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Researchers find Zika has been 'silently circulating' in Africa for 2 decades

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April 13, 2017

An analysis of blood samples collected from febrile patients from 1992 to 2016 in West Africa revealed that Zika virus has been “silently circulating” in the region for 2 decades, researchers reported in the Journal of Infectious Diseases.

Zika virus (ZIKV) was first isolated in 1947 from a rhesus monkey in Uganda. The first human disease related to Zika was reported in 1954 in Nigeria, according to Bobby Brooke Herrera, PhD, of the department of immunology and infectious diseases at Harvard T.H. Chan School of Public Health in Boston, and colleagues.

“Zika remained obscure with only 14 documented human cases confined to Africa and Asia, until a 2007 ZIKV fever epidemic in Yap Island in Micronesia,” they wrote.

Since then, larger outbreaks occurred in French Polynesia, Latin America, and Cape Verde Archipelago in Africa. In 2015, local ZIKV transmission was reported for the first time in Brazil. The virus became endemic in Latin America, spreading to 40 countries and territories in the region and causing severe neurological disorders, including microcephaly in fetuses and infants and Guillain-Barré syndrome in adults.

“While ZIKV was responsible for significant neuropathology throughout French Polynesia, Latin America, and Cape Verde, human infections prior to 2015 were not associated with neurological disease,” Herrera and colleagues wrote. “Recent hypotheses suggest that the genetic diversification of ZIKV may be responsible for its emergence, neurotropism, and expansion.”

Phylogenetic analyses of ZIKV genomes indicate that the virus evolved into two distinct groups known as the African and Asian lineages. The recent outbreak in the Americas has been traced to the Asian lineages, according to the researchers.

To better understand the geographical distribution of ZIKV, the researchers evaluated blood samples collected from patients in West Africa, where approximately 450 million people inhabit areas that are environmentally suitable for transmission of mosquito-borne pathogens, they wrote. The analysis involved data from three cohorts, including HIVinfected female sex workers in Senegal, malaria in Senegal and HIV in Nigeria. The samples were obtained from participants (70% women; median age, 35 years) while they were receiving care at local clinics for febrile illnesses from 1992 to 2016.

Overall, the researchers screened 387 serum and plasma samples for ZIKV. Twenty-four were positive for ZIKV and negative for Dengue virus, yielding a ZIKV seroprevalence rate of 6.2%. All of the positive samples were collected throughout the 2-decade timespan; however, the researchers found that the odds of ZIKV positivity were 20% lower during 2010 to 2016 vs. 1992 to 1999 (OR = .80; P = .003).

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The ZIKV envelope gene was amplified in four samples through reverse transcriptase (RT)-PCR assay testing. Evidence showed that the viruses belonged to the African lineage, as expected. Three viruses were grouped with a Nigerian sub-lineage, and the other was grouped with a MR766 sub-lineage, which was mostly of East African ZIKVs.

“Our study emphasizes the need for improved detection methods for ZIKV, in order to distinguish among fever-causing pathogens,” Herrera and colleagues concluded. “Further studies will help elucidate the impact of ZIKV on patient outcomes, leading to improved understanding of the pathogenesis of ZIKV disease in Africa.” – by Stephanie Viguers

Disclosure: The researchers report no relevant financial disclosures.