Norovirus Epidemiology in Africa: A Review

Abstract

Norovirus (NoV) is recognised as a leading cause of gastroenteritis worldwide across all age groups. The prevalence and diversity of NoVs in many African countries is still unknown, although early sero-prevalence studies indicated widespread early infection. Reports on NoVs in Africa vary widely in terms of study duration, population groups and size, inclusion of asymptomatic controls, as well as genotyping information. This review provides an estimate of NoV prevalence and distribution of genotypes of NoVs in Africa. Inclusion criteria for the review were study duration of at least 6 months, population size of >50 and diagnosis by RT-PCR. As regions used for genotyping varied, or genotyping was not always performed, this was not considered as an inclusion criteria. A literature search containing the terms norovirus+Africa yielded 74 publications. Of these 19 studies from 14 out of the 54 countries in Africa met the inclusion criteria. Data from studies not meeting the inclusion criteria, based on sample size or short duration, were included as discussion points. The majority of studies published focused on children, under five years of age, hospitalised with acute gastroenteritis. The mean overall prevalence was 13.5% (range 0.8-25.5%) in children with gastroenteritis and 9.7% (range 7-31%) in asymptomatic controls, where tested. NoV GII.4 was the predominant genotype identified in most of the studies that presented genotyping data. Other prevalent genotypes detected included GII.3 and GII.6. In conclusion, NoV is a common pathogen in children with diarrhoea in Africa, with considerable carriage in asymptomatic children. There is however, a paucity of data on NoV infection in adults.

Fig 1. Map of Africa indicating the countries from which prevalence and diversity data was obtained (light blue) and countries where only NoV genotype data was available (dark blue).

BF—Burkina Faso, BW—Botswana, CF—Central African Republic, CM—Cameroon, DJ—Djibouti, EG—Egypt, ET—Ethiopia, GH—Ghana, KE—Kenia, LY—Libya, MA—Morocco, MW—Malawi, NG—Nigeria, SN—Senegal, TN—Tunisia, TZ—Tanzania, ZA—South Africa. Reprinted from d-maps.com under a CC BY license, with permission from Daniel Dalet, original copyright 2007–2015 (http://d-maps.com/carte.php?num_car=737&lang=en).

Fig 2. Prevalence of various NoV GI, GII and GIV capsid-based genotypes detected in children with gastroenteritis in 18 African countries between 1976–1979 and 1997–2013.

A total of 940 NoV strains were genotyped, the percentage of each genotype out of the total typed strains is indicated above each circle. The size of the circle represents the geographical distribution of a given genotype. The smallest circle represents 1/18 countries and the largest circle represents 14/18 countries.

Fig 3. Circulation of NoV GII.4 variants between 1998 and 2013 in 12 African countries.