Cross-Species Deworming

Q.  We have a stable yard with over 50 horses. The horses are on a quarterly deworming program. In the middle of the summer, we deworm the horses for tapeworms. How do the worm infestations of horses and domestic pets, such as dogs and cats, correspond with each other, if at all? If we deworm the horses now, but horse owners' pets are carrying a load of worms, can these animals reinfect the horses again?

Would it be beneficial to run horses and domestic pets (and even their owners) on the same deworming program?

Claire, South Africa


A. An animal in which a parasite lives is termed the "host," and most parasites demonstrate a characteristic known as "host specificity." For biological reasons that we do not understand, most parasites are only suited to live within certain animal species, and, more specifically, only within certain organs of that host. The parasites of equids are probably more exclusive than those of any other domestic animal. For instance, some cattle parasites can infect sheep and goats, and some dog parasites can possibly infect cats and even humans, but virtually none of the parasites that have equids as their primary hosts are capable of infecting other domestic animals or humans. So, all the animals on a farm do not exchange their parasites on a regular basis, nor does one neglected component represent a source of worm infection for the other species on the premises.

About the Author

Craig R. Reinemeyer, DVM, PhD

Craig R. Reinemeyer, DVM, PhD, is president of East Tennessee Clinical Research, Inc., an independent business in Knoxville, Tenn., that conducts clinical pharmaceutical research for animal health companies.

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