Credit ECDC
#17,917
Over the weekend we looked at the biannual report on MERS-CoV from Saudi Arabia, which has reported more than 80% of > 2,600 known MERS cases globally since 2012. Other countries on the Arabian Peninsula, including the UAE, Qatar, Yemen, and Jordan have reported cases as well.
We've also seen rare exported cases to a number of countries, including the UK, Germany, France, Italy, China, Thailand, the Philippines, and the United States.
While secondary transmission outside of the Middle East has been rare, in 2015 a single infected traveler to South Korea sparked an epidemic which eventually infected 185 people across 16 hospitals, and claimed 38 lives (see Superspreaders & The Korean MERS Epidemiological Report).
Just over a year after the first human infection with MERS-CoV was announced, dromedary camels were identified as a host species for the MERS coronavirus (see 2013's The Lancet Camels Found With Antibodies To MERS-CoV-Like Virus).
While bats are believed to be the primary host reservoir for MERS, SARS, and an array of other novel pathogens (see Curr. Opinion Virology: Viruses In Bats & Potential Spillover To Animals And Humans), camels - due to their close contact with people in the Middle East - are the main conduit by which the virus appears to spillover to humans.
Since then researchers have identified MERS-CoV and MERS-like viruses in camels in a number of countries outside of the Middle East (see 2019's Epi.& Inf.: Global Status Of MERS-CoV In Camels - A Systemic Review).
We've seen a similar lack of reporting of avian flu cases in these same regions (see The Challenge Of Avian Flu Surveillance In Sub-Saharan Africa), despite circulation of HPAI H5 viruses.
All of which brings us to an EID Dispatch which finds serological evidence of MERS-CoV in dromedary camels in Kenya, as well as limited evidence of transmission to humans. Complicating studies like this, MERS-CoV antibodies often wane relatively quickly.
In 2016's EID Journal: Antibody Response & Disease Severity In HCW MERS Survivors, we looked at a study that tested 9 Health care workers who were infected during the 2014 Jeddah outbreak (2 severe pneumonia, 3 milder pneumonia, 1 URTI, and 3 asymptomatic), that found only those with severe pneumonia still carried detectable levels of antibodies 18 months later.
I've only posted some excerpts, so follow the link to read it in its entirety.
Biphasic MERS-CoV Incidence in Nomadic Dromedaries with Putative Transmission to Humans, Kenya, 2022–2023
Brian Maina Ogoti1, Victor Riitho1, Johanna Wildemann1, Nyamai Mutono, Julia Tesch, Jordi Rodon, Kaneemozhe Harichandran, Jackson Emanuel, Elisabeth Möncke-Buchner, Stella Kiambi, Julius Oyugi, Marianne Mureithi, Victor M. Corman, Christian Drosten, Samuel M. Thumbi1, and Marcel A. Müller1
Abstract
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.
Middle East respiratory syndrome coronavirus (MERS-CoV) is endemic in dromedary camels from the Arabian Peninsula and Africa; seroprevalence is >75% (1–3). Zoonotic transmission to humans has occurred sporadically, mainly on the Arabian Peninsula; >2,400 MERS cases and >800 deaths have occurred (4). Despite Kenya being a major camel-breeding country, only 3 potentially autochthonous camel-exposed humans with subclinical MERS-CoV infections were identified in 2019 (5). The apparent regional epidemiologic differences might be linked to factors such as limited diagnostics, local risk factors (e.g., human comorbidities, camel herding practices, seasonality), or MERS-CoV strain–specific features (6).
(SNIP)
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.
Even if, as suggested, that clade C MERS-CoV strains circulating in central Africa are less pathogenic than their Arabian counterparts, history has shown that coronaviruses are fully capable of making abrupt and impactful evolutionary leaps (e.g. SARS-CoV, MERS-CoV, SARS-CoV-2, etc.).
Meaning we should be prepared for the status quo to change over time.
