A study led by Chinese researchers published on Friday, Dec. 18, in the journal Science revealed that the Middle East Respiratory Syndrome (MERS) coronavirus is hosted by dromedary camels in Saudi Arabia and has diverged into five different variants, the Xinhua News Agency reported.
Researchers have also designed a vaccine shown to be effective in protecting dromedaries against the virus, as published in a second study in the same journal.
The report said that several MERS outbreaks have been reported in the Middle East and most recently in South Korea, with a fatality rate of roughly 35 percent over the past three years.
The researchers said that Arabian camels are a common host for the MERS virus, which have become one of the most likely sources of human infection. They said that the virus can diversify in the animals and then passed to people, but little is known about the route by which it is transmitted to humans.
Between May 2014 and April 2015, the researchers took samples from more than 1,300 camels in Saudi Arabia, to gain more insights on MERS.
Based on the study, led by Professor Yi Guan and Assistant Professor Huachen Zhu at the University of Hong Kong, in collaboration with King Abdulaziz University, Saudi Arabia, and scientists from Mainland China, Australia and Egypt, the overall infection rate of the MERS virus among this sample was 12 percent, with a peak during the winter season (Dec. 2014 to Jan. 2015) at 21-23 percent.
The report said that researchers took the MERS virus 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," they concluded.
The researchers also conducted genetic sequencing to identify the five different lineages of the virus, all of which have the ability to infect both humans and camels.
The study showed that the viruses in the South Korean outbreak and the recent human infections in the Middle East were from lineage 5, generated by recombination between viruses of lineages 3 and 4.
"This novel recombinant virus lineage appeared in Saudi Arabian camels as early as July 2014, while human infections with viruses of this lineage were only reported from Feb. 2015 onwards," Zhu said.
"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," Zhu added.
The researchers also found two other coronaviruses circulating with the MERS coronavirus in the camels, which also include one that is closely related to the human 229E coronavirus that causes common colds.
According to the results of the study, around 6.9 percent of Saudi Arabian camels were 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.
The researchers said that camels were frequently infected with different coronavirus species, pointing out the role of dromedary camels as host for coronaviruses.
In addition, young dromedary camels played an important role in maintaining and spreading this virus.
The second study said that European researchers have found that all camels developed antibodies against the MERS virus within three weeks, after the researchers administered a candidate vaccine both nasally and intramuscularly.
The vaccinated camels only had mild clinical symptoms and were found to have significantly lower levels of the virus compared to those who did not receive the vaccine, the researchers said.
"This is nonetheless a very significant step forward in the fight against this pathogen," study author Joaquim Segales, lecturer at the Universitat Autonoma de Barcelona, said in a statement.
"Now we need to delve more deeply into the duration of the immunity and dosage before applying it in real situations," Segales added.