How Infectious Diseases Spread Between Horses

Wildlife can spread rabies and equine protozoal myeloencephalitis (EPM) to horses, so secure your barn against unwanted visitors.

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Understanding how infectious diseases spread can help owners keep their horses safe. | Photo: iStock

Controlling infectious diseases relies on understanding how they spread. Infectious organisms are transmitted to horses through the following routes:


Respiratory droplets from sick horses become airborne through coughing, snorting, or sneezing. Residue from evaporated droplets and infected dust particles can also become suspended in the air. Infectious organisms are transferred when they contact the eyes, nose, or mouth. Pathogens vary in their ability to survive and transmissibility in the air, which are impacted by environmental factors including wind, humidity, and temperature.

Diseases capable of transmission by aerosols include equine influenza and equine herpesvirus.

Airborne diseases are challenging to contain and can spread quickly. To reduce the rate of transmission, keep distance between horses, keep dust down, and ensure proper ventilation in enclosed spaces.

Direct Contact

Some diseases spread through close physical contact with infected animals, their body fluids or tissues, and direct touching of wounds, skin, or mucous membranes around the nose, eyes, and mouth. Affected animals can infect other animals through nose-to-nose contact or biting.

Equine influenza is an example of a disease spread by nose-to-nose contact.

Limit contact with horses between stalls, in aisle ways, and at crossties or wash racks; do not tie horses near each other; and clean and disinfect water troughs regularly to reduce direct contact.

Indirect Contact

Objects contaminated with infectious organisms are called fomites. These can include tack, buckets, grooming supplies, hoses, clothing, and vehicles.

Diseases spread by indirect contact include strangles and equine herpesvirus-1.

Avoid sharing equipment between horses. If equipment must be shared, clean and disinfect it between uses. Dedicate separate supplies and equipment for sick horses. Keep vehicles and trailers in designated areas. Limit traffic, people, and other animals in horse areas to minimize spread through indirect contact.


Horses can consume pathogens in feed or water contaminated by feces or urine from infected animals. Licking or chewing contaminated objects in the environment can also lead to ingestion of pathogens.

Diseases spread through oral transmission include salmonellosis and equine coronavirus.

Control feed sources, ensure feed quality, and handle and store feed properly. Clean stalls regularly, manage fecal piles in fields and turnouts, and ensure proper waste management. Avoid natural water sources such as streams that might be contaminated with feces or urine from wildlife and livestock.


Insects, such as mosquitoes and flies, or ticks can transmit infectious organisms between animals.

Vector-borne diseases include West Nile virus and Eastern and Western equine encephalitis.

Proper vector control is an essential part of any biosecurity plan. Use insecticide applications as appropriate. Fence off areas with high insect and tick populations, and keep horses inside when these vectors are active (dusk to dawn). Eliminate insect breeding areas, including standing water and decaying organic matter.


Rodents, skunks, opossums, bats, birds, and other wildlife can also act as disease vectors.

Diseases spread by wildlife include rabies and equine protozoal myeloencephalitis (EPM).

Prevent wildlife from accessing barn areas, sweep regularly, keep barns and tack rooms tidy, and clean up and store feed in containers with securable lids. Patch holes and gaps in buildings to prevent wildlife access. Do not leave pet food or water out overnight, and keep compost piles away from barns.

This article was originally written by Amy Young and published in the Horse Report from the Center for Equine Health at the UC Davis School of Veterinary Medicine in Summer 2020.


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