Zoonotic Diseases Hub

Pathogens circulate among animals in their natural environments, regardless of whether they cause illness in those animals. When humans and animals interact at the human-animal-environment interface, transmission from animals to humans can occur, a process known as spillover. The transmissibility of these pathogens depends on several variables, including pathogen, host, human, vector (if applicable), environmental, and other factors.

There are five main mechanisms of transmission from animals to humans:

• foodborne: from food contaminated with feces from an infected animal,
• waterborne: from water contaminated with feces from an infected animal,
• vector-borne: such as being bitten by a tick, mosquito or flea carrying the pathogen,
• direct contact: coming into contact with body fluids of an infected animal including bites and scratches, or
• indirect contact: through contact with inanimate objects or environmental contamination, such as pet habitats, barns, aquariums, soil, food and water dishes.

Reverse zoonoses (humans to animals) are usually transmitted through direct contact.

Everyone is vulnerable to zoonotic diseases, but some individuals are at a higher risk of experiencing severe illness or death if they become infected. Those at greater risk should take precautions to protect themselves and their family members from exposure to specific pathogens. These groups include:

• Children under the age of 5
• Adults older than 65
• Immunocompromised individuals
• Pregnant women

It is advisable to consult with your local or state public health department, particularly the state public health veterinarian, for guidance on infection control practices related to suspected or confirmed zoonotic infections. Standard precautions should be implemented for all patients in every setting. These standard precautions include:

• Hand hygiene  
• Environmental cleaning and disinfection  
• Injection and medication safety  
• Risk assessment that involves using appropriate personal protective equipment based on the activities being performed  
• Minimizing potential exposures, such as respiratory hygiene  
• Reprocessing reusable medical equipment between each patient or when the equipment becomes soiled  

As part of the risk assessment, if the mode of transmission for the zoonotic disease involves aerosols or respiratory droplets for human-to-human transmission, specific infection control measures for aerosol exposure are necessary. This requires a combination of engineering controls, personal protective equipment, and safe clinical practices to reduce the generation and inhalation of infectious particles.

Everyone should wash their hands thoroughly with running water and soap after handling animals, their bodily fluids and excretions, their food, and other supplies.

Some pets are considered higher-risk animals because they are more likely to carry pathogens that can infect humans. These animals may appear healthy but can still carry harmful pathogens, and their living areas can be contaminated as well. These higher-risk animals include:

• Reptiles and amphibians
• Backyard poultry
• Rodents
• Exotic pets (such as monkeys or other wild animals)

People who are immunocompromised should be especially cautious, as they are at increased risk of infection from high-risk animals. They should consider different types of pets or to have someone else in the household care for these animals.

Pregnant women should be aware of specific risks, such as toxoplasmosis, which can be transmitted by cats, and lymphocytic choriomeningitis virus (LCMV), which can be spread by some rodents. It is recommended that pregnant women avoid cleaning the cat's litter box whenever possible, avoid contact with wild rodents, and take precautions when handling pet rodents.