Daily Bulletin

The Conversation

  • Written by The Conversation Contributor

This week the World Health Organisation declared Zika virus a public health emergency of international concern.

Despite high rates of infection, the outbreak would not have been particularly alarming – since the infection is usually asymptomatic (80% of cases) or mild and self-limiting – had it not been for the sudden and (apparently associated) increase in numbers of infants born with microcephaly.

What is microcephaly?

Microcephaly is a condition in which the infant’s head is smaller than “normal” for the infant’s age and gender, because of delayed or arrested brain growth. There is no universally agreed definition. Most authorities suggest it should be defined by a head circumference of two – but some say three – standard deviations or more below the average.

It is often first diagnosed by ultrasound examination during pregnancy. The incidence of microcephaly – in the absence of Zika virus infection – is difficult to determine.

Apart from the lack of an agreed definition or definitive diagnostic test, there is probably significant under-reporting of the condition. State-based surveillance in the United States – where Zika virus is not endemic – suggests it occurs in between two and 12 infants per 10,000 live births. Rates vary from 0.5 to 19 in 10,000 live births in different states.

If the incidence were similar in Brazil, where about three million infants are born each year, this would represent 600-3,600 cases a year. This is more than estimates based on recent review of birth certificates – approximately 0.5 per 10,000 live births.

Some of the approximately 4,000 cases reported in Brazil during 2015 may have been due to increased awareness and reporting – although there appears to have been a real increase also.

Microcephaly is often associated with other developmental abnormalities and with varying degrees of intellectual and developmental delay, seizures, and visual and hearing loss. In severe cases it can be life-threatening.

Causes

There are many recognised causes of microcephaly including a number of other infections in pregnant women. These include rubella, cytomegalovirus (a common virus that causes asymptomatic infection or a mild glandular fever-like illness in otherwise healthy people and severe disease in people with severe immune suppression such as AIDS), herpes simplex virus infections, syphilis and toxoplasmosis (a parasitic disease).

Chikungunya, a virus spread by the same mosquito responsible for spreading Zika (the Aedes aegypti, or yellow fever mosquito), has also been shown to cause brain damage in infants of women infected during pregnancy in a naïve population (one without previous exposure to the virus).

Noninfective causes of microcephaly include a variety of genetic disorders, maternal exposure to drugs, alcohol, chemical toxins and radiation and severe malnutrition.

Is Zika to blame?

Although Zika virus has not yet been definitively proven to be the cause of the increased numbers of infants with microcephaly in Brazil, there is strong circumstantial and epidemiological evidence that it is, at least partly, responsible.

Many of the mothers of affected babies in Brazil reported an illness consistent with Zika virus infection in early pregnancy. However, this was often mistaken for dengue and not confirmed by laboratory tests.

The peak incidence of microcephaly occurred in the same geographic region (northeastern Brazil) about a year after an outbreak of dengue-like illness, with fever and rash, started. Six months later Zika virus was identified as the cause.

There have been several reports of detection of Zika virus genetic material (nucleic acid) in amniotic fluid, placentas, tissues of infants who have died with microcephaly and in live-born infants, with or without microcephaly, of mothers who have had Zika virus infection during pregnancy. It is highly likely that maternal Zika virus infection can damage the developing foetal brain. But the level of risk is unknown.

The other major uncertainly about Zika virus infection and microcephaly is the level of risk at different stages of pregnancy. Because the infection is so frequently asymptomatic or easily mistaken for other viral infections, the number of pregnant women infected and the stage of pregnancy at which infections occur are unknown.

For most intrauterine (within the uterus) infections that cause foetal damage (such as rubella or cytomegalovirus, for which these risks are well-known), the risk of the foetus being infected from the mother is relatively low in early pregnancy and increases with increasing gestation.

However, if foetal infection does, in fact, occur early in pregnancy, the foetus is more likely to be severely affected than if it occurs in the later stages of pregnancy. This is yet to be determined for Zika virus infection.

Hopefully, studies and enhanced surveillance of Zika virus infection and birth defects will provide answers to these questions. These are underway in Brazil.

In the meantime, while overall rates of Zika virus remain high, pregnant women are being advised to defer travel to Zika-affected countries if possible. Those who live there are advised to defer pregnancy or take extra precautions to avoid mosquito bites.

Authors: The Conversation Contributor

Read more http://theconversation.com/explainer-what-is-microcephaly-and-what-is-its-relationship-to-zika-virus-54049


The Conversation

Politics

Making suicide prevention a national priority

Providing greater support for all Australians needing mental health and suicide prevention services is a key priority of my Government.   Suicide takes far too many Australians, devastating famili...

Scott Morrison - avatar Scott Morrison

Scott Morrison interview with Leigh Sales

LEIGH SALES: Prime Minister, welcome back, and congratulations on your re-election.   PRIME MINISTER: Well, thank you very much, Leigh. It's very good to be back.   SALES: Why is Labor's offer t...

Leigh Sales - avatar Leigh Sales

Employsure welcomes workplace relations system review

Employsure’s founder and managing director, Ed Mallett has welcomed the Prime Minister’s announcement that the government will take a fresh look at Australia’s workplace relations system. “The federa...

Media Release - avatar Media Release

Business News

How to get the most out of a Premium Graduate Placement

An internship placement from PGP Australia can be a really rewarding and beneficial experience for anyone looking to get their foot in the door in a certain industry like human resources, accounting...

News Company - avatar News Company

Why having a website is so important for SEO purposes, even if you don’t have a lot of traffic

What most people out there can agree on is the fact that they will feel like they have something burning inside of them that they want to share. It may be to write a book, to create a product, to cr...

News Company - avatar News Company

Career Opportunities and Relocating

Moving for work can be an incredibly exciting opportunity. Yes, the amount of work will likely be larger, but so will the pay as well as the recognition. Despite the common nervousness, it is import...

News Company - avatar News Company

Travel

8 Tips How to Make Your Travels Memorable

Traveling the world is on every little kid's bucket list, and it usually remains to be there among top three well into the age as well. However, what makes traveling so fun and exciting is the nov...

Diana Smith - avatar Diana Smith

5 Reasons Why You Should Partake In Community Sporting Activities

Partaking in sports isn’t for everyone. Maybe you played a bit of sport as a child at school, but as an adult, you’ve barely picked up a tennis racket or kicked a ball, and that’s OK! However, there...

News Company - avatar News Company

Just a Few Fun Facts about Australia

Everybody calls Australia the land down under but if you turn the map around so that Australia would be in the Northern Hemisphere, the country would sit on top of the world! Everyone knows that Aus...

News Company - avatar News Company

ShowPo