Evidence of link between Zika virus and birth defect 'boosted'

Behind the Headlines

Thursday February 18 2016

The virus may disrupt the development of the brain and nervous system

A baby with a small head, characteristic of microcephaly

"Brazilian study boosts theory that Zika causes birth defect," The Guardian reports.

Researchers have detected the virus in amniotic fluid surrounding two unborn babies known to have abnormally small heads (microcephaly).

There had been speculation that other infections may be causing the birth defect, but no other type of infection was found.

The news comes from a case study of two women in Brazil who had clinical symptoms of the Zika virus in the first or second trimester of pregnancy. The women's babies were later diagnosed with microcephaly.

The researchers analysed samples of amniotic fluid – the fluid that surrounds and supports the baby – taken at 28 weeks, and detected the Zika virus. This suggests unborn babies are exposed to the virus while still in the womb.

They also found the DNA of the Brazilian Zika virus is very similar to those isolated during an outbreak in French Polynesia in 2013, as well as outbreaks in North and South America, southeast Asia, and the Pacific region.

But this research cannot prove Zika causes unborn babies to develop microcephaly – it can only show an association.

That said, this is arguably currently the strongest piece of circumstantial evidence that Zika is directly responsible for the alarming increase in the number of microcephaly cases in Brazil. 

Advice for pregnant women

If you're pregnant or planning to become pregnant and are about to visit a part of the world known to be affected by the Zika virus, you should discuss your travel plans with your doctor.

 

Public Health England provides regular updates about the current spread of the disease. The current advice for pregnant women is to consider postponing travel to any region where a known outbreak of the Zika virus is occurring.

 

If travel is unavoidable, you should take extra care to avoid being bitten by mosquitoes.

 

Read more advice about the Zika virus.

Where did the story come from?

The study was carried out by researchers from a number of institutions, including Instituto Nacional de Infectologia Evandro Chagas and Laboratório de Pesquisa Clínica em Doenças Febris Agudas.

It was funded by Consellho Nacional de Desenvolvimento e Pesquisa and Fundação de Amparo a Pesquisa do Estado do Rio de Janeiro.

The study was published in the peer-reviewed journal, The Lancet: Infectious Diseases.

This research has been widely and accurately covered by the UK media, clearly stating that these findings do not prove there is a link between the virus and birth defects, just an association.

Experts have been quoted in many of the reports. Professor Jimmy Whitworth of the London School of Hygiene and Tropical Medicine said that while the research cannot prove there is a link: "This study does strengthen the body of evidence that Zika virus is the cause of foetal microcephaly in Brazil".  

What kind of research was this?

This was a case study of two women in Brazil who presented with clinical symptoms of the Zika virus, such as a rash and fever, during pregnancy. Their babies were diagnosed with microcephaly while they were still in the womb.

Researchers aimed to detect the Zika virus genome in amniotic fluid, as to date there has been no clear evidence available to confirm the virus could be passed from a mother to her unborn baby.

This type of study can show an association, but cannot prove Zika causes babies in the womb to develop microcephaly. The findings will add to the body of evidence in the area and provide a route for further research.  

What did the research involve?

Two women in Brazil with clinical symptoms of the Zika virus in their first or second trimester of pregnancy were assessed by ultrasound at approximately 22 weeks, and their babies were later diagnosed with microcephaly.

The researchers took samples of amniotic fluid by amniocentesis, a diagnostic test carried out during pregnancy, at 28 weeks of pregnancy to try to find the cause of the microcephaly.

The amniotic fluid samples were filtered and concentrated to analyse the DNA and RNA. The findings were compared with other Zika strains and viruses present in similar regions of Brazil.  

What were the basic results?

Analysis of both amniotic fluid samples taken at 28 weeks detected Zika. However, the virus was not found in the urine or blood of either mother.

Tests for other viruses that could have caused the microcephaly were all negative. This means the unborn babies had only been exposed to the Zika virus while still in the womb.

The researchers found the DNA sequencing of the Brazilian Zika virus is very similar to those isolated during an outbreak in French Polynesia in 2013, and also had similar sequences to those from North and South America, southeast Asia, and the Pacific region.  

How did the researchers interpret the results?

The researchers reported their findings add strength to the association between the Zika virus and microcephaly in babies in Brazil, and suggest the virus can cross the placental barrier.

They went on to say this case study shows the Zika virus should be regarded as a possible causative agent in cases of microcephaly, especially during virus outbreaks in endemic regions.

They stated that while no vaccine or antiviral for Zika is currently available, it is important to control the mosquito population, as well as conduct further studies to understand the mechanisms that may lead to microcephaly. 

Conclusion

This was a case study of two women in Brazil who had clinical symptoms of the Zika virus during pregnancy. Their babies were later diagnosed with microcephaly while still in the womb after ultrasound examination.

Researchers aimed to detect the Zika virus in amniotic fluid and conduct DNA analysis to ascertain the geographic origin of the virus.  

Since 2015, Brazil has seen 4,783 cases of microcephaly in newborn babies, 20 times higher than in previous years. Microcephaly is associated with a number of causes, including:

  • genetic disorders
  • alcohol and drug use
  • maternal malnutrition
  • transmission of infections through the placenta
  • maternal viral infections

It has been suggested contracting the Zika virus in pregnancy could be associated with a rise in the number of microcephaly cases reported in Brazil.

Despite an increase in research, there are many unknowns. These include how big the risk of microcephaly is if a woman is infected with the Zika virus during pregnancy, and whether the timing of the infection makes a difference.

The main limitation of this research is it cannot prove Zika causes babies to develop microcephaly – it can only show an association.

The findings of this study will add to the body of evidence, and suggest a causal relationship might exist between the virus and microcephaly. However, more research is needed to test this further. 

In the meantime, precautions should be taken if you are currently pregnant or planning to become pregnant, and have plans to travel to a region where there is an increased risk of the Zika virus. Seek further advice from your doctor before travelling.

To reduce the risk of infection, you should avoid being bitten by mosquitoes. The best ways to avoid bites are to:

  • use a DEET-based insect repellent – this is safe to use during pregnancy and should be applied to skin after sunscreen
  • wear loose clothing that covers your arms and legs
  • use a mosquito net

Analysis by Bazian. Edited by NHS Choices. Follow NHS Choices on Twitter. Join the Healthy Evidence forum.

Analysis by Bazian

Edited by NHS Choices

Links to the headlines

Brazilian study boosts theory that Zika causes birth defect. The Guardian, February 17 2016

Zika virus: Study supports link to microcephaly. BBC News, February 18 2016

Zika 'CAN cross the placenta and infect unborn babies': Traces of virus found in the amniotic fluid surrounding two fetuses diagnosed with microcephaly. Mail Online, February 17 2016

Links to the science

Calvet G, Agular RS, Melo ASO, et al. Detection and sequencing of Zika virus from amniotic fluid of fetuses with microcephaly in Brazil: a case study. The Lancet: Infectious Diseases. Published online February 17 2016

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