Comparison of diagnostic methods for laboratory diagnosis of the zoonotic tapeworm Dipylidium caninum in cats

The tapeworm Dipylidium caninum is the most widely distributed cestode infecting dogs, cats, and sometimes humans, worldwide. The diagnosis of the infection caused by D. caninum is achieved via the visualization of proglottids in feces or with traditional microscopic tests, but both lack sensitivity. The present study has evaluated and compared the diagnostic performance of a PCR protocol on different feline biological samples to detect D. caninum. A sample of feces, a Scotch tape test from the perianal area, and a rectal swab were collected from a total of 100 privately owned cats from Italy and Greece. All fecal samples were subjected to macroscopic examination and to floatation. Based on the results of the above tests the cats were divided in three groups, i.e. (i) cats positive for D. caninum (regardless of positivity for other endoparasites (Group A; n = 50 cats), (ii) cats negative for D. caninum but infected by other helminths (Group B; n = 25 cats), and (iii) cats negative for intestinal endoparasites (Group C; n = 25 cats). For each sample, the DNA was extracted from feces, floatation supernatant, Scotch tape test and rectal swabs and subjected to PCR. For 33 cats from Group A, at least one sample type scored positive at PCR. Of these, all were PCR-positive in the floatation aliquot, while nine and one cats were positive by PCR on feces and Scotch tape test, respectively. Swabs were negative by PCR for all the cats. None of the samples from cats of Groups B and C was positive by any PCR. Sequences obtained from amplicons generated from samples of cats enrolled in Italy had 99-100 % identity with the recently described D. caninum feline genotype. The data presented here suggest that PCR could be a useful tool for diagnosing D. caninum infections, under certain circumstances, e.g. when proglottids are unidentified, unseen or overlooked, even though it has limitations, e.g. false negative results due to fecal PCR inhibitors, uneven distribution of parasitic elements, or to intermittent proglottid and/or egg shedding. Thus, it may not be, currently, the best diagnostic choice for dipylidiosis.