Antibodies against tapeworms were found in nearly 30% of saliva samples taken from nearly 400 horses in the wider Berlin area, indicating an infection rate many times higher than that shown by fecal analysis.
It is well recognised that, since the eggs from tapeworms are not evenly distributed in dung, fecal analysis is not reliable for the detection of this parasite.
Even so, the differences in results between fecal testing and analysis of serum and saliva samples for antibodies against the parasite provided marked contrasts.
Laura Jürgenschellert and her fellow researchers conducted tests on fecal, serum and saliva samples from horses across 48 horse farms around the Berlin and Brandenburg area of Germany.
Fecal samples from 484 horses were tested for tapeworm eggs using two well-recognised techniques — 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 subjected to molecular-based testing to determine antibody levels against tapeworms.
Tapeworm eggs were detected in 0.6% of fecal samples without differences between the two methods, representing 6.3% of the farms in the study.
In contrast, antibodies against tapeworms were detected in 16.2% of the serum samples (representing 52.1% of the farms) and in 29.5% of the saliva samples (representing 75.7% of the farms).
The findings indicate that tapeworm prevalence in Berlin and Brandenburg horse farms is much higher than would be anticipated by using conventional fecal analyses, the study team reported in the journal Parasites & Vectors.
Most of the tapeworm-positive horses had not received a drug targeting this parasite at their last treatment, they noted.
Considering the already known low sensitivity of fecal-based detection, equine veterinary diagnostics could be enhanced by the use of antibody detection methods, the researchers said.
The study team noted that the non-invasive saliva-based test detected significantly more horses with tapeworm antibodies than the serum-based test.
The research, which also involved questionnaires filled out by the farm manager or horse owner, identified permanent pasture access, large pastures, regular pasture changes and high strongyle egg counts as risk factors for positive serum antibody responses to tapeworms.
Protective factors included treatment with praziquantel (which targets tapeworms), the presence of foals and high numbers of horses on the farm. The latter two effects are difficult to explain, they said, but might be due to different farm management practices.
Daily removal of faeces from the pasture and horse age did not have a significant effect.
Discussing their findings, the authors noted that it can take several weeks to months for antibody levels to return to low levels after tapeworm treatment. In one study, specific-antibody levels against tapeworms were reduced to below the treatment threshold for all horses in six weeks.
The evidence suggests that most of the horses that tested positive in the present study were actually, or at least recently, infected at the sampling time point.
The study team comprised Laura 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 England; and Eric Bousquet, with Virbac in France.
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