Expanding upon this month’s topic of Biosecurity I wanted to address a common question we as vets get asked by clients: Can I catch that from my horse? The answer in some cases is yes; there are certain viruses, bacteria, protozoan, and fungi that can be transmitted back and forth between owners and their horses. In the United States the list includes; rabies virus, bacteria such as Brucella abortus, Brucella suis, Bacillus anthracis, Salmonella typhimurium, and Methicillin resistant Staphyloccocus aureus, the protozoan parasiteCryptosporidium parvum, and the fungal species Microsporum. I will describe the disease that each pathogen causes in horses, how it is transmitted, and prevented.
Rabies is a viral disease which can infect both horses and humans. While it is fairly rare in horses, (approximately 40-50 cases are reported each year) it is 100% fatal and should not be overlooked. In infected animals the virus is most concentrated in the saliva and blood and thus can be spread to humans through bites, scratches, or saliva contacting any mucous membrane. Rabies can manifest in one of 3 ways; there is a dumb form, furious form, or paralytic form however in horses it is known as the great pretender. This is because infected horses can present with colic, depression or excitability, choke, excessive salivation, lack of coordination, convulsions, or paralysis. A horse suspected to have rabies should be isolated and the number of people exposed limited to reduce the number of people who will need post exposure treatment (serial vaccines). Unfortunately the only diagnostic test for rabies is post mortem and although rabies is fatal in horses it is preventable with annual vaccination.
Brucellosis is another rare disease of horses and it is caused by bacterium, Brucella abortusor Brucella suis. The bacterium typically infects soft tissues or joints and is most commonly associated with fistulous withers or abortion in horses. Drainage from infected soft tissues or aborted fetal membranes or fluid carries high numbers of the bacteria which can infect humans through open abrasions, wounds, inhalation or oral ingestion. Careful disinfection and proper protective gear when handling possibly infected animals is key to prevention.
Bacillus anthracis is the causative bacterium of anthrax, and can infect any animal. It is spread through skin exposure to the bacterium or inhalation of infective spores from the soil or infected animals. In horses it may present as sudden death, colic or severe diarrhea leading to death. Distinctive signs include blood emitting from the nose, mouth or other orifices and any animal displaying these signs should be isolated and a state health official should be notified. In humans It causes pneumonia and pustule formation and can be fatal. Thus careful handling of suspected infected animals or carcasses is vital.
Salmonella typhimurium is just one of thousands of types of zoonotic (contagious from animals to humans) Salmonella species but is the only one transmitted between people and found commonly in horses. Symptoms include diarrhea and localized infections (joints, eyes etc.). The bacteria is spread by fecal-oral transmission and this is generally the result of improper hand washing. Good hygiene is critical to prevention and any horse with diarrhea should be evaluated by a veterinarian and isolated.
Methicillin resistant Staphylococcus aureus is a strain of bacteria which typically infects superficial wounds and is of concern because, as the name implies, it is resistant to several antibiotics and is difficult to treat. It can be transmitted from horses to people and vice versa. This is why it is important to wear gloves any time you handle a wound on your horse; keep your Staph to yourself! Humans most at risk include medical professionals, including veterinarians. It is becoming increasingly more prevalent in veterinary patients and again prevention is achieved through good hygiene and disinfection.
Cryptosporidium parvum is a protozoan (monocellular, motile organisms with plant like behavior) which infects the intestines of young calves. Foals also carry crypto but do not appear sick. They do however shed the organism in their feces which can be infective to people so once again hand washing and hygiene is vital.
The Microsporidium species are the causative agent of ringworm which is highly contagious because it can be spread through direct contact or indirect contact (brushes, tack, bedding). Signs in horses include small hairless areas most commonly over the face and legs. A secondary bacterial skin infection commonly develops. Diagnosis is made through physical exam and evaluation of hair samples. The disease is often self-limiting in animals with a normal immune system and is readily treatable with topical and oral antifungals.
Besides these pathogens there are numerous others which occur outside this country and are infective to people such as Glanders, Hendra virus, and Venezuelan equine encephalomyelitis. Some frequently seen diseases in horses which are not transmissible from horse to human include West Nile Virus, Eastern Equine Encephalomyelitis, Lyme disease, Equine Influenza, Strangles, and Equine Herpesvirus. If you have any question if your horse may have a contagious disease please take the necessary precautions and call your veterinarian.