Australian and international experts are warning that the threat of a Zika virus epidemic and Zika congenital syndrome in the Asia Pacific region – particularly in Bali and Papua New Guinea (PNG) – could lead to an Australian outbreak if exotic vector mosquitoes become established here.
Meanwhile, as the World Health Organization (WHO) has declared what some experts say is a premature end to the Zika global emergency, Australian governments are implementing strategies to prevent the Zika vectors Aedes aegypti and Aedes albopictus becoming endemic.
Professor Albert Ko, an epidemiologist from Yale University and member of the Global Virus Network’s Zika Virus Task Force said there were “important threats” to Australia given the large numbers of travellers to regions where Zika is circulating, particularly Southeast Asia.
Professor Ko said he believed WHO had ‘jumped the gun’ in ending the emergency because the spectrum of manifestations associated with Zika congenital syndrome had still not been delineated.
There appeared to be growing evidence that populations in regions outside the Americas that had not experienced Zika may be susceptible to infection with the virus, as well as Zika congenital syndrome, he said.
“Of particular concern is the degree to which heavily populated regions in South and Southeast Asia are susceptible given that there is heavy infestation with Aedes mosquitoes.
“[Another] key question is whether microcephaly is just the most severe form and the tip of the iceberg and that newborns whose mothers were exposed to the virus have less obvious but significant defects such as ocular and auditory lesions.”
Professor Scott Ritchie from the Australian Institute of Tropical Health and Medicine at James Cook University in Queensland, said the extent of the Zika risk from PNG and Bali was unknown, but there may have been ongoing Zika transmission in Bali for decades. He said dengue fever was introduced to northern Australia via these regions.
“No-one has been looking [at Zika] until the last couple of years. Normal Zika infection was relatively pedestrian compared to others – we didn’t know about the neurological and fetal issues at the time.”
Professor Ritchie said another threat was the Asian tiger mosquito, endemic in the Torres Strait, which could undermine efforts by Queensland Health to infect Zika-vector mosquitoes with the bacteria Wolbachia in order to stop transmission of Zika and Dengue viruses.
“They have isolated Zika from this mosquito,” he said. “It could invade and establish in the Australian mainland. This has potential to displace mosquitoes infected by Wolbachia – and all that good work by Eliminate Dengue and Queensland Health could be undermined.”
In this issue of Public Health Research & Practice, two medical entomologists from Sydney University, Dr Cameron Webb and Dr Stephen Doggett, write about preventing exotic mosquitoes from breaching Australian borders and establishing themselves, particularly in urban areas. (The issue also contains a review of the efficacy of mosquito repellents).
Professor Ritchie agreed that more prevention work was needed, particularly in urban areas such as Brisbane where he said exotic vector mosquitoes could establish themselves, as they have in the past.
Dr Ann Schuchat, Principle Deputy Director of the US Centers for Disease Control and Prevention, said that vector control was an essential element of the fight against Zika, as was a system for rapid detection of birth defects potentially associated with Zika infection.
To contain and mitigate the spread of Zika virus, she said the CDC recommended effective national surveillance systems including: capacity for epidemiologic investigations of travel-related or locally acquired infections; enhanced case identification, including testing of at-risk pregnant women and people with clinically-compatible illness in areas with competent vectors and where travel-associated cases have been identified; a surveillance system for rapid ascertainment of birth defects potentially associated with Zika infection; and integrated vector management. Planning should also be undertaken for services for adverse outcomes related to Zika.
Georgetown University Professor of Global Health Law and Director of the WHO Collaborating Center on Public Health Law & Human Rights, Professor Lawrence Gostin, said the southern regions of the globe would soon enter the summer season, which is peak time for mosquito breeding and biting.
On his blog on STAT health news Professor Gostin said: “So far, there are no indicators that Zika won’t re-emerge with a vengeance. And those regions — Latin America, southern Asia, and southern Africa — tend to have poor countries that are least prepared to fight a Zika epidemic.”
Although vaccines are under development, Professor Ko said it could take two or more years to know whether they were safe and effective.
A spokeswoman from the Australian Government Department of Health said there had been 79 cases reported in Australia since 2012, all infected overseas, and no reported cases of locally acquired Zika infection in Australia. With the distribution of vector mosquitoes limited to central, north and southwest Queensland, there was a very low risk of an outbreak in Australia, she said.
Measures were in place at all international air and sea ports to prevent the entry and establishment of exotic mosquitoes that can carry the virus.
Dr Kishen Lachireddy from NSW (New South Wales) Health said the department had drafted a ‘Response plan for exotic mosquito incursions (Aedes aegypti and Aedes albopictus)’.
The strategy would include surveillance to identify the extent and spread of any incursion; mosquito control and management to eradicate exotic mosquitoes; surveillance after the response to monitor its success; and undertaking long-term surveillance to demonstrate proof of freedom from incursion of the detected species.
A spokesperson for Queensland Health said its Zika strategy was based on the state’s dengue management plan, which was applicable to Zika control/management.