Increasing density and Borrelia burgdorferi infection of deer-infesting Ixodes dammini (Acari: Ixodidae) in Maryland.

A statewide survey of Ixodes dammini Spielman was done in November 1991 as a follow-up to a study in 1989. In total, 3,434 adult ticks were collected from 922 hunter-killed white-tailed deer processed at 22 check stations (1 per county in 22 of 23 counties in the state). Significantly more male than female ticks were collected. Tick infestation was significantly heavier on male than female deer. The pattern of tick distribution was similar to that in 1989, with low prevalence (percentage tick-infested deer) and abundance (mean ticks per deer) in the Appalachian region, moderate values in the Piedmont, and high values in the western and eastern Coastal Plains regions. The pattern of tick infection with Borrelia burgdorferi spirochetes (determined by polyclonal immunofluorescence assay) was similar to the tick distributional pattern. Overall, tick prevalence and abundance were higher in 1991 than in 1989, as was the spirochete infection rate in ticks. Multiple regression analysis of tick prevalence against six selected physical and biotic parameters (elevation, rainfall, summer and winter temperature, percentage of forest land, deer density) showed a significant relationship with rainfall and elevation in 1989 and elevation alone in 1991. A more extensive study in Caroline and Dorchester counties in the eastern Coastal Plains region (which showed exceptionally low tick density indices in a generally tick-abundant region in 1989) demonstrated that I. dammini was well established in Caroline but not in Dorchester County.

Distribution, density, and Lyme disease spirochete infection in Ixodes dammini (Acari: Ixodidae) on white-tailed deer in Maryland.

A Statewide survey of ticks parasitizing white-tailed deer was carried out in Maryland during November 1989 to assess the status of the deer tick, Ixodes dammini Spielman, Clifford, Piesman & Corwin, the major vector of Lyme disease in the northeastern United States. Ticks were collected from deer carcasses brought in by hunters at 23 check stations (one per county). A total of 3,437 I. dammini were collected from 538 of 1,281 deer (42%), together with 2,013 Dermacentor albipictus (Packard) and 23 Amblyomma americanum (L.) from 34 and 0.5% of deer respectively. I. dammini prevalence ranged from 0 to 79% of deer and mean abundance from 0 to 7.3 ticks per deer at different check stations. Lyme spirochete, Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner, infection rates in ticks ranged from 0 to 21%, with a mean of 8%. Deer-tick density and spirochete infection rates varied with physiographic region and were low in the Appalachian, intermediate in the Piedmont, and high in the Western and Eastern Coastal Plains regions. County-based human case rates correlated positively with I. dammini abundance. We concluded that I. dammini was well established except in the mountainous western region of Maryland and was involved in Lyme disease transmission.

Aedes (Finlaya) japonicus (Diptera: Culicidae), a newly recognized mosquito in the United States: analyses of genetic variation in the United States and putative source populations.

Introduction of potential disease vectors into a new geographic area poses health risks to local human, livestock, and wildlife populations. It is therefore important to gain understanding of the dynamics of these invasions, in particular its sources, modes of spread after the introduction, and vectorial potential. We studied the population genetics of Aedes (Finlaya) japonicus japonicus (Theobald), an Asian mosquito that was recognized for the first time in the United States in 1998. We examined patterns of genetic diversity using random amplified polymorphic DNA and sequences of ND4 of mtDNA by comparing samples from populations spanning the range of this mosquito in Japan (six samples) and the United States (nine samples) as well as specimens intercepted in New Zealand in 1999. We found geographically differentiated populations in Japan, indicating limited gene flow even on small spatial scales. In the United States, we found evidence of significant genetic differentiation between samples from New York, Connecticut, and New Jersey and those from mid-Pennsylvania and Maryland. We were unable to pinpoint the source location(s) in Japan, although some of the U.S. samples are genetically close to samples from south Honshu and western Kyushu. Further studies should include samples from Korean populations. Distinct genetic signatures in U.S. populations undergoing expansion suggest the possibility of local increases in genetic diversity if and where they meet.

Efficacy of eastern equine encephalitis immunization in whooping cranes.

An epizootic of eastern equine encephalitis (EEE) at the Patuxent Wildlife Research Center (PWRC), Laurel, Maryland (USA), in 1989 provided an opportunity to determine if EEE immunization protected whooping cranes (Grus americana). Based on seroconversion of 31% of sympatric hatch-year sandhill cranes, Grus canadensis, and a previous 35% case fatality rate in whooping cranes, 17 (37%) of the 46 susceptible whooping cranes should have been exposed to virus and six should have died. As there were no deaths in these birds, the EEE vaccination program appeared to be efficacious in this whooping crane population.

Eastern equine encephalomyelitis virus and Culiseta melanura activity at the Patuxent Wildlife Research Center, 1985-90.

Mosquito population densities, virus isolations and seroconversion in sentinel quail were used to monitor eastern equine encephalomyelitis virus (EEE) activity at the Patuxent Wildlife Research Center, Laurel, Maryland, from 1985 through 1990. A dramatic increase in the number of Culiseta melanura collected in 1989, as compared with the 3 previous years, was associated with virus isolations from this species (5/75 pools; n = 542 mosquitoes) and with seroconversion in sentinel quail (4/22 birds positive). This was the first detection of EEE virus activity in this area since a 1984 EEE outbreak killed 7 whooping cranes.

New state record for Culiseta impatiens in Maryland.

Culiseta impatiens is reported for the first time from Maryland. Collections from the southwestern border of Fort George G. Meade extend the range of this species over 400 km farther south than previous records. Multiple collections from 4 separate traps during 2 years indicate a population of Cs. impatiens is probably established in the collection area.

A prospective field evaluation of an enzyme immunoassay: detection of eastern equine encephalomyelitis virus antigen in pools of Culiseta melanura.

A prospective field study was conducted to determine the sensitivity and specificity of an enzyme immunoassay (EIA) compared to virus isolation in cell culture for the detection of eastern equine encephalomyelitis (EEE) virus in naturally infected mosquitoes. A total of 10,811 adult female Culiseta melanura were collected in light traps during 1985 from four locations in Maryland. Eastern equine encephalomyelitis virus was isolated from 5 of 495 mosquito pools in African green monkey kidney and baby hamster kidney cell cultures. All five virus-infected pools were detected by the EIA, and all 490 uninfected pools were correctly scored as not containing virus. The EIA did not produce false positive or false negative results. Results support the assertion of previous researchers that the antigen detection EIA is a rapid, sensitive, specific, and simple alternative to traditional bioassays for the detection of EEE virus in mosquitoes.