September 20, 2013
Complex Animal, Human Transmission Patterns Seen In MERS-CoV
Lawrence LeBlond for redOrbit.com - Your Universe Online
As the Middle East Respiratory Syndrome Coronavirus (MERS-CoV) continues to spread, researchers have been asking one big question: Has it jumped from animals to humans just once or has it made several jumps throughout its history?A new study published in The Lancet indicates that the virus may have jumped numerous times, based on the genetic diversity found in virus sampling from 25 Saudi Arabian MERS patients. Researchers from Saudi Arabia, the UK and the US sequenced the genomes of 21 isolates and found too much diversity to support a single jump hypothesis.
The findings also suggest that human-to-human transmission is much more complex than previously expected and undetected infections in people may be spreading the virus more easily than thought. But based on the genetic sampling, the virus may also be continuously jumping from animals to human.
Globally, more than 130 people have fallen ill to MERS-CoV since the virus was first reported a year ago. The World Health Organization (WHO) reported Sept. 19 of 18 new cases of the virus since Sept. 1, 2013, along with three more deaths. The virus has shown variable mortality rates, hovering near 50 percent, but currently down to 44 percent, as 58 people have so far died, most with underlying health conditions.
The researchers, who hail from Wellcome Trust Sanger Institute, Edinburgh University and University College London, are working closely with the Saudi Arabia Ministry of Health to sequence MERS-CoV in hopes of discovering how this deadly virus spreads. Knowing how it spreads will help researchers develop effective intervention measures.
Through the sequencing, the Sanger Institute team analyzed the 21 isolates taken from the 25 patients and combined that data with geographic locations of the people and the time that they were infected as well as the amount of genetic differences seen between each virus. This work gave the team a clearer picture on how the virus has spread and how the virus’ genome changed over time.
"We deep-sequenced the genomes of MERS-CoV taken from 21 infected people to calculate accurately the rate of evolution of the virus," said first author Dr Matthew Cotten, from the Sanger Institute. "Using this evolution rate, we could define genetically plausible transmission pairs. However, of the 13 transmission events that were predicted from the epidemiology, the genetic evidence we gathered could only support eight."
The team’s findings supports the idea that either unknown human transmitters are still out there, or more infections are surfacing from animals. The sequencing reveals the possibility that there may be undetected, asymptomatic people who are carrying and spreading the virus.
"The genome differences we discovered in some infected people were too great to be explained by replication errors occurring in the virus as it is passed from human to human during a single chain of infection," explained Professor Paul Kellam, senior author of the study from the Sanger Institute. "Instead our findings suggest that different lineages of the virus have originated from the virus jumping across to humans from an animal source a number of times."
While researchers have found genetic evidence of MERS-CoV antibodies in camels, and one team made a 100 percent genetic match of the virus in a bat sample, there is yet no animal identified as a true source of the MERS-CoV infections. Still, research continues to try and find a likely reservoir species, and testing continues on both camels and bats, as well as goats, sheep, dogs, cats, rodents and a number of other animals found in Saudi Arabia and surrounding Middle Eastern countries.
Further genomic studies of this virus are necessary to discern how this virus is spreading among people, noted corresponding author Professor Ziad Memish, Deputy Minister of Health, Riyadh, Kingdom of Saudi Arabia.
"The animal source of MERS-CoV and the way that it is transmitted to humans is not yet known. This information is critical for developing interventions for reducing the risk of transmission, defining the epidemiology and developing effective control measures," he said.
Through the analysis of genetic data, the researchers have found that despite first being reported in September 2012, the virus may have emerged much earlier – in July 2011; some evidence points out that it may have even emerged as early as July 2007.
Interestingly, no evidence was seen of MERS-CoV spreading during last year’s annual Hajj in October, when as many as eight million pilgrims arrived in Mecca, Saudi Arabia. As well, the July 2013 Ramadaan Umrah season had come and gone virus-free, according to Professor Ali Zumla, senior coauthor from UCL.
"In lieu of our study's genomic findings, watchful surveillance and vigilance is required despite the current minimal risk of global spread," he urged.
In a second paper, published in the journal Eurosurveillance, researchers from the National Institute of Allergy and Infectious Diseases (NIAID) discovered that MERS-CoV and its cousin virus SARS had very similar stability profiles. They also found that MERS-CoV can survive much longer than the 2009 H1N1 flu virus.
Using virus grown from MERS-CoV samples provided by Erasmus University, the NIAID team found that it was more stable than H1N1 under low temperature and low humidity conditions and could still be recovered after 48 hours. This discovery suggests the virus can be transmitted by direct contact or fomites -- inanimate objects or substances capable of transmitting germs, bacteria or viruses.
Also, the researchers found that MERS-CoV can remain viable in an airborne state, suggesting that it could be easily transmitted through the air. Also, prolonged survival on surfaces can increase the likelihood of fomite transmission, NIAID reported. However, the virus’ stability drops in higher temperatures, indicating that fomite transmission would be unlikely during the warmer months in the Arabian Peninsula.