Dr. Stafford Tick Management Handbook - Newtown, CT

56StaffordHuman BabesiosisThe Connecticut Agricultural Experimentation StationHuman babesiosis is a malaria-like illness that is caused by a protozoan organism found in thered blood cells of many wild and domestic animals.Babesiosis is caused by Babesia microti in thenortheast and upper mid-west United States. Babesiamicroti is a parasite of white-footed mice, as wellas voles, shrews, and chipmunks. Other speciesor variants of Babesia are associated with humandisease in other parts of the United States (i.e.,California and Missouri), Europe, and Asia. Humanbabesiosis has been recognized since the early 1970’sin parts of Massachusetts (particularly NantucketIsland), Block Island, Rhode Island, and the easternparts of Long Island, New York. Most reportedBabesia microti in red blood cells (CDC).cases of babesiosis have been from New York, Massachuetts, Connecticut, and Rhode Island. The. rst Connecticut case of human babesiosis was reported from Stonington in 1988. The majority ofcases continue to be reported from the southeastern portion of that state, although recent evidenceindicates that the organism has become more widely distributed in inland areas. Most cases in RhodeIsland are reported from the southern coastal regions. The number of con. rmed cases has increasedin New Jersey in recent years, which may represent increased risk or increased awareness. Thenumber of reported cases is probably only a small fraction of clinically diagnosed cases with manyother subclinical or mild cases going undetected and unreported. Nevertheless, the distribution andnumber of reported cases of babesiosis appears to be increasing.The white-footed mouse is the primary reservoir for B. microti, which is transmitted by I.scapularis. While data on the prevalence of infection in P. leucopus and particularly in I. scapularisare limited to a few studies, babesial parasites have been observed in up to 41% of mice andover 90% can carry antibodies to this agent in endemic areas. Infection in mice may be life long.Infections in ticks generally appear to be lower than that of B. burgdorferi, but in highly endemicareas, tick infection may be equally prevalent. Maintenance of the parasite seems to requiremoderate to high tick densities. Most human cases occur during the summer months when nymphsof the blacklegged tick are active. Babesia also can be transmitted through blood transfusions fromasymptomatic donors.A mouse (or other reservoir competent rodenthost, such as the meadow vole) and the blackleggedtick are required to complete different aspects of theBabesia lifecycle. Larval or nymphal ticks acquirethe parasites when feeding on an infected mouse. Inthe tick gut, male and female gametes unite to formzygotes. Subsequently, a stage of the parasite reachesthe salivary glands and becomes dormant until thetick feeds again. The parasite is passed to the nextstage of the tick (transstadial transmission). Upontick attachment, infectious sporozoites are formedand shed in the saliva of the tick. It may require asmany as 54 hours of attachment before transmissionoccurs. Adult I. scapularis also can transmit theparasite. During transmission, the sporozoites enterWhite-footed mouse, Peromyscus leucopus. red blood cells, reproduce asexually, and emerge toBulletin No. 1010 2755