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Biomedical subjects

T W Scott

Publications and source records attributed to T W Scott.

At least 55 records · Page 3Linked to original sources
PubMed1995

The effect of multiple host contacts on the infectivity of dengue-2 virus-infected Aedes aegypti.

This study was designed to determine if transmission rates for dengue-2 virus by Aedes aegypti are altered by mosquitos probing a host for blood or imbibing blood prior to attempting transmission. Aedes aegypti is known to contact multiple hosts during each egg-laying cycle and multiple host contacts might diminish the amount of virus in infected mosquito's salivary glands or ducts and render them functionally uninfective. Probing a host 5, 10, or 20 consecutive times did not significantly alter the infectivity of parenterally infected mosquitoes. However, orally infected Ae. aegypti that probed 20 times transmitted dengue viruses at a significantly higher rate than controls. Infectivity of orally infected Ae. aegypti was unaffected by blood feeding. Our data suggest that (1) dengue virus-infected Ae. aegypti remain infective regardless of their probing or engorging history, and (2) once Ae. aegypti become infective they are extremely efficient disseminators of dengue virus.

Aedes↗
PubMed1995

Evaluation of enemas for exposing Aedes aegypti to suspensions of dengue-2 virus.

To determine if enemas could be used to simulate oral exposure of Aedes aegypti to dengue-2 virus, we compared infection rates of mosquitoes administered an enema of a blood suspension containing dengue-2 virus to infection rates in mosquitoes that imbibed the same suspension from a drop of blood. In 1 of 4 experiments infection rates were significantly different. More importantly, during 2 of the 4 trials, 100% of the mosquitoes in the enema treatment group were infected. We speculate that the capillary tube used to administer the enemas abraded the hindgut of mosquitoes in the groups with 100% infection rates and, therefore, virus was inoculated directly into the mosquitoes' hemocoel. We conclude that the method we used for administering enemas cannot be used to simulate oral exposure of Ae. aegypti to dengue-2 virus.

Aedes↗
PubMed1995

Failure of immune sera to neutralize dengue-2 virus in intrathoracically inoculated Aedes aegypti.

Aedes aegypti became infected when inoculated with a mixture of dengue-2 virus and anti-dengue-2 antibodies, but not when they were exposed to the same mixture per os. This phenomenon merits more detailed investigation. Understanding why this difference in mosquito infection rate occurs may lead to improved dengue virus assays or provide insights into the nature of dengue virus-antibody interactions.

Aedes↗
PubMed1994

Reproductive fitness and survivorship of Aedes aegypti (Diptera: Culicidae) maintained on blood, with field observations from Thailand.

Daily survivorship and fecundity of Aedes aegypti mosquitoes were monitored for cohorts provided with five nutritional treatments: water, 2% sucrose, blood from a live chicken plus water, blood plus 2% sucrose, and blood alone. The median mortality time (LT50) for these females was 6, 54, 16, 12, and 29 d, respectively. There was no significant difference in the number of eggs laid by females in any of the treatments containing a host. Females maintained on blood alone laid as many or more eggs during their lifetime as females with access to sugar who had a greater life expectancy. Males maintained on sugar alone survived significantly longer than those in any of the other treatments. Large- and small-bodied, sugar-starved Ae. aegypti females that were marked, released, and recaptured in a Thai village survived as well as the replicate cohorts that received sugar or sugar plus blood during the 36 +/- 12 h period from emergence until their release. These results indicate that Ae. aegypti females live longer in the laboratory if they are provided a source of carbohydrate, but the increased survival associated with sugar feeding does not increase reproductive success.

Aedes↗
PubMed1994

Evolution of alphaviruses in the eastern equine encephalomyelitis complex.

Evolution of viruses in the eastern equine encephalomyelitis (EEE) complex was studied by analyzing RNA sequences and oligonucleotide fingerprints from isolates representing the North and South American antigenic varieties. By using homologous sequences of Venezuelan equine encephalomyelitis virus as an outgroup, phylogenetic trees revealed three main EEE virus monophyletic groups. A North American variety group included all isolates from North America and the Caribbean. One South American variety group included isolates from the Amazon basin in Brazil and Peru, while the other included strains from Argentina, Guyana, Ecuador, Panama, Trinidad, and Venezuela. No evidence of heterologous recombination was obtained when three separate regions of the EEE virus genome were analyzed independently. Estimates of the overall rate of EEE virus evolution (nucleotide substitution) were 1.6 x 10(-4) substitution per nucleotide per year for the North American group and 4.3 x 10(-4) for the Argentina-Panama South American group. Evolutionary rate estimates for the North American group increased over 10-fold (from about 2 x 10(-5) to 4 x 10(-4)) concurrent with divergence of two monophyletic groups during the early 1970s. The North and South American antigenic varieties diverged roughly 1,000 years ago, while the two main South American groups diverged about 450 years ago. Analysis of multiple strains isolated from an upstate New York transmission focus during the same years suggested that, in certain locations, EEE virus may be relatively isolated for short time periods.

Antigens, Viral↗
PubMed1994

Predicting Ixodes scapularis abundance on white-tailed deer using geographic information systems.

We collected 1,410 Ixodes scapularis from 139 white-tailed deer in Kent County, Maryland during the 1990 hunting season. A geographic information system was used to extract 41 environmental variables in the areas surrounding the collection sites of the deer. Stepwise linear regression was used to evaluate the association between the abundance of ticks on deer and the environmental data. A significant statistical association was observed between the abundance of I. scapularis and seven environmental variables (R = 0.69). Tick abundance was negatively correlated with urban land use patterns, wetlands, the amount of privately owned land, soils that tended to be saturated with water, and one drainage system. Tick abundance was positively correlated with well-drained, sandy soils having low water tables. These results indicate that geographically referenced environmental data may be useful in anticipating the risk of exposure to vectors over large areas.

Animals↗
PubMed1993

Diversity within natural populations of eastern equine encephalomyelitis virus.

We evaluated genetic and phenotypic diversity within natural populations of the alphavirus, Eastern equine encephalomyelitis (EEE) virus. RNA fingerprinting revealed that most populations within infected hosts (unpassaged isolates) contained a consensus genotype along with minority genotypes differing in one to three T1-resistant oligonucleotides. Mutation frequencies appeared to be similar to those reported for other RNA viruses, suggesting that the slow rate of EEE virus evolution is not limited by fidelity of genome replication. Within a given year, genetic diversity was generally greater among geographically distant isolates than among those from the same transmission focus, suggesting that dispersal among EEE viruses in North America is not complete annually. Two of three bird isolates from Maryland and New York contained relatively distantly related genotypes, differing in 15-19 oligonucleotides. A 1985 mosquito isolate from Maryland contained stable, small plaque variants which comprised the majority of that population. These small plaque variants differed by up to eight T1-resistant oligonucleotides when compared with their large plaque counterparts. Temperature sensitive virus was not detected in six unpassaged mosquito isolates from Maryland and New York.

Amino Acid Sequence↗
PubMed1993

A comparison of the nucleotide sequences of eastern and western equine encephalomyelitis viruses with those of other alphaviruses and related RNA viruses.

The complete nucleotide sequence of a 1982 Florida strain of eastern equine encephalomyelitis (EEE) virus, and partial sequence of the nonstructural protein genes of western equine encephalomyelitis (WEE) virus, were determined. The EEE virus genome was 11,678 nucleotides in length, excluding the cap nucleotide and poly(A) tail, and the nucleotide composition was 28% A, 24% G, 25% C, and 23% U. The organization of both EEE and WEE virus genomes was like that of other alphaviruses and included a termination codon between the nsP3 and nsP4 genes. Codon usage for 10 of 20 amino acids was nonrandom in the EEE genome, and dinucleotide CpG-containing codons were underutilized in both genomes. The slight CpG deficiency was similar to that seen in other alphaviruses and plant viruses in the alphavirus-like group, but less than that of poliovirus and yellow fever virus. This slight deficiency may reflect adaptation for replication in both CpG-deficient vertebrates, as well as insects which do not have CpG-deficient genomes. Phylogenetic analyses using nonstructural protein amino acid sequences indicated that alphaviruses evolved from a common ancestor which existed a few thousand years ago. An intercontinental introduction of an ancestral virus from the Old to New World, or vice versa, probably resulted in two main extant groups: one includes New World (EEE and Venezuelan equine encephalitis) viruses, while the other includes Old World (Sindbis, Middelburg, O'nyong-nyong, Ross River, and Semliki Forest) viruses. The position of WEE virus in the phylogenetic trees indicated that, in addition to its capsid gene (C. S. Hahn et al. (1988) Proc. Natl. Acad. Sci. USA 85, 5997-6001), WEE virus acquired its nonstructural genes from an EEE-like ancestor during recombination.

Alphavirus↗
PubMed1993

Detection of multiple blood feeding in Aedes aegypti (Diptera: Culicidae) during a single gonotrophic cycle using a histologic technique.

We evaluated a histologic technique for its usefulness in detecting multiple blood feeding by Aedes aegypti (L.) in a single gonotrophic cycle. To standardize the procedure, we carried out a laboratory study in which 166 mosquitoes imbibed two blood meals at known intervals. Eighty percent (78/98) of the multiple meals were detected when the interval between meals was from 1 to < to = 24 h and the time from the second meal to fixation ranged from 0 to 12 hr. At intervals outside this range, only 34% (23/68) of the multiple meals were detected. Overall, 61% (101/166) of the double meals were detected. Examination of 96 engorged Ae. aegypti collected by aspiration from inside houses in San Juan, Puerto Rico, indicated that 50% had imbibed multiple meals. Most wild-caught mosquitoes took their last meal the day before capture, and most multiple feeders fed twice on consecutive days. A dark line of digested blood, or heme, around the first meal and a physical separation between meals were the most useful histologic parameters for detecting multiple feeding in wild Ae. aegypti. An association of multiple feeding with advanced stages of oocyte development suggests that, at the time of collection, most Ae. aegypti from the study site had fed twice in each gonotrophic cycle. We conclude that, although it is labor intensive, histologic examination is an appropriate technique for a longitudinal, community-wide survey of multiple feeding by Ae. aegypti.

Aedes↗
PubMed1993

Distribution of western equine encephalomyelitis virus in the alimentary tract of Culex tarsalis (Diptera: Culicidae) following natural and artificial blood meals.

The distribution of western equine encephalomyelitis (WEE) virus in the alimentary tract of Culex tarsalis (Coquillett), following blood feeding, was examined using autoradiography. Following engorgement on chicks circulating radiolabeled virus, WEE virus in all mosquitoes was concentrated at the margins of the abdominal midgut, adjacent to the epithelium. Thirty percent of mosquitoes also contained small amounts of virus in the foregut, ventral diverticulum, and/or thoracic midgut. Mosquitoes imbibing labeled virus in hanging drops containing washed blood cells and sucrose showed an altered distribution of WEE virus. Virus was not concentrated adjacent to the abdominal midgut epithelium, and all mosquitoes contained large amounts of WEE virus in most regions of the thoracic alimentary tract. These findings may help explain the increased thresholds of infection associated with artificial feeding techniques and indicate that artificial blood meals may alter the sites of initial arbovirus infection within the alimentary tract of mosquito vectors.

Animals↗
PubMed1993

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.

Animals↗
PubMed1993

Blood-feeding patterns of Aedes aegypti (Diptera: Culicidae) collected in a rural Thai village.

Aedes aegypti (L.) were collected by aspiration once each week from in and around houses in a rural village in Chachoengsao Province. Thailand, during May 1990 to June 1991. Of the 1,230 specimens analyzed with a sandwich ELISA, 73% reacted to one or more of the seven hosts which we tested. Eighty-eight percent (789/896) of all detectable meals were identified as being from a single host (human). Patent multiple meals (double and triple), of which one was always human, were detected in 7% (66/896) of the specimens. The probability of feeding on a human, either as a single host or in a patent mixed meal, was > 0.90 during 12 of the 14 mo of the study; this probability never dropped below 0.85. The probability of Ae. aegypti taking multiple blood meals during a single gonotrophic cycle varied widely from 0.0 to 1.0. The possibility is discussed, including epidemiological significance, that there are seasonal fluctuations in the frequency of multiple feeding by Ae. aegypti and that multiple feeding increases in concert with seasonal trends for dengue infections of humans in Thailand.

Aedes↗
PubMed1993

Identification of blood meals in Aedes aegypti by antibody sandwich enzyme-linked immunosorbent assay.

A comparative study of 3 ELISA protocols was performed for host blood meal identification in Aedes aegypti. In the sandwich-B ELISA, which used a combination of heavy and heavy+light chain conjugates, specificity was improved to such a degree that conjugates no longer required cross-adsorption with heterologous sera. Using the sandwich-B assay, human blood meals in laboratory reared Ae. aegypti could be detected longer after feeding (100% at 32 h and 80% at 42 h) than with a direct assay (100% at 20 h). Efficacy of the sandwich-B and direct ELISAs in field analyses was studied in parallel) using 80 field collected mosquitoes from Thailand. The sandwich-B assay was superior (88% detection rate) to the direct assay (41% detection rate) and was thus selected as the method of choice for future field studies.

Aedes↗
PubMed1993

Effect of fish oil supplementation on the composition of molecular species of choline and ethanolamine glycerophospholipids in ruminant muscle.

Choline glycerophospholipids and ethanolamine glycerophospholipids of ruminant skeletal muscle contain approximately 40% and 65% plasmalogen, respectively. In the 1,2-diacyl-sn-glycero-3-phosphocholine (diacyl CPG), 16:0-18:2(n-6) and 16:0-18:1(n-9) accounted for about 50% of the total molecular species; in the 2-acyl-1(1-alkenyl)-sn-glycero-3-phosphocholine (alkenyl CPG), 16:0-18:2(n-6) was the predominant species. Fish oil supplementation resulted in a sixfold increase in the proportion of 16:0-20:5(n-3) and a two- to threefold increase in the proportion of 18:1-20:5(n-3) and 16:0-22:6(n-3) in the diacyl CPG, and there was a 40% decrease in the proportion of 16:0-18:1(n-9). In the alkenyl CPG, fish oil supplementation increased the proportion of molecular species containing C20 and C22 polyenoic fatty acids from 34% to 64%; in both sheep and cattle, the proportion of 16:0-20:5(n-3) was greater than any other molecular species. In contrast to the diacyl CPG, there was also an increase in the proportion of 18:0-20:5(n-3) in the alkenyl CPG. In the 1,2-diacyl-sn-glycero-3-phosphoethanolamine (diacyl EPG), 18:0-20:4(n-6) represented about 30% of the molecular species and this was reduced to less than 20% by fish oil supplementation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Incorporation of n-3 fatty acids of fish oil into tissue and serum lipids of ruminants.

This study examines the biohydrogenation and utilization of the C20 and C22 polyenoic fatty acids in ruminants. Eicosapentaenoic (20:5n-3) and docosahexaenoic (22:6n-3) acids were not biohydrogenated to any significant extent by rumen microorganisms, whereas C18 polyenoic fatty acids were extensively hydrogenated. The feeding of protected fish oil increased the proportion of 20:5 from 1% to 13-18% and 22:6 from 2% to 7-9% in serum lipids and there were reductions in the proportion of stearic (18:0) and linoleic (18:2) acids. The proportion of 20:5 in muscle phospholipids (PL) increased from 1.5% to 14.7% and 22:6 from 1.0% to 4.2%; these acids were not incorporated into muscle or adipose tissue triacylglycerols (TAG). In the total PL of muscle, the incorporated 20:5 and 22:6 substituted primarily for oleic (18:1) and/or linoleic (18:2) acid, and there was no consistent change in the porportion of arachidonic (20:4) acid.

Adipose Tissue↗
PubMed1992

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.

Animals↗