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The Daily Vet by petMD

The Daily Vet is a blog featuring veterinarians from all walks of life. Every week they will tackle entertaining, interesting, and sometimes difficult topics in the world of animal medicine – all in the hopes that their unique insights and personal experiences will help you to understand your pets.

Hazards in the Field: Zoonotic Diseases in Large Animals

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

Comments  4

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  • Antibiotic Resistant Stuf
    10/05/2012 10:57am

    You mention MRSA and that it's resistant to Methicillin.

    Do you treat it with several things and hope the critter gets better? Or do you just have to grit your teeth and hope the critter's body can fight the infection on its own?

    Out of curiosity, how do you handle hand-washing in a farm setting? Do you carry your own super-soap?

  • 10/15/2012 11:55pm

    Apologies for my tardiness in this response. MRSA infections are dealt with in different ways depending on location in the body and severity of infection/tissue damage. Many times, if it's a localized wound, the injury is cleaned and debrided as much as possible (and maybe multiple times). Cultures have likely already been taken that confirm MRSA, but these cultures (and sensitivity testing) may show other antibiotics the bug is sensitive too and we'll try one or more of those.

    As far as cleanliness on the road, after each appointment, I try to wash my hands at the farm - there's usually soap and water around somewhere. I also carry a giant tub of hand sanitizer in my truck, but this doesn't do any good unless my skin is clean to begin with. Another big issue is the cleanliness of my boots - especially going between large hog and/or dairy farms. I have special rubber pull-on boots for these visits and after the visit, I pull out a large scrub brush and scrub down my boots with water and chlorhex solution. Boots are a very common way to spread junk from one farm to the next so we try to be very careful with this.

  • TB
    10/07/2012 03:47am

    For the sake of accuracy - human TB is caused by Mycobacterium tuberculosis, not Mycoplasma. They're entirely different organisms, and there are actually several other mycobacterial diseases that humans can get, usually in immunocompromised people. Otherwise, interesting article, thanks for the info, I always enjoy reading your articles.

  • 10/15/2012 11:47pm

    Oh my goodness - Thank you for your correction!!! Darned bacteria and their crazy names - you're so right - Mycoplasma is a COMPLETELY different beast! My apologies, dear readers! Luckily, I can rely on your keen eyes for my taxonomic goofs. Thanks again.

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