Equine tapeworms are internal parasites that infect the gastrointestinal tract and can cause colic, diarrhea, weight loss and poor performance.

Horses become infected by ingesting these flatworms while grazing. Once inside the horse’s digestive system, the tapeworms attach themselves to the intestinal lining, resulting in inflammation and an immune response.

Tapeworms are a unique parasite, as many common deworming medications are ineffective against them, and their eggs are rarely detected in the horse’s feces. This makes diagnosis and treatment of equine tapeworms difficult. [2]

Effective parasite control is key to protecting your horse’s health. Regular deworming and fecal testing can reduce the risk of parasite infestations in horses. [3]

What are Equine Tapeworms?

Parasites are organisms that live in or on the horse and rely on the horse for sustenance while often causing harm or disease. These include internal parasites such as roundworms, tapeworms, and bots, as well as external parasites such as ticks and lice. [1]

Equine tapeworms are parasitic flatworms that infest the intestines of many mammals, including horses, donkeys and other equids.

There are three species of tapeworms found in horses: [4][5][9]

  • Anoplocephala perfoliata: The most common type of tapeworm in North American horses, has a flat body with four suckers on its head for attaching to the intestinal wall; mature tapeworms measure between 2 to 8 cm (0.8 to 3.1 in) in length and 1 cm (0.4 in) in width
  • Anoplocephaloides mamillana: A relatively rare type, with mature worms measuring around 5 cm (2 in) in length and 5 mm (0.2 in) in width
  • Anoplocephala magna: Notably longer than the other types, with mature worms reaching lengths of up to 80 cm (31 in) and widths of 2.5 cm (1 in)

Despite their differences in size, all three species produce irregularly shaped eggs with a similar structure.

All species of tapeworms pose a significant health risks to horses. Following best management practices and veterinary deworming guidelines is essential to prevent infestations and related complications.

Symptoms

Tapeworm infections in horses are often asymptomatic, meaning the horse may not show any noticeable signs of infection. In some populations, up to 80% of horses may carry A. perfoliata in their intestines without ever displaying symptoms. [2][6][5][3]

When horses do show symptoms of a tapeworm infestation, they may exhibit signs such as: [2]

  • Colic
  • Weight loss
  • Diarrhea
  • Poor coat condition
  • Lethargy
  • Poor performance

Symptoms vary in severity depending on the extent of the infestation and any concurrent health issues.

Risk Factors

Tapeworms are easily transmitted from the environment to horses, so all equines are at some risk of infection. It’s generally assumed that horses have some internal parasites, including tapeworms, at any given time.

Particular risk factors for tapeworm infection include: [2][3][5]

  • Age: Younger horses have less developed immune systems, making them more susceptible to parasitic infections than older horses.
  • Time of Year: The highest intensity of tapeworm infection occurs in late summer and fall.
  • Access to Pasture: Grazing on pasture exposes horses to oribatid mites, which serve as intermediate hosts for tapeworms.

Unlike other equine parasites, maintaining good pasture hygiene may not reduce mite prevalence.

Surprisingly, having more pasture area per horse increases the risk of tapeworm infection, possibly because large pastures with ample vegetation benefit mite populations. [5]

Conversely, horses kept on the same pasture year-round and relying on hay supplementation may be less likely to ingest mites and tapeworms. [5]

Transmission

Understanding the equine tapeworm life cycle is critical for horse owners to effectively manage parasites, reduce transmission risks, monitor horse health, and implement preventative measures. [2]

The tapeworm life cycle comprises five stages: [2][3][4][7][8]

  1. Egg shedding: The life cycle begins when adult tapeworms residing in the horse’s intestines produce eggs. These eggs pass out of the horse’s body through the feces into the environment.
  2. Intermediate host ingestion: The tapeworm eggs are ingested by oribatid mites, which are small arthropods commonly found in soil, hay, and grass. These mites act as intermediate hosts, harboring the juvenile parasites while they mature.
  3. Larval development: The tapeworm eggs hatch within the mite’s body, and the larvae develop into a specialized stage called a cysticercoid, which is the infective stage of the tapeworm.
  4. Horse infection: Mites containing the infective larva are ingested by the horse while grazing. Inside the horse’s intestines, the larva is released from the mite’s body and develops into the head of the tapeworm, called the scolex. The scolex attaches to the cecal wall using its suckers and hooks, often clustering around the ileocecal valve.
  5. Maturity and reproduction: Once the tapeworm larvae attach to the cecal wall, they mature into adult tapeworms within 6-10 weeks. As the worms grow, they create body segments called proglottids. These segments fill with eggs. Eventually, they break down, releasing the eggs into the intestine. These eggs are then excreted in the horse’s feces, completing the life cycle.

Infection and Pathogenesis

Once tapeworms attach to the lining of the horse’s intestines, they can have different local effects. Initially, they might disturb normal intestinal movements, which can cause irregular bowel movements or blockages. [2]

In mild infections, tapeworms can lead to congestion at the attachment sites, resulting in the buildup of blood or fluid (edema) and cells. This congestion is part of the body’s immune response to the parasites and can contribute to overall inflammation in the intestine. [3]

Severe tapeworm infections can cause significant changes in the intestinal lining, including swelling, ulceration, and inflammation.

Complications

If left untreated, horses with a severe tapeworm infection can develop a heavy parasite load. The growing population of adult parasites in the gastrointestinal tract can cause complications and lead to more severe disease.

Horses with tapeworm infections have a higher risk of colic, because the worms can cause inflammation and blockages in the intestines. However, most horses with tapeworm infestations have relatively small parasite burdens, which are unlikely to cause colic. [7]

Specific types of colic, such as spasmodic colic, ileal impaction, and ileocecal intussusception, have been linked to tapeworm infestations in horses. [4][9] Clinical signs of colic may include: [6][10][11]

  • Typical colic signs (rolling, pawing, lying down, kicking at the abdomen, etc.)
  • Moderate to high heart rate (tachycardia)
  • Poor gut motility
  • Increased gut sounds (borborygmi)
  • Abdominal pain (moderate to severe)
  • Dehydration

Spasmodic Colic

Spasmodic colic in horses presents as sharp abdominal pain triggered by sudden, irregular contractions of the intestinal muscles. Unlike other forms of colic, which may involve physical blockages or twists in the intestines, the exact cause of spasmodic colic is often unclear. [10][12]

Tapeworms attaching to the intestinal walls can cause irritation and inflammation, leading to spasms of the intestinal muscles and bouts of abdominal pain.

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Ileal Impaction

When a large number of tapeworms attach themselves to the walls of the ileum, the final section of the small intestine, it can lead to obstruction or blockage of the intestinal passage. [4][2]

This obstruction prevents the normal movement of food and digestive contents through the intestines, causing an impaction to form.

The presence of tapeworms exacerbates this condition by contributing to inflammation and mucosal damage in the ileum, further impairing intestinal function. [12]

Ileocecal Intussusception

Intestinal intussusception is a rare condition in which one part of the intestine slips or telescopes into another, leading to blockage and abdominal pain. It may occur secondary to sudden dietary changes, foreign body obstructions, neoplasia (tumours) or parasitic infestations. [13]

In horses with ileocecal intussusception, the ileum moves into the cecum or large intestine. This can cause severe discomfort and may require surgical intervention to correct. [11]

Diagnosis

Diagnosing tapeworm infections in horses is challenging because tapeworm eggs are not consistently present in fecal samples, unlike other parasites. This inconsistency makes traditional fecal examination methods unreliable for detecting tapeworms.

Even if a fecal test does not show tapeworm eggs, it does not mean the horse is free of tapeworms. [9][7]

To improve the sensitivity of tests for detection of tapeworm eggs, modified egg-counting techniques have been developed. These are adapted versions of traditional fecal flotation methods used in horses. [4]

Some centrifugal flotation techniques involve centrifuging a larger fecal sample mixed with a flotation solution to bring parasite eggs to the surface. These tests can achieve sensitivities of 50-62%, and up to 90% in infections with more than 20 tapeworms. [2][5]

Although fecal testing can be unreliable in diagnosing tapeworms, following current veterinary best practices for routine fecal testing is key to equine parasite control.

 

Serum ELISA test

Given the limitations of traditional diagnostic methods, alternative approaches like serum ELISA tests may be necessary for accurately diagnosing tapeworm infections in horses.

When tapeworms infect a horse, the immune system produces antibodies to combat the infection. A serum ELISA (Enzyme-Linked Immunosorbent Assay) test detects these antibodies against tapeworm proteins in the horse’s bloodstream. [7]

This test is relatively accurate, with a sensitivity of 62%, meaning it correctly identifies tapeworm infections about 62% of the time. However, false negatives may occur, especially in cases where there are lower numbers of tapeworms present. [2]

The serum ELISA test can provide more reliable results than fecal examinations and is particularly useful for diagnosing tapeworm infestations in horses. [5]

Saliva ELISA test

The saliva ELISA test involves collecting saliva samples from horses and testing for antibodies against tapeworm proteins.

This is a non-invasive testing method with a sensitivity of 83%, but it is currently only available in the United Kingdom. [2][8][7]

The saliva ELISA test can identify tapeworm infections regardless of their severity — whether the horse has a low, moderate, or high worm burden. However, for accurate results, it is essential that the horse has not been treated with dewormers specifically targeting tapeworms for at least four months before the test. [5]

Laparotomy

A laparotomy is a surgical procedure sometimes used to access and inspect the abdominal cavity for the presence of parasites. This involves creating a small incision in the horse’s abdomen to gain access to its contents. [2]

During an exploratory laparotomy, the surgeon examines internal organs, focusing on areas like the cecum and ileum, where tapeworms commonly attach.

While laparotomy offers a direct diagnostic approach, it is invasive and usually reserved for cases with significant tapeworm burdens leading to colic.

Prevention & Control

Regular deworming with anthelmintic medications that target tapeworms helps prevent and control infestations in horses. By reducing tapeworm burdens, deworming can lower the risk of health problems and enhance the overall health and performance of horses.

Praziquantel

Unlike other deworming agents, praziquantel specifically targets tapeworms and is not effective against other common horse parasites. Due to this limited scope, praziquantel is usually combined with macrocyclic lactones, such as ivermectin or moxidectin, to provide broader protection against various parasites. [1]

Praziquantel works by paralyzing the tapeworms, causing them to detach from the intestinal wall. [1]

Praziquantel is available in various formulations, including oral paste and tablets, making it convenient for horse owners and veterinarians to administer. It should be given once a year, in late fall or early winter, to all horses on the property to prevent transmission. [1][7]

Praziquantel specifically targets tapeworms and is not effective against other types of worms or external parasites found in horses.

 

Pyrantel pamoate

Pyrantel pamoate is a broad-spectrum anthelmintic medication commonly used in veterinary medicine to treat parasitic infections in various animals, including horses.

It works by paralyzing the parasite’s neuromuscular system, causing them to die and detach from the intestines, where they are eventually excreted with the feces. [2][6][3]

Parasite Resistance

Anthelmintic resistance occurs when parasite populations become resistant to deworming medications, reducing their effectiveness in controlling infestations. This happens because deworming medications kill susceptible parasites, allowing resistant ones to survive and reproduce. [1]

This challenge highlights the importance of strategic deworming to maintain the effectiveness of anthelmintics.

Currently, anthelmintic resistance in tapeworms is not considered widespread, and both praziquantel and pyrantel pamoate remain effective. [1]

Summary

Equine tapeworms, primarily A. perfoliata, are common parasites found in horses.

  • Tapeworm infections in horses are often asymptomatic, with up to 80% of horses harboring tapeworms showing no clinical signs. Affected horses may have weight loss, poor body condition and bouts of colic.
  • Diagnosis of tapeworms in horses is challenging compared to other internal parasites, as tapeworm eggs are not usually seen in fecal samples. Diagnostic methods like serum and saliva ELISA tests are relatively accurate.
  • Treatment involves anthelmintic (deworming) medications such as praziquantel or double doses of pyrantel pamoate.

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References

  1. Decoding Dewormers: Types, Resistance Concerns, and Use for Horses.
  2. Lloyd, S. and Menzies-Gow, N.J. Tapeworm infection in Horses (Equis). Vet Lexicon
  3. Craig, T.M. et al. Comparison of Anthelmintic Activity of Pyrantel, Praziquantel, and Nitazoxanide against Anoplocephala Perfoliata in Horses. Journal of Equine Veterinary Science. 2003.
  4. Nielsen, M.K. Tapeworm-Associated Colic in Horses – Digestive System. Merck. 2019.
  5. Jürgenschellert, L. et al. Investigations on the Occurrence of Tapeworm Infections in German Horse Populations with Comparison of Different Antibody Detection Methods Based on Saliva and Serum Samples. Parasites & Vectors. 2020.View Summary
  6. Nielsen, M.K. Apparent Treatment Failure of Praziquantel and Pyrantel Pamoate against Anoplocephalid Tapeworms. International Journal for Parasitology: Drugs and Drug Resistance. 2023.View Summary
  7. Internal Parasite Control Guidelines.
  8. Lightbody, K.L. et al. Validation of a Novel Saliva-Based ELISA Test for Diagnosing Tapeworm Burden in Horses. Vet Clin Pathol. 2016.View Summary
  9. Anoplocephala and Paranoplocephala – Learn About Parasites. Western College of Veterinary Medicine. 2021
  10. Baxter, R. et al. Abdomen: pain – spasmodic colic in Horses (Equis). Vet Lexicon.
  11. Williams, J. and Rakestraw, P. Gastrointestinal: small intestine – intussusception in Horses (Equis). Vet Lexicon.
  12. Proudman, C.J. and Holdstock, N.B. Investigation of an Outbreak of Tapeworm‐associated Colic in a Training Yard. Equine Veterinary Journal. 2000.View Summary
  13. Sasani, F. et al. Occurrence of Jejunojejunal and Ileocecal Intussusceptions in a Thoroughbred Stallion. Asian Pac J Trop Dis. 2013.