Researchers have discovered what they believe could be the animal origin of Middle East respiratory syndrome (MERS) - after examining a bat in Saudi Arabia near where the first person was infected with the mystery virus.

Extensive blood tests from the insect-eating bat found a 100% genetic match for MERS infection.

However, if bats are indeed the source, then the team suggests it is likely another intermediary animal host is getting the virus from bats and then infecting humans.

The researchers, from New York's Columbia University, the international EcoHealth Alliance, and the Ministry of Health in the Kingdom of Saudi Arabia, report their findings online in Emerging Infectious Diseases, a journal of the US Centers for Disease Control and Prevention.

Earlier this month, the Lancet Infectious Diseases published a study that hinted camels could be a coronavirus carrier, based on finding traces of antibodies to the MERS virus in blood taken from dromedary camels in the Middle East in Oman and on Spain's Canary Islands.

However, the researchers behind this latest study say theirs is the first to find a genetic match in an animal in the search for a potential reservoir for MERS.

Co-author Professor W. Ian Lipkin, director of the Center for Infection and Immunity at Columbia University's Mailman School of Public Health, says:

"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."

What is the MERS coronavirus?

The MERS microbe is a member of the coronavirus family (so-called because of the crown-like spikes on their surface), a family that includes the common cold virus and the virus behind Severe Acute Respiratory Syndrome (SARS).

MERS was first seen in humans around April 2012. Infection leads to serious, and often deadly illness.

Since September 2012, when MERS was first described, nearly 100 cases have been reported worldwide, with around half of them fatal. 70 of the people infected were in Saudi Arabia.

Until now, the origin of the virus was unknown. Bats have been suspected because they are reservoirs of viruses that cause a range of human diseases, including rabies, Hendra, Nipah, Marburg, and SARS.

For some of these diseases, the infection comes directly from contact with bats, for instance by breathing in infected air, eating contaminated food, or through a bite wound, although this is rare.

But infection can also come from bats to humans via other animals. This is what Prof. Lipkin and colleagues believe is the case with MERS.

A thousand samples from seven bat species

For their study, the team undertook field expeditions in 2012 and 2013 and collected over 1,000 samples from seven species of bat in three Saudi Arabian regions that have seen human cases of MERS: the cities of Bisha and Unaizah, and the capital, Riyadh.

The researchers captured the bats in traps, and after species identification, took various measurements and samples, including blood, throat swabs, rectal swabs, and fecal pellets, before releasing them again.

Using polymerase chain reaction and DNA sequencing, they found genetic evidence of an extensive range of coronaviruses in up to a third of the samples.

But one fecal sample from an insect-eating Egyptian Tomb Bat (Taphozous perforatus), contained sequences identical to that of the virus sampled from the first person reported to be infected with MERS.

The bat was trapped just a few kilometers from the victim's home.

The team is continuing to search for evidence of the MERS virus in other animals, both wild and domesticated. They expect soon to be in a position to report findings related to camels, sheep, goats, and cattle.

They are also looking at various ways the virus causes human disease, says Prof. Lipkin, who adds:

"This is but the first chapter in a powerful collaboration amongst partners committed to global public health."

Lead author Ziad Memish, deputy minister for health in the Kingdom of Saudi Arabia, says:

"There is no evidence of direct exposure to bats in the majority of human cases of MERS."

"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."

Written by Catharine Paddock PhD