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Oribatid Mites: The Good, Bad and Ugly Truth Behind Tapeworm Infections

New York, NY (October 7, 2008) -- Veterinary science suggests that oribatid mites may be the key to understanding the tapeworm threat. As the intermediate hosts of tapeworms, these insects are highly prevalent worldwide. As microscopic decomposers, these mysterious mites can exist by the thousands or even millions per square meter of soil. Any horse that grazes on pastures, eats hay or is bedded with straw or wood products is likely exposed to oribatid mites, which could translate into tapeworm infections.

Oribatid mites are tiny insects that act as the intermediate host to Anoplocephala perfoliata -- the most common species of tapeworm infecting domestic horses. Also known as soil mites, oribatid mites live in the top layer of the soil, leaf litter or other debris1. Growing to only about a millimeter in length, hundreds of thousands of these animals can live in one square meter of soil1. Oribatid mites are kin to ticks and spiders, however unlike those species, they feed on fungi, algae and dead plant matter1.

“Tapeworm infections can be very difficult to detect in horses, because many horses fail to show any clinical signs until a colic episode occurs. In fact, research shows that a significant percent of spasmodic and ileocecal impaction colics are caused by tapeworms,” said Dr. Robert Holland, DVM, PhD, senior veterinarian at Pfizer Animal Health. “Horses across the country may be exposed to oribatid mites that are infected with tapeworm larvae. As a result, a better understanding of the lifecycle of the oribatid mite can help veterinarians and horse owners to combat tapeworm infections before they lead to bigger issues, such as colic.”

Oribatid mites have been studied extensively due to their importance in maintaining healthy forests, pastures and soils. They are commonly known as “recyclers” because of their ability to break down organic materials that then allow plants to grow. A green, lush pasture often serves as a good indication that a healthy oribatid mites population can be found in that area. While this is great for the ecosystem, it’s problematic for horse owners trying to protect their herds against potential tapeworm infections.

As decomposers, mites ingest tapeworm eggs passed in equine feces. The eggs hatch inside the oribatid mites and the infective stages of the parasite, also known as cysticercoids, develop within the mite’s body cavity in about two to four months2. Horses become infected with A. perfoliata when oribatid mites are consumed along with forage. The digested mites release the cysticercoids in the horse’s intestinal tract and the immature parasites then develop into adult tapeworms that attach to the ileocecal junction-- the meeting place of the small intestine and the cecum2. The tapeworms mature and reproduce inside the horse. Eggs are released through the feces and the cycle starts all over again2.

Research has suggested that horses younger than two years old may be more susceptible to tapeworm infection than adult horses over two years old3,4. This may be due to the young horse’s developing immune system5. At the same time, research has indicated that mites are always present, no matter the season or environmental changes; therefore horses of all ages are exposed and are at risk for infection. While oribatid mite populations are at their greatest density between the spring and autumn months, the low temperatures and humidity of the winter season offer little protection from mite infestation and potential tapeworm transmission3. Veterinarians recommend that horse owners utilize a year-round treatment program for tapeworm protection.

Active tapeworm infection is difficult for veterinarians to diagnose. This limitation often contributes to an underestimation of the true prevalence of tapeworm infection in a herd, which in turn can encourage negligence in tapeworm control. In many cases, horse owners will simply resort to routine deworming instead of performing a diagnostic test that can confirm active tapeworm infection. Also, horse owners may mistakenly assume that broad spectrum dewormers such as macrocyclic lactones (avermectins), such as ivermectin alone or moxidectin alone, or benzimidazoles will control tapeworms, unaware that neither of these classes has any effect on the tapeworm parasite6.

Horse owners can ensure their herd is protected by incorporating a praziquantel dewormer into their deworming program7. This class of anthelmintic has been proven effective against tapeworm infections and is commercially available. Recent studies have shown praziquantel to be effective against the tapeworm species, A. perfoliata, known to infect horses7. Praziquantel is available in the U.S. only in combination with ivermectin as a broad spectrum anthelmintic with efficacy against various worms, bots and tapeworms.

Pfizer Animal Health’s EQUIMAX(R) (ivermectin 1.87%/praziquantel 14.03%), was recently evaluated for efficacy in 26 tapeworm-infected horses maintained for a year on contaminated pastures. Treatment with EQUIMAX proved to be 100 percent effective for tapeworms, with all horses having negative fecal egg test results for the first two months after treatment. The percentage of tapeworm-negative horses gradually declined during the year after treatment, indicating a re-infection pattern that can be anticipated following treatment of horses maintained on contaminated premises8. This also indicates that semi-annual treatment is recommended in endemic herds8. Research indicates that young horses may be more susceptible to tapeworm infection. EQUIMAX is the only combination dewormer, with tapeworm control, approved as safe in foals as young as four weeks of age.

“Eliminating oribatid mites from pastures is not feasible and is counterindicated for maintaining healthy pastures,” said Holland. “However, if horse owners become more aware of the issue, assume their horse has exposure to tapeworms and work with an equine health professional to take appropriate action, the problem then becomes manageable with effective dewormers, such as EQUIMAX.”

Pfizer, Inc. (NYSE: PFE), the world’s largest research-based biomedical and pharmaceutical company, also is a world leader in discovering and developing innovative animal vaccines and prescription medicines. Pfizer Animal Health is dedicated to improving the safety, quality and productivity of the world’s food supply by enhancing the health of livestock and poultry; and in helping horses and pets to live longer and healthier lives. For additional information on Pfizer Animal Health’s portfolio of equine products, visit http://www.PfizerAH.com.


1 Soil Mites: Oribatidae Family. http://www.fcps.edu/islandcreekes/ecology/soil_mite.htm

2 Tapeworm Prevalence in the U.S. Varies by Region. http://equimax.horse.com/map.asp.

3 Reinemeyer CR, Farley AW, Kania SA, et al. A prevelance survey of antibiotics to Anoplocpehala perfoliata in horses from the United States (abstract). Proceedings, 48th Ann Meet, Am Assoc Vet Parasitol 2003;40.

4 Meana A, Luzon M, Bohorquez A, et al. Some factors related to the infection of Anoplocephala magna (poster). World Association Adv, Vet Parasitol 21st International Conference, 19-23. August, 2007, Ghent, Belgium.

5 Proudman CJ, Holmes MA, Sheoran AS, et al. Immunoepidemiology of the equine tapeworm Anoplocephala perfoliata: age-intensity profile and age dependency of antibody subtype responses. Parasitology 1997; 114 (Pt 1): 89-94.

6 Lyons, E.T., Tolliver, S.C., Drudge, J.H., Collins, S.S. Vet 32: Tapeworms in Horses. University of Kentucky College of Agriculture. 1997; p. 6.

7 Slocumbe JO, Heine J, Barutzki D, et al. Clinical trials of efficacy of praziquantel horse paste 9% against tapeworms and its safety in horses. Vet. Parasitol 2007; 144; 366-370.

8 Mercier P., Bousquet E., Sanquer A, et al. Time of re-appearance of fecal tapeworm eggs in horses treated with an ivermectin-praziquantel combination and left in their contaminated environment. World Association Adv. Vet Parasitol 21st International Conference. 19-23 August, 2007, Ghent, Belgium.


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