MERS-CoV in Africa: a One Health review of the silent reservoir

Africa harbours more than 80% of the world's dromedary camels, with a pooled MERS-CoV seroprevalence of 73·7%; however, no autochthonous outbreak in humans has been documented. In this Review, we weigh five interacting explanations for the absence of documented human outbreaks based on the strength of the evidence for each explanation. The primary explanation is virological; many, although not all, African clade C MERS-CoV strains show reduced replication competence in human respiratory tissues, and clade C strains have not become established in Arabian camels or humans despite decades of large-scale export from the Horn of Africa into the world's most intensively monitored MERS-CoV surveillance system. Environmental contexts, including dry-season herd aggregation, drought, and calving-linked shedding, influence when MERS-CoV exposure occurs in humans. Surveillance limitations, dispersed exposure among the African population particularly pastoralists, lower comorbidity burden than that in affected populations in the Arabian regions, and absent nosocomial amplification are secondary explanations, largely downstream of the primary factors. Although longitudinal cohort studies using enhanced diagnostics detected sporadic spillover in Africa, these infections were asymptomatic. The presence of clade B strains and interclade B×C recombinants in Egyptian camels are surveillance priorities and not evidence of MERS-CoV emergence in humans. Africa's silent reservoir is therefore not a safe one: continued clade C circulation, alongside emerging clade B introductions and interclade recombinants, could shift this balance, underscoring the need for sustained genomic and human surveillance of the reservoir.