Climate Variability and Ross River Virus Transmission in Townsville Region, Australia 1985 to 1996

Background How climate variability affects the transmission of infectious diseases at a regional level remains unclear. In this paper, we assessed the impact of climate variation on the Ross River virus (RRv) transmission in the Townsville region, Queensland, north-east Australia. Methods Population-based information was obtained on monthly variations in RRv cases, climatic factors, sea level, and population growth between 1985 and 1996. Cross-correlations were computed for a series of associations between climate variables (rainfall, maximum temperature, minimum temperature, relative humidity and high tide) and the monthly incidence of RRv disease over a range of time lags. The impact of climate variability on RRv transmission was assessed using the seasonal auto-regressive integrated moving average (SARIMA) model. Results There were significant correlations of the monthly incidence of RRv to rainfall, maximum temperature, minimum temperature and relative humidity, all at a lag of 2 months, and high tide in the current month. The results of SARIMA models show that monthly average rainfall (β=0.0012, p=0.04) and high tide (β=0.0262, p=0.01) were significantly associated with RRv transmission, although temperature and relative humidity did not seem to have played an important role in the Townsville region. Conclusions Rainfall, and high tide were likely to be key determinants of RRv transmission in the Townsville region

Rainfall and sentinel chicken seroconversions predict human cases of Murray Valley encephalitis in the north of Western Australia

Background Murray Valley encephalitis virus (MVEV) is a flavivirus that occurs in Australia and New Guinea. While clinical cases are uncommon, MVEV can cause severe encephalitis with high mortality. Sentinel chicken surveillance is used at many sites around Australia to provide an early warning system for risk of human infection in areas that have low population density and geographical remoteness. MVEV in Western Australia occurs in areas of low population density and geographical remoteness, resulting in logistical challenges with surveillance systems and few human cases. While epidemiological data has suggested an association between rainfall and MVEV activity in outbreak years, it has not been quantified, and the association between rainfall and sporadic cases is less clear. In this study we analysed 22 years of sentinel chicken and human case data from Western Australia in order to evaluate the effectiveness of sentinel chicken surveillance for MVEV and assess the association between rainfall and MVEV activity. Methods Sentinel chicken seroconversion, human case and rainfall data from the Kimberley and Pilbara regions of Western Australia from 1990 to 2011 were analysed using negative binomial regression. Sentinel chicken seroconversion and human cases were used as dependent variables in the model. The model was then tested against sentinel chicken and rainfall data from 2012 and 2013.Results Sentinel chicken seroconversion preceded all human cases except two in March 1993. Rainfall in the prior three months was significantly associated with both sentinel chicken seroconversion and human cases across the regions of interest. Sentinel chicken seroconversion was also predictive of human cases in the models. The model predicted sentinel chicken seroconversion in the Kimberley but not in the Pilbara, where seroconversions early in 2012 were not predicted. The latter may be due to localised MVEV activity in isolated foci at dams, which do not reflect broader virus activity in the region. Conclusions We showed that rainfall and sentinel chickens provide a useful early warning of MVEV risk to humans across endemic and epidemic areas, and that a combination of the two indicators improves the ability to assess MVEV risk and inform risk management measures

Biting midges (sand flies) at Palmerston

Investigations to date indicate enormous numbers of biting midges in the mangrove areas near Palmerston. The predominant pest species, Culicoides ornatus breeds in the seaward zone of the coastal mangrove belt. This species is currently under investigation and several possible options are under consideration to help reauce the pest numbers

Interim control measures for biting insects at Palmerston

The results of collections thus far during the monitoring of biting insects at Palmerston have shown that, whilst the Culicidae (mosquitoes) may be a significant localized problem in some residential areas, the Ceratopogonidae (biting midges) are the most important nuisance pest group. Data from 1981/82 collected by the Medical Entomology Section suggest that the problems of mosquitoes are much higher than are apparent in this much reduced wet season. Among the biting midges two species groups dominate collections, Culicoides ornatus and C. marmoratus. Of these C. ornatus is the major pest species and a resume of its biology is presented in Appendix 1

Biting insects at Palmerston, mosquitoes

Biting insects at Palmerston fall into three main groups : Culicidae (Mosquitoes); Culicoides (Biting Midges) and Tabanidae (March Flies). The March flies appear to be a relatively minor problem near some areas of the mangrove margin in the early wet season. The other two groups are more prominent and may occur at times in significant pest levels. A separate report has been prepared dealing with the biting midges and this report will cover only mosquitoes

Complete genome sequences of the prototype isolates of genotypes 2, 3, and 4 of Murray Valley encephalitis virus

Murray Valley encephalitis virus (MVEV) (Flaviviridae family, Flavivirus genus), a mosquito-borne pathogen of humans and horses, is endemic to the Australasian region. We report here the complete genomes of the prototype strains of MVEV genotypes 2, 3, and 4