Abstract
BackgroundDeer tick-transmitted human babesiosis due to Babesia microti appears to be expanding its distribution and prevalence in the northeastern United States. One hypothesis for this emergence is the introduction of parasites into new sites from areas of long-standing transmission, such as Nantucket Island, Massachusetts.MethodsWe developed a typing system based on variable number tandem repeat loci that distinguished individual B. microti genotypes. We thereby analyzed the population structure of parasites from 11 sites, representing long-standing and newly emerging transmission in southern New England (northeastern United States), and compared their haplotypes and allele frequencies to determine the most probable number of B. microti populations represented by our enzootic collections. We expected to find evidence for a point source introduction across southern New England, with all parasites clearly derived from Nantucket, the site with the most intense longstanding transmission.ResultsB. microti in southern New England comprises at least two major populations, arguing against a single source. The Nantucket group comprises Martha's Vineyard, Nantucket and nearby Cape Cod. The Connecticut/Rhode Island (CT/RI) group consists of all the samples from those states along with samples from emerging sites in Massachusetts.ConclusionsThe expansion of B. microti in the southern New England mainland is not due to parasites from the nearby terminal moraine islands (Nantucket group), but rather from the CT/RI group. The development of new B. microti foci is likely due to a mix of local intensification of transmission within relict foci across southern New England as well as long distance introduction events.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-014-0546-y) contains supplementary material, which is available to authorized users.
Highlights
Deer tick-transmitted human babesiosis due to Babesia microti appears to be expanding its distribution and prevalence in the northeastern United States
We developed variable number tandem repeat (VNTR) markers based on the published B. microti genome [13], and used the resulting allele frequencies to determine the most probable number of B. microti populations represented by our enzootic collections
With the availability of the B. microti genome [13], we developed an assay for typing B. microti based on variable number tandem repeats (VNTRs)
Summary
Deer tick-transmitted human babesiosis due to Babesia microti appears to be expanding its distribution and prevalence in the northeastern United States. One hypothesis for this emergence is the introduction of parasites into new sites from areas of long-standing transmission, such as Nantucket Island, Massachusetts. Babesiosis due to Babesia microti (Apicomplexa:Sporozoea) was first recognized as a zoonosis in 1969 when a resident of Nantucket Island, Massachusetts, sustained a malaria-like illness. B. microti on Nantucket and elsewhere in coastal New England, subsequently providing the basis for our rapid understanding of that of the spirochetal agent of Lyme disease (Borrelia burgdorferi), once I. dammini was incriminated as the vector of that bacterial zoonosis. The potential for enzootic transmission of B. microti would seem to rest mainly on the presence of a suitable Ixodes sp. vector and small rodents or insectivores
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