Biomedical subjects

B H Kay

Publications and source records attributed to B H Kay.

At least 55 records · Page 3Linked to original sources

PubMed1998

Susceptibility of selected strains of Australian mosquitoes (Diptera: Culicidae) to Rift Valley fever virus.

We evaluated the ability of selected strains of the Australian mosquitoes, Aedes notoscriptus (Skuse), Ae. vigilax (Skuse), Culex annulirostris Skuse, and Cx. quinquefasciatus Say, to function as potential vectors of Rift Valley fever (RVF) virus, should that virus be introduced accidentally into Australia. After feeding on a hamster with a viremia of 10(7) plaque-forming units/ml of blood, Ae. notoscriptus and Cx. annulirostris were the most susceptible, with infection rates of 86 and 55%, respectively. Female Ae. vigilax and Cx. quinquefasciatus also were susceptible, with infection rates of 38 and 30%, respectively. All of these species transmitted RVF virus by bite 7-10 d after intrathoracic inoculation, and all, except Cx. quinquefastiatus (not tested), transmitted RVF virus 10-16 d after oral exposure. The presence of competent mosquito vectors for RVF virus in Australia indicates the potential for RVF virus epizootics to occur should this virus be introduced into Australia.

Aedes↗

PubMed1998

Aedes aegypti survival and dispersal estimated by mark-release-recapture in northern Australia.

The survival and dispersal of adult Aedes aegypti were estimated in northern Australia where sporadic outbreaks of Ae. aegypti-borne dengue viruses have occurred in recent years. Standard mark-release-recapture methods were used. In addition, a new sticky trap was used to capture the mosquitoes. Prior to the field study, the survival and effect of marking Ae. aegypti with fluorescent powder were determined in the laboratory. Mortality was age-dependent and the marked cohorts had higher survival rates than the untreated cohorts. Recapture rates of 13.0% and 3.6% over a seven-day period were achieved for two batches of marked Ae. aegypti released simultaneously at the field site. More males than females were recaptured although the proportion of females increased with time. The probability of daily survival was 0.91 and 0.86 for the blue- and pink-marked females, respectively, and 0.57 and 0.70 for the blue- and pink-marked and males, respectively. The mean distance traveled of recaptured Ae. aegypti was 56 m and 35 m for females and males, respectively. The maximum observed distance traveled of 160 m was the same for both sexes. The warm to hot and dry climatic conditions may have restricted the dispersal of released mosquitoes in this study. The frequency of recaptures at certain trap locations suggested that shade, wind, and the availability of hosts affected the distribution of Ae. aegypti within the study site.

Aedes↗

PubMed1998

Eradication of Aedes aegypti from a village in Vietnam, using copepods and community participation.

In northern Vietnam, copepods of the genus Mesocyclops were used for biological control of Aedes aegypti, the principal vector of dengue viruses, by inoculation into wells, large cement tanks, ceramic jars, and other domestic containers that served as Ae. aegypti breeding sites. The use of Mesocyclops was complemented by community participation with respect to recycling to eliminate unused and discarded containers that collected rainwater and provided Ae. aegypti breeding sites that could not be treated effectively with Mesocyclops. Aedes aegypti disappeared from 400 houses of the treated village in August 1994 and has not reappeared, a result of particular significance, because there are virtually no other recorded instances of eradicating this mosquito anywhere in the world during the past 25 years, and certainly not with community-based approaches. When used in combination with community recycling, Mesocyclops is an easy and inexpensive method of Ae. aegypti control that should be effective for many communities in Vietnam and elsewhere.

Aedes↗

PubMed1998

Acute toxicity of selected pesticides to the Pacific blue-eye, Pseudomugil signifer (Pisces).

Because the larvivorous fish Pseudomugil signifer is native to southeastern Queensland and is abundant in shallow estuarine habitats, intertidal marshes, wetland habitats, and freshwater streams, it was chosen as an indicator species for toxicologic studies with pesticides. Acute toxicity studies with 2 organophosphorus pesticides (pirimiphos-methyl and temephos) and 3 alternate compounds under evaluation for registration in Australia (Bacillus thuringiensis var. israelensis, s-methoprene, and pyriproxyfen), were tested in 96-h laboratory trials. Pirimiphos-methyl was the most toxic compound, with a median lethal concentration (LC50) of 0.091 ppm (0.3 times the estimated field concentration [EFC] for a 15-cm-deep pool). Temephos had an LC50 value of 0.594 ppm (9.9 times the EFC). Bacillus thuringiensis var. israelensis and pyriproxyfen produced LC50 values of 6.1 x 10(11) International Toxic Units (477 times the EFC) and 0.854 ppm (106 times the EFC), respectively. s-Methoprene was the least toxic compound, with no mortality recorded at 500 times the EFC.

Animals↗

PubMed1998

A method for assessing the effects of runneling on salt marsh grapsid crab populations.

Runneling, a type of habitat modification using shallow channels, is an effective method for controlling mosquitoes that breed in intertidal salt marshes. Grapsid crab populations were studied to assess the environmental effects of runneling on nontarget species. Pitfall traps provided a means of monitoring crab distribution and relative abundance at Coomera Island in southeastern Queensland. The study indicated that although runneling does not have a significant effect on the total number of crabs, it may have a significant impact on species distribution. Significantly greater numbers of Parasesarma erythrodactyla were found at the runneled site. In contrast, Helograpsus haswellianus was more abundant at the unrunneled control site. Associations were also found between species abundance, distance from the tidal inlet, and vegetation type. Helograpsus haswellianus was associated with mixed vegetation, whereas Parasesarma erythrodactyla was associated with tall, dense salt marsh couch. No correlation was found between the number of crab burrows present at the study site and the number of crabs caught in the traps. However, the runneled site had approximately twice the number of crab burrows of the unrunneled control site. These results were consistent for 3 consecutive monthly sampling periods. The method has proven suitable for further studies on the long-term environmental impact of runneling.

Animals↗

PubMed1998

Laboratory and field evaluation of efficacy of VectoBac 12AS against Culex sitiens (Diptera: Culicidae) larvae.

Laboratory bioassay studies of the efficacy of VectoBac 12AS (active ingredient: 1,200 International Toxic Units [ITU]/mg Bacillus thuringiensis var. israelensis) against field-collected late 3rd/early 4th-instar larvae of Culex sitiens indicated excellent control potential. A 95% lethal concentration (LC95) value of 1.381 x 10(7) ITU was calculated, which equated to a dosage of 0.011 liters/ha. This dosage represented 1.8% of the recommended lowest dosage rate for the product. A field trial of VectoBac 12AS against late 3rd/early 4th-instar field specimens of Cx. sitiens in floating mesh cylinders was then conducted in salt-marsh pools near Coomera Marina, southeast Queensland, Australia. At a rate of 0.5 liters/ha, 100% mortality of Cx. sitiens larvae was recorded at 24 h posttreatment.

Animals↗

PubMed1998

An overview of remote sensing and GIS for surveillance of mosquito vector habitats and risk assessment.

This paper provides a brief nontechnical overview of the use of remote sensing to achieve multiple objectives, focusing on mosquito management. It also shows how Geographic Information Systems, combined with remote sensing analysis, have the potential to assist in minimizing disease risk. Examples are used from subtropical Queensland, Australia, where the salt marsh mosquito, Aedes vigilax, and the freshwater species, Culex annulirostris, are vectors of human arbovirus diseases such as Ross River and Barmah Forest virus disease. Culex annulirostris is also implicated in the transmission of Japanese Encephalitis. Mapping the breeding habitats of the species facilitates assessment of the risk of contracting the diseases and also assists in control of the vectors. First, it considers a simple risk model that is applied to data for the city of Brisbane in southeast Queensland. This is then linked to computer-aided analysis of remotely sensed data to map potential ephemeral freshwater breeding sites of Cx. annulirostris. This has the potential to guide control at critical times, for example after heavy summer rainfall or when there is an outbreak of Ross River virus disease. Second, the use of color infrared aerial photography is used to identify the specific parts of the salt marsh in which larvae and eggs of Ae. vigilax are found. Finally, we explore novel ways to map the detailed pattern of water under mangrove forest canopy to identify where mosquitoes are breeding and as an aid to planning modification. For each we discuss the limitations and advantages and the possibilities for combining methods and/or using a single method for multiple objectives.

Animals↗

PubMed1997

Ross River virus in mosquitoes (Diptera:Culicidae) during the 1994 epidemic around Brisbane, Australia.

During the summer 1994 outbreak of epidemic polyarthritis in suburban Brisbane, 29,931 adult female mosquitoes were collected by octenol-CO2 light traps and tested for virus by species in pools of approximately 20 using an in situ enzyme-linked immunoassay. Overall, 63 isolations of Ross River (RR) virus were made from 7 different mosquito species, including 23 from freshwater-breeding Culex annulirostris Skuse, 13 from peridomestic Aedes notoscriptus (Skuse), 4 from Aedes procax (Skuse), 12 from the brackish water-breeding Aedes funereus (Theobald), 9 from saltmarsh Aedes vigilax (Skuse), and 1 each from Culex sitiens Wiedemann and Aedes alternans (Westwood). The RR virus minimum infection rate in mosquitoes ranged from 1.6 to 2.5/1,000 from March to June 1994. This study implicates freshwater and brackish water mosquitoes as important suburban vectors of RR virus and indicates the need for refocusing mosquito control priorities.

Aedes↗

PubMed1997

Investigation of gray-headed flying foxes (Pteropus poliocephalus) (Megachiroptera: Pteropodidae) and mosquitoes in the ecology of Ross River virus in Australia.

Entomologic and virologic factors were investigated to determine whether gray-headed flying foxes (Pteropus poliocephalus) from Indooroopilly Island, Brisbane, Australia could be vertebrate hosts of Ross River (RR) virus. Aedes funereus was the most abundant mosquito species with 6,300-38,700 females per light trap night in the flying fox camp containing gray-headed, black (P. alecto), and little red (P. scapulatus) flying foxes. Sixteen Ae. funereus blood meals from this collection were analyzed by hemoglobin electrophoresis and were found to be from P. alecto. From pledget feeding with RR virus, the infectious dose required to infect 50% of wild caught Ae. funereus was log10 4.2 50% tissue culture infectious doses per mosquito, with a transmission rate to mice of 17% at 9-10 days post infection. Experimental infection of 10 juvenile P. poliocephalus produced viremias of low titer in five animals, with a duration of 1-4 days and a mean of two days. Three percent of colonized Ae. vigilax that fed on the 10 animals during this period became infected. One of the five viremic flying foxes and two of the five aviremic animals produced a detectable immune response by either neutralization or hemagglutination-inhibition tests. Based on the low to moderate vector competence of Ae. funereus for RR virus, and evidence that P. poliocephalus is a poor vertebrate host of RR virus, it is unlikely that RR virus transmission would be maintained between these two species, but it could be maintained by other more competent vector/host pairs.

Aedes↗

PubMed1997

Response of Culex quinquefasciatus to visual stimuli.

The vision of Culex quinquefasciatus was studied in the laboratory. The attractiveness of colors (black, white, brown, yellow, blue, a skin tone) was evaluated with respect to the collection of Cx. quinquefasciatus in natural light, in the dark, and in ultraviolet light. Culex quinquefasciatus prefers both black and brown in natural light and ultraviolet light, but, as expected, there is no preference in the dark. There were no significant differences among the other 4 colors in natural light and ultraviolet light.

Analysis of Variance↗

PubMed1997

Acute and sublethal effects of (S)-methoprene on some Australian mosquitoes.

Laboratory bioassays were used to determine the efficacy of (S)-methoprene against 7 species of Australian mosquitoes. The 90% lethal concentration (LC90) ranged from 0.17 ppb for Aedes vigilax to 6.54 ppb for Culex sitiens. The survival of adults exposed as larvae to 2 sublethal dosages of (S)-methoprene was compared to a control group. Little effect was noted for Cx. sitiens and Culex annulirostris. However, survival of male and female Ae. vigilax was significantly reduced and appeared to be dose related. Bloodfeeding success of female Ae. vigilax was also significantly reduced.

Aedes↗

PubMed1997

Importance of Hydrilla verticillata (hydrocharitaceae) as habitat for immature mosquitoes at the Ross River reservoir, Australia.

From November 1990 to November 1992, immature mosquitoes were sampled from the shoreline and from emergent beds of the submerged aquatic plant Hydrilla verticillata at the Ross River reservoir, northern Australia. Aerial mapping of Hydrilla beds was done in conjunction with sampling to estimate total immature mosquito numbers. Larvae of 7 species were found. Culex annulirostris. Anopheles annulipes s.l., and Anopheles amictus comprised 80.4% of the total. Peak larval densities occurred in the late wet season period in both habitat types (March to May) but Hydrilla generally supported higher densities, particularly of An. annulipes s.l. (43.7% of the total sample), than the shoreline habitats. Anopheles annulipes replaced Cx. annulirostris as the predominant taxon when 1990-92 data were compared with data for 1985-86. The Hydrilla beds supported on the order of 5.6 x 10(9) immatures during the period of peak density. This suggests that where human exposure is of concern, mosquito control in habitats such as Hydrilla is warranted.

Analysis of Variance↗

PubMed1996

Surveillance of the mosquito Aedes aegypti and its biocontrol with the copepod Mesocyclops aspericornis in Australian wells and gold mines.

A survey of the dengue vector mosquito Aedes aegypti was undertaken using funnel traps to detect immature stages (larvae and pupae) in flooded disused mine shafts and wells in Charters Towers, Queensland, Northern Australia. The town has a history of dengue fever since 1885 when goldminers were the first recorded victims. During the latest dengue epidemic in 1993, 2% of the population had laboratory-confirmed dengue virus Type 2, despite source reduction of Ae.aegypti breeding-sites at ground level or above. This led to suspicions that dengue vector Ae.aegypti breeding-sites might be below ground level. When surveyed in March 1994, Ae.aegypti immatures were found in 9/10 wells and 1/6 mine shafts. The water in wells and mines had similar characteristics-except that turbidity was higher in the mines, which more often contained predators of mosquito immatures. The copepod Mesocyclops aspericornis was collected from water in 1/10 wells and 2/6 mine shafts. Laboratory predation trials resulted in 95.5-100% predation by 25 copepods/l on Ae.aegypti first-instar larvae up to 200 larvae/l. Five wells containing Ae.aegypti in the survey were inoculated with fifty indigenous M.aspericornis, and five wells (one positive and four negative in the survey) were left untreated as controls. Nine months later, in December 1994, Ae.aegypti had been eliminated from all five treated wells but all untreated control wells contained Ae.aegypti, except for one well that contained a natural population of M.aspericornis. The role of wells and mines as winter/ dry season refuges of Ae.aegypti in northern Australia is reviewed, and we recommend the use of M.aspericornis as a cost-effective, environmentally acceptable and persistent agent for the sustainable control of Ae.aegypti, especially in inaccessible breeding sites.

Aedes↗

PubMed1996

Critical examination of Aedes aegypti indices: correlations with abundance.

The following immature stage indices for Aedes (Stegomyia) aegypti surveillance were evaluated in four north Queensland, Australia towns with respect to their relationship to immature and adult female densities: Breteau, House, Container, Larval Density, Stegomyia (and modifications thereof), and a newly created Adult Productivity Index. Spearman's correlations of indices that considered larval or immature (larvae and pupae) numbers had a better relationship with immature abundance but this was not necessarily the case against adult abundance. To examine the robustness of the indices, data from 758 premises in Townsville, Charters Towers, Ravenswood, and Mingela were pooled and 30 random subsamples, each consisting of 50 premises were taken. After each subsample was taken, the premises selected were reintroduced into the original data bank of 758 premises, and therefore, were available for further selection, i.e., sampling with replacement. Indices were calculated for each of the 30 subsamples and the coefficients of variation of each index were estimated from these. The Breteau, Adult Productivity, House, and Adult density indices proved to have the smallest coefficients compared with index size. No alternate index was regarded as being superior to the Breteau, including the Adult Productivity Index measuring both container type frequency and immature density. For this reason and in view of the labor intensiveness of estimating immature indices that incorporate productivity, it is recommended that new and cost-effective methods of adult surveillance be pursued.

Aedes↗

PubMed1996

Evaluation of Mesocyclops aspericornis (Cyclopoida:Cyclopidae) and Toxorhynchites speciosus as integrated predators of mosquitoes in tire habitats in Queensland.

This study addressed biological control of peridomestic Aedes notoscriptus, known to be a highly effective colonizer of tire habitats and a possible vector of Ross River virus. A laboratory trial of the compatibility of the predators Mesocyclops aspericornis and Toxorhynchites speciosus in small container habitats showed that 4th-instar Tx. speciosus did not significantly affect M. aspericornis mortality. Introduced M. aspericornis and naturally occurring Tx. speciosus were found to form a compatible predator pair for reduction of larval Ae. notoscriptus and Culex quinquefasciatus populations in tire habitats. Over 22 months of field survey, 97% of tires without predators contained mosquito larvae, at a median density of 43 larvae/liter. By comparison, 51% of tires containing both predator species held mosquito larvae at a median density of 4 larvae/liter. Predation by Tx. speciosus persisted for the duration of the study. The inability of the Lake Kurwongbah strain of M. aspericornis to tolerate temperatures of < or = 10 degrees C, which are prevalent in Brisbane during winter, resulted in a failure to deliver persistent reduction of mosquitoes in tires. The temperature-dependent population characteristics of M. aspericornis emphasize the long-recognized importance of matching a biological control candidate's physiological requirements to the environment in which control is sought.

Aedes↗

PubMed1996

Alphavirus infection in mosquitoes at the Ross River reservoir, north Queensland, 1990-1993.

This study addresses the potential problem of alphavirus infection associated with recreational use of the Ross River reservoir in north Queensland, Australia. From 1990 to 1993, 51,497 adult female mosquitoes were collected mainly by CO2-supplemented light traps. Four localities within the reservoir were considered and compared with mosquitoes collected during 1991 from 2 public localities around Townsville City. Ten isolates of Ross River virus, one of Barmah Forest virus, and 2 of Sindbis virus were recovered from Aedes normanensis, Anopheles amictus, and Culex annulirostris. All isolates were collected during the wet seasons of 1991 and 1992 using an enzyme immunoassay and cross-checked using a polymerase chain reaction assay Estimation of relative hazard was based on total mosquito abundance, prevalence of vector species, and on mosquito infection rates. Based on 1990-93 data, it was concluded that the Big Bay area of the Ross River dam, currently being considered as a primary recreational locality, was relatively safer than Antill Creek, Ross River, and Toonpan and presented no greater hazard than localities around urban Townsville, away from the reservoir. However, because of the changing ecology of the reservoir and lack of a full understanding of annual alphavirus activity, periodic surveillance is recommended.

Aedes↗

PubMed1996

Acute toxicity of selected pesticides to the estuarine shrimp Leander tenuicornis (Decapoda:Palaemonidae).

The shrimp Leander tenuicornis is abundant in southeastern Queensland intertidal marsh pools and was chosen as an indicator species for toxicological studies with pesticides. Acute toxicity to this crustacean of temephos and 3 pesticide compounds under evaluation for registration in Australia (Bacillus thuringiensis var. israelensis, s-methoprene, and pyriproxyfen) was tested in 96-h laboratory trials. Temephos was the most toxic compound, with a median lethal concentration (LC50) of 0.01 ppm (0.33 times the estimated field concentration [EFC] for a 15-cm-deep pool). s-Methoprene was the least toxic compound, with an LC50 of 14.32 ppm (1,790 times the EFC). Bacillus thuringiensis var. israelensis and pyriproxyfen produced LC50 values of 60.9 x 10(6) ITU (176 times the EFC) and 0.098 ppm (12.25 times the EFC), respectively.

Animals↗

PubMed1995

Specific enzyme immunoassays for the rapid detection of Ross River virus in cell cultures inoculated with infected mosquito homogenates.

BACKGROUND: Ross River (RR) virus is a mosquito-borne alphavirus and one of the aetiological agents of epidemic polyarthritis in humans. Early detection of increased virus activity in mosquito populations enables public health authorities to implement measures to reduce the number of human infections during epidemics. However, current surveillance techniques require a minimum of four weeks for viruses to be isolated and identified. OBJECTIVES: This study was carried out to assess the use of enzyme immunoassays (EIA) as rapid alternatives to traditional cell culture techniques for detection of RR virus in mosquitoes. STUDY DESIGN: Enzyme immunoassays and immunoperoxidase assays were developed using RR-specific monoclonal antibodies and compared to traditional methods for detection of RR virus in field-caught mosquito samples. RESULTS: By inoculation of C6/36 cell cultures with mosquito homogenates and testing monolayers and culture supernatant by EIA, RR virus was detected and identified in all infected samples within 6 days. CONCLUSIONS: The use of EIA provides a rapid, sensitive and specific alternative to traditional methods for the detection of RR virus in mosquito vectors.

Journal Article↗