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Zika virus has hit the headlines recently, as the disease continues to spread through Brazil and around the world. The WHO has announced that cases have been reported in 23 countries and territories in the Americas, and that the disease is spreading explosively, with the potential for 3 - 4 million cases in the next year. Zika is spread by Aedes mosquitoes and, if contracted by pregnant women, is thought to be behind a big rise in cases of microcephaly - a severe deformity in which infants are born with abnormally small heads - in Brazil. A recording is now available of a background briefing, where experts discussed what we know about the virus and its spread, and the likelihood of it reaching Australia and spreading through the country.

Organisation/s: Australian Science Media Centre, The University of Sydney, The Australian National University, University of South Australia, Monash University

Media Briefing

From: World Health Organisation

*Briefing recording now available, see link below*


  • Dr Grant Hill-Cawthorne is a Medical Virologist and Senior Lecturer in Communicable Disease Epidemiology, University of Sydney
  • Dr Cameron Webb is Medical Entomologist and Principal Hospital Scientist at the University of Sydney
  • Professor Lyn Gilbert, is Clinical Lead, Infection Prevention and Control, Western Sydney Local Health Network and Marie Bashir Institute, University of Sydney.

The briefing was chaired by Professor Tania Sorrell from Sydney Medical School.

DATE: 2nd Feb 2016
DURATION: 53 minutes
VENUE: University of Sydney and Online


  • World Health Organisation
    Web page
    WHO press conference audio file
  • World Health Organisation
    Web page
    Dr Margaret Chan, Director- General of WHO remarks on Zika virus
  • World Health Organisation
    Web page
    WHO information page
  • Australian Science Media Centre
    Web page
    Link to full briefing recording
  • World Health Organization
    Web page
    Link to WHO's announcement of a Public Health Emergency of International Concern

Expert Reaction

These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.

Professor Suresh Mahalingam is head of the Emerging Viruses and Inflammation Research Group at Griffith University

It is possible for there to be an outbreak of Zika virus in Australia, but the chances of this happening are small. However, for the sake of caution, travel warnings shouldn’t be confined to Brazil and elsewhere in South America, but should apply to all countries where mosquitoes are a problem.

Last updated: 03 Nov 2016 6:03pm

Associate Professor Ian Mackay is a Virologist at The University of Queensland

Zika virus (ZIKV) is a mosquito-borne virus. Infection of humans can result from the bite of an infected Aedes mosquito and if disease (Zika virus disease; ZVD) results, it is usually mild and may include a fever, rash and conjunctivitis. There has been justifiable concern about a ZIKV epidemic in Brazil that is occurring at the same time as a reported 20-fold increase in cases of congenital disease, most notably microcephaly. There has also been rise in Guillain-Barre syndrome cases, an auto-immune disease.

There is no drug or vaccine for ZIKIV or ZVD and while vaccine work is beginning, a safe product will be some years away. ZIKV was first identified in 1947 in Uganda and has since slowly spread through the Pacific and now into the Americas.

The best ways to reduce risk of infection is by avoiding the bite of mosquitoes - long clothes, the use of safe insecticides including DEET and picardin and sleeping under nets in areas where mosquitoes are known to be infected.

Australia has at least one species of mosquito that could carry ZIKV (Aedes aegypti), found in Queensland, but no local mosquitoes populations are known to be infected. Australia has recorded detection of ZIKV infected individuals, but those infections were in international travelers infected elsewhere.

Last updated: 03 Nov 2016 5:43pm
Associate Professor Craig Williams is from the Sansom Institute for Health Research at the University of South Australia

Zika virus was first isolated in Africa in the 1940s, and outbreaks in people have been recorded sporadically since then in various locations in Africa and Asia. It is transmitted by the same group of mosquitoes that spread the dengue viruses (to which it is related) and chikungunya. These mosquitoes are typically urban breeders, called Aedes. Those infected with Zika virus may develop symptoms such as fever, rash, and headache (similar to other mosquito-borne viruses). In 2013, a Zika outbreak was recorded from islands of French Polynesia, and 2015 bore witness to a significant outbreak in Brazil.

An alarming development from the Brazil outbreak is the strong association with microcephaly, a birth deformity linked with women who have had Zika infection. Prevention of Zika virus is the same as for other mosquito-borne diseases, namely prevention of bites. Any traveller heading to a region where dengue, chikungunya, malaria or zika are active should take the same precautions (use repellent, wear clothing that covers the body if possible). The additional risk that Zika poses is to pregnant women. Whilst the link between microcephaly and Zika infection has not been conclusively proven, the evidence is sufficiently strong to warrant warnings against pregnant women travelling to areas of Zika activity.

Returning travellers carrying Zika virus have the potential to introduce the infection into Australian mosquitoes. However, the risks of local transmission here in Australia are uncertain, and likely to be restricted to northern Queensland where the right sort of mosquitoes exist. Whilst a vaccine will probably be developed, it may take many years to become available

Last updated: 03 Nov 2016 5:02pm
Associate Professor Sanjaya Senanayake is a specialist in Infectious Diseases and Associate Professor Of Medicine at The Australian National University

Zika is a virus that was found in monkeys in the Zika forest in Uganda in the 1940s. It is transmitted to people through the bite of the Aedes mosquito, which also transmits other infections, such as dengue, chikungunya and Yellow Fever. Till 2007, human cases were limited to sporadic outbreaks in Africa and Asia. But around 2007, it spread to the Pacific islands and has been found in places such as the Cook Islands, Easter Island, Samoa, and New Caledonia. But in the last year or so, Zika has been introduced to Central and South America where people weren't immune to the virus; hence, the large number of cases in so short a time. This introduction was due to the ease of global travel combined with the Aedes mosquito's presence there. Brazil alone may have had over a million cases in the last year.
It is a risk for Australians travelling to countries with established Zika. Brazil is a particular concern due to the influx of tourists for the Rio Olympics.
We do not have local transmission of Zika in Australia; however, the Aedes mosquito is established in Far North Queensland, which is the reason for sporadic dengue outbreaks around Cairns. Therefore, it is possible for Zika to cause a local outbreak here.
About 75% of people with Zika don't have symptoms, but they can be a source of infection to others if bitten by a mosquito. The other 25% tend to get a mild flu-like illness with fevers, body aches and a rash that improves after about a week. Very few people get hospitalized and deaths are rare. There have been reports of a neurological condition called Guillain- Barre syndrome possibly being linked to Zika, but this is very uncommon. In fact, if there weren't concerns about the microcephaly birth defect, Zika wouldn't be an emergency. There is no cure and no vaccine, although work on the latter has started but may take 1-2 years to develop. Mosquito control is vital.
We are still waiting to confirm if Zika is causing the microcephaly birth defect. There definitely is an association and no other cause has been found, so it is a good idea to institute the warnings to women considering becoming pregnant in a Zika-endemic region. In countries such as El Salvador, with strong religious beliefs with regard to contraception and abortion, asking women to not get pregnant for up to 2 years will be a challenge for the health authorities.
The WHO has an opportunity to take the major lead in this outbreak.

Last updated: 03 Nov 2016 4:46pm
Professor Allen Cheng is the Director of the Infection Prevention and Healthcare Epidemiology Unit at Alfred Health and an Adjunct Professor at Monash University

Zika virus infection presents similarly to some other mosquito borne viruses like Dengue fever. Symptoms include fever, aches and pains in muscles and joints (particularly of the hands and feet) and a fine rash that looks a little like sunburn. In most people these pass over a few days or weeks and are not regarded as serious or life threatening. 
The current concern is about two complications. In Brazil, the onset of the Zika virus outbreak has coincided with a sharp increase in cases of microcephaly, a serious birth defect. In a small number of cases, Zika virus has been detected in babies that have died with this complication. It is possible that there is another factor involved, and unusually, this complication had not been reported in previous outbreaks of Zika virus elsewhere. 
The second complication that has been linked to Zika virus infection is Guillain Barre syndrome, an inflammatory condition of the nerves that can cause severe weakness. This may occur in anyone, but relatively small numbers of GBS cases have been reported to date, and GBS may also complicate other infections (eg influenza).
What are the risks for Australians both here and when travelling
Currently, there is only a very limited risk to Australia - the mosquito that transmits Zika virus is only present in Far North Queensland, and only a small number of cases have been reported in returning travellers. 
The risk to pregnant travellers depends on two main factors - the risk of getting Zika virus (which depends on the destination, nature and duration of travel), and the risk of infection of the unborn baby with Zika virus (which is currently unknown). Until these risks are better quantified, it would seem sensible for pregnant women to defer non-essential travel, and if they must travel to areas with Zika virus, to take measures to avoid being bitten by mosquitoes

Last updated: 03 Nov 2016 4:16pm
Dr Mike Catton is Director of the Victorian Infectious Diseases Reference Laboratory and Deputy Director of the Peter Doherty Institute for Infection and Immunity

Zika virus is an emerging mosquito-borne flavivirus, closely related to dengue virus. About one in four people infected with Zika virus experience a mild febrile rash illness similar to dengue fever.

Zika was initially discovered in Uganda in 1947, only spreading into and across the Asia-Pacific region from 2007 following the distribution of the Aedes aegypti mosquito which carries it. There was a large Zika outbreak in 2013/14 in French Polynesia and after further spread in the Pacific, a large outbreak occurred in 2015 in northeast Brazil. After the emergence in Brazil, an unexplained twenty fold increase in cases of microcephaly has occurred, leading to concern that Zika virus may be involved. Zika virus genetic material has subsequently been detected in the tissues of one such affected infant, and in amniotic fluid samples from two other children born with microcephaly. This limited evidence will require considerable strengthening before a causative role for Zika virus in microcephaly can be proven, but national and international health authorities are taking a precautionary approach with advice for pregnant women in the interim. In the absence of a vaccine or effective treatments, prevention is being emphasised.

Australia is free of the Aedes aegypti mosquito except for part of far north Queensland, where local health authorities have been effective at containing and stamping out occasional incursions by Zika’s relative dengue virus, which shares the same mosquito vector. The first Australian case of Zika virus was detected by the Doherty Institute in 2013, with a further 11 cases (approximately) detected in Australia from returned travellers from the Asia-Pacific since then.

The Doherty Institute has the capacity to diagnose Zika virus during illness in either blood or urine using nucleic acid tests.   

Last updated: 03 Nov 2016 4:00pm

Professor Edward Holmes is a NHMRC Australia Fellow at the Charles Perkins Centre, Sydney Medical School, The University of Sydney

Zika virus has been causing disease sporadically in humans for many decades, including in South-East Asia and Polynesia. However, the current outbreak is unprecedented and alarming, although many cases will not result in any symptoms. Unfortunately, little is known about how the virus has managed to spread so quickly and why it results in microcephaly. Clearly, pregnant women should avoid traveling to affected countries at present.

Last updated: 03 Nov 2016 3:58pm
Professor Raina MacIntyre is the Head of School and Professor of Infectious Diseases Epidemiology at the University of New South Wales. She is also Director of the NHMRC Centre For Research Excellence "Integrated Systems for Epidemic Response ".

Zika virus is related to dengue and yellow fever, and comes from the same family of viruses, flaviviruses.  It is spread by the mosquito Aedes Egypti, but the extent to which it can be spread by other Aedes species mosquitoes is uncertain.  
It was first identified in 1947 during surveillance of mosquitoes in Uganda, and has caused occasional disease in the equatorial belt from Africa to Asia. Large outbreaks were noted in French Polynesia in 2013, and during this outbreak, a rise in cases of Guillain- Barre Syndrome (a serious neurological disease which causes paralysis) were also noted. In 2015, a large epidemic began in Brazil, the current epicentre of Zika virus. During this epidemic, an increase in babies with microcephaly (an abnormally small head) and other neurological abnormalities has been noted.  Zika, therefore, has been associated with both microcephaly and Guillain-Barre Syndrome. 
Cases have occurred outside of Brazil, mostly in travellers who have been in Brazil, with 31 cases documented in the US. There has been no documented transmission of the virus within the US, but the mosquito Aedes Egypti is present in the Southern states of the US. It is also present in northern Australia.  The species Aedes Albopictus is more widespread in the US and Australia, and it would be of concern if Zika can be transmitted through Aedes Albopictus.
The other concern is the mode of transmission, and whether the entire epidemic in Brazil can be attributed to mosquitoes. The rapid spread is cause for concern, and is not funky explained.  There has been a case of human to human transmission documented in the US, when a US scientist contracted Zika in Senegal, and then infected his wife upon returning to the US.  In the French Polynesian outbreak, a man complaining of blood in his semen was tested and found to have Zika virus in his semen.  The fact that 31 imported cases have occurred in the US and no transmission from these people has been observed indicates that human to human transmission, is less common that mosquito borne transmission.
So, the burning questions are:

  1. Is the association of Guillain-Barre Syndrome and microcephaly with Zika virus a causal one. 
  2. Can Zika virus be spread by other aedes species and if so, how extensively?
  3. Is there any human to human transmission occurring in Brazil, and what is the contribution of this to the scale and speed of the epidemic?

Meanwhile, travellers to affected areas should take strict precautions to avoid being bitten by mosquitoes. The WHO is urging caution for pregnant women intending to travel to affected areas.  There is no commercial test for Zika virus, and no vaccine.  Vaccines can take many years to develop. There is a dengue vaccine which is effective against all 4 serotypes of dengue.  Interestingly, in blood tests, antibodies to Zika cross-react with dengue. A research question would be if the dengue vaccine confers any cross protection against Zika virus

Last updated: 03 Nov 2016 3:51pm

Expert Recommendations

This expert list has been collated by the Science Media Centre to provide a variety of expert perspectives and reflect independent opinion on this topic.

Name Organisation Expertise
Dr Cameron Webb The University of Sydney Mosquito, mosquitoes, mosquito-borne disease, Ross River virus, Ross River fever, Barmah Forest virus, dengue, mosquito control, insect repellents, why mosquitoes bite, wetlands, constructed wetlands.

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  • Zika virus
    Zika virus

    This is a transmission electron micrograph (TEM) of Zika virus, which is a member of the family Flaviviridae. Virus particles are 40 nm in diameter, with an outer envelope, and an inner dense core

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  • Microcephaly

    Baby with Microcephaly

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    Microcephaly and Typical Head Size Comparison

    Microcephaly and Typical Head Size Comparison

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  • A mosquito that is able to carry the Zika virus
    A mosquito that is able to carry the Zika virus

    A mosquito (Aedea aegypti) that is able to carry the Zika virus

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  • Countries and territories with active Zika virus transmission
    Countries and territories with active Zika virus transmission

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