Middle East respiratory syndrome coronavirus (MERS-CoV) represents a novel human coronavirus that was initially reported from Saudi Arabia in 2012.
It was isolated from a male Saudi Arabian patient who died from respiratory failure as a result of pneumonia, with associated kidney failure.
The virus is taxonomically similar to the severe acute respiratory syndrome coronavirus (SARS-CoV) and has been associated with serious respiratory illness.
Three main elements play a role in the transmission of MERS-CoV: the virus, the host and the environment.
Accordingly, cases have occurred as sporadic infections, and limited interfamilial transmission, but also as clusters of healthcare associated infections.
The emergence of MERS-CoV caused substantial attention to the emergent respiratory pathogens and revealed the potential for worldwide spread of the disease.
Geographic Distribution of MERS-CoV
Since 2012, when the virus emerged, almost 2000 laboratory-proven human infections with MERS-CoV have been reported to the World Health Organization (WHO), appearing primarily in the countries of the Arabian peninsula.
Most of the cases have occurred in Saudi Arabia, but cases have also been seen in other regions, including Europe, Asia, North America and North Africa.
Still, it must be noted that in countries that were not the part of the Arabian peninsula, patients developed signs and symptoms of the illness after coming back from this region, or following close contact with infected individuals.
This was in spite of the fact, which became apparent very early on, that human-to-human spread of MERS-CoV was relatively ineffective.
Accordingly, a first case of MERS-CoV infection in the US was identified on May 2, 2014, in a traveler who returned from the Kingdom of Saudi Arabia. A second one was recorded just nine days later, following a similar scenario.
The largest outbreak outside the Arabian Peninsula was noted in the Republic of Korea, which was initiated by the index patient upon returning from a trip to multiple countries in the Middle East (Bahrain, Saudi Arabia, Qatar and UAE).
The outbreak in the Republic of Korea involved 72 health care facilities (with six of them showing nosocomial transmission), and 36 deaths were reported.
Reservoir of MERS-CoV and Modes of Transmission
MERS-CoV is an example of a zoonotic virus transmitted from animals to humans. Although the origins of the virus are still not fully elucidated, the analysis of the virus genome showed that it may have originated as a bat virus, and was subsequently transmitted to dromedary camels at some point in the distant past.
Correspondingly, published research indicates that the natural reservoirs of MERS-CoV are camels. Many affected individuals (particularly primary cases) have been in close contact with camels and sometimes also drank camel milk or ate camel meat.
During August 2013 there was a report in the Lancet (Infectious Diseases) on the finding of specific antibodies against MERS-CoV in 100% of Oman and 14% of Spanish camels.
In addition, various other research studies suggest that individuals who are in regular contact with camels show higher seropositivity rates than individuals without any contact with camels.
However, it must be noted that most of the primary cases do not give a history of any contact with animals.
On the other hand, the virus does not seem to be easily transmitted from person to person in the natural setting, unless there is a close contact (for example, administering unprotected care to an infected individual).
Clusters of cases in healthcare institutions have been described where human-to-human transmission is a more realistic scenario, most notably when prevention and control practices are deficient. No preserved community transmission has been recorded thus far.