Tropical Rat Mites as newly emerging disease pathogens in rodents and man

Abstract

Different mite species, generally found on various animals, may temporarily also infest man and consequently, such arthropods may be responsible for pruritic skin reactions which are often misdiagnosed. Mite dermatitis caused by the Tropical Rat Mite Ornithonyssus bacoti occurs in several small mammals and rodents under tropical and temperate climatic conditions. This mite was identified in 1923 as a cause of human dermatitis in the United States. In Europe, the Tropical Rat Mite was first detected in the German seaport of Hamburg in 1931, a site indicating the mite was carried across the oceans along with infested ship rats, probably in the times of sailing vessels. According to various observations in Germany, O. bacoti appears in wild rodents more frequently than it seems. In most cases, symptoms of mites are recognized only when they attack humans, but the diagnosis of a rat mite dermatitis requires identification of the parasite, which however is more likely to be found in the environment of its host than on the hosts’ skin itself. Here, three different outbreaks from Bavaria are reported. As a clinical example is presented the case of a 23-year-old medical student and several other residents inhabiting a rat- and mice-infested house in Munich. The arthropods originally came from an Italian restaurant and surrounding facilities. Mites were found in large number in the students’ flat. The patient was suffering from severe itching and papular urticaria. He consulted a dermatology clinic complaining of a pruritic dermatitis for at least 2 weeks. Dermatitis was misdiagnosed as allergy, treatment with the antiphlogistic agent fluocinolonacetonid remained unsuccessful. Eradication of rodents and treatment of the rooms of the house with a pyrethroid were performed to prevent reinfestations. O. bacoti is a periodic hematophageous parasite and spends relatively short time on a host. Causal therapy by antiparasitic agents on human patients is not necessary. If indicated, treatment should be symptomatic.