Website Leaves Us With More Questions Than Answers

Several worried readers contacted us about the alleged discovery of a ”mutated,” ”resistant,” or different ”strongyle-like” parasite circulating in the horse’s blood stream. This parasite was said to be resistant to current deworming drugs and causing a wide variety of illnesses in horses. Our readers wanted to know what we knew about it.

We looked at the Indiana Horse-Rescue website and found the article under the ”research” button (see and click the ”research” tab). This parasite is said to infect horses, humans and dogs. It’s supposedly the microscopic larval form of a nematode (intestinal parasites other than tapeworms are nematodes).

We later learned that the authors believe it could even be associated with a syndrome like angiostrongylosis, a central-nervous-system disease caused by the migration of a specific type of parasite (Angiostryngolus) that is normally found in tropical and subtropical areas, primarily in rats, and can occasionally get into the body of people or other animals if they accidentally eat raw snails.

According to the website, the same parasite was allegedly found in different species, and the authors speculated that transmission likely was occurring between species (dogs, horses and humans).

However, the parasitology experts we consulted agreed this was not likely, as there are no known parasites shared by these three species and because parasites are usually species-specific.

The website article speculates this parasite is involved in a large number of equine ailments, including allergies, amyotrophy, anemia, assorted joint disorders, colic, dermal lesions, dermatitis, edema, gastritis, heaves, inferior performance, laminitis, lethargy, general lameness, muscle wasting, neurological deficit, pleurisy and chronic respiratory infections. (Note: Our experts were particularly concerned about a suggestion that these parasites could be at the root of EPM. Anyone interested in information on EPM should start at the EPM Society website at

The site stated that the parasites were found in hundreds of equine blood samples from five states and most of the horses tested had them. Some horses were healthy, others had a variety of problems. Some horses apparently showed improvement after treatment with the site’s recommended protocols, others did not.

Many Questions
Because we were unaware of the existence of this parasite, we communicated with experts from the American Association of Veterinary Pathologists (AAVP) about the website. Our experts agreed that none of the slides on the website at the time they looked showed parasites, and certainly not nematodes, which normally have microscopic characteristics like segmented intestinal tracts. Our experts agreed that the photos are of environmental contaminants commonly mistaken for parasites by untrained personnel.

”It’s very unfortunate that this sort of thing occurs, but it is not the first time this has happened,” stated Dr. Kevin Kazacos, from the Department of Pathobiology, School of Veterinary Medicine at Purdue University.

”The most famous case was when a group of physicians published the ‘real cause’ of toxic-shock syndrome in women,” said Kazacos, ”which they said was a worm, since wormlike things were recovered from samples. This actually made its way into a medical journal due to poor and/or incompetent review. This was later debunked by parasitologists who identified the ‘organisms’ as cotton fibers coming from gauze, again a contaminant. It has been well established that toxic-shock syndrome is due to bacterial toxemia from uterine infection following prolonged tampon use,” said Kazacos.

Worrisome Treatments
However, what concerned us more than the slides was that among the current recommended treatments for this alleged parasite was the off-label use of deworming drugs, including moxidectin. Originally marketed as Quest by Fort Dodge, moxidectin has a known narrow safety range. These drugs are safe only when used within their known margin of safety, both in terms of dosage given and how often the animal is dosed.

”As with any FDA-approved pharmaceutical product, it is important to use equine de-worming medications only according to label directions,” stated Dr. Kenton Morgan, of the Professional Services division of Fort Dodge Animal Health. ”Fort Dodge does not recommend or support the off-label use of Quest Gel in horses. Horse owners should always consult with their veterinarian to set up an appropriate and effective internal parasite control program for their animals. If horse owners or veterinarians have questions regarding the use of Quest Gel, please contact Fort Dodge Animal Health Professional Services at 800-533-8536.”

Bottom Line
Despite repeated efforts, we have been unable to get further questions answered by the people involved in the website article, as we go to print.

We requested additional information about the scientific methods used to prove a parasite’s existence in the test horses, if any parasitologists were involved in the study, how the slides were prepared, and if a licensed veterinary lab was used. We have not yet received any verifiable evidence to support the website’s conclusions. If we obtain acceptably scientific findings at a later date, we will share that information with you.

Until that time, we suggest you exercise caution when administering any treatment that alleges to address an illness that has not been properly documented by scientific methods. Be wary of off-label uses concerning any drug and always check with your veterinarian or the experts at your nearest veterinary school about drug use, illnesses, and parasite identification and control.

What did you think of this article?

Thank you for your feedback!