ROCKY MOUNTAIN SPOTTED FEVER ON LONG ISLAND

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Abstract
An endemic focus of Rocky Mt. spotted fever on Long Island, New York, provided opportunity to study an arthropod transmitted disease, the epidemiology of which depends on biology, ecology, and control of the vector, the American dog tick, Dermacentor variabilis. Transovarial and stage to stage transmission of the incitant, Rickettsia rickettsii, the survival of nymphs and adults through the cold seasons, proper climatic conditions, and mammalian hosts as a source of the blood meal that is essential to the life cycle are factors in maintenance of a focus. Small rodents are hosts of the larval forms; nymphs and adults feed on larger spp., particularly dogs, foxes, and raccoons, in which specific complement-fixing antibodies have been demonstrated. Pathogenic rickettsiae were not recovered from spleens of any hosts, and infection was not induced by inoculation of a virulent strain in foxes and raccoons but specific complement-fixing antibodies were demonstrated. Certain factors contributing to a static focus are enumerated. Few unfed ticks survive the active season. The influence of residence in the vector and its hosts, particularly immune animals, on the virulence of strains is emphasized. The history of the disease on Long Island from the first proven clinical case in 1912 is reviewed and an analysis of seasonal incidence, age and sex distribution, case fatality, prophylaxis and therapy is presented. The human disease is not significantly different from that elsewhere in the U. S. A. The general case fatality rate of 17% is less than in the western areas because of the higher incidence of the disease there, more than 50% in the first 2 decades of life, when mortality is least. Extensive search of historical and scientific documents and vital statistics covering Long Island in the 18th and 19th centuries failed to indicate how the vector was introduced or to present evidence of cases prior to 1908. There is evidence that the vector was present at least 35 yrs. prior to the first case in 1912. Doubt is cast on the importation of the vector by domestic animals or migratory birds. Field studies indicate that application of DDT along the routes of human and animal passage to which the vector is attracted by scent is an effective means of control and eradication of ticks.

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