick. Reptiles pose a particular risk. Turtles, snakes and iguanas can transmit Salmonella bacteria to their owners. You can get rabies from an infected dog or toxoplasmosis from handling kitty litter of an infected cat. The chance that your dog or cat will make you sick is small. You can reduce the risk by practicing good hygiene, keeping pet areas clean and keeping your pets' shots up-to-date.

People can come in contact with animals in many places. This includes at home and away from home, in places like petting zoos, fairs, schools, stores, and parks. Insects, like mosquitoes and fleas, and ticks bite people and animals day and night. Thankfully, there are things you can do to protect yourself and your family from zoonotic diseases.

• Keep hands clean. Washing your hands right after being around animals, even if you didn’t touch any animals, is one of the most important steps you can take to avoid getting sick and spreading germs to others.
  • Always wash your hands after being around animals, even if you didn’t touch the animals.
  • Many germs are spread by not washing hands properly with soap and clean, running water.
  • If soap and water are not readily available, you can use an alcohol-based hand sanitizer that contains at least 60% alcohol.
  • Because hand sanitizers do not get rid of all types of germs, it is important to wash your hands with soap and water if they are available.
• Know the simple things you can do to stay safe around your pets.
• Prevent bites from mosquitoes, ticks, and fleas.
• Learn more about ways to handle food safely—whether it’s for yourself or your family, your pet, or other animals.
• Be aware of zoonotic diseases both at home, away from home (such as at petting zoos or other animal exhibits), in childcare settings or schools and when you travel.
• Avoid bites and scratches from animals.