Antibody detection methods were better at identifying horses exposed to tapeworms than analysis of their faeces for eggs, the findings of a German study show.
Tapeworms – the most common of which is Anoplocephala perfoliata – latch on to a horse’s intestinal wall with a mouth-like structure of four specialized suckers.
Mature tapeworms don’t produce eggs continuously as with most parasites, instead releasing them in occasional packets from their tail region, which then pass out of the horse in its faeces.
This means a conventional faecal egg count is not a reliable way to assess whether a horse is carrying tapeworms, as there is no guarantee that a dung sample will contain eggs.
Even if a packet of eggs is present in a pile of faeces, evidence suggests they are unlikely to be evenly distributed, meaning that coming across them in a small sample under a microscope could well be a matter of chance.
However, other faecal analysis methods have been shown to be superior to a conventional egg count.
This means the detection of tapeworm prevalence in horses strongly depends on the methods used.
For their study, Laura Jürgenschellert and her fellow researchers set out to learn more about the occurrence of tapeworm infections in German horses using analysis of dung and different antibody detection methods based on saliva and serum samples.
They also produced a questionnaire to learn more about risk factors for tapeworm infection.
Their work, reported in the journal Parasites & Vectors, focused on 48 horse farms the federal states of Berlin and Brandenburg in Germany.
In total, faecal samples from 484 horses were analysed using the double centrifugation/combined sedimentation-flotation and mini-FLOTAC methods.
Serum samples from 481 of the horses and saliva samples from 365 of them were analysed to determine antibody levels against tapeworms.
Tapeworm eggs were detected in 0.6% of faecal samples, representing 6.3% of the farm, without differences between the two methods used.
In contrast, antibodies against tapeworms were detected in 16.2% of the serum samples, representing 52.1% of the farms, and 29.5% of the saliva samples, representing 75.7% of the farms.
Based on the questionnaire results, permanent pasture access, large pastures and regular pasture changes, and high strongyle egg counts were identified as risk factors for positive serum antibody responses to tapeworms.
Treatment with a dewormer that targets tapeworms was protective.
Other protective factors identified by the researchers were the presence of foals and high numbers of horses on the farm. “Both effects are difficult to explain, but might be due to different farm management practices,” the authors said.
Daily removal of faeces from the pasture and horse age did not have a significant effect.
The authors noted that access to pasture also meant access to oribatid mites, which are intermediate hosts, and must be considered a risk factor for exposure to the parasite.
The researchers concluded that the serological investigation indicates that tapeworm prevalence in Berlin/Brandenburg horse farms is much higher than would be anticipated by using conventional faecal analyses.
Moreover, most of the positive horses had not received a drug targeting tapeworms at their last deworming treatment.
Considering the already known low sensitivity of faecal detection methods, diagnostics can be enhanced by the use of antibody detection methods such as the saliva-based ELISA (enzyme-linked immunosorbent assay) test used in the study.
The study team comprised Jürgenschellert, Jürgen Krücken and Georg von Samson-Himmelstjerna, all with the Free University of Berlin; Corrine Austin and Kirsty Lightbody, with Austin Davis Biologics Ltd in Britain; and Eric Bousquet, with animal health company Virbac.
Jürgenschellert, L., Krücken, J., Austin, C.J. 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 13, 462 (2020). https://doi.org/10.1186/s13071-020-04318-5