Biomedical subjects
Publications and source records attributed to T N Mather.
Nymphal Ixodes dammini transmitted Borrelia burgdorferi to 1 of 14 rodents exposed for 24 h, 5 of 14 rodents exposed for 48 h, and 13 of 14 rodents exposed for greater than or equal to 72 h. Prompt removal of attached ticks is a prudent public health measure, especially in regions where Lyme disease is endemic.
Permethrin-treated cotton, intended as rodent nesting material, was distributed in wooded sites in which the agents of Lyme disease and babesiosis were enzootic, in order to kill immature Ixodes dammini, the ticks that transmit these human pathogens. Such ticks feed most abundantly on white-footed mice (Peromyscus leucopus), apparently the main reservoir hosts of these agents, and tend to concentrate in mouse burrows. Mice captured after permethrin-treated cotton was distributed, were infested by a tenth as many ticks as were those captured in adjacent nontreated sites, a difference that continued throughout the 4-month period of observation. On average, 72% of all mice captured in treated sites were free of ticks, while virtually all mice captured in nontreated sites were infested. Voles (Microtus pennsylvanicus), however, were tick-infested, regardless of site of capture. Laboratory-reared I. dammini failed to attach to mice captured in treated sites, and most such exposed ticks died. Distribution of permethrin-treated cotton appears to be a means for preventing transmission of the pathogens that cause human babesiosis and Lyme disease.
We investigated whether concurrent ingestion of dengue 2 virus and microfilariae of Brugia malayi would increase viral infection and dissemination rates in Aedes aegypti. Infection rates were similar in mosquitoes that ingested virus alone or both virus and microfilariae concurrently. However, viral dissemination rates, as determined by recovery of dengue virus from both legs and bodies separately, were significantly greater in mosquitoes that ingested both agents concurrently than in those that ingested virus alone. This study confirms that vectorial capacity of a natural vector of an arbovirus may be enhanced by the concurrent ingestion of microfilariae.
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Ixodes dammini nymphs were examined for evidence of concurrent infection with Borrelia burgdorferi and Babesia microti. A total of 19 nymphs (18.6%) from Nantucket Island were simultaneously infected, as were 24 nymphs (8.2%) from Naushon Island. These observations are consistent with a common reservoir host for both I. dammini-transmitted pathogens.
To test the possibility that immature deer ticks (Ixodes dammini) may concentrate in the nests of their mouse hosts, we recorded their pattern of detachment. In laboratory experiments, most engorged larvae (greater than 90%) and nymphs (greater than 80%) detached from hamsters between 1200-2000 hours when the 14-hr photophase began at 0600 hours. Time of drop-off was similar regardless of when ticks attached to hosts, but attachment late in the day delayed drop-off by one full day. Ticks detached similarly from naturally-infested Peromyscus leucopus. A post-attachment cue or cues appeared to regulate time of detachment. Such synchronous diurnal detachment may serve to concentrate ticks in the nests of their nocturnal mouse hosts, thereby enhancing pathogen transmission.
We determined the prevalence of Babesia microti and Borrelia burgdorferi in four populations of Ixodes dammini in eastern Massachusetts. The Feulgen's reaction was more sensitive than the Giemsa method for detecting salivarian Babesia. A combination of darkfield and direct-fluorescent-antibody examination proved more sensitive than either method alone for detecting spirochetal infection. The prevalence of spirochetes was greater than the prevalence of Babesia in each of the tick populations studied. Overall, 24% of nymphs and 47% of adults examined were infected with spirochetes; in contrast, 11% of nymphs and 14% of adults were infected with Babesia. The difference between the spirochetal and babesial prevalence was greatest in the most recently infested site. The rising incidence of Lyme disease, as compared to the stable incidence of human babesiosis, may result from the relatively greater abundance of Bo. burgdorferi infected I. dammini ticks in newly infested locations.
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Primarily in order to facilitate future studies on venereal transmission of La Crosse encephalitis virus by Aedes triseriatus, tests were conducted to identify conditions that maximize insemination rates in caged populations of Ae. triseriatus derived from field-collected eggs. All tests were conducted at 21 degrees C +/- 1 degree C, which is approximately the mean temperature during July and August in southwestern Wisconsin where La Crosse virus is endemic. Non-bloodfed females exposed on their 5th through 8th day of adult life showed little sexual receptivity to either 5- to 6-day-old males or 8- to 9-day-old males. F1 females were no more receptive than their mothers had been at a similar age. Mean insemination rates did not exceed 32.6% in any of these age combinations at sex ratios ranging from 4 males: 1 female-1 male: 4 females. Mean insemination rates ranged as high as 89.0% when non-bloodfed females were exposed on their 9th through 12th day of adult life to 5- to 6-day-old males in a 4 male: 1 female ratio. In females given a bloodmeal on their 4th day of life and exposed on their 5th through 8th day to 5- to 6-day-old males, mean insemination rates ranged as high as 91.7% at a ratio of 2 males: 1 female.
Host blood source was found to affect both the fecundity and the duration of te gonotrophic cycle of Aedes triseriatus. Mosquitoes were fed on restrained deer, chipmunks, squirrels, humans and suckling mice. Results showed that mosquitoes fed on chipmunks or squirrels, the major La Crosse virus vertebrate amplifier hosts, had greater fecundity but longer gonotrophic time intervals (approximately 2 more days per ovarian cycle) than mosquitoes fed on deer, which is a non-amplifier species. Results were similar for both first and second mosquito gonotrophic cycles. Application of these data to a model determining differential reproductive capacity showed a 24% reduction in the number of second cycle eggs laid by Ae. triseriatus taking the initial blood meal on amplifier species as compared to those taking the initial blood meal from deer. As only those uninfected mosquitoes that feed on an amplifier species have a chance of becoming orally infected and producing infected eggs, this reduced reproductive capacity reduces correspondingly the potential number of vertical infections that can be established during the amplification process.
Highlands J (HJ) virus is an arbovirus frequently recovered at high rates in mosquitoes collected in the eastern United States. HJ virus is primarily a veterinary pathogen causing disease in domestic birds including turkeys, chickens, and partridges. It has an enzootic cycle similar to eastern equine encephalitis (EEE) virus and is often used as an indicator species in EEE surveillance programs. Current immunologic techniques to identify HJ virus are often inefficient and can involve cross-reactivity of antibodies. Therefore, we developed a molecular-based assay by a reverse transcriptase (RT)-polymerase chain reaction (PCR) technique. Primers were constructed from conserved sequences of the E1 coding region from 19 strains of HJ virus. PCR amplifications from serial dilutions of HJ virus-infected Vero cell culture supernatants indicated that this assay could detect viral RNA at concentrations of 10 plaque-forming units per reaction. Extracted RNAs from western equine encephalitis, EEE, LaCrosse, and Jamestown Canyon viruses were not detected with this assay. RNA extracted directly from the brain tissue of a dead house sparrow and from a pool of Culiseta mosquitoes yielded a PCR product of the expected size. The RT-PCR technique developed was both sensitive and specific for detecting HJ virus from infected cell culture supernatants, bird brain tissues, and mosquitoes. This new assay will permit rapid and accurate diagnosis of HJ virus, both enhancing surveillance activities for EEE transmission risk and monitoring infections in domestic poultry and wild birds.