The Impact of Local Government Mosquito Control Programs on Ross River Virus Disease in Queensland, Australia

Abstract

In this study, I have investigated the relationship between mosquito control and mosquito-borne disease rates within Queensland, Australia. The thesis considers the most prevalent arbovirus causing human disease in Australia (Ross River virus) and estimates, how much Ross River virus disease is avoided through local government mosquito control in Queensland, and then compares the monetary value of avoided Ross River virus disease with the financial costs of local government mosquito control. A survey to collect information about mosquito control costs and practices was designed and implemented in each of the 125 local governments in Queensland. This survey collated previously dispersed information; because, although local governments in Queensland are legally obliged to perform mosquito control for disease prevention and nuisance reduction, there is no formal or regular reporting of mosquito control costs and practices to the State. A substantive conclusion from this research is that mosquito control has resulted in lower Ross River virus disease notifications in some local government areas. Ross River virus disease notifications are consistently lower in local government areas that implement mosquito control programs that pre-empt mosquito outbreaks using routine surveillance and then reduce mosquito abundance using mosquito control. Furthermore, there is evidence that local governments using extensive freshwater mosquito control, in addition to saltwater mosquito control, have relatively lower annual Ross River virus disease rates and lower standard deviations of the annual Ross River virus disease rates (indicating the freshwater mosquito control is important in suppressing outbreaks of Ross River virus disease). In contrast, mosquito control practices in the inland local government areas tend to be reactive to community complaints of mosquito abundance causing nuisance, and generally include ad-hoc mosquito control treatments. There is no evidence that reactive, adhoc mosquito control programs result in reduced Ross River virus disease notifications. The numbers of avoided Ross River virus notifications were estimated for the local governments that are located in the south eastern coastal region of Queensland. It has been estimated that an annual average of 2206 Ross River virus disease notifications have been avoided through effective mosquito control; and, for each actual notification of Ross River virus disease in the southern coastal local governments, two notifications have been avoided. The survey revealed that in excess of $10 million was spend by local governments implementing mosquito control in Queensland in 2004. The majority of this expenditure occurs in the more densely populated local governments located in the southern coastal strip of the state. A comparison of the financial costs of mosquito control and the financial value of avoided disease produced a cost-benefit ratio of 0.37, meaning that on average, 37% of the costs of mosquito control are directly recouped through the value of avoided Ross River virus disease. In years when the risk of Ross River virus outbreaks is relatively low, due to below average rainfall, the costs of mosquito control exceed the value of avoided Ross River virus notifications—but in years where the risk of an epidemic of Ross River virus is high, effective mosquito control practices can avoid an epidemic of Ross River virus disease, and in this situation the financial value of avoided disease exceeds the costs of the mosquito control program.