Epidemiological and phylogenetic analyses of COVID-19 in Africa using
open-source sequence data.
Abstract
Between late December 2019 to early September 2020, over 10 million
people globally were reportedly infected by the severe acute respiratory
syndrome coronavirus-2 (SARS-CoV-2), responsible for the coronavirus
disease-2019 (COVID-19). In Africa, more than 300,000 infection occurred
within the period, from which several viral genetic sequences were
generated. Phylogenetic reconstruction of genomic data can provide
epidemiological inferences about time of pathogen introduction, epidemic
growth rate and temporal-spatial spread of the infection during disease
outbreak. In this work, we studied the genetic epidemiology of COVID-19
in Africa. Genetic sequence data of SARS-CoV-2 and metadata from African
countries were obtained from open-source sequence database hosted by the
GISAID initiative. Whole genome sequences were subjected to multiple
sequence alignment, from which Maximum Likelihood phylogenetic tree was
constructed based on the general time reversible model. Of the 227
genetic sequences obtained for 9 African countries (DRC=133, Senegal=23,
South Africa=20, Ghana=15, Tunisia=6, Algeria=3, Gambia=3, Egypt=2 and
Nigeria=2), 220 were whole genome sequences while 7 were partial genome
sequences of the surface glycoprotein S. Phylogenetic analysis confirmed
multiple introductions of the virus to the continent from multiple
external sources prior to local adaptation and spread. The very close
alignment of three viruses -
Ghana/1659_S14/2020|EPI_ISL_422405,
DRC/KN0054/2020|EPI_ISL_417437, and
South_Africa/R05475/2020|EPI_ISL_435059 – to
the reference Wuhan strain on the time tree, suggests possible
introduction and circulation of the virus into the continent much
earlier than when the first case was announced on February 15 2020. In
conclusion, this study provided evidence to support multiple
introductions of SARS-CoV-2 into Africa, and further suggests that the
virus may have already been circulating in the continent prior to
official reporting of the first case. Also, there is strong impression
to infer likely genetic adaptation of the virus in the continent that
may account for the close clustering of isolates from different
countries.