Environment

Climate change could worsen diseases like Zika virus, experts say

The recent outbreak of the mosquito-borne Zika virus in South America serves as a stark reminder of the health risks linked to a warming world, health experts say.

The virus, linked to brain damage in thousands of babies in Brazil, has already been discovered in Australian travellers returning from South America, and was detected in six Australians last year.

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Zika defects link needs more research

The World Health Organisation (WHO) says it suspects a link between the mosquito-borne Zika virus and a rare birth defect involving abnormally small heads, but so far the evidence is circumstantial.

Zika is spread by the Aedes aegypti mosquito, which also spreads the dengue and chikungunya viruses. The Zika virus generally only causes symptoms in one in five people.

While authorities confirm there have been no locally acquired cases reported in Australia, more than 20 "countries of concern" have been listed around the world which pregnant women and those considering pregnancy have been advised to avoid, after links were made between the virus and microcephaly.

A doctor measures the head of a baby with microcephaly in Brazil. The baby's mother was diagnosed with the Zika virus ...
A doctor measures the head of a baby with microcephaly in Brazil. The baby's mother was diagnosed with the Zika virus during her pregnancy.  Photo: Getty Images

Microcephaly is a condition in which babies are born with abnormally small heads. It can be deadly, or cause intellectual disability.

Climate and Health Alliance executive director Fiona Armstrong said the regions most at risk of mosquito-borne diseases are those with "increasing average temperatures" where the invertebrates thrive.

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"Zika is the latest example of the many mosquito-borne viruses which pose an increasing threat to humans due to warmer and wetter conditions associated with climate change," Ms Armstrong said.

In Australia, one of the most important climate-sensitive viruses is the Ross River virus, a disease closely studied by zoologist and general practitioner David Harley.

A worker fumigates the Sambadrome ahead of Carnival celebrations in Rio de Janeiro.
A worker fumigates the Sambadrome ahead of Carnival celebrations in Rio de Janeiro. Photo: Bloomberg

Also spread by the bite of mosquitoes, Ross River virus infects about 5000 people every year, causing rash, fever, fatigue and headaches which can last many months.

Dr Harley said the prevalence of diseases like Ross River and Zika can be associated with changing rainfall, daily temperature range and humidity.

Dangerous meal: a female Aedes aegypti mosquito.
Dangerous meal: a female Aedes aegypti mosquito. Photo: AP

"In my own work on dengue, which has the same effect as Zika, my team and others around the world have found those associations ... [because] mosquitoes are impacted by those things; the temperature affects their reproduction, the evaporation of water, humidity.

While there are no locally contracted cases of Zika in Australia, Dr Harley said it was not impossible for the mosquito-borne disease to make its way to Australia.

Brazilian soldiers inspect a home in an attempt to eradicate mosquito larvae.
Brazilian soldiers inspect a home in an attempt to eradicate mosquito larvae. Photo: Getty Images

"We would only expect it to be transmitted in far north Queensland, and the city most likely affected would be Cairns, because it is reasonably large and it has a sizeable Aedes aegypti population ... and also Townsville," Dr Harley said.

"The incidence of infectious diseases will change with changes in climate, but we need to be nuanced and sophisticated in thinking about how they might change. We can't assume just because it's getting warmer we will see more of the diseases."

Human travel patterns, changes in the way people live and even whether people use air-conditioning could all have just as much of an impact on infectious diseases as changing weather patterns.

"If there are large migrations of people, conflict, changes in resource availability, certainly those things are likely to impact on those incidences."