Global health experts and the UK government have expressed concern over the potential for the Zika virus to spread from Latin America to impoverished countries in Africa and south-east Asia.

Surveillance projects are being set up in Africa, in an attempt to track cases of microcephaly, a congenital condition associated with incomplete brain development, which has been linked to the mosquito-borne Zika virus. The projects are hoping to spot any potential surge in cases.



But the dearth of knowledge about the virus and the absence of any test that can show whether somebody has been infected in the past are major handicaps for the project.

Brazil, where about 1.5 million people have been infected with the virus, is investigating the potential link between Zika infections and more than 4,000 suspected cases of microcephaly.

Researchers have identified evidence of Zika infection in 17 of these cases, either in the baby or in the mother, but have not confirmed that Zika can cause microcephaly.

Cassiana Severino holds her daughter Melisa Vitoria, born with microcephaly at the IMIP hospital in Recife, Brazil. Photograph: Felipe Dana/AP

There may be immunity among many Africans to the virus now spreading across Latin America. Zika virus was first detected in Uganda in the 1940s and among the few studies is one carried out in Nigeria in 1983 looking at the whole family of arboviruses, which also include dengue and yellow fever.



“56% of the population had antibodies to Zika virus in that study,” said Philip McCall of the Liverpool School of Tropical Medicine. “If that was a common experience across much of central and west Africa and it is true that you get lifelong protection, we would be reassured.

“But it is possible that the Zika that has ended up in Latin America is a different strain. It does appear to be an Asian strain, which infected people in French Polynesia.”

The strain in Africa has not been linked to any cases of microcephaly. However, because of the stigma around birth defects and the low standard of healthcare available in impoverished parts of sub-Saharan Africa, any past surge in the numbers of babies born with small heads and abnormal brain development might not have been recognised.

Jimmy Whitworth, professor of international public health at the London School of Hygiene and Tropical Medicine, said it would not be surprising if somebody who had become infected with the virus in Latin America, possibly without symptoms and unaware of it, travelled to Africa and was bitten by mosquitoes there, starting a new chain of transmission.

Not enough was known to say whether the level of immunity in the population would be enough to stop an outbreak.

“Young people and children would presumably be most vulnerable to getting it because they would have had less time to get exposure to it,” Whitworth said.

“The other element here is that it looks pretty clear that this has evolved somewhat as a virus in the last 10 years when we started noticing it in Asia, in the Pacific and now in the Americas.

“It is clear that there is an African lineage and there is an Asian lineage of this. In the Brazilian outbreak it looks like it’s been Asian lineage and that has had one or two changes. That probably makes it easier for the virus to infect human cells, which means it’s been adapted for transmission in the human population,” added Whitworth.

“Whether those changes are sufficient to mean it escapes from immune control in African populations or not we don’t know. I suspect it wouldn’t be enough so pre-existing immunity would give you reasonable protection.”

Anthony Costello, director of the department of maternal, newborn, child and adolescent health at the World Health Organisation, said they were setting up surveillance studies in low-income countries, because without any idea of the baseline of Zika and microcephaly, it is impossible to know that an outbreak is taking place.

“That’s what the big challenge is,” he said. “We run a lot of studies already across Africa. We are trying to get the data together on head circumference and so on. We have got to be prepared for this.”

A government employee fumigates a house during a campaign preventing the possible spreading of the Zika virus in Catacamas, Honduras. Photograph: Honduran Presidential House/EPA

Microcephaly can be caused by genetic factors or triggered by a number of infections – rubella, toxoplasmosis, syphilis, cytomegalovirus and herpes. It can also be caused by severe malnutrition. It is relatively rare, at about one birth in 5,000 – although there is quite a wide range. But the frequency in many countries in Africa and south-east Asia is unknown because records are poor.

Even if Zika virus is to blame for the surge of cases in Brazil, nobody yet knows if there are additional causal factors that may not be replicated elsewhere. There have been no other cases in Latin America yet, although it may be just a matter of time.

Colombia has now reported more than 20,000 Zika infections, but the first was some five months after the virus was first identified in Brazil. If babies are born with microcephaly as a result, Costello says we will probably see it within a couple of months.

Cape Verde, off the west African coast – which began to report cases of infection in October, will also be closely watched.

“I think the next two or three months is very crucial,” he said. “If the virus is behaving in a fairly standard way in all populations we would unfortunately expect to see more cases of microcephaly emerge in other countries in Latin America.”

What Costello is sure about it is that it cannot be stopped from returning to Africa. “If it is sexually transmitted and given the rapidity of its spread and the fact that mosquitoes can be carried in boats and people travel, it seems very unlikely to me that it wouldn’t go back into Africa and Asia,” he said.

The British government is planning for such an eventuality. The department for international development (DfiD) has little involvement in Latin America but much in Africa.

Responding to questions on Africa in the House of Commons, DfID minister Nick Hurd said: “We will obviously review intensively what we can do to work with our partners in countries that face risks, not least in respect of improving and strengthening the resilience of their health systems so that they can educate and communicate with their citizens effectively.”