Development of a PCR technique specific for Demodex injai in biological specimens

The identification of Demodex injai as a second Demodex species of dog opened new questions and challenges in the understanding on the Demodex –host relationships. In this paper, we describe the development of a conventional PCR technique based on published genome sequences of D . injai from GenBank that specifically detects DNA from D . injai . This technique amplifies a 238-bp fragment corresponding to a region of the mitochondrial 16S rDNA of D . injai . The PCR was positive in DNA samples obtained from mites identified morphologically as D . injai , which served as positive controls, as well as in samples from three cases of demodicosis associated with proliferation of mites identified as D . injai . Furthermore, the PCR was positive in 2 out of 19 healthy dogs. Samples of Demodex canis and Demodex folliculorum were consistently negative. Skin samples from seven dogs with generalized demodicosis caused by D . canis were all negative in the D . injai -specific PCR, demonstrating that in generalized canine demodicosis, mite proliferation is species-specific. This technique can be a useful tool in the diagnosis and in epidemiologic and pathogenic studies.