A researcher looks at Aedes aegypti mosquitoes kept in a container at a lab of the Institute of Biomedical Sciences of the Sao Paulo University, on January 8, 2016 in Sao Paulo, Brazil. Researchers at the Pasteur Institute in Dakar, Senegal are  in Brazil to train local researchers to combat Zika virus epidemic.  AFP PHOTO / NELSON ALMEIDA / AFP / NELSON ALMEIDA        (Photo credit should read NELSON ALMEIDA/AFP/Getty Images)

The photographs of the Brazilian babies, their small, distorted faces peering out from the laps of their parents are distressing. They may come to represent the lost children of the Americas: a generation of small-headed infants born to mothers thought to have been infected with the mosquito-borne Zika virus.

Zika is the latest pathogen seemingly to have come out of nowhere and gone rogue. The arbovirus (so-called because it is arthropod-borne) has made headlines because a surge of Zika infections in Brazil last year coincided with a rise in the number of babies born with microcephaly. The brain fails to grow and, because skull expansion is dictated by brain growth, the skull doesn’t develop normally. Affected children generally have learning disabilities, a distinctive appearance (cruelly, the face continues to grow, even though the head does not) and can die young. Last week, the Centers for Disease Control in the US advised pregnant women to postpone travel to the 21 affected countries.

Meanwhile, Anthony Fauci, one of America’s top immunologists, has described Zika as “a pandemic in progress”, thanks to urban crowding, international travel and human encroachment into new ecological niches.

Now scientists are seeking to discover whether there is a definite causal link between Zika and microcephaly, and to develop a vaccine. This rapidly unfolding health crisis will also be the first major test of the post-Ebola World Health Organisation. Some global health experts are pressing for the WHO to convene an emergency committee, which triggers a cascade of international measures, such as enhanced surveillance, travel restrictions and fast-track vaccine development.

Zika was first isolated in 1947 from rhesus monkeys in the Zika forest of Uganda, and is a member of the flavi­virus family, which includes yellow fever, West Nile virus and dengue fever. Devastatingly, many women will not even know they have the infection, as symptoms can be mild.

Brazil reported its first case of Zika infection in May 2015. The virus whirled quickly across the country and into new terrain — by December, it was in Colombia and Mexico. It is now predicted to reach all territories in the Americas bar Chile and Canada — wherever the day-biting aedes aegypti mosquito thrives. The WHO is also investigating whether Zika is linked to cases of Guillain-Barré syndrome in El Salvador; this rare syndrome, which affects the nervous system, often follows viral-type illnesses, and can paralyse or kill.

Zika’s rapid geographical spread and its suspected ability to jump the placental barrier suggest that the virus may have mutated recently. That gives the virus a higher chance of being passed on; the chain of transmission involves a mosquito biting an infected human, and then passing the infection on to other humans that it subsequently bites.

The virus is currently a suspected, rather than confirmed, cause of microcephaly (other causes include maternal exposure to mercury, drugs or alcohol, and other infections such as rubella and toxoplasmosis).

This year, by mid-January, Brazil’s Ministry of Health had catalogued nearly 4,000 cases of microcephaly across the country, a roughly twentyfold increase on previous years. Many of the babies’ mothers reported symptoms consistent with Zika infection during pregnancy. The virus was also found in amniotic fluid of affected mothers, and in the tissue of dead babies with microcephaly.

Virologists at the University of Texas Medical Branch have now set up facilities in Brazil to test umbilical cord blood for the antibodies to Zika. This study could provide the clue to causation that scientists so desperately seek.

The writer is a science commentator

Letter in response to this column:

Zika threat demands a global response / From Keizo Takemi

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