Outbreak of rat mite dermatitis in medical students.

BACKGROUND

The tropical rat mite, Ornithonyssus bacoti (0. bacoti), is an ectoparasite on many rodents, but when the rodent is not available, humans may become the victim of the mite's bite. The bite induces a nonspecific dermatitis; therefore, it is not easy to diagnose rat mite dermatitis unless the parasites are found.

MATERIALS AND METHODS

Ten cases of rat mite dermatitis were found in medical students who had studied in the same room of the library. Their nonspecific dermatitis consisted of small papules, and parasites were found in the skin or in the environment. The mites were collected and identified as O. bacoti, female. Histopathologic studies showed moderate perivascular lymphohistiocytic infiltrations intermingled with some eosinophils. The presence of rodents in or around the room was confirmed by the students, but there had been no preceding rodent eradication. Although the rats were not captured in the library, insecticides were sprayed, and no further problem with either mites or dermatitis developed during the follow-up period.

CONCLUSIONS

Rat mite dermatitis can occur in clusters that involve a common source of exposure to the rat mite epidemiologically. Prompt identification of rat mites and the eradication of mites and rodents from the environment can prevent further spreading of the disease.