Detection of filarial parasites in domestic cats by PCR-RFLP of ITS1

Lymphatic filariasis has been targeted by the World Health Organization (WHO) to be eliminated by the year 2020. In addition to chemotherapy and vector control, the control of reservoir hosts is necessary for the control program to succeed. Malayan filariasis, caused by Brugia malayi, is endemic in the South of Thailand where domestic cats serve as the major reservoir host. However, in nature, domestic cats also carry B. pahangi, Dirofilaria immitis and D. repens infections and it is difficult to distinguish the different filarial species from each other just by morphology. To assess the burden of filarial parasites, we performed a study on domestic cats in an endemic area of malayan filariasis in the Prasang district, of Surat Thani, a province in Southern Thailand. Together with Giemsa staining and acid phosphatase activity studies, we performed PCR-RFLP analysis on the first internal transcribed spacer (ITS1) region of ribosomal DNA (rDNA). PCR-RFLP with Ase I could clearly differentiate between B. malayi, B. pahangi, D. immitis and D. repens. Out of the 52 cats studied, filarial parasites were identified in 5 (9.5%) cats, of which 4 (7.6%) were B. pahangi and 1 (1.9%) D. immitis. This PCR-RFLP technique detected two additional cats that were not detected by microscopy. The domestic cats are not an important host of B. malayi in this region. We could develop the PCR-RFLP assay test for differentiating filarial nematodes which can be applied to survey human, animal reservoir hosts and mosquito vectors in endemic areas.