In a follow-up investigation into Angola's unusual rise in microcephaly cases in 2017, an international research group today reported that the Asian Zika virus strain that cause birth defects in the Americas outbreak was the cause, a first for an African country.
A team from Oxford University and Angola's health ministry reported their findings in The Lancet Infectious Diseases. Zika virus has been circulating in Africa for centuries, but only the African lineage. So far, only the Asian lineage has been linked to large epidemics and a related rise in microcephaly in the Americas.
In December 2017, the World Health Organization's (WHO's) African regional office warned that Angola was experiencing a slow but steady rise in microcephaly that might be related to Zika virus, especially in the suburbs of Luanda, the country's capital. At that point, there were 42 cases since September 2017, 39 involving live births.
Blood specimens were negative but didn't rule out exposure during the mothers' pregnancies. A few Zika cases had been confirmed in Luanda, one in a stillborn baby, but no genotyping was done and surveillance hadn't picked up any signs of ongoing active Zika transmission.
Gene sequencing, blood sampling clues
For the study, the team conducted molecular testing and genome sequencing to trace the history of the virus from patients in Angola. They also undertook an epidemiologic investigation.
Findings revealed that the Asian Zika genotype had been circulating in Angola since at least 2016, and the strains circulating in Angola were probably introduced from Brazil, likely because of the high volume of travelers flying between Angola and Brazil. The researchers concluded that the Asian genotype is likely linked to Angola's surge in microcephaly cases.
Nuno Faria, PhD, lead author of the study who is with the zoology department at Oxford University, said in press release from the school that that the virus was probably introduced by an infected traveler. "Our study highlights the need of increased surveillance in areas that are connected by travellers to regions where Zika and other mosquito-borne viruses circulate," he said.
Also, Sara Hill, DPhil, the study's first author who is also with Oxford's zoology department, said the study involved screening symptomatic patients and hundreds of asymptomatic ones. A detailed investigation found that the mothers had Zika antibodies and their babies had brain abnormalities consistent with congenital Zika syndrome.
Zika virus was detected in only five patients, but by using genetic sequencing the researchers were able to reconstruct the outbreak, finding that the virus probably circulated for more than 17 months, hinting that the scale of the outbreak was probably larger than the number of confirmed cases suggest.
Surveillance key to picking up early threat
In a related commentary in the same issue, three experts from the US Centers for Disease Control and Prevention (CDC) wrote that the study authors make a compelling argument that the Asian lineage triggered the outbreak. The authors are Suzanne Gilboa, PhD, Christopher Gregory, MD, MPH, and Margaret Honein, MD.
They also wrote that the timing of the first suspected microcephaly birth, in January 2017, fits with the findings that Zika virus was likely circulating in early 2016.
Delays in recognizing Zika virus aren't unusual for countries with little surveillance capacity to detect arboviruses and birth defects, they note. "For Zika virus, the absence of adequate surveillance could lead to severe consequences—specifically, infants with congenital Zika syndrome," they group said.
Both the African and Asian lineages could have been causing harm for the past 50 years, but some countries in the Americas had surveillance infrastructure that was well positioned to identify and respond to the outbreak, which helped clarify the impact of the Asian strain, they said.
Oct 1 Lancet Infect Dis abstract
Dec 5, 2017, CIDRAP News scan "Angola reports 42 microcephaly cases but no Zika involvement"
Sep 26 University of Oxford press release
Oct 1 Lancet Infect Dis commentary