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Biomedical subjects

T W Scott

Publications and source records attributed to T W Scott.

At least 73 records · Page 4Linked to original sources
PubMed1992

Female Aedes aegypti (Diptera: Culicidae) in Thailand rarely feed on sugar.

Female Aedes aegypti (L.) of two different body sizes and provided with different diets (20% sucrose, water only, or 20% sucrose + human blood) were marked and released together in a rural Thai village. Recaptured marked and unmarked (wild) adults were tested for fructose by the cold-anthrone reaction. Both released and wild females showed a low frequency of sugar feeding in nature; both small-bodied and large-bodied individuals failed to sugar feed significantly. Marked females released with sugar in their crop utilized this energy source over the following 2-3 d but failed to replenish it. In contrast, about one-third of wild, resting males showed evidence of recent sugar feeding. This indicated that the absence of plant sugar in females was not caused by a shortage of nectar sources in this rural domestic environment. Presumably, the nonutilization of plant sugar as an energy source increases the frequency of blood feeding and, therefore, the vectorial capacity of Ae. aegypti.

Aedes↗
PubMed1992

Manipulation of the fatty acid composition of milk by feeding protected canola seeds.

The feeding to dairy cows of canola seed protected from ruminal metabolism by emulsification and encapsulation in a matrix of aldehyde-treated protein resulted in a 10% increase in milk fat and no change in milk yield or protein content. Feeding the protected canola supplement significantly reduced the proportions of saturated fatty acids C16:0, C14:0, and C12:0 in milk fat; there were corresponding increases in proportions of C18:0, C18:1, C18:2, and C18:3. Yield of C18 monounsaturated and polyunsaturated fatty acids increased by 54%, which is equivalent to 143 g/d. Canola seed, enriched in C18:1, can be included in the diet and can result in significant changes in the proportions of saturated and unsaturated fatty acids in milk fat.

Animal Feed↗
PubMed1992

Pathologic changes in the midgut of Culex tarsalis following infection with Western equine encephalomyelitis virus.

Midguts of two strains of the mosquito vector Culex tarsalis were examined by light and electron microscopy following infection with western equine encephalomyelitis virus. Infection of the highly susceptible Knight's Landing strain with high-titered blood meals resulted in pathologic changes in the midgut epithelium after 2-4 days of incubation; lesions included sloughing of epithelial cells into the lumen and necrosis of cells in situ. Infection of Knight's Landing strain mosquitoes with low-titered blood meals and infection of the less susceptible Fort Collins strain with high-titered blood meals did not result in a significant increase in detached luminal cells, with respect to uninfected controls. Sloughing of infected cells into the midgut lumen may contribute to modulation of the mosquito infection. Lesions in the midgut of Cx. tarsalis are inconsistent with traditional views that regarded arbovirus infections of mosquito vectors as non-pathologic. These findings demonstrate that mosquito pathology is not an oddity limited to the previously described interaction between Culiseta melanura and eastern equine encephalomyelitis virus, and suggest that alphaviruses in general may adversely affect their mosquito vectors in nature.

Animals↗
PubMed1991

Molecular species analysis of 1,2-diacylglycerols and phosphatidic acid formed during bombesin stimulation of Swiss 3T3 cells.

Swiss 3T3 cells were labelled with [3H]glycerol and stimulated with bombesin over a time course of 20 min. The individual 1,2-diacylglycerols produced were quantified by acetylation followed by analysis by HPLC and argentation chromatography. The major phospholipids and phosphatidic acid were acetolysed and then analysed in the same manner. The data show that even at an early time of stimulation (30 s), stimulated diacylglycerol formation comes from at least two sources--phosphoinositides and phosphatidylcholine.

Animals↗
PubMed1991

Molecular evolution of eastern equine encephalomyelitis virus in North America.

We examined the rate and spatial pattern of eastern equine encephalomyelitis virus (EEEV) evolution in North America using primer-extension sequencing of viral RNA. Nucleotide sequences of the entire 26 S structural gene region of four EEEV strains revealed remarkable conservation between 1933 and 1985, with an estimated 0.7% divergence or 1.4 x 10(-4) nucleotide substitutions per site per year. Sequences from smaller 26 S regions of nine additional strains suggested that EEEV evolves in North America in a single lineage, with genetic exchange regularly occurring among enzootic transmission foci. In these limited 26 S genome regions, only synonymous nucleotide substitutions became fixed between 1933 and 1988, implying a high degree of conservation in protein structure. Short nucleotide sequences from a Panamanian, South American variety isolate revealed a relatively distant relationship to North American serotype viruses. This suggested genetic divergence between antigenic varieties, and independent evolution of EEEV in North and South America. Factors related to replication and epidemiology of EEEV, which may constrain its evolution in nature, are discussed. Possible mechanisms of genetic exchange among enzootic foci are also considered.

Amino Acid Sequence↗
PubMed1991

Enzyme immunoassay for detection of antibodies against eastern equine encephalomyelitis virus in sentinel chickens.

We developed an enzyme immunoassay (EIA) for the detection of immunoglobulin M (IgM) and IgG subclass antibodies directed against eastern equine encephalomyelitis (EEE) virus in chickens. The assays were compared with the serum plaque reduction neutralization test (PRNT) and the hemagglutination inhibition (HI) test for ability to detect antibodies against EEE virus in laboratory-infected birds. No cross-reactivity was detected in serum from chickens inoculated with St. Louis encephalitis or Highlands J virus. The interval after infection when EEE virus-specific antibodies were first detected by IgM and IgG EIAs was found to be similar to that determined by the PRNT and HI tests: 2 to 4 days. The IgG EIA, PRNT, and HI test detected antibodies to EEE virus for at least 27 to 30 days after inoculation. In contrast, serum from five of seven chickens did not contain detectable IgM 30 days after infection. Similarly, in all three naturally infected sentinel chickens from Maryland, IgM class antibody was undetectable 1 to 5 weeks after IgM was initially detected. EIAs provide simple and rapid alternatives to traditional tests for monitoring EEE virus infections in sentinel chicken flocks. Moreover, the IgM EIA provides a means to separate recently infected chickens from those infected greater than or equal to 1 month earlier.

Animals↗
PubMed1991

Detection of eastern equine encephalomyelitis virus deposition in Culiseta melanura following ingestion of radiolabeled virus in blood meals.

We examined deposition of eastern equine encephalomyelitis virus (EEEV) in the alimentary tract of its enzootic mosquito vector, Culiseta melanura, to detect potential sites of initial infection. Artificial viremias were created by injecting purified [3H]uridine-labeled EEEV intravenously into one-day-old chicks. Mosquitoes were allowed to engorge, incubated 1-2 hr, fixed, and whole abdomens and thoraces of 25 specimens embedded. Tagmata were sectioned, mounted on slides and coated with autoradiographic emulsion. Following exposures of 1-4 months, slides were developed and examined microscopically. In the majority of mosquitoes, label (virus) was detected only within the midgut; most virus was concentrated in a band of expressed serum adjacent to the abdominal midgut epithelium. Small amounts of virus were also deposited within folds in the cardial thoracic midgut of 96% of mosquitoes. Viral penetration into epithelial cells was detected throughout the abdominal midgut in all mosquitoes, and in the thoracic midgut of 20%. A small number (4/25) of mosquitoes examined showed signs of leaky abdominal midguts, with virus detected in the abdominal hemocoel. Concentration of EEEV in expressed serum adjacent to the abdominal midgut epithelium may enhance initial midgut infection. Leaky abdominal midguts exhibited by some mosquitoes may also facilitate rapid systemic infections of Cs. melanura. Deposition of virus in thoracic alimentary tissues suggests the possibility of early EEEV infection of the anterior midgut.

Animals↗
PubMed1990

Ultrastructural changes in the abdominal midgut of the mosquito, Culiseta melanura, during the gonotrophic cycle.

Abdominal midguts of the mosquito, Culiseta melanura, were examined by light and electron microscopy 1 hr-14 days days after blood feeding. Epithelial cells were drastically altered from columnar to squamous in form after engorgement, and returned to columnar by day 4 after feeding. Accumulation of mitochondria along brush borders of digestive cells, followed by the appearance of large secondary lysosomes, accompanied blood digestion. Evidence was obtained that myelin-like material in the lysosomes, probably the result of mitochondrial autolysis, is extruded into the lumen. Digestive cells resumed their pre-blood meal appearance by 10-14 days post-engorgement. Regenerative cells were scattered throughout the basal portion of the epithelium, along with endocrine cells. Other midgut cells containing large, microvilli-lined apical cavities were identified in most specimens. No evidence of division or differentiation was obtained for any cell types.

Animals↗
PubMed1990

Effects of house sparrow age and arbovirus infection on attraction of mosquitoes.

To test the hypothesis that arbovirus infection or advancing age increases the attractiveness of avian hosts to vector mosquitoes, we used an olfactometer that measures the response of mosquitoes to the passive, vertical diffusion of host-related cues. St. Louis encephalitis or western equine encephalomyelitis virus infection in house sparrows (Passer domesticus (L.], regardless of age, had no detectable effect on Culex quinquefasciatus Say or Cx. tarsalis Coquillett attraction, respectively, at close range. Sparrow age, however, was associated positively with increased Cx. quinquefasciatus attraction; i.e., nestlings were significantly less attractive than adults, and there was a trend for increased mosquito attraction as nestling age increased. When birds were examined in groups, attraction was not equal to the sum of the individual birds in the group. Nestlings, either alone or in a group, were less attractive than a single adult. One adult plus three older nestlings were more attractive than one adult with three young nestlings, but no more attractive than one adult alone. We speculate on the epidemiological significance of these laboratory results to arbovirus epizootic transmission.

Age Factors↗
PubMed1990

Peritrophic membrane formation and cellular turnover in the midgut of Culiseta melanura (Diptera: Culicidae).

Midguts of the mosquito Culiseta melanura (Coquillett) were examined by light and electron microscopy at varying intervals after blood feeding. Peritrophic membrane deposition first appeared 6 h after engorgement as a thin, electron-translucent band adjacent to epithelial cells throughout the abdominal midgut and reached maximum thickness at 12 h. Cell loss was apparently low in the abdominal midgut, with occasional cellular debris detected in the lumen 3-5 d after engorgement. Sloughing of cytoplasmic dropletlike evaginations, devoid of organelles, occurred infrequently in the abdominal midgut between 5 and 7 d after feeding. In contrast, cellular and cytoplasmic loss occurred continuously in the thoracic midgut. Epithelial cell replacement and regenerative cell mitosis were not detected in the abdominal or thoracic midgut.

Animals↗
PubMed1990

Patterns of eastern equine encephalomyelitis virus infection in Culiseta melanura (Diptera: Culicidae).

Infection of the mosquito Culiseta melanura (Coquillett) by eastern equine encephalomyelitis virus was examined using transmission electron microscopy (TEM) of whole tagmata and fluorescent antibody assay (FA) and infectious assay (IA) of dissected tissues. Following infectious blood meals from chicks circulating different virus titers, mosquitoes were examined after extrinsic incubation intervals of 1-22 d. Virus was first detected by FA and IA in midguts and nonalimentary tissues 24 h after infection. Nascent virus was first visualized by TEM in several tissues, including midgut, fat body, and salivary glands, of high-titer-infected mosquitoes 48 h after they engorged. Moderate- and low-titer blood meals resulted in slightly slower appearance and dissemination of virus. Results were consistent with dissemination of virus from the posterior midgut to salivary glands via the hemolymph. Neural tissues contained little or no virus, whereas fat body appeared to be an important organ for virus replication and dissemination. Dissemination barriers did not accompany mosquito infections.

Animals↗
PubMed1990

Rubidium and cesium as host blood-markers to study multiple blood feeding by mosquitoes (Diptera: Culicidae).

We have developed an experimental technique to quantify multiple blood feeding by mosquitoes during a single gonotrophic cycle on conspecific or closely related vertebrate hosts. Rubidium and cesium were detected in mosquitoes that fed on chickens injected with these elements 3 d earlier. Experimentally induced double blood meals were confirmed by the presence of both rubidium and cesium in individual mosquitoes. Multiple blood feeding by Culiseta melanura also was demonstrated in nature using this technique. This was the first simultaneous use of two alkali metals as host blood-markers for the study of mosquito blood-feeding behavior.

Aedes↗
PubMed1990

The relationship between size and parity status of field collected Culiseta melanura.

The relationship between body size and parity status of adult female Culiseta melanura collected from 3 locations in northeastern United States was studied by measuring wing lengths and examining ovaries of individual mosquitoes. Virus isolation was attempted from Cs. melanura collected in Maryland and in New Jersey. At all 3 locations, the size of Cs. melanura collected varied from large in the spring, to small in the summer. In New Jersey and Maryland mosquitoes collected in the fall were again large. The size of Massachusetts mosquitoes collected in the summer versus the fall was not different. In general, parous mosquitoes were larger than nulliparous mosquitoes in the spring but smaller than nulliparous ones in the fall. Eastern equine encephalomyelitis (EEE) and Highlands J (HJ) viruses were recovered from Cs. melanura only during the late summer when mosquitoes were small or during the fall months when larger mosquitoes were collected. We conclude that there is no detectable association between Cs. melanura size and parity status and that there is no obvious effect of mosquito size on EEE or HJ virus transmission.

Animals↗
PubMed1990

Susceptibility of Aedes albopictus to infection with eastern equine encephalomyelitis virus.

We examined susceptibility of a strain of Aedes albopictus from Houston, Texas to experimental infection with eastern equine encephalomyelitis (EEE) virus. After 15 days of extrinsic incubation, all Ae. albopictus examined by the cell culture assay and fluorescent antibody staining were infected but only 57% (4/7) of the mosquitoes that refed transmitted virus by bite. Data supported the concept of a salivary gland infection barrier to EEE virus in Ae. albopictus and the conclusion that virus replicates in fat body following dissemination from the midgut and prior to infection of salivary glands. Assay of adult progeny from females that fed on viremic chicks and fluorescent antibody studies of infected females failed to provide evidence that EEE virus is transmitted vertically by Ae. albopictus.

Aedes↗
PubMed1989

Effects of triturated Culiseta melanura (Diptera: Culicidae) on recovery of eastern equine encephalomyelitis virus.

Experiments were done to determine the effect, if any, of larval and adult Culiseta melanura (Coquillett) suspensions on the recovery of eastern equine encephalomyelitis (EEE) virus in baby hamster kidney (BHK) and Vero cell cultures. Although triturated pools of this mosquito reduced the titer of EEE virus added to suspensions, suspensions prepared from as many as 100 Cs. melanura larvae or adults did not reduce titers of virus to undetectable levels. Similarly, the titer of EEE virus in orally infected female Cs. melanura remained detectable when a single infected mosquito was triturated in a pool with 99 uninfected mosquitoes. These results show that in BHK or Vero cell culture assay systems, triturated Cs. melanura do not completely prevent the detection of EEE virus. The results therefore indicate that mosquito suspensions would not interfere with the isolation of virus from field-collected mosquitoes. This conclusion suggests that mosquito suspensions were not a factor in previous studies that were unsuccessful at detecting transovarial transmission of EEE virus by Cs. melanura.

Alphavirus↗
PubMed1989

Histological parameters useful in the identification of multiple bloodmeals in mosquitoes.

Culex nigripalpus females were given double and, in 2 cases, triple (interrupted) bloodmeals separated by various intervals. Mosquitoes given single meals served as controls. Using Azan-stained serial paraffin sections, we could identify multiple meals separated by 1-72 hr in 44 of 53 cases (84.6%). Among the histological parameters of importance in the identification of double and triple bloodmeals are the peritrophic membrane secreted around each bloodmeal, the plug which forms between the anterior and posterior midgut, the layer of heme which forms as a bloodmeal is digested, and remnants of the pupal meconium and/or pupal-pharate adult peritrophic membranes. The parameters we have identified will help determine the incidence of double bloodfeeding in wild populations which, in turn, should enhance our understanding of the transmission of pathogens by mosquitoes.

Animals↗
PubMed1988

Togavirus-associated pathologic changes in the midgut of a natural mosquito vector.

Arthropod-borne viruses were not previously believed to cause discernible pathologic changes in their natural mosquito vectors. We report cytopathologic lesions in the midgut of the mosquito, Culiseta melanura, 2 to 5 days after oral infection with eastern equine encephalomyelitis virus. Sloughing of densely staining, heavily infected epithelial cells into the midgut lumen was observed by light and transmission electron microscopy, along with degeneration of cells within the epithelium. Pathological changes in midgut epithelial cells sometimes included loss of brush border and basal lamina integrity. Disruption of the midgut basal lamina could result in bypassing of barriers to virus dissemination within the mosquito and allow rapid transmission to occur. Alternatively, luminal sloughing of heavily infected midgut epithelial cells may serve to modulate mosquito infections. These findings challenge previous beliefs regarding the benign nature of arbovirus-invertebrate host relationships.

Alphavirus↗