An Aedes albopictus female mosquito feeding on a human blood meal. Photo: James Gathany
The Zika virus spreading “explosively” through the Americas is likely to reach Australia through a return traveller at some stage, experts say, but there is hope it will be swiftly contained if it does arrive on our shores.
While dozens of mosquitoes in Australia are capable of spreading viruses such as Ross River, only one – the Aedes aegypti or yellow fever mosquito in far north Queensland – is capable of transmitting Zika.
Despite fears Zika can also be spread through sex and the bite of an infected monkey (rare isolated cases have been reported), Cameron Webb, an expert on mosquito-borne viruses, said the yellow fever mosquito would play the most important role in its transmission if it does arrive here this year.
Dr Webb said that for Australia’s yellow fever mosquito to spread Zika, one of the insects would have to bite an infected traveller shortly after that person returned from a country where the virus is circulating. The same mosquito could then bite other people who have never left the country. This is the same process that occurs with dengue fever outbreaks in far north Queensland.
Dr Webb, of Sydney University, said if there was an outbreak, local health authorities would try to kill the mosquitoes and their eggs in the affected area quickly, while infected people would be isolated to limit the spread of their blood through other mosquitoes.
On Monday, the World Health Organisation will host an emergency meeting about Zika after officials said it was “spreading explosively” across the Americas and that 4 million people could be infected with it this year.
Local transmission of the virus through Aedes aegypti mosquitoes is occurring in 23 countries in the region, where there are fears it can cause potentially fatal birth defects.
While the virus does not usually cause symptoms for 80 per cent of people (and when it does, the symptoms are mild), Brazilian health authorities are investigating links between the virus and a rare brain condition called microcephaly in infants, as well as a nervous system syndrome known as Guillain-Barre that can cause paralysis.
Dr Webb said the outbreak highlighted the importance of Australia’s efforts to keep exotic mosquitoes out of the country, particularly Aedes albopictus or the Asian tiger mosquito, which is also capable of transmitting Zika.
He said that while the yellow fever mosquito was unlikely to become established in southern cities of Australia, even with a warming climate, there was great potential for the Asian tiger mosquito to establish itself in such cities as Melbourne and Sydney.
The species, which can also carry dengue and chikungunya viruses, is found in the Torres Strait.
Associate Professor Nigel Beebe, of the University of Queensland, said that to prevent this species and others from entering Australia, there were traps designed to catch them within 400 metres of every Australian port.
He said these foreign species occasionally “popped in” and hit the traps after travelling on aeroplanes and ships. When this happens, researchers examine them and their eggs to see where they have come from. This information is then used to inform health, agriculture and travel authorities.
Associate Professor Beebe said given Zika had been in French Polynesia and the Western Pacific in recent years, it was “probably more due to luck” that Australia had been spared local transmission of the virus so far.
However, if it did arrive this year, he said, Australia’s health system was well equipped to diagnose it and contain it quickly.
“If you can diagnose it early, you can go in and suppress it,” he said.