WHO: Risk assessment of the introduction, spread, and zoonotic spillover of MERS-CoV Clade B in camel populations of the Nile Basin and Across Africa

 

#19,285

While the number of human MERS-CoV cases reported over the past six years has fallen dramatically, this high morbidity/mortality coronavirus continues to pose a significant public health threat ((Referral) Nature: Human MERS-CoV cases are falling but pose an ongoing pandemic threat) as it spreads and evolves in camels in the Middle East and Africa.

Some of this decline may be due to difficulties in identifying cases, while some Middle Eastern countries have shown past reluctance to report cases. It also seems likely that cases are being missed in North and Central Africa as well (see EID Journal: Geographic Distribution of MERS-CoV among Dromedary Camels, Africa). 

As of 11 June 2026, the WHO had reported a total of 2,637 laboratory-confirmed human cases have been reported - mostly from countries in the Arabian Peninsula - with an estimated case fatality ratio (CFR) of approximately 37%.   

But both the  EID Journal: Estimation of Severe MERS Cases in the Middle East, 2012–2016 and Presence of Middle East respiratory syndrome coronavirus antibodies in Saudi Arabia: a nationwide, cross-sectional, serological study by Drosten & Memish et al., suggest that far more MERS-CoV cases have occurred than have been reported.

  

MERS-CoV clade B is most common on the Arabian peninsula, while Africa is dominated by clade C, which is thought to be less well adapted to human physiology.  Clade A hasn't been reported in humans or camels since 2015, and is now considered extinct. 

But over the past year at least two studies have reported evidence that clade B-like viruses (or clade B/C recombinants) may be circulating in Africa. Today's risk assessment cites:

• In Egypt, phylogenetic analyses of a camel-derived sample identified genome fragments clustering with clade B viruses from the Arabian Peninsula, circulating alongside endemic African clade C viruses (Gomaa, Edwards, Wang, Taweel, et al., 2025).

• In a separate study (Hassan et al., 2025), metagenomic sequencing of nasal swabs from camels imported from Sudan also detected MERS-CoV genome fragments clustering with clade B human and camel strains

In both cases, the available sequences were limited and less than 100% complete, and so they must be regarded as preliminary, and will require full-genome confirmation.

The 24-page  FAO–WHO–WOAH GLEWS+ assessment (below) reached three primary conclusions; the first two question only deal with the impact on dromedaries, while the third deals with the public health risk.

Confidence in the two camel specific answers is low, while the confidence in the public health question is moderate. 

The section discussing question 3, provides the following rationale (excerpt):

Once introduced into camels in the Nile Basin countries, the likelihood of MERS-CoV clade B spillover to occupationally exposed humans is assessed as very likely, reflecting the intensity of human-camel contact, weak and uneven implementation of biosecurity and hygiene measures and constraints in surveillance and early detection systems.

The consequences are assessed as moderate. MERS-CoV Clade B can cause severe disease in humans and is associated with a high case fatality ratio, particularly among those with underlying medical conditions, and immunocompromised individuals. 

In the absence of licensed vaccines for the general population or widely available specific treatments, spillover events have the potential to result in severe clinical outcomes, especially in settings with limited access to advanced healthcare. Healthcare-associated outbreaks also remain a concern where infection prevention and control measures are insufficient. However, despite its high replication competence, a substantial proportion of MERS-CoV infections are asymptomatic or mild.

Furthermore, sustained human-to-human transmission is generally limited and typically requires close and prolonged contact. Consequently, widespread community transmission is not expected. Overall, the public health risk of MERS-CoV clade B spillover from camel populations to humans exposed to camels or their products in the Nile Basin countries is assessed as high.

The level of confidence in the assessment is considered moderate, reflecting evidence of frequent human–camel contact and known zoonotic potential of MERS-CoV clade B, but also important uncertainties regarding the frequency of spillover events, the role of specific exposure pathways, and gaps in surveillance and epidemiological data from the Nile Basin region.

The full risk assessment is well worth reading in its entirety.