Immunoassay for detection of Dipylidium caninum coproantigen in dogs and cats

Abstract

Dipylidium caninum infections in dogs and cats are underestimated because of a lack of proglottid observations and poor recovery of parasite elements by centrifugal flotation. We developed an immunoassay that employs a pair of monoclonal antibodies to capture D. caninum-specific coproantigen in fecal extracts from dogs and cats. Real-time PCR for D. caninum DNA in perianal swabs and observation of proglottids were used as reference methods. In 6 experimentally infected dogs, parasite DNA, coproantigen, and proglottid segments were first detected at 22, 23, and 26 d post-infection, respectively. Praziquantel treatment of 3 experimentally infected dogs resulted in the elimination of both coproantigen and proglottid shedding within 1-5 d post-treatment; however, parasite DNA persisted for 14 d. Immunohistochemistry on immature and mature tapeworm segments using an antibody against the coproantigen supports the premise that the antigen is produced in mature segments. We assessed the performance of our coproantigen test in natural infections in 78 dogs from a flea-endemic area. Of the 12 antigen-positive samples, 11 were confirmed with a positive PCR test and/or proglottid observation. Finally, we evaluated a convenience sample set of 730 canine and 163 feline fecal samples obtained from a commercial diagnostic laboratory; D. caninum antigen was detected in 4.1% of the canine and 12.9% of the feline samples, whereas parasite elements were observed in only 0.028% of samples. Our coproantigen immunoassay provides a sensitive method for the detection of D. caninum infection in dogs and cats.

Keywords: antigen; canine; cestode; feline; flea; tapeworm.

Figure 1.

Schematic of Dipylidium caninum experimental infection protocol. Six dogs were infested with 3 batches of infected fleas by topical administration and gavage. Animals were dewormed at day 39. Proglottid shedding period is indicated by the gray box. First and last day of D. caninum detection by antigen (gray arrows) and PCR (black arrows) are indicated. Frequency of fecal specimen and perianal swab collection is indicated below the timeline.

Figure 2.

Time course of Dipylidium caninum experimental infection. Dogs were treated with praziquantel 39 d post-infection. Coproantigen assay median fluorescence intensity (MFI) results (black line and open circles), proglottid counts (gray line and open squares), and perianal swab rtPCR results (+ = positive; − = negative) are indicated for 3 dogs: (A) 4, (B) 5, (C) 6.

Figure 3.

Immunohistochemistry of Dipylidium caninum proglottid segments. A. Little-to-no significant detection of the antigen in an immature proglottid segment. B. Positive antigen labeling in the tegument of a mature segment.

Figure 4.

Dipylidium caninum immunoassay results for antigen-positive fecal samples from 730 naturally infected dogs and 163 cats. Dotted line is the immunoassay cutoff of 500 median fluorescence intensity (MFI).