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MERS-CoV: Towards a Better Understanding of the Disease


06 May 2014 - The Middle East Respiratory Syndrome Coronavirus (MERS-CoV) first emerged in 2012 and has caused 4991 human infections, including 137 deaths based on reports from affected countries as of 4 May 2014. The majority of cases have been detected in Saudi Arabia although cases were also reported in Jordan, Oman, Qatar, the United Arab Emirates and Yemen. Countries in Asia, Europe and North Africa have reported individual cases in travellers returning from the Middle East. The last countries that reported their first imported MERS-CoV case include Egypt and the United States of America.

The past few weeks have seen a sharp increase in the number of human cases, mostly in Saudi Arabia and the United Arab Emirates. Multiple new infections have been reported on a frequent basis since early April 2014 in Jeddah, Mecca and Riyadh prompting speculation that the virus may have evolved. This has caused concern among health professionals, in particular in light of the frequent religious event (Umrah) and the upcoming Hajj, the world's largest mass gathering. Nevertheless, recent investigations showed no significant changes in the genome of MERS-CoV isolates from Jeddah compared to previous sequences, suggesting that the MERS-CoV genomes have remained stable during recent outbreaks. The reason behind the seasonal increase in MERS-CoV cases in April 2013 and again in April 2014 remains unclear at present.

Although the majority of MERS-CoV cases reported have occurred through human-to-human transmission, primary cases are more likely to have been acquired through contact with non-human sources of the virus, including environmental or unknown animal sources.

Over the past months research activity on MERS has been accelerating and a number of recent studies have offered a better understanding of the disease and provided evidence of the infection of dromedary camels (Camelus dromedarius) with MERS-CoV.

MERS-CoV Antibodies in Camels

Camels have been suspected as a reservoir for the MERS virus and a possible source for human infection on the basis of the presence of MERS-CoV neutralizing antibodies. Many studies have reported a high prevalence of MERS-CoV antibodies in dromedaries in Egypt, Jordan, Oman, Saudi Arabia, the Canary Islands (Spain) and the United Arab Emirates. Further proof of widespread circulation of MERS-CoV among dromedaries was provided by additional studies from Ethiopia, Nigeria and Tunisia. The authors of these studies concluded that MERS-CoV or a similar virus circulated in dromedaries in Africa and the Arabian Peninsula long before 2012 (when the first human infections surfaced), including in places where no human cases have been detected. Studies have shown that MERS-CoV was found in camels in Saudi Arabia since 1992 and in the United Arab Emirates since 2003. In addition, limited studies in other domestic species (i.e. sheep and goats) have been repeatedly negative.

MERS-CoV Isolates in Camels

In October 2013, investigations on a camel farm associated with human MERS-CoV cases in Qatar found dromedaries and humans to be infected with similar strains of MERS-CoV. Out of fourteen camels, three were found infected with MERS-CoV and reported by Qatar to the World Organisation for Animal Health (OIE).

A recent study conducted in Saudi Arabia showed that MERS-CoV isolates from camels match MERS-CoV samples from humans and can be grown in non-human primate cells in the laboratory, indicating that the virus in camels is capable of infecting humans and could be the source of infection. The authors also found that viral particles from individual camels contained more genetic variation than MERS-CoV isolates from humans, suggesting that if camels are passing the virus to humans, only certain genotypes can infect humans. This perhaps partially explains why human MERS-CoV cases are overall uncommon.

Further Studies Needed

The above studies have produced evidence that virus sequences from dromedaries and humans are identical and demonstrate a widely spread distribution of MERS-CoV or a closely related virus in camels. These findings constitute a significant breakthrough in the understanding of this emerging disease and suggest camels may act as an intermediate host of MERS-CoV. Nevertheless, further studies are needed to verify the potential role of camels as a source of infection for humans and to determine how the virus passes from its natural host or reservoir to humans. The strength of the association between infection in camels and humans must be assessed to determine if people that are in contact with infected camels are more likely to contract the disease than people with no such contact. This information is crucial in order to devise a strategy aimed at halting the source of infection and protecting humans. The Food and Agriculture Organization of the United Nations (FAO), in close coordination with its global partners, is working with national authorities to facilitate and support animal investigations on MERS-CoV.

It is essential that countries and the international community commit to targeted investigations, information sharing and coordination so that this potential threat to global health is contained. National public health and veterinary authorities are urged to collaborate with each other and coordinate joint investigations of MERS-CoV cases in humans as well as establish a systematic search for the source of infection in animals and the environment. Furthermore, it is imperative that veterinary services in affected and at-risk countries monitor MERS-CoV reports and report any animal cases of infection with MERS-CoV to the OIE.

General Hygiene Practices

Specific advice on biosecurity and preventive measures to avoid the transmission of the MERS virus from its possible animal source to humans is difficult to establish as camels do not have noticeable clinical signs. General statements suggesting that humans stay away from camels are not warranted. Until more information on the mode of transmission of the disease to humans becomes available, general hygiene practices and proper food preparation, including cooking and pasteurization of milk of animals (including camels) for human consumption must be observed to protect humans against a wide range of diseases from animals, animal products and the environment.

Upcoming Consultation Meeting in Muscat

In ongoing efforts to better understand the role of animal species in the epidemiology of MERS-CoV and in response to the surge in MERS-CoV cases and recent findings on camels as a possible source of infection, FAO, in close collaboration with its global and regional partners, is convening a regional technical consultation meeting on MERS-CoV in Muscat, Oman on 20 and 21 May 2014 with the participation of the main stakeholders from the region.

The main objectives of this meeting are to:

  • review current knowledge on the disease in affected countries and the potential role of animal species in the epidemiological cycle of MERS-CoV;
  • analyse the recent developments in diagnostic and surveillance tools to support animal investigations;
  • identify and agree on actions that will minimize disease spread, based on current epidemiological knowledge; and
  • discuss and agree on mechanisms for intra-regional cooperation in investigations, research and knowledge sharing.

The main expected outcomes of the meeting will be a better understanding of MERS-CoV overall, and in particular of the link between MERS-CoV and animal species, as well as the establishment of coordinated initiatives among countries for the effective monitoring of MERS-CoV in animal species.




1 As of 26/04/2014 the World Health Organization has been informed of a total of 264 laboratory-confirmed human cases, including 93 deaths. The count will be updated with 138 cases identified between 11 to 26 April 2014 in Saudi Arabia.

 

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©FAO/Ami Vitale

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©FAO/Ami Vitale

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