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| Fig. 2. Virological and serological evidence for MERS CoV in dromedary camels. |
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While the WHO Epi curve (below) suggests that the threat from MERS-CoV - which first emerged a dozen years ago on the Arabian Peninsula - has declined since the start of the COVID pandemic, various clades of this novel coronavirus continue to circulate in camels (see map above) - and occasionally spill over into humans - primarily in Saudi Arabia.
Surveillance and reporting of cases hasn't always been robust from the Middle East (and has been nearly non-existent in Africa where the virus can also be found), leading many researchers to believe that a significant number of cases go unreported (see EID Journal: Estimation of Severe MERS Cases in the Middle East, 2012–2016).
Earlier this week CIDRAP News carried a report on a study where Researchers identify episodic MERS cases in Kenyan camels, evidence of infection in people.
While unproven, it has been suggested that COVID infection - or receipt of the pandemic vaccine - might provide some protection against severe MERS-CoV infection. But since MERS-CoV continues to evolve, and immunity tends to wane over time, it is unknown how long any benefit might last.
Saudi Arabia - which used to report daily, and in far more detail - now provides an update every 6 months to the WHO. Interim monthly reports can also be found on the WHO EMRO Outbreaks page, although details are often lacking, and cases are often reported belatedly.
Yesterday's bi-annual update reports 4 new cases (2 fatal) which occurred in September (n=3) and October (n=1) of 2023. While two cases had known camel contact, for two cases, there was `no clear history of exposure to known risk factors'.
Due to its length, I've only posted some excerpts from the WHO update. Follow the link to read it in its entirety. I'll have a bit more after the break.
Middle East Respiratory Syndrome Coronavirus - Kingdom of Saudi Arabia
16 February 2024
Situation at a Glance
This is the bi-annual update on the Middle East Respiratory Syndrome Coronavirus (MERS-CoV) infections reported to the World Health Organization (WHO) from the Kingdom of Saudi Arabia (KSA). From 13 August 2023 to 1 February 2024, four laboratory-confirmed cases of MERS-CoV, including two deaths, were reported to WHO by the Ministry of Health of the KSA, with the last case being reported on 26 October 2023. Close contacts of the four cases were followed up by the Ministry of Health, and no secondary cases were identified.
The notification of these four cases does not change the overall risk assessment, with the risk being moderate at both the global and regional level. The reporting of these cases reiterates the need for global awareness of MERS-CoV as the virus continues to pose a threat in countries where MERS-CoV is circulating in dromedary camels, including those in the Middle East.
Description of the Situation
Between 13 August 2023 and 1 February 2024, the Ministry of Health (MoH) of the Kingdom of Saudi Arabia (KSA) reported four cases of Middle East respiratory syndrome coronavirus (MERS-CoV), including two deaths. The cases were reported from the Riyadh, Eastern, and Qassim regions of the KSA (Figure 1). Laboratory confirmation of the cases was performed by real-time polymerase chain reaction (RT-PCR) between 10 October 2023 and 16 November 2023.
All four cases had co-morbidities and none were health care workers. Two cases were male and two female, ranging in age from 59 to 93 years. The cases developed symptoms, including fever, cough, and shortness of breath, between 15 September 2023 and 26 October 2023. The two deaths occurred on 19 October 2023 and 24 December 2023.
Of the four cases, one was a camel owner, and another one had a history of indirect contact with dromedary camels as their family members were camel owners. For the other two cases, there was no clear history of exposure to known risk factors. None of them reported having a history of consumption of raw camel milk in the 14 days prior to the onset of symptoms. There are no known epidemiological links among the cases.
Since the first report of MERS-CoV in KSA in 2012, a total of 2200 human cases have been reported, including 858 deaths. Overall, human infections of MERS-CoV have been reported from 27 countries, in all six WHO regions. Of the 2609 MERS-CoV cases and 939 deaths reported globally, 84% and 91%, respectively, have been reported from KSA, including these newly reported cases and deaths. (Figure 2). Since 2019, no MERS-CoV cases have been reported from countries outside the Middle East.
Figure 1. Geographical distribution of MERS-CoV cases between 13 August 2023 to 1 February 2024 by city and region, KSA (n=4).
Epidemiology
Middle East respiratory syndrome (MERS) is a viral respiratory infection caused by the MERS-CoV. Approximately 36% of patients with MERS have died, though this may be an overestimate of the true mortality rate, as mild cases of MERS-CoV may be missed by existing surveillance systems, and the case fatality ratio (CFR) is calculated based only on laboratory-confirmed cases.
Humans are infected with MERS-CoV from direct or indirect contact with dromedary camels, which are the natural host and zoonotic source of the virus. MERS-CoV has demonstrated the ability to transmit between humans. So far, non-sustained human-to-human transmission has occurred among close contacts and in health care settings. Outside of health care settings there has been limited human-to-human transmission to date.
MERS disease ranges from having no symptoms (asymptomatic) or mild respiratory symptoms, to severe acute respiratory disease and death. A typical presentation of MERS disease is fever, cough, and shortness of breath. Pneumonia is a common finding, but not always present. Gastrointestinal symptoms, including diarrhoea, have also been reported. Severe illness can cause respiratory failure that requires mechanical ventilation and support in an intensive care unit. The virus appears to cause more severe disease in older people, persons with weakened immune systems, and those with comorbidities or chronic diseases such as renal disease, cancer, chronic lung disease, and diabetes.
The number of MERS-CoV cases reported to WHO has substantially declined since the beginning of the ongoing COVID-19 pandemic. Initially, this was likely the result of epidemiological surveillance activities for COVID-19 being prioritized. The similar clinical picture of both diseases may result in reduced testing and detection of MERS-CoV cases.
In addition, measures taken to reduce SARS-CoV-2 transmission (e.g., mask-wearing, hand hygiene, physical distancing, improving the ventilation of indoor spaces, respiratory etiquette, stay-at-home orders, reduced mobility) also likely reduced opportunities for onward human-to-human transmission of MERS-CoV. Potential cross-protection conferred from infection with or vaccination against SARS-CoV-2 and any reduction in MERS-CoV infection or disease severity and vice versa has been hypothesized but requires further investigation.
No vaccine or specific treatment is currently available, although several MERS-CoV-specific vaccines and therapeutics are in development. Treatment is supportive and based on the patient’s clinical condition and symptoms.WHO Risk Assessment
The notification of these four cases does not change the overall risk assessment, with the risk being moderate at both the global and regional level. The four new cases reported between 13 August 2023 and 1 February 2024 are believed to have acquired MERS-CoV infection locally and not to have transmitted it further.
WHO expects that additional cases of MERS-CoV infection will be reported from the Middle East and/or other countries where MERS-CoV is circulating in dromedaries, and that cases will continue to be exported to other countries by individuals who were exposed to the virus through contact with dromedaries or their products (for example, consumption of raw camel milk), or in a health care setting.
WHO continues to monitor the epidemiological situation and conducts risk assessment based on the latest available information.
Concerns that MERS-CoV and SARS-CoV-2 might infect a common host and produce a dangerous recombinant are mostly theoretical, but have been given serious consideration in scientific journals, including:
Nature: CoV Recombination Potential & The Need For the Development of Pan-CoV Vaccines
Co-infection of MERS-CoV and SARS-CoV-2 in the same host: A silent threat by Buket Baddal
The Recombination Potential between SARS-CoV-2 and MERS-CoV from Cross-Species Spill-over Infections by Abdulrahim A Sajini, Almohanad A Alkayyal & Fathi A Mubaraki
Even if MERS-CoV continues its downward trend, it is just one of many novel coronaviruses with zoonotic potential in the wild. Some related blogs include:
V. Sinica: Pangolin HKU4-related Coronaviruses Found in Greater Bamboo Bat From Southern China
Nature: Comparative Susceptibility of SARS-CoV-2, SARS-CoV, and MERS-CoV Across Mammals
