The Zika virus strain responsible for the outbreaks in Brazil has been detected in Cape Verde in Africa.
Dr Nathalie MacDermott, Wellcome Clinical Research Training Fellow at Imperial College London, said:
‘Reports that the Asian strain of the Zika virus that is currently circulating in South America has reached the Cape Verde islands are of significant concern. While at present it seems isolated to the islands making mainland spread more difficult, it is likely only a matter of time before an infected traveller makes their way to mainland Africa, the most likely initial destination being West Africa, although flights to all parts of Africa are possible from Cape Verde with connections.
‘The Aedes Aegypti mosquito is present in large numbers in many countries in West Africa (as well as East, Central and Southern
Africa) and so the potential for the Zika virus to spread widely in this region is high. Antenatal facilities for the care of pregnant women are significantly more limited in many West African nations than in South America and so the monitoring of pregnancies and birth outcomes will be much more challenging. Intensive care facilities are also not widely available for patients who may develop Guillain-Barre syndrome.
‘Those nations which have been heavily affected by the Ebola outbreak are in the process of trying to re-build their health infrastructures, which were significantly limited even prior to the Ebola outbreak. An epidemic of Zika virus infection in these nations with the potential for causing severe neurological damage to unborn infants would be a catastrophe right now.’
Dr Anna Checkley, Hospital for Tropical Diseases, University College London Hospitals said:
“There has been an outbreak of zika virus infection in Cape Verde since October 2015, and today the World Health Organisation confirmed that it is the Asian, rather than the African strain of the virus that is causing these infections.
“The Asian strain was responsible for the outbreak in Polynesia in 2007, and it is also responsible for the current zika epidemic. Prior to 2007 there were no known outbreaks of zika virus infection, with just occasional cases (caused by the African strain) reported from countries in Africa.
“It is not known why the virus has become so much more aggressive since it was first described in 1947, and there are a number of possible explanations for this.
“It has probably been circulating at a low level in African countries for more than 50 years, so some of the population may already be immune. It is likely that the South American, Caribbean and Polynesian populations had no prior immunity to the virus, so a high proportion of people who are bitten by infected mosquitos caught the disease.
“It may be that the Asian strain of the virus is more infectious to humans, so it spreads from human (via mosquito) to human. The African strain is probably more infectious to primates other than humans, causing the occasional sporadic human case.
“There is a theory that people who have previously been infected by dengue, an infection that is widespread in South and central America, may develop a more severe form of zika when they are infected. There is very little evidence for this at the moment.
“Zika infection in pregnancy in the Americas has been linked to infants developing Congenital Zika Syndrome, which includes microcephaly as well as other developmental problems. It was probably also responsible for cases of microcephaly in Polynesia.
“Since human cases in Africa are so few and far between, we don’t yet know whether the African strain of the virus also causes Congenital Zika Syndrome. For the same reason we do not know whether people who have been infected with the African strain are protected against catching the Asian strain. In fact, we do not even know whether individuals who have recovered from the Asian strain are protected against a second infection with the same strain.”