Human illness from horses in the United States is rare, but it can happen.
The most common diseases associated with horses that can cause human illness are:
Read below to learn about diseases that can be spread by horses and visit the Healthy People section to learn about staying healthy around horses.
Anthrax (Bacillus anthracis)
Anthrax is a naturally occurring disease of animals caused by bacteria found in the environment. Although it is rare in the United States, people can get sick with anthrax if they come in contact with infected animals, including horses. People who live in areas where anthrax has occurred should consider vaccinating their livestock against the disease every year.
How it spreads: Horses can become infected with anthrax when they ingest spores in contaminated soil, plants, or water. People get infected by having contact with sick, dead animals or eating meat contaminated with spores. People can also get anthrax through a cut or scrape in the skin. Anthrax is not contagious, which means it can’t be spread from person to person.
Who is at risk: Anthrax is rare in the United States, but anyone who comes in contact with anthrax spores can get sick. People at higher risk for anthrax include veterinarians, livestock producers, laboratory professionals, and people who handle animal products.
Signs in horses: Signs of anthrax in horses may include fever, chills, severe colic, anorexia, depression, weakness, bloody diarrhea, and swellings. Anthrax is usually fatal in horses.
Symptoms in people: The symptoms of anthrax in people depend on the type of infection and can take anywhere from 1 day to more than 2 months to appear.
- Cutaneous (skin) anthrax: A group of small blisters or bumps, a painless skin sore (ulcer) with a black center (scar) appearing after the small blisters, and swelling.
- Inhalation anthrax (from breathing in spores): Fever and chills, shortness of breath and chest discomfort, confusion, nausea or vomiting, headache, sweats, extreme tiredness, and body aches. This type of anthrax is very rare and mostly associated with an intentional spore release (bioterrorism).
- Ingestion (stomach & intestines) anthrax: Fever and chills, swelling of neck or neck glands, sore throat, painful swallowing, diarrhea or bloody diarrhea, red face and eyes, and stomach pain.
All types of anthrax have the potential, if untreated, to spread throughout the body and cause severe illness and even death.
Brucellosis (Brucella spp.)
Brucellosis is a bacterial disease caused by contact with infected animals and contaminated animal products like raw milk. In horses, brucellosis can cause lameness due to joint infection, including fistulous withers and “poll evil.” It can also cause abortions in pregnant mares, although this is less common.
How it spreads: The most common way people get brucellosis is by eating or drinking unpasteurized/raw dairy products. People can also get brucellosis by coming in contact with infected animals or contaminated animal tissues or fluids (such as blood) and getting the bacteria in skin wounds or mucus membranes.
Who is at risk: Anyone can get brucellosis, but people who drink raw milk or work closely with animals may be more at risk. It is rare for people to get brucellosis from horses.
Signs in horses: In horses, brucellosis causes fistulous withers, or “poll evil,” which is when there is inflammation and swelling in the bursa (the sac of fluid between bone and soft tissue) of ligaments. This inflammation and swelling typically affects the withers (highest part of the horse’s back) or poll (the part of the horse’s head behind the ears). The inflamed tissue might eventually burst, resulting in drainage of pus and further infection of the surrounding tissue. Brucellosis can also affect an animal’s ability to reproduce, though it rarely causes abortions in horses.
Symptoms in people: People with brucellosis will usually become sick within 2-4 weeks of exposure, but symptom onset can begin anywhere between 5 days to 6 months after exposure. Sick people will have flu-like symptoms. Sometimes brucellosis can become a chronic illness that can be difficult to treat and potentially lead to more severe health consequences. Occasionally, brucellosis can affect reproductive organs and cause miscarriage.
Cryptosporidiosis (Cryptosporidium spp.)
Cryptosporidiosis is a parasitic disease caused by the germ Cryptosporidium (or Crypto for short), which is spread by swallowing poop from an infected person or animal.
How it spreads: Crypto spreads through swallowing poop containing the germ, after contact with an infected person or animal or through food or water contaminated with poop. The risk of getting Crypto from animals is hard to predict, because many animals can be infected with the parasite but not have any signs of being sick.
Who is at risk: Anyone can been infected with Crypto, people with weakened immune systems and young children are more at risk of serious illness. For tips on how to protect yourself and loved ones.
Signs in horses: Horses infected with Crypto might or might not have any signs of being sick. If infected with Crypto, pre-weaned foals appear to be more likely to experience diarrhea than weanlings and yearlings, and older horses.
Symptoms in people: People infected with Crypto might or might not have signs of being sick. Patients with healthy immune systems can experience frequent, non-bloody, watery diarrhea (typically lasting 1–2 weeks) with nausea, vomiting, abdominal pain, and fever. Patients with weakened immune systems can experience profuse watery diarrhea lasting weeks to months or even life-threatening malnutrition and wasting.
Diseases that cause encephalitis
In the United States, mosquitoes spread several viruses that can cause encephalitis in horses, including eastern equine encephalitis (EEE), West Nile, and western equine encephalitis (WEE). Horses can be vaccinated for EEE, West Nile virus, and WEE. Venezuelan equine encephalomyelitis (VEE) can also affect horses, but it is incredibly rare in the United States.
How it spreads: Mosquitoes spread these viruses through infective bites. Animals, including birds and horses, can get infected through mosquito bites. Mosquitoes get infected after biting an infected bird or animal. Mosquito prevention and reducing the number of mosquitoes on your property can help prevent the spread.
Who is at risk: People and horses with weakened immune systems are at greater risk of illness. People at high risk include infants, older adults, and people with certain medical conditions. People who spend time outside are at greater risk of being bitten.
Signs in horses: Horses infected with one of these viruses may or may not show signs of disease. Signs and symptoms range from mild illness to death. Horses with nervous system disease can have depression, trouble walking, paralysis, convulsions, or other neurologic signs. These diseases are potentially life-threatening, so it’s important to contact your veterinarian immediately if you are concerned that your horse could be sick with one of these viruses.
Symptoms in people: Most people with EEE or SLE have no symptoms, but for those who become sick, symptoms can range from mild flu-like symptoms to complex neurologic problems and death. Neurologic signs can include arthritis, respiratory distress, gastrointestinal (stomach) upset, myelitis (spinal cord inflammation), encephalitis (brain inflammation), retinitis, severe muscular weakness, Guillain-Barré syndrome, and partial paralysis, shock, or death.
Leptospirosis (Leptospira spp.)
Leptospirosis is a bacterial disease that can affect people and animals. Many kinds of animals can carry the bacteria in their urine, including horses.
How it spreads: The bacteria that cause leptospirosis spread through the urine of infected animals, which can get into water or soil and survive there for weeks to months. People get infected through contact with urine or other body fluids (except saliva) from infected animals, or through contact with water, soil, or other materials (such as animal bedding) contaminated with urine from infected animals.
Who is at risk: Leptospirosis occurs worldwide, but is most common in tropical and subtropical climates. It has been associated with contact with infected animals and activities in contaminated lakes and rivers, such as swimming, wading, kayaking, and rafting. It is also a risk for people in certain jobs that involve contact with animals or their waste, like farmers, sewer workers, slaughterhouse workers, and veterinarians. People working directly with horses or cleaning up after them (such as mucking stalls) may be at risk for leptospirosis.
Signs in horses: In horses, leptospirosis is most often associated with eye problems, such as cloudiness or the eye or uveitis (inflammation in the eye). It can also cause other symptoms such as fever, stillbirths and abortions, and kidney failure.
Symptoms in people: People with leptospirosis might not have any symptoms, but those who do will usually become sick within 2 days to 4 weeks of exposure and can have high fever, headache, chills, muscle aches, vomiting, jaundice, red eyes, abdominal pain, diarrhea, and rash. A small number of people with leptospirosis can have more severe disease, such as liver and kidney failure, hemorrhagic pneumonia, and even death. Early treatment with antibiotics is important, and can reduce the duration and severity of illness.
MRSA (Methicillin-Resistant Staphylococcus aureus)
Staphylococcus aureus is a common type of a bacteria normally found on the skin of people and animals. MRSA is Staphylococcus aureus bacteria that have become resistant to some antibiotics. MRSA can cause a variety of infections, including skin infections, pneumonia (lung infection), and other problems.
How it spreads: MRSA can spread between people and animals through direct contact (touching). Even horses that aren’t sick can carry MRSA and spread it to people.
Who is at risk: Anyone can get a MRSA infection.
Signs in horses: Horses carrying MRSA might not necessarily show signs, but MRSA can cause skin and wound infections, respiratory tract infections, and septic arthritis. Horses are more likely to carry MRSA if they live on a farm with more than 20 horses.
Symptoms in people: Most people with MRSA will carry it without symptoms. For people who develop a MRSA infection, the most common type is a skin infection. If left untreated, MRSA can rarely spread to the lungs or bloodstream and become life-threatening.
Rabies
Rabies is a deadly neurologic disease caused by a virus that spreads primarily through bites of infected animals. Though rabies is very rare in horses, it is still a concern. Horse owners should vaccinate their animals against rabies.
How it spreads: Rabies is spread through contact with saliva or brain/nervous system tissue from an infected animal, usually through scratches or bites.
Who is at risk: Rabies in people and domestic animals is rare in the United States because of successful animal control and vaccination programs, but the disease is still found in wild animals such as bats, foxes, raccoons, and skunks. You or your horse could be at risk for rabies if you come into contact with an infected animal.
Signs in horses: Rabies in horses is very rare. Horses with rabies might have a variety of signs that rapidly worsen. Most frequently, rabid horses will have abrupt changes in their behavior (depression, agitation, aggressiveness) and may develop paralysis. Rabid horses can be very dangerous and have attacked people.
Symptoms in people: Symptoms of rabies in people can appear days to months after exposure. Once symptoms appear, it is almost always too late for treatment, so if you have been bitten by an animal, you should wash the wound immediately and see a doctor right away.
Ringworm
Ringworm is an infection caused by fungus that can infect the skin, hair, or nails of people and animals.
How it spreads: Ringworm spreads through direct contact with (touching) an infected animal or person, or from the environment.
Who is at risk: Anyone can get ringworm.
Signs in horses: Some horses might not show signs of ringworm infection, but others can have circular areas of hair loss anywhere on their bodies, redness, dry skin, depression, and severe dehydration.
Symptoms in people: Ringworm can affect skin on almost any part of the body as well as fingernails and toenails. The symptoms of ringworm often depend on which part of the body is infected, but they generally include itchy skin, ring-shaped rash, red, scaly, cracked skin, and hair loss.
Salmonellosis (Salmonella spp.)
Salmonellosis is a disease caused by Salmonella bacteria, which are most commonly spread through contaminated food. Salmonella can also spread from animals, including horses, to people and between people.
How it spreads:Salmonella most often spread to animals and people through the feces (poop) of infected animals, contaminated food, or the environment. People can become infected if they don’t wash their hands after touching a horse or its poop, food, toys, or habitat.
Who is at risk: Anyone can get a Salmonella infection, but children younger than 5 years old, adults 65 and older, and people with weakened immune systems are more at risk for serious illness. People who are in contact with horses should be aware that they are at an increased risk for Salmonella infection.
Signs in horses: Horses infected with Salmonella might show no signs of illness, or they may experience diarrhea, dehydration, or depression. One of the most common causes of diarrhea in adult horses is from infection with Salmonella, so if your horse appears sick, call your veterinarian. The diarrhea and dehydration can be severe and even life threatening.
Symptoms in people: People with a Salmonella infection may experience diarrhea, fever, and abdominal cramps. Symptoms usually start 6 hours–4 days after infection and last 4–7 days.
Tickborne Diseases
Horses are at risk for tickborne infections, including Lyme disease, tularemia, and anaplasmosis. Horse owners should talk to a veterinarian about preventing ticks on horses. Treating horses for ticks can reduce the risk of tickborne diseases for you and your horse.
How it spreads: Ticks get infected after biting an infected animal. Tickborne germs are spread through the bite of an infected tick.
Who is at risk: People and horses that spend time in grassy, wooded, or brushy areas are at risk for tick bites. Horses may have ticks in and around the ears, around the eyelids, under front legs, between back legs, or around the tail. Remove ticks from horses promptly or treat your horse for ticks to reduce disease risk.
Signs in horses: Horses infected with a tickborne disease may or may not show signs of disease. Signs and symptoms range from mild illness to death.
For example, anaplasmosis is caused by the bacteria Anaplasma phagocytophilum. In horses, signs and symptoms can include fever; depression; lack of appetite; swelling of limbs, the underside of the chest, or abdomen; and discoloration of mucous membranes.
Symptoms in people: Symptoms of tickborne diseases in people can vary, but usually include fever, chills, body aches, and sometimes a rash. Some tickborne diseases can be very serious and even deadly. See your healthcare provider if you have been in tick habitat or been bitten by a tick and develop any of these symptoms.