Other Diseases of the Spotted Fever Group

Three other major tick-borne rickettsioses are known throughout the world. Usually mild diseases, these three spotted fever group maladies are generally fatal only to the aged or debilitated patients. All exhibit a distinctive diagnostic characteristic, an eschar, or dark scab, that forms over the wound caused by the initial tick bite. Lymph nodes draining the eschar also swell and become tender.

Boutonneuse fever, named for the buttonlike eschar, was the earliest of these spotted fever group diseases identified. Described by Alfred Conor in

North Africa in 1910, the disease has also been known by many other local names, including Mediterranean spotted fever, fièvre boutonneuse, Marseilles exanthematic fever, Indian tick-typhus, South African tick-bite fever, and Italian eruptive fever. Its most common etiologic agent is Rickettsia conorii, the species name given in honor of Conor. In recent decades, other variant spotted fever group strains have also been identified as causing this disease. A number of different ticks are responsible for its transmission, the most common being R. sanguineus. In Africa, many people apparently gain immunity during childhood through a mild infection, for the disease is primarily seen in tourists or in new residents. From its local names, it is apparent that boutonneuse fever is known from Africa throughout the Mediterranean basin and into India. During the 1970s an increase paralleling that of Rocky Mountain spotted fever in the United States was reported in the Mediterranean basin.

Siberian tick-typhus was first documented during the 1930s, when exploitation of Siberian forest and steppes brought many people into the habitat of its vector ticks. Transmitted by several species of ixodid ticks, it is believed to be far more widespread than reported statistics indicate. Its etiologic agent is Rickettsia siberica. Known as well as North Asian tick-typhus, this disease is also found in China and in other north Asian republics.

Queensland tick-typhus, caused by Rickettsia aus-tralis, was first reported in North Queensland, Australia, in 1946. Its vector tick, Ixodes holocyclus, parasitizes marsupials in addition to wild rodents. In general, people working in forest and scrub areas in northern and southern Queensland are at risk of contracting this disease, although in 1979 an urban focus was reported in Sydney.

The final member of the spotted fever group of diseases is unique in being the only member not transmitted by a tick. Its name, rickettsialpox, clearly reflects its history as a disease defined by the investigators who first studied it. In 1946 a strange disease resembling mild chickenpox and exhibiting an eschar, or initial lesion, was reported in a New York apartment building. Charles Pomerantz, a local exterminator and amateur entomologist, had alerted New York health authorities to the possibility of some sort of arthropod-borne disease after he found mite-infected mice in the apartment-complex basement. New York investigators collaborated with the U.S. Public Health Service, and within 8 months the entire picture of the disease had been elucidated. The etiologic agent of the disease was shown to be a hitherto unknown rickettsia of the spotted fever group. Because the organism was found to inhabit the mite Allodermanyssus sanguineus, a parasite of the house mouse, it was named Rickettsia akari, the species designation meaning "mite." Epidemiological research determined that the disease was contracted wherever mites had access to human living areas. In the case of the original apartment complex, the mites climbed up a central incinerator and infested the carpeting in apartments, thus rendering young children especially susceptible. In 1949-50 the illness was also identified in the Soviet Union, and was known there as vesicular rickettsiosis. A mild, nonfatal disease, rickettsialpox has not been reported in recent years in the United States and only sporadically in the former Soviet Union.

Victoria A. Harden

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