Rain predicts Ross River virus outbreaks

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Rain predicts Ross River virus outbreaks

Heavy wet season rain is the best early-warning system for predicting outbreaks of the Ross River virus disease in Darwin, a Charles Darwin University student has confirmed.

Susan Jacups, who will receive a PhD on Thursday night, has undertaken research that will help to inform mosquito control programs in Darwin, where housing estates continue to be developed near mosquito breeding areas.

“With about 4800 cases reported in Australia each year, Ross River virus disease is our most common and widespread mosquito-borne disease and arguably the most important public health arbovirus,” she said.

Dr Jacups analysed 15 years of data including rainfall, temperature, humidity, tidal data, Ross River virus disease cases, and several species of mosquitoes known to carry the virus finding that rain was the best warning for mozzie virus outbreaks.

“The data shows that accumulated rainfall of 279 mm or more in December or January was the best predictor of an outbreak of the disease,” she said.

Dr Jacups said Darwin had averaged about 113 cases of Ross River virus per 100,000 people each year in the 15 years to 2005.

“While more cases are reported during the wet season when mosquito numbers are higher, there are other important factors. The virus has a natural vertebrate host in which it completes its lifecycle, usually a marsupial,” she said.

“These marsupials were more abundant when food was plentiful after heavy rains at the beginning of the wet.”

Dr Jacups also found that a decision to create drains in Leanyer Swamp, Casuarina Swamp and Coconut Grove Swamp in the early 1980s was responsible for a significant reduction in the number of potentially virus-carrying mosquitoes.

“There was a huge reduction in dry season mosquito numbers, particularly for Aedes vigilax (northern salt-marsh mosquito), and Culex annulirostris (common banded mosquito) that can carry the potentially fatal Murray Valley encephalitis virus.”

Dr Jacups, who is now undertaking mosquito research on dengue prevention in northern Queensland, worked at CDU and Menzies School of Health Research during her 18 years in Darwin.

“Mosquito research has allowed me to combine my interests in landscape ecology with my background in statistics and health,” she said.

(Source: Charles Darwin University)