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Biomedical subjects

S A Ritchie

Publications and source records attributed to S A Ritchie.

At least 19 recordsLinked to original sources
PubMed2003

Vector competence of Australian mosquitoes (Diptera: Culicidae) for Japanese encephalitis virus.

Australian mosquitoes were evaluated for their ability to become infected with and transmit a Torres Strait strain of Japanese encephalitis virus. Mosquitoes, which were obtained from either laboratory colonies and collected using Centers for Disease Control and Prevention light traps baited with CO2 and octenol or reared from larvae, were infected by feeding on a blood/sucrose solution containing 10(4.5 +/- 0.1) porcine stable-equine kidney (PS-EK) tissue culture infectious dose50/mosquito of the TS3306 virus strain. After 14 d, infection and transmission rates of 100% and 81%, respectively, were obtained for a southeast Queensland strain of Culex annulirostris Skuse, and 93% and 61%, respectively, for a far north Queensland strain. After 13 or more days, infection and transmission rates of > 90% and > or = 50%, respectively, were obtained for southeast Queensland strains of Culex sitiens Wiedemann and Culex quinquefasciatus Say, and a far north Queensland strain of Culex gelidus Theobald. Although infection rates were > 55%, only 17% of Ochlerotatus vigilax (Skuse) and no Cx. quinquefasciatus, collected from far north Queensland, transmitted virus. North Queensland strains of Aedes aegypti L., Ochlerotatus kochi (Dönitz), and Verrallina funerea (Theobald) were relatively refractory to infection. Vertical transmission was not detected among 673 F1 progeny of Oc. vigilax. Results of the current vector competence study, coupled with high field isolation rates, host feeding patterns and widespread distribution, confirm the status of Cx. annulirostris as the major vector of Japanese encephalitis virus in northern Australia. The relative roles of other species in potential Japanese encephalitis virus transmission cycles in northern Australia are discussed.

Animals↗
PubMed2002

Isolation of arboviruses from mosquitoes (Diptera: Culicidae) collected from the Gulf Plains region of northwest Queensland, Australia.

As part of investigations into Japanese encephalitis (JE) virus and related flaviviruses in northern Australia, 153,529 mosquitoes were collected and processed for virus isolation from the Gulf Plains region of northwest Queensland. Collections from within 30 km of each of the townships of Croydon, Normanton and Karumba yielded 3,087 (2.0%), 66,009 (43.0%), and 84,433 (55.0%) mosquitoes, respectively, from which 16 viruses were isolated. Four isolates of Murray Valley encephalitis (MVE), two of Kunjin (KUN), three of Ross River (RR), and one of Sindbis (SIN) viruses were obtained from Culex sitiens subgroup mosquitoes. Molecular identification of the mosquito species composition of these virus positive pools revealed that most isolates were from pools containing mainly Culex annulirostris Skuse and low numbers of Culex palpalis (Taylor). Only three pools, one each of MVE, KUN, and RR, were from mosquitoes identified exclusively as Cx. annulirostris. Other viruses isolated include one Edge Hill virus from Ochlerotatus normanensis (Taylor), an isolate of SIN from Anopheles meraukensis Venhuis, two isolates of RR from Anopheles amictus Edwards, and single isolates of RR from Anopheles bancroftii Giles andAedes lineatopennis (Ludlow). The isolate of RR from Ae. lineatopennis was the first reported from this species. The public health implications of these isolations in the Gulf Plains region are discussed briefly.

Aedes↗
PubMed2001

An epidemic of dengue 3 in far north Queensland, 1997-1999.

OBJECTIVES: To describe an epidemic of dengue type 3 that occurred in far north Queensland in 1997-1999 and its influence on the further development of dengue prevention and control strategies. DESIGN: Epidemiological and laboratory investigation of cases, entomological surveys and phylogenetic analysis of dengue virus isolates. MAIN OUTCOME MEASURES: Numbers and characteristics of confirmed cases; Breteau Index (BI; number of containers breeding Aedes aegypti per 100 premises); effect of control measures on mosquito populations; genetic homology of epidemic virus with other dengue virus isolates. RESULTS: The epidemic lasted 70 weeks and comprised 498 confirmed cases in three towns (Cairns, Port Douglas and Mossman); 101 patients (20%) were admitted to hospital. Median interval between symptom onset and notification was seven days (range, 0-53 days), and cumulative duration of viraemia of public health significance was 2,072 days. BIs in affected areas were high, particularly in Mossman (45) and Port Douglas (31). Control measures significantly reduced mosquito populations (assessed as number of ovitraps containing Ae. aegypti eggs and mean number of eggs per trap [P< 0.05 for both]). However, transmission persisted in several foci, in part due to undetected waterfilled containers breeding Ae. aegypti. The epidemic virus belonged to serotype 3; phylogenetic analysis suggested it was imported from Thailand. CONCLUSIONS: The epidemic had greater morbidity than other recent Queensland epidemics of dengue and was harder to control, necessitating substantial revision of the Dengue Fever Management Plan for North Queensland. The epidemic's severity supports the hypothesis that dengue viruses from South East Asia are more virulent than others.

Aedes↗
PubMed2001

Entomological investigations of an outbreak of Japanese encephalitis virus in the Torres Strait, Australia, in 1998.

Japanese encephalitis (JE) virus first appeared in Australia in 1995, when three clinical cases (two fatal) were diagnosed in residents on Badu Island in the Torres Strait, northern Queensland. More recently, two confirmed human JE cases were reported in the Torres Strait Islands and Cape York Peninsula, in northern Queensland in 1998. Shortly after JE virus activity was detected in humans and sentinel pigs on Badu Island in 1998, adult mosquitoes were collected using CO2 and octenol-baited CDC light traps; 43 isolates of JE virus were recovered. Although Culex sitiens group mosquitoes yielded the majority of JE isolates (42), one isolate was also obtained from Ochlerotatus vigilax (Skuse). Four isolates of Ross River virus and nine isolates of Sindbis (SIN) virus were also recovered from members of the Culex sitiens group collected on Badu Island in 1998. In addition, 3,240 mosquitoes were speciated and pooled after being anesthetized with triethylamine (TEA). There was no significant difference in the minimum infection rate of mosquitoes anesthetized with TEA compared with those sorted on refrigerated tables (2.8 and 1.6 per 1,000 mosquitoes, respectively). Nucleotide analysis of the premembrane region and an overlapping region of the fifth nonstructural protein and 3' untranslated regions of representative 1998 Badu Island isolates of JE virus reveled they were identical to each other. Between 99.1% and 100% identity was observed between 1995 and 1998 isolates of JE from Badu Island, as well as isolates of JE from mosquitoes collected in Papua New Guinea (PNG) in 1997 and 1998. This suggests that the New Guinea mainland is the likely source of incursions of JE virus in Australia.

Animals↗
PubMed2001

Emerging viral diseases of Southeast Asia and the Western Pacific.

Over the past 6 years, a number of zoonotic and vectorborne viral diseases have emerged in Southeast Asia and the Western Pacific. Vectorborne disease agents discussed in this article include Japanese encephalitis, Barmah Forest, Ross River, and Chikungunya viruses. However, most emerging viruses have been zoonotic, with fruit bats, including flying fox species as the probable wildlife hosts, and these will be discussed as well. The first of these disease agents to emerge was Hendra virus, formerly called equine morbillivirus. This was followed by outbreaks caused by a rabies-related virus, Australian bat lyssavirus, and a virus associated with porcine stillbirths and malformations, Menangle virus. Nipah virus caused an outbreak of fatal pneumonia in pigs and encephalitis in humans in the Malay Peninsula. Most recently, Tioman virus has been isolated from flying foxes, but it has not yet been associated with animal or human disease. Of nonzoonotic viruses, the most important regionally have been enterovirus 71 and HIV.

Animals↗
PubMed2001

Murray Valley encephalitis virus surveillance and control initiatives in Australia. National Arbovirus Advisory Committee of the Communicable Diseases Network Australia.

Mechanisms for monitoring Murray Valley encephalitis (MVE) virus activity include surveillance of human cases, surveillance for activity in sentinel animals, monitoring of mosquito vectors and monitoring of weather conditions. The monitoring of human cases is only one possible trigger for public health action and the additional surveillance systems are used in concert to signal the risk of human disease, often before the appearance of human cases. Mosquito vector surveillance includes mosquito trapping for speciation and enumeration of mosquitoes to monitor population sizes and relative composition. Virus isolation from mosquitoes can also be undertaken. Monitoring of weather conditions and vector surveillance determines whether there is a potential for MVE activity to occur. Virus isolation from trapped mosquitoes is necessary to define whether MVE is actually present, but is difficult to deliver in a timely fashion in some jurisdictions. Monitoring of sentinel animals indicates whether MVE transmission to vertebrates is actually occurring. Meteorological surveillance can assist in the prediction of potential MVE virus activity by signalling conditions that have been associated with outbreaks of Murray Valley encephalitis in humans in the past. Predictive models of MVE virus activity for south-eastern Australia have been developed, but due to the infrequency of outbreaks, are yet to be demonstrated as useful for the forecasting of major outbreaks. Surveillance mechanisms vary across the jurisdictions. Surveillance of human disease occurs in all States and Territories by reporting of cases to health authorities. Sentinel flocks of chickens are maintained in 4 jurisdictions (Western Australia, the Northern Territory, Victoria and New South Wales) with collaborations between Western Australia and the Northern Territory. Mosquito monitoring complements the surveillance of sentinel animals in these jurisdictions. In addition, other mosquito monitoring programs exist in other States (including South Australia and Queensland). Public health control measures may include advice to the general public and mosquito management programs to reduce the numbers of both mosquito larvae and adult vectors. Strategic plans for public health action in the event of MVE virus activity are currently developed or being developed in New South Wales, the Northern Territory, South Australia, Western Australia and Victoria. A southern tri-State agreement exists between health departments of New South Wales, Victoria and South Australia and the Commonwealth Department of Health and Aged Care. All partners have agreed to co-operate and provide assistance in predicting and combatting outbreaks of mosquito-borne disease in south-eastern Australia. The newly formed National Arbovirus Advisory Committee is a working party providing advice to the Communicable Diseases Network Australia on arbovirus surveillance and control. Recommendations for further enhancement of national surveillance for Murray Valley encephalitis are described.

Animals↗
PubMed2001

The appearance of a second genotype of Japanese encephalitis virus in the Australasian region.

In mid-January 2000, the reappearance of Japanese encephalitis (JE) virus activity in the Australasian region was first demonstrated by the isolation of JE virus from 3 sentinel pigs on Badu Island in the Torres Strait. Further evidence of JE virus activity was revealed through the isolation of JE virus from Culex gelidus mosquitoes collected on Badu Island and the detection of specific JE virus neutralizing antibodies in 3 pigs from Saint Pauls community on Moa Island. Nucleotide sequencing and phylogenetic analyses of the premembrane and envelope genes were performed which showed that both the pig and mosquito JE virus isolates (TS00 and TS4152, respectively) clustered in genotype I, along with northern Thai, Cambodian, and Korean isolates. All previous Australasian JE virus isolates belong to genotype II, along with Malaysian and Indonesian isolates. Therefore, for the first time, the appearance and transmission of a second genotype of JE virus in the Australasian region has been demonstrated.

Animals↗
PubMed2001

First records of Culex gelidus from Australia.

Culex gelidus Theobald was recorded for the 1st time in Australia in May 1999 from 2 locations (Brisbane and Mackay, Queensland) approximately 820 km apart. Larval samples were collected from a semi-permanent freshwater swamp and an open drain and reared to adults in laboratories. Implications for Australia are discussed.

Animals↗
PubMed2001

Efficacy of Australian quarantine procedures against the mosquito Aedes aegypti.

Methods employed by Australian quarantine officers to control Aedes mosquitoes in containers were tested against all stages of Aedes aegypti. Saltwater emersion killed all larvae but not pupae or eggs that were briefly exposed. Swimming pool chlorine, methyl bromide fumigation, and permethrin (2% active ingredient) spray provided 100% mortality of eggs, larvae, and pupae. Aerosol sprays incorporating synthetic pyrethrins are practical and also provide effective control of adults.

Aedes↗
PubMed2001

Efficacy of an aerosol surface spray against container-breeding Aedes.

The effectiveness of a residual insect surface spray against container-breeding mosquitoes was tested in Cairns, Australia. A formulation containing imiprothrin and cypermethrin (Mortein Plus Cockroach Lure 'n' Kill High Performance Surface Spray) was selected based on the label claim to "kill continuously for up to 6 months." A 1-sec spray was applied to the water and interior surface of partially flooded tires and terra-cotta pots. Treatments were paired with a control and replicated at 2 sites within 3 residential properties for a total of 6 replicates. All mosquito larvae were removed and counted weekly, and a representative sample was identified in the laboratory. Complete control of Aedes species was achieved for 4 and 5 months in all tires and pots, respectively.

Aedes↗
PubMed2000

An alternative, human SRC promoter and its regulation by hepatic nuclear factor-1alpha.

The SRC gene encodes the proto-oncogene pp60(c-)(src), a tyrosine kinase implicated in numerous signal transduction pathways. In addition, the SRC gene is differentially expressed, developmentally regulated, and frequently overexpressed in human neoplasia. However, the mechanisms regulating its expression have not been completely explored. Here we describe the isolation of a new distal SRC promoter and associated exon, designated 1alpha, which we mapped to a position 1.0 kilobase upstream of the previously described SRC1A housekeeping promoter. Differential use of these promoters and their associated exons coupled with subsequent splicing to a common downstream exon results in c-Src transcripts with different 5' ends but identical coding regions. Promoter analysis following transient transfections into HepG2 cells mapped the minimal 1alpha promoter to a region 145 bp upstream of the major transcription start site. This region contained a consensus binding site for hepatic nuclear factor-1 (HNF-1), a liver-enriched transcription factor implicated in the regulation of a number of genes in liver, kidney, stomach, intestine, and pancreas. Subsequent mobility shift assays confirmed that HNF-1alpha isoform was the predominant factor interacting with this region of the promoter. Mutation of the HNF-1 site resulted in a dramatic reduction in SRC promoter activity. Cotransfection studies demonstrated the promoter could be strongly transactivated by the HNF-1alpha isoform but not by the related HNF-1beta factor. Consistent with these results, we demonstrated that transcripts originating from the SRC1alpha promoter display a tissue restricted pattern of expression with highest levels present in stomach, kidney, and pancreas. These results indicate that SRC transcriptional regulation is much more complex than previously realized and implicates HNF-1 in both the tissue-specific regulation of the SRC gene in normal tissues and the overexpression of c-Src in certain human cancers.

Base Sequence↗
PubMed2000

Definition of species in the Culex sitiens subgroup (Diptera: Culicidae) from Papua New Guinea and Australia.

Japanese encephalitis is a disease of major importance in Asia, which from 1995 has extended its range into the north of Australia. Culex annulirostris Skuse of the Culex sitiens subgroup of Culex was incriminated as the most likely mosquito vector. Because misidentifications previously have occurred within this subgroup, our paper defines electrophoretic methods to identify Culex specimens from Queensland and the Northern Territory in Australia and from Western Province in Papua New Guinea. In collections from 1996 to 1998 Culex sitiens Wiedemann, Cx. palpalis Taylor, and Cx. annulirostris comprised 93.1% of the total banded proboscis Culex mosquitoes collected; 6.9% remained unidentified to species by morphological or electrophoretic examination. The prevalence of Cx. palpalis was variable and appeared to be associated with below average rainfall during 1997. In Papua New Guinea, this species comprised up to 97.4% of banded proboscis Culex, with smaller numbers collected from the Torres Strait Islands and Cape York; none was collected from other Queensland localities. Cx. annulirostris was more prevalent during years of average or above average rainfall and was predominant in most localities, especially in the Torres Strait and Queensland. These data confirmed the problems in separating Cx. sitiens from Cx. palpalis and Cx. annulirostris using morphological characters.

Alleles↗
PubMed2000

Isolation of Japanese encephalitis virus from mosquitoes (Diptera: Culicidae) collected in the Western Province of Papua New Guinea, 1997-1998.

After Japanese encephalitis (JE) virus emerged in the Torres Strait in Australia in 1995, investigations were initiated into the origin of the incursion. New Guinea was considered the most likely source, given its proximity to islands of the Torres Strait. Almost 400,000 adult mosquitoes were processed for virus isolation from 26 locations in the Western Province of Papua New Guinea (PNG) between February 1996 and February 1998, yielding three isolates of JE virus. Two isolates of Murray Valley encephalitis, 17 isolates of Sindbis, and 1 each of Sepik and Ross River viruses were also obtained. Nucleic acid sequences of the PNG JE isolates were determined in the prM region, and in a region overlapping a part of the fifth nonstructural protein and the 3' untranslated region. The PNG isolates belonged to genotype II, and shared > 99.2% identity with isolates from humans and mosquitoes from the Torres Strait, suggesting that PNG is the source of incursions of JE virus into Australia.

3' Untranslated Regions↗
PubMed1999

Japanese encephalitis in north Queensland, Australia, 1998.

OBJECTIVE: To describe the circumstances of two cases of Japanese encephalitis (JE) in north Queensland in 1998, including one acquired on the Australian mainland. DESIGN: Serological surveillance of sentinel pigs for JE virus activity; serological surveys of humans and pigs and viral cultures of mosquito collections. SETTING: Islands in the Torres Strait and communities in the Northern Peninsula Area (NPA) and near the mouth of the Mitchell River in Cape York, Queensland, in the 1998 wet season (December 1997-May 1998). RESULTS: Sentinel pigs in the Torres Strait began to seroconvert to JE virus in February 1998, just before onset of JE in an unvaccinated 12-year-old boy on Badu island. By mid-April, most sentinel pigs had seroconverted. Numerous JE viruses were isolated from Culex annulirostris mosquitoes collected on Badu. In early March, a person working at the mouth of the Mitchell River developed JE. Serological surveys showed recent JE virus infection in 13 young pigs on a nearby farm, but not in 488 nearby residents. In NPA communities, sentinel pigs seroconverted slowly and JE viruses were isolated from three, but none of 604 residents showed evidence of recent infection. Nucleotide sequencing showed that 1998 JE virus isolates from the Torres Strait were virtually identical not only to the 1998 isolate from an NPA pig, but also to previous (1995) Badu isolates. CONCLUSIONS: JE virus activity was more widespread in north Queensland in the 1998 wet season than in the three previous wet seasons, but ecological circumstances (e.g., less intensive pig husbandry, fewer mosquitoes) appear to have limited transmission on the mainland. Nucleotide sequencing indicated a common source for the 1995 and 1998 JE viruses. Circumstantial evidence suggests that cyclonic winds carried infected mosquitoes from Papua New Guinea.

Adult↗
PubMed1999

Population structure and dispersal of the saltmarsh mosquito Aedes vigilax in Queensland, Australia.

Population genetics of the mosquito Aedes vigilax (Skuse) (Diptera: Culicidae), a major vector of arboviruses (e.g. Barmah Forest, Ross River), were investigated to obtain an indirect estimate of mosquito dispersal characteristics in typical habitats of Aedes vigilax in south-east Queensland: on the off-shore islands of Moreton Bay and on the mainland where disjunct breeding populations of Ae. vigilax are distributed along intertidal marsh. Six allozyme loci were assessed for genetic differentiation between samples from 11 localities. Significant larval variation between some breeding sites was attributed to site-specific selection. Nonsignificant genetic differentiation was found among collections of adult mosquitoes caught in light traps throughout the study area (exceeding 60x27 km), indicating widespread dispersal. As distances of < or = 9 km over water did not appear to act as effective barriers to Ae. vigilax dispersal, localized control activities applied to Ae. vigilax breeding sites are unlikely to be effective against the vagile adult population. Therefore, the contiguous shires programme of broad acre control is endorsed to prevent the spread of arboviruses carried by Ae. vigilax

Aedes↗
PubMed1999

Eggshell sampling: quantitative or qualitative data?

This research evaluated the use of qualitative presence/absence data compared with quantitative real number counts of Aedes vigilax eggshell data to obtain information on the spatial distribution of eggshells in several salt marsh vegetation types. Eggshells were extracted by subsampling and flotation, a method that does not recover all eggshells. The results of the analysis of presence/absence data were compared with those of real numbers. The general conclusions were similar by either method, suggesting that presence/absence data may be sufficient to rapidly determine eggshell distribution patterns.

Aedes↗