Detection of tapeworm-specific antibodies in horse saliva

01 September 2016, at 1:00am

Corrine Austin of Austin Davis Biologics discusses the significant threat of tapeworm infections in horses and the introduction of a test which uses saliva to diagnose burdens

THE REVOLUTIONARY EquiSal test, using horse saliva to diagnose tapeworm burdens, was first made available to horse owners in 2014. Validation of the test has since been published by Veterinary Clinical Pathology, and reports the accuracy of the saliva test in comparison to blood testing and to tapeworm numbers counted at post mortem. 

Tapeworm infections pose a significant threat to horse health as they are associated with clinical cases of colic. Of the three species of tapeworm capable of infecting horses, Anoplocephala perfoliata is the most common worldwide. A. perfoliata adult worms can grow up to 8cm long by approximately 1.5cm wide. Although relatively small, they can cause significant problems due to clustering around their preferred site for colonisation: the caecal wall and the ileocecal junction.

Currently there are only two effective drugs for the control of tapeworm in horses: praziquantel and pyrantel pamoate. Resistance to anthelmintics has not yet been reported in tapeworms, but increasingly frequent reports of resistance to various anthelmintics in other equine parasites, such as cyathostomins, make it imperative for special attention to be paid to the management of tapeworm in horses. The potential for the development of resistance to the two available drugs could result in problems with the control of tapeworm burdens in the future.

The intensity of infection in the horse is important to consider as larger burdens are more likely to cause colic symptoms, but even moderate burdens can result in damage to the intestinal mucosa. Given the correlation of infection intensity to horse intestinal health, and concerns for anthelmintic resistance, there is an increasingly recognised need for accurate diagnostic tests.

Standard faecal egg count (FEC) methods, such as the McMaster method, are widely used for detecting cyathostomins (redworms) and ascarids (roundworms) but, due to the way in which tapeworm eggs are released, these methods are generally considered unreliable for the diagnosis of tapeworm burdens. FECs tend to substantially underestimate the true level of tapeworm infection and sensitivity has been shown to be highly variable. A commercial blood testis available; however, it requires a veterinarian to take the blood sample, resulting in the test being relatively expensive.

EquiSal Tapeworm detects tapeworm-specific antibodies in horse saliva to provide a tapeworm burden diagnosis of low, borderline or moderate/high. The test has the bene t that horse owners themselves can collect the sample to send back to the laboratory for analysis.

Scientific validation of the test has been peer- reviewed and published in the journal Veterinary Clinical Pathology.

To summarise the validation, serum and saliva samples were collected from horses at a UK abattoir where tapeworms had been counted. Samples were then analysed in the EquiSal Tapeworm test or blood test. EquiSal saliva scores had strong correlations with both tapeworm numbers and the blood test results.

The majority of horses with one or more tapeworms at post-mortem were correctly identified by the test. The remaining few were diagnosed as being low, but these horses had burdens considered by experts to be not pathogenic – fewer than 20 tapeworms present.

Most importantly, no high burden (more than 20 tapeworms) horses were misdiagnosed by the test. This is similar to the current guidelines for redworm FEC, where a result of fewer than 200 eggs/gram is not considered harmful. The EquiSal Tapeworm test can be relied upon to correctly identify the majority of horses with one or more tapeworms and correctly identify all horses with pathogenic burdens.

In scientific terms, the EquiSal Tapeworm test has both high sensitivity (83%) and specificity (85%), which is important for correctly identifying horses with more than one tapeworm present, and the test has equivalent accuracy to the blood test.

Two-week testing

In an ongoing study, EquiSal Tapeworm testing is carried out every two weeks following tapeworm treatment on horses diagnosed with tapeworm but with no access to grazing.

Data collected so far (19 horses) show that 50% of horses’ saliva scores had reduced to low within six weeks, 90% had reduced within 10 weeks and the remaining 10% of horses taking a further two weeks to drop to low. This suggests that antibody responses in saliva have less memory to tapeworm infection than that reported for antibodies in blood.

It is important to understand that the situation is complicated in grazing horses by the risk of reinfection from tapeworm larvae after worming treatment. Tapeworm reinfection is evident in studies undertaken using horses kept in poorly managed paddocks where reinfection can obviously happen very easily.

But, given that the tapeworm’s life- cycle requires an intermediate host (an oribatid mite), even well managed paddocks containing horses with high tapeworm burdens could harbour infected oribatid mites within the grass. This means that there is still a reinfection risk after worming for horses grazing in these circumstances too.

Salivary tapeworm-specific IgG(T) antibodies are part of the mucosal immune response to tapeworm infection. A previous study showed tapeworm-speci c IgG(T) antibodies being produced at the site of infection and secreted as a local mucosal antibody response. In contrast to humoral antibody responses (detected in blood testing), mucosal antibody responses have a much shorter persistence and immunological memory.

It can, therefore, be reasonably concluded that the tapeworm-specific antibodies measured in the EquiSal Tapeworm test are mucosal antibodies produced in the salivary glands by plasma cells that originated as recirculating (via the lymphatic system) B-blasts triggered in the gut submucosa at the site of infection.

It remains possible that low levels of humoral antibodies could leak into the saliva by transudation or passage through the gingival crevicular space; however, our data suggest that this is not a significant factor.

In summary, the EquiSal Tapeworm test has been scientifically validated to accurately diagnose tapeworm burdens in horses and can be used to target worming for tapeworm burdens. Current advice is to integrate tapeworm testing into your existing worm egg count schedule by using EquiSal Tapeworm every six months before worming.