Wednesday 3 February 2016 11:07am
Here at the Brain Health Research Centre (BHRC) we have many researchers who are interested in how the brain develops in the early years of life. So, when we see a health event emerging that impacts on these developmental processes we want to make sure that everybody has the best information possible. Here is our summary of what is known so far:
The World Health Organisation declared a public health emergency of international concern on the 1st February in response to the recent zika virus outbreak in the Americas. The virus itself is not of great concern; it is the rise in birth defects associated with the virus which spurred the decision toward declaring an emergency. WHO Director-General Dr Margaret Chan stated “After a review of the evidence, the committee advised that the clusters of microcephaly and other neurological complications constitute an extraordinary event and public health threat to other parts of the world.”
Zika virus was confirmed to have spread to South America in May of 2015, and since its outbreak the rate of microcephaly in newborns has risen dramatically, from about 6 in every 100,000 live births to around 100. While it is unclear exactly what the relationship is between the contraction of zika virus and the development of microcephaly, their coincidence is deeply concerning.
There are two strains of zika virus: an African strain and an East Asian strain. While the African strain is relatively harmless and easy to control, the East Asian strain is of concern. Biochemist and BHRC researcher, Dr Stephanie Hughes noted “Zika virus was first discovered in Uganda in 1947, slowly spreading through Africa, South East Asia and the Pacific. Only recently, and so far only in Brazil, has the link emerged between zika and microcephaly. It is likely that mutations of the viral genome have allowed the virus to affect fetal brain development”. The East Asian zika virus tends to spread from human to mosquito to human which is very unlike its African counterpart. This pattern has allowed for mutations to the viral genome which have resulted in it being better at infecting humans and also better at replicating once it is inside a human host.
The virus is primarily spread to humans by mosquitos, specifically the aedes aegypti mosquito. Unlike most breeds the aedes aegypti bite primarily during the day, with their activity peaking around dawn and dusk. These mosquitoes are not born with the virus, they must contract it from a human in order to become infected. After the virus has infected the mosquito it can then infect any individual the mosquito bites. If that individual happens to be pregnant there appears to be a risk of them passing on the virus to their unborn child.
How zika virus impacts the developing fetus is unclear. Professor Stephen Morse of Columbia University has stated that “The concern is when someone, especially a pregnant woman, develops symptoms like rash, fever, joint pain, or conjunctivitis” suggesting that it may be the symptoms of zika fever in the mother, not transmission of zika virus to the fetus, which is resulting in the development of microcephaly. However, the possibility of zika virus directly disrupting fetal development cannot be ruled out, and to other researchers the pattern of the microcephaly looks like a primary effect of the virus in the fetal brain and not a by-product of a maternal response to the infection. Zika virus has a known capacity for hijacking cell metabolism for viral production, which could explain impeded development in these early stages.
For these reasons it is believed that the zika outbreak may be primarily responsible for the more than 4,000 cases of microcephaly reported in South America since November 2015.
It is unclear how severe these cases of microcephaly are, and whether there are other yet unidentified health issues associated with them. In cases of microcephaly individuals with head development 5-7% smaller than the norm may suffer some intellectual and health issues. At the more severe end of the scale, those with a reduction of head size of 7% or more will suffer from more severe intellectual disabilities and health issues. Microcephaly is detectable via ultrasound between 18-20 weeks gestation, or earlier in these more extreme cases. Zika virus can also be detected in the amniotic fluid surrounding the fetus. However, these procedures are not common in many of the nations affected.
Most individuals infected with zika virus are asymptomatic, and those who do develop symptoms tend to display a rash or light fever. It is important to note that casual human contact cannot spread the virus, so there should be no concern about coming into contact with infected individuals. On February 2nd the CDC confirmed a case of sexual transmission of zika virus in Texas, and have advised that condoms should be used to prevent further spread of the virus by individuals who are already infected. On February 4th the National Health Services in the UK implemented a 28-day blood donation deferral to prevent people who had recently visited areas affected from zika virus from giving blood. A spokeswoman for the NHS stated: “The safety of the blood supply is paramount and it is important we implement any precautionary blood safety measures agreed here as a result of an increasing prevalence of infectious diseases found around the globe.”
Aedes mosquitoes live in tropical and subtropical climates and are not currently present in New Zealand. At the moment we believe that they are the only mosquitoes capable of carrying zika virus and so we do not expect an outbreak to occur here. They are, however, present in many parts of the Pacific and in Northern Australia.
The declaration by the World Health Organisation demonstrates a commitment to controlling the spread of the virus, which is expected to infect up to 4 million people this year, in the hopes of reducing the rate of microcephaly. As the only individuals at risk are first and second trimester fetuses the WHO has not issued travel warnings related to zika. However, Dr Chan has advised pregnant women to delay travelling to affected areas if at all possible. Meanwhile, as the development of a vaccine is likely to be some time off, the approach being taken by most agencies is to minimise potential exposure and to target the mosquito through eradication and control programs.