Hazards in the Field: Zoonotic Diseases in Large Animals

October 05, 2012
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A zoonotic disease is one that can be transmitted from animals to humans. A few of the most familiar examples are rabies and the plague, and, more applicable in the U.S. over the past few years, certain strains of influenza virus. Given the nature of veterinary medicine, vets are prone to contracting some diseases from their very patients. Here’s a little overview of the creepy crawlies a large animal vet has to be aware of.

1. Ringworm

A fungal infection rather than an actual worm, this skin disease is very common in ruminants, particularly 4-H animals that are housed close together and bathed and groomed constantly, which dries out the skin, while the shared grooming tools hasten the spread of disease. Not fatal, ringworm is mostly an annoyance, especially due to the fact that no animals with ringworm lesions are allowed on the fairgrounds. It doesn’t seem too annoying to the animals unless a calf or lamb gets a really bad case of it, and it’s more of just an embarrassment when a human gets it by having direct skin contact with an active lesion.

2. Orf

Also called sore mouth or contagious ecthyma, orf is a poxvirus that infects goats and sheep. Causing small blisters usually along the lips, orf is painful and can cause weight loss, but, like ringworm, is not fatal. In countries with foot and mouth disease, orf must be differentiated as the two diseases can have similar appearances. Luckily, in the U.S. we don’t currently have to worry about that. What we do have to worry about is contracting orf ourselves. Orf infection in humans occurs through direct skin contact with open lesions on animals. This usually results in blisters along the fingers. I have heard from clients that it is very painful.

3. Diarrhea-causing bugs

I lump these all into one group because usually you don’t know what you’ve caught, but you know you’ve caught something. Gastroenteritis in any farm animal should be considered zoonotic. Bacteria like Salmonella and E. coli are everywhere in every barn, I don’t care how clean it is. Other diarrhea causing single-cell organisms like coccidia and giardia can readily be picked up from livestock regardless of whether they have diarrhea at the time of contact. These bugs have no qualms about what species they initially live in and it will take a lot more than a few cups of Activia yogurt to get you back on track, if you know what I mean. How to prevent such a bowel-shaking event? Hand washing.


Methicillin-resistant Staphylococcus aureus is a terrifying organism that seems to be running rampant in human hospitals. Troubling is the fact that small animal hospitals are culturing it as well. Large animals are not exempt from this scary, antibiotic-defying bacterium and all infected skin wounds, particularly equine, should be treated as if they have MRSA just to be on the safe side, unless bacterial culture says otherwise. Oh, and wash your hands to prevent its spread.

5. Tuberculosis

Although this is not a commonly encountered animal disease in the U.S. anymore due to the USDA’s eradication process, I thought I’d throw it in this list for completeness. Many states are considered “TB free” (from livestock TB, that is) and we do intradermal TB tests on many a cow each year as required by interstate health papers. However, let me state that cattle TB is not the same as human TB. The former is caused by the bacterium Mycoplasma bovis, while the latter is caused by a related Mycoplasma, M. tuberculosis. While humans can contract TB from infected cattle, it’s rare. Most cases of bovine TB in the U.S. originate from white-tailed deer. Most humans cases of TB originate from foreign travel.


Although there are some nasty things out there, the good thing is that proper hygiene and common sense will protect you from most of it. Washing your hands, if I haven’t mentioned that enough already, is really the key in preventing many zoonotic diseases. And don’t go touching icky-looking things with your bare hands; wear gloves! Lastly, I frown on kissing your goats. People understand orf on your hands, but orf on your mouth? That might get people talking.

Dr. Anna O’Brien

Image: Kletr / via Shutterstock