AsianScientist (Dec. 28, 2015) – An international research team has revealed that the Middle East Respiratory Syndrome (MERS) coronavirus has become enzootic in dromedary camels in Saudi Arabia and diverged into five distinct lineages, as reported in Science.
Additionally, the researchers report that the viruses that led to the Korean outbreak and the recent human infections in the Middle East were from lineage 5 and generated by recombination between viruses of lineages 3 and 4. Also reported were two other coronaviruses co-circulating with the MERS coronavirus in the camels, including one closely related to the human 229E coronavirus that causes common colds in humans. Co-infections of these different coronavirus species were frequently detected in camels, with over half of the MERS coronavirus-positive camels also carrying at least one of the other coronaviruses.
To date, over 1,300 laboratory-confirmed cases of human infection with the MERS coronavirus have been reported in 26 countries since 2012, with more than 500 deaths recorded by the World Health Organisation (WHO) and a fatality rate of 38 percent. Saudi Arabia is the country most affected, with over 75 precent of cases, followed by South Korea.
To understand more about the source of this disease in animals, and how it might develop to threaten public health, researchers from the Hong Kong University (HKU) and other institutions jointly investigated the prevalence and evolution of coronaviruses in camels from Saudi Arabia.
The team was led by Professor Yi Guan and Dr. Zhu Huachen of the State Key Laboratory of Emerging Infectious Diseases and School of Public Health, Li Ka Shing Faculty of Medicine, HKU, in collaboration with King Abdulaziz University, Saudi Arabia. Scientists from Mainland China, Australia and Egypt also contributed.
The research team conducted surveillance in Jeddah, Taif and Riyadh from 2014 to 2015 and found coronaviruses were highly prevalent in dromedary camels from western and central Saudi Arabia. These viruses were predominantly shed from the respiratory tracts of camels, with over 25 percent of nasal swabs positive for coronaviruses, and only 1 percent of samples from digestive tracts positive. Thus, air-borne transmission is the most likely way to spread the virus.
By testing samples collected at wholesale markets, slaughterhouses and farms, the researchers found that the majority of the coronavirus-positive camels came from wholesale markets, where indigenous camels mixed with camels imported from Africa. Local camels had significantly higher positive rates for coronaviruses than imported camels. Young camels, under one year old, had the highest levels of respiratory infections, at 34 percent, with MERS or the other coronaviruses; approximately twice the rate seen in camels of other age groups.
Notably, the overall positive rate from the nasal swabs of the camels for the MERS coronavirus was 12 percent, with a peak during the winter season, December 2014 to January 2015, at 21-23 percent. This led the researchers to conclude that the MERS virus has become enzootic in dromedary camels in Saudi Arabia. Most affected camels show no overt signs of infection, which has made the recognition of infected camels and tracing the source of the virus difficult.
By utilising next generation sequencing, the researchers obtained 93 full genomic sequences of camel coronaviruses, including 67 MERS coronaviruses. Systematic evolutionary studies found the MERS coronavirus has diverged into five distinct lineages. Viruses from lineage 5 were generated by recombination between those of lineages 3 and 4, and led to the recent outbreaks in Korea and the Middle East. This novel recombinant virus lineage appeared in Saudi Arabian camels as early as in July 2014, while human infections with viruses of this lineage were only reported from February 2015 onwards.
The human MERS coronavirus identified in South Korea early this summer shows extremely high similarity to a camel virus sampled in March 2015 in Riyadh, indicating the origin of Korean viruses is from camels of the Middle East.
In addition to the MERS coronaviruses, the researchers also found two other coronavirus species co-circulating in Saudi Arabian camels, with one closely related to the human 229E coronavirus and the other similar to the HKU23 coronavirus previously reported in camels from Dubai. The 229E-like virus was found in the respiratory tract of 20 percent of Saudi Arabian dromedaries.
In humans, coronavirus 229E is one of the most frequently detected causal agents of the common cold. Around 6.9 percent of Saudi Arabian camels were simultaneously infected by two or three coronavirus species, and over half of the MERS coronavirus-positive camels were also infected with at least one other coronavirus. Co-infections of different coronavirus species occur frequently in camels, highlighting the role of dromedary camels as an important host for coronaviruses.
The researchers suggest that policies to prevent direct contact with camels, especially their oral and nasal tracts, to maintain good personal hygiene and to avoid exposure to contaminated materials or environments should be reinforced. Together with effective surveillance and control measures, this will break the transmission chain of the virus and reduce the threat to public health.
The article can be found at: Sabir et al. (2015) Co-circulation of Three Camel Coronavirus Species and Recombination of MERS-CoVs in Saudi Arabia.
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Source: The University of Hong Kong.
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