A letter in The Lancet: Zika virus epidemic: Africa should not be neglected.
The Zika virus was first isolated in Uganda in 1947. Despite the recent severe outbreak of Zika virus in Cape Verde, with 7557 suspected cases between Oct 21, 2015, and May 8, 2016, very little attention has been paid to the African continent for participation in Zika virus outbreak preparedness programmes.
Since the mid-1950s, findings from seroepidemiological surveys have suggested a high prevalence of Zika virus IgG positivity in western, central, and eastern Africa, with up to 60% people with previous exposure to the virus. However, interpretation of these historical results is problematic because of important cross-reactivity of Zika virus serological assays with those of other flaviviruses (eg, dengue viruses), and because of the interference of malaria with modern Zika virus ELISA that results in reduced specificity.
Aedes aegypti, the main vector of Zika virus, and Aedes albopictus, a convincing alternative candidate, are mainly present in sub-Saharan Africa (figure). Therefore, most of the 936 million inhabitants of the continent (World Bank estimates, 2013) are potentially exposed to Zika virus arthropod vector bites.
The incidence and prevalence of microcephaly and Guillain-Barré syndrome, the two main neurological manifestations of Zika virus infection, in Africa are unknown. However, one of the few studies on systematic measurement of head circumference at birth reported a prevalence of microcephaly (according to WHO definition) of 10·6% in more than 3000 consecutive births in Lagos, Nigeria, in 2012.
Results from a phylogenetic study suggested a central role of two African countries, Côte d'Ivoire and Senegal, in the worldwide spread of Zika virus, and that not only the Asian lineage but also the African lineage of the virus might be involved in the spread of Zika virus outside of Africa since 2007.
However, a comparison of the neurovirulence and neurotropism of African versus Asian strains remains to be reported to improve prediction of potential neurological complications that are attributable to African strains.
It is plausible that Zika virus outbreaks occurred in recent years in Africa and remained unnoticed because of the very low capacities for detection of emergent conditions in most of the continent. Surveillance in sentinel populations, increased capacity for laboratory tests and antenatal echography, reporting systems on the emergence of Zika virus-related neurological conditions, intensification of vector control, and education on emerging infectious threats are all of utmost priority in outbreak preparedness programmes.
Not long ago, many west African communities were taken by surprise by the Ebola virus epidemic. National and international health organisations made very strong statements about the importance of learning from the Ebola experience and to improve preparedness for future emergent outbreaks.
Now that we know that Zika virus, its vectors, and favourable environmental conditions for their spread are present in Africa, there should be no place for complacency. There is no reason to neglect Africa in international preparedness programmes. Networks of national health agencies (such as African public health institutes and surveillance systems) should be urgently mobilised and empowered to play this crucial part.