Incidence of Chirodiscoides caviae in Laboratory Rats-Screening, Identification and Treatment
This is a report on the incidence and treatment of the guinea pig fur mite Chirodiscoides caviae, which was so far considered as host specific, in a conventional colony of laboratory rats. Chirodiscoides caviae infestation in laboratory rats was accidentally observed during the screening of Syphacia obvelata by the peri-anal cellophane tape test (CTT). The organism was identified by comparing the morphology described by various researchers and was differentially diagnosed from other common mites of rat, Radfordia ensifera and Notoedres muris. The adult male mites (n=15) were of 330.2±13.3 μm long and the females (n=15) 495.5±25.2 μm. Later on, the entire rat colony consisting of Wistar, Sprague Dawley and Spontaneously Hypertensive Rats (SHR) and the mice colony of Balb/c and Swiss Albino were randomly sampled and screened for the presence of the mite by the cellophane tape technique. All the rat strains were found positive for C. caviae infestation, which was more concentrated towards the posterior region of the body and, collectively, the screening results of C. caviae revealed that the posterio-dorsal and peri-anal regions are most suitable for sampling-suggesting that, the infestation pattern of C. caviae in rats has similarities to that of guinea pigs. Interestingly the mice colony was found free from the infestation.
The Cellophane tape test was found to be an easier method than fur examination by hair plucking and equally accurate for screening of fur mite in a colony of laboratory rats. No clinical symptoms were observed in any of the animals in the colony, which possessed infestation. The facility strictly practised physical separation of animals by species, which pointed to the only possibility of cross infestation being through indirect contact between guinea pigs and laboratory rats and thereby questioning previous reports on the mode of transmission of C. caviae. The entire colony was effectively treated with 0.2% Ivermectin spray followed by 1% spray in an interval of 2 weeks. This report is the first one, which demonstrates the guinea pig fur mite in laboratory rats. It also questions the so far documented “host specificity” and “direct contact” mode of transmission and demonstrates indirect contact as a possible mode of transmission.