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Tapeworm-associated Colic in Horses

By

Martin K. Nielsen

, DVM, PhD, DACVM, University of Kentucky

Last full review/revision Dec 2019 | Content last modified Dec 2019
Topic Resources

Several studies have documented that horses with ileal colics, including impactions and intussusceptions, are significantly more likely to harbor Anoplocephala perfoliata infection. The distribution is worldwide, but prevalence is low in arid climates and in areas with limited access to pasture. Cases can present with a variety of clinical signs, depending on the severity of the lesions. Ileal impactions and intussusceptions present with clear signs of pain and require surgery. Gastric reflux can occur, and rectal examination often reveals a firm mass in the ileocecal region. Standard fecal tests lack diagnostic sensitivity, but modified techniques with improved sensitivity exist. Treatment includes fluid therapy, anti-inflammatory drugs, and surgery, where indicated. Anticestodal therapy should be considered once the colic has been resolved and the patient is stabilized.

Three tapeworm species infect horses: Anoplocephaloides mamillana (formerly Paranoplocephala mamillana), Anoplocephala magna, and A perfoliata. In recent years, the two former species have become rare in managed horses. The only species with documented clinical impact is A perfoliata. This parasite commonly occurs in grazing horses throughout the world but tends to be rare or absent in arid climates.

Free-living and commonly occurring oribatid mites act as intermediate hosts, and horses accidentally ingest these while grazing. The mites carry the infective stage of the parasite, the cysticercoid, which is digested free of the mite’s tissue in the intestinal tract of the horse and forms a scolex. The scolices attach to the cecal wall and tend to cluster around the ileocecal valve. In cases of large burdens, worms can be found in the ileum as well. As the worms mature, they form proglottids (tapeworm segments), which are released into the intestinal content as they mature and fill with eggs. The proglottids subsequently disintegrate, releasing the eggs into the intestinal lumen.

Tapeworm-associated colic occurs when a large number of A perfoliata attach to the cecal and ileal walls. This can lead to a mechanical obstruction as well as mucosal damage, ranging from hyperemia to areas with multiple confluent necrotic ulcers at the attachment sites. The latter is speculated to cause intestinal hyperperistalsis, leading to intestinal spasms, ileal impactions, and ileocecal intussusceptions.

In countries with distinct seasonality and grazing seasons, the presence of mature tapeworms in the intestines is often lowest during summer and highest over winter and early spring, reflecting fluctuations in pasture infectivity.

Clinical Signs of Tapeworm-associated Colic in Horses

Cases of tapeworm-associated colic occur at any age and can present with a variety of signs, depending on the pathology in the affected organs. In cases of ileal impactions or ileocecal intussusceptions, horses can present with the following clinical signs:

  • moderate to high heart rate

  • decreased or increased intestinal peristalsis

  • firm intestinal mass that can be palpated rectally

  • moderate to severe pain

  • positive gastric reflux

  • dehydration

Clinical laboratory findings are generally unremarkable, but can include:

  • increased white blood cell counts

  • neutrophilia

Diagnosis of Tapeworm-associated Colic in Horses

A tentative diagnosis of ileal impaction or intussusception is made based on the clinical findings, and this can be supported by ultrasonography.

Although diagnosing the parasitic etiology has limited implications for managing the patient in the acute phases, it does have value when subsequently advising the client. The reliability of currently available equine tapeworm diagnostic methods are well investigated, and standard egg-counting techniques such as the McMaster have a diagnostic sensitivity of <10%, making them practically useless for this purpose. However, modified egg-counting techniques exist. These have a sensitivity of ~60% for detecting any tapeworm burden and 90% for detecting the more clinically relevant burden of >20 worms. These techniques involve processing larger amounts of fecal matter and centrifugation to concentrate and float the eggs.

Repeated episodes of spasmodic colic are sometimes assumed to be caused by tapeworm infection. Although this cannot be ruled out, other etiologies need to be considered as well. A positive fecal test can help support the tentative tapeworm diagnosis. Commercially available ELISAs exist to measure anti-tapeworm antibodies in serum or saliva, but these have limited utility on an individual case basis because they reflect recent parasite exposure and not necessarily current infection.

Treatment of Tapeworm-associated Colic in Horses

Cases of ileal impaction or ileocecal intussusception require surgery, which should be combined with general supporting measures:

  • fluid therapy

  • correction of acidosis/alkalosis

  • anti-inflammatory therapy

The current recommendation is to only consider anticestodal treatment once the colic has been resolved and the patient has stabilized. A double dose of pyrantel pamoate/embonate (13.2 mg/kg) or products containing praziquantel are effective options.

Prevention of Tapeworm-associated Colic in Horses

Current parasite control recommendations are designed to reduce the risk of parasitic disease. Serum or saliva antibody testing can help determine the tapeworm infection pressure within an equine operation. This, in turn, can guide decisions about including anticestodal treatments as part of the control strategy. On most farms, current recommendations are to treat for tapeworms at least once a year in the autumn. Evidence of high infection pressure or cases of tapeworm-associated colic on the farm can justify treating more frequently. Overall, the aim is to reduce parasite contamination of pastures and thereby reduce the infection pressure.

A detailed presentation of current recommendations for equine parasite control can be found in the American Association for Equine Practitioners (AAEP) Guidelines (see below).

Zoonotic Risk of Tapeworm-associated Colic in Horses

None.

Key Points

  • Anoplocephala perfoliata can cause colic in the ileocecal region.

  • Lesions can include ileal impaction and ileocecal intussusception.

  • The parasite is also implicated as a cause of spasmodic colic.

  • Modified egg-counting techniques reliably detect larger tapeworm burdens.

  • Current recommendations for equine parasite control are designed to reduce the risk of parasitic disease, including tapeworm-associated colic.

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