Zoonoses Associated with Horses
This document provides information on various diseases that can be passed from horses to humans. Often these diseases do not make the animal appear sick but can cause serious illness in humans. Persons with specific medical conditions such as an immunodeficiency and pregnancy may be at higher risk of developing disease or complications from a zoonotic disease and should consult with their physician before working with horses. The diseases associated with horses include rabies, ringworm, methicillin-resistant strains of Staphylococcus aureus, leptospirosis, salmonellosis, campylobacterosis, cryptosporidiosis and infections with Rhodococcus equi, brucellosis, and Anthrax. Additional information on zoonotic diseases can be found on the Center for Disease Control and Prevention Website, Healthy Pets, Healthy People.
Diseases associated with direct contact:
Rabies is a fatal viral infection that can be transmitted by bites, and mucus membrane exposure from an infected animal. Rabies in horses in the Northwest is very rare but horses can be infected from contact with wildlife such as bats, skunks, and raccoons. Infected animals often exhibit neurological symptoms and unusual behavior. There is an effective vaccine available for people and most domestic animals including horses.
Dermatophytosis is a fungal skin infection commonly known as “ringworm” and is seen in both animals and people as scaly round areas of hair loss. Transmission of ringworm is by direct contact with an infected animal. For prevention, wear gloves when handling infected animals and wash hands after contact.
Methicillin-resistant Staphylococcus aureus (MRSA) has been identified in both normal horses and those with clinical symptoms of wound infections. It is possible to contract the infection through direct contact with an infected horse. Once infected, people may or may not develop symptoms. If people are not treated, the infection can progress to septicemia and affect other organs including the lungs.
While transmission is unlikely, it is recommended to wash your hands after handling horses and to cover any open wounds that are susceptible to infection.
Diseases associated with vectors or contaminated materials:
Leptospirosis is most commonly associated with eye infections, abortion or kidney disease in horses and is typically shed in the urine of infected animals. People acquire the infection by accidental ingestion and contact with contaminated urine, placenta, and fetal tissues. The organism can infect people through abraded skin. In people, the disease causes fever, headache, abdominal and muscle pain, vomiting, diarrhea, jaundice, and rash. In more severe cases, it can cause hemorrhagic pneumonia, liver and kidney failure and can lead to death.
Rhodococcus equi is a bacterium that causes pneumonia in foals and is found in manure and contaminated soil around horse facilities. Inhalation of dust particles laden with virulent R. equi is the major route of infection. R. equi is an opportunistic pathogen that causes pneumonia or other symptoms in immunocompromised people and does not usually cause disease in persons with normal immune function.
Salmonellosis, campylobacterosis, and cryptosporidiosis are acquired by contact and accidental ingestion of fecal material from infected animals. Animals infected with these diseases typically have diarrhea, but some animals may show no symptoms of disease. Any animal with diarrhea should be suspect of having a zoonotic disease. Symptoms in people include abdominal pain, diarrhea, and fever.
Brucellosis is a bacterial infection that can rarely spread from horses to people. Infection happens via direct contact with affected animals or body fluids, and mucus membrane exposure. The bacterium can penetrate abraded skin. In horses, this bacterium causes joint problems and lameness, inflammation and swelling of the withers, and in rare cases abortion in pregnant mares. Infected people typically experience flu-like symptoms and the disease can affect the reproductive organs and cause miscarriages.
Anthrax is caused by a bacterium (Bacillus anthracis) that is present in the environment and can infect animals, including horses, through ingestion of contaminated water, soil, or plants. Although Anthrax is rare in the United States, it is still of concern. People can become infected and severely ill after contact with affected animals (live or dead) or by consuming food contaminated with bacterial spores. Infection can happen via accidental ingestion of spores or by penetration of bacteria through abraded skin. Infected animals can die quickly so owners do not always perceive any signs of illness. Signs in horses affected by this disease can include fever, chills, severe colic, depression, lack of appetite, weakness, bloody diarrhea, and swellings. Symptoms in people can include skin reactions in the case of cutaneous Anthrax, with formation of blisters followed by ulceration of skin, or in the case of infection via ingestion of spores, symptoms include stomach pain, diarrhea (that could be bloody), sore throat and difficulty swallowing, swelling of neck, fever, chills, and redness in the eyes and face.
Individuals with exposure to animals and animal environments may develop allergic reactions to animal proteins (allergens). Approximately 20-30 percent of individuals working with laboratory animals will develop an allergic reaction to animal proteins and 5-10 percent of individuals will develop asthma. Personnel may be exposed to allergens through inhalation and contact with skin, eyes and mucous membranes. Animal allergens may be present in animal dander, hair, skin, urine, saliva, serum and any contaminated feed or bedding materials. Risk factors for developing an allergic reaction include history of previous allergies to animals. The signs and symptoms of an allergic reaction are nasal discharge and congestion, conjunctivitis, tearing and eye itching, skin redness, rash or hives and lower airway symptoms (coughing, wheezing and shortness of breath). Individuals with symptoms suggestive of an allergic reaction related to a workplace allergen should report their concerns to their supervisor and consult a physician.
Transmission of zoonotic diseases from horses is primarily by direct contact when handling and grooming horses, contact with contaminated objects such as grooming tools, accidental ingestion of feces or urine or inhalation of aerosolized materials. We can protect ourselves from most diseases by using the following procedures:
- Handle animals appropriately and safely to avoid bites, kicks, trample, crush and other injuries.
- Thoroughly wash bite wounds and report injuries.
- Do not eat, drink, apply cosmetics or use tobacco products while handling horses or in horse stalls or pens.
- Wash hands after handling animals or their waste and before eating or drinking.
- Wear clothing appropriate for handling large animals including long pants and shoes or boots that cover your feet (no sandals). Launder the soiled clothing separate from your personal clothes and preferably at the animal facility.
- Wear respiratory protection when appropriate.
- Keep animal areas clean and disinfect equipment after using it on animals or in animal areas.
Most importantly, familiarize yourself about the animals that you will be working with and the potential zoonotic diseases associated with each species. If at any time, you suspect that you have acquired a zoonotic disease, inform your supervisor and seek medical care.
**Prepared by Office of the Campus Veterinarian and the Office of Research Assurances January 2021
- Centers for Disease Control and Prevention. Healthy Pets, Healthy People.(https://www.cdc.gov/healthypets/pets/horses.html)