August 22, 2013
Bat Virus A 100-Percent Genetic Match To Human MERS
Lawrence LeBlond for redOrbit.com - Your Universe Online
Earlier this month scientists from The Netherlands found a correlation between MERS and camels, discovering Middle Eastern and African dromedaries had carried coronavirus antibodies genetically similar to the virus infecting humans.
Now, researchers from Columbia University, EcoHealth Alliance and the Saudi Arabia Ministry of Health have discovered the first concrete evidence of animal to human transmission. The results of this find could have strong implications in finding a cure, or at least a vaccine, for MERS coronavirus in humans.
Ian Lipkin, MD, director of the Center for Infection and Immunity at Columbia’s Mailman School of Public Health, and colleagues discovered the MERS virus in a bat that was taken near the site of the first outbreak in Saudi Arabia. The team said the virus found in the bat is a 100 percent genetic match to that found in humans, indicating a strong likelihood this disease originated in bats. However, they cannot rule out an intermediary animal that may be involved in transmission.
This was the first study to actively seek out an animal reservoir for MERS in Saudi Arabia and to identify a genetic match between animal and human. Results of this discovery are published in the online edition of the CDC journal Emerging Infectious Diseases.
"There have been several reports of finding MERS-like viruses in animals. None were a genetic match. In this case we have a virus in an animal that is identical in sequence to the virus found in the first human case. Importantly, it's coming from the vicinity of that first case," said Lipkin.
The virus, which was first found in humans nearly a year ago in a Qatari man, has continued to spread, with nearly 100 cases confirmed throughout the Middle East, Europe and Africa. Initially, the virus was labeled Novel coronavirus and was determined to be SARS-like in nature. Eventually, it was given the Middle East Respiratory Syndrome name as it was determined to contain a new causative agent not seen in other coronaviruses.
While the origin of MERS was not known, it had been reported it was similar to the coronavirus found in bats last November. Other experts pointed out the virus could also have originated in goats, sheep and possibly camels.
In fact, a camel link was found earlier this month when researchers, led by Chantal Reusken of the National Institute for Public Health and the Environment (RIVM) in The Netherlands, discovered MERS antibodies in several camel populations in the Middle East and Africa. The evidence of antibodies suggests camels at one time had suffered an outbreak of the virus, but were able to fight it off and develop protection against future infection.
While the team was able to make a suggestive correlation between camel antibodies and human infection, there was no direct evidence coronavirus in camels was the root cause of the disease in humans.
As for bats, the new evidence is much more associable to humans.
During six-week field expeditions in October 2012 and April 2013, researchers collected more than 1,000 samples from seven bat species in regions where MERS cases were identified – Bisha, Uniazah and Riyadh. The research team performed extensive analysis using polymerase chain reaction and DNA sequencing on the samples. The analysis had revealed the presence of a wide range of alpha and beta coronaviruses in as many as a third of the bat samples.
In all of the samples, none were definitively linked to human MERS, except one. A fecal sample taken from an Egyptian Tomb bat (Taphozous perforates) was shown to be exactly identical to the first known human infection. What’s more, the bat was found within 1.5 miles of the initial victim’s home.
Bats are known reservoirs of a host of viruses that can cause human maladies, such as rabies, Marburg, Nipah and SARS. In some instances, the infection can spread directly from bats to humans through inhalation of infected aerosols, ingestion of contaminated food, or a bite from an infected animal. As well, bats can first infect intermediary hosts, which then go on to infect humans.
With this knowledge in hand, it could plausibly make sense bats infected camels, which in turn infected humans. However, whereas the bat MERS is exactly identical to the human MERS, the camel MERS antibodies are only similar to those in the human disease. Still, the researchers are not ready to blame bats for direct infection in humans.
"There is no evidence of direct exposure to bats in the majority of human cases of MERS," said Ziad Memish, MD, Deputy Minister of Health, Kingdom of Saudi Arabia, and lead author of the study. "Given that human-to-human transmission is inefficient, we speculate that an as-yet-to-be determined intermediate host plays a critical role in human disease."
"We are continuing to look for evidence of the virus in wildlife and domestic animals, and investigating the mechanisms by which the virus causes human disease," added Dr. Lipkin. "This is but the first chapter in a powerful collaboration amongst partners committed to global public health."
The research group said it plans to further report the results of its investigation into the possible presence of MERS in other animals, including goats, sheep, cows and camels.