Rickettsialpox

INTRODUCTION

Rickettsialpox is an uncommon, mite-borne rickettsial disease caused by the agent Rickettsia akari. R. akari was first isolated in 1946 from a patient, mites, and a naturally infected house mouse in Queens, New York [1]. The disease was named rickettsialpox because of its resemblance to chickenpox. The etiologic agent was named Rickettsia akari because the causative agent belonged to the genus Rickettsia and because akari is Greek for "mite." R. akari is a member of the spotted fever group of rickettsiae of which R. rickettsii is the prototype. (See "Biology of Rickettsia rickettsii infection".)

EPIDEMIOLOGY

R. akari is transmitted to the common house mouse (Mus musculus) by the bloodsucking mite Liponyssoides sanguineus (formerly Allodermanyssus sanguineus). The mouse serves as the reservoir for the disease. L. sanguineus is a small (0.75 to 1.5 mm), colorless arthropod that swells to many times its normal size after a blood meal and becomes bright red in color. L. sanguineus rarely bites humans when mice are plentiful. However, when mouse populations are reduced (eg, by vermin eradication programs), this mite will bite humans and transmit the disease. Although natural infection is thought to occur exclusively by the bite of an infected mite, transmission has occurred in laboratory settings via inhalation of infectious aerosols [2].

Occurrence — Rickettsialpox has been detected in urban areas in New York, Pittsburgh, Cleveland, Boston, as well as Arizona, Utah, South Africa and the Ukraine. Although over 800 cases of rickettsialpox have been reported since the initial description of the infection in 1946, it is widely assumed that this infection is underrecognized and underreported [3,4].

Rickettsialpox may have a wider geographic occurrence than previously realized. For example, R. akari was isolated from a 36 year-old man from Croatia, an area in which rickettsialpox had not been previously recognized [5]. Others have speculated that R. akari is widespread in southern and eastern Europe [6]. In another report, sera reactive with R. akari antigens were detected among patients from Mexican states of Yucatan and Jalisco who were initially thought to have dengue fever [7]. Another serosurvey done in southern California suggested that R. akari or an akari-like rickettsiae are present in wild rodents in Orange County, California [8]. A single case of rickettsialpox was diagnosed in a man who worked at a suburban golf course in North Carolina [9].

Incubation period — The incubation period for rickettsialpox has not been conclusively established but is thought to range from 10 to 14 days. One patient developed fever nine days after an apparent single exposure to a known focus of infection. In a second, laboratory-acquired case, a primary lesion at the site of inoculation appeared on the seventh day and fever appeared ten days after exposure [10].