Biphasic MERS-CoV Incidence in Nomadic Dromedaries with Putative Transmission to Humans, Kenya, 2022–2023

Middle East respiratory syndrome coronavirus (MERS-CoV) is endemic in dromedaries in Africa, but camel-to-human transmission is limited. Sustained 12-month sampling of dromedaries in a Kenya abattoir hub showed biphasic MERS-CoV incidence; peak detections occurred in October 2022 and February 2023. Dromedary-exposed abattoir workers (7/48) had serologic signs of previous MERS-CoV exposure.


Conclusions
Our sustained sampling of dromedary camels showed a biphasic MERS-CoV incidence in northern Kenya not observed in previous studies (1,10,13).One explanation might be the short time of virus excretion in MERS-CoV-infected dromedaries (14), making viral RNA detection difficult without daily surveillance.Phylogenetic analysis suggests that we identified >3 MERS-CoV clusters over 3 different weeks in dromedaries originating from different wards.The first potential factor likely influencing the outbreaks is increased animal-to-animal interactions, because camels from different herds are transported to Isiolo and kept in holding pens together before slaughter, which could enhance MERS-CoV outbreaks.Second, increased interactions between immunologically naive and infected animals during transport and in holding pens increases the probability of transmitting MERS-CoV.That hypothesis is supported by the high percentage of IgG-negative adult camels (19.24%,ODR<0.3)(1,7).Although identifying the exact MERS-CoV transmission scenario between camels is logistically difficult, rapid point-of-care tests might help trace infections even in resource-limited conditions.
The overall biphasic MERS-CoV incidence might be linked to seasonal factors, such as the biannual alternating wet and dry seasons in northern Kenya.During dry seasons, herds congregate using limited forage, then migrate back to the point of origin in wet seasons.Because calves are mainly born during the 2 wet seasons, the loss of protection by maternal antibodies coincides with the dry seasons.Of note, the 2 dry seasons during July-October 2022 and January-February 2023 matched the peaks of MERS-CoV RNA-positivity in October 2022 and February 2023.The combination of immunologically naive, possibly infected camel calves and the dry season-specific increased population density and probability of contact at limited waterholes might encourage MERS-CoV infections and transmissions among camels.
We identified 7/48 abattoir workers with putative MERS-CoV exposure or past subclinical infection by implementing ELISA ODR cutoffs previously shown to be suitable for seroepidemiologic studies outside clinical settings.In 1/7 cases, we confirmed MERS-CoV neutralizing antibodies by VSVpp-based NT and PRNT.None of the abattoir workers experienced severe symptoms in recent years, supporting the hypothesis that clade C strains might have limited pathogenicity and transmissibility (15).Identifying defined factors that drive MERS-CoV outbreaks will assist in predictive epidemiology, risk assessment, and timely precautionary interventions for public and occupational health.

Figure 1 .
Figure 1.Biphasic Middle East respiratory syndrome coronavirus (MERS-CoV) incidence in dromedaries sampled in an abattoir hub, northern Kenya, 2022-2023.A) MERS-CoV RNA detection rates in nasal swab specimens from dromedary camels tested by MERS-CoV upE quantitative reverse transcription PCR.Continuous 12-month sampling (4-5 days per week) took place in Isiolo abattoir from mid-September 2022 to mid-September 2023.Sampling was suspended for 1 week in December 2022 and 1 week in July 2023.B) Detailed weekly overview of MERS-CoV RNA detections, peaking in October 2022 and February 2023.

Table .
Overview of camel samples and MERS-CoV RNA positivity in study of MERS-CoV incidence in nomadic dromedaries with putative transmission to humans, Kenya, 2022-2023* *MERS-CoV, Middle East respiratory syndrome coronavirus.