Researchers have confirmed in a new study animals have infected humans with the MERS virus several times and health experts are beginning to show concern, NBC News reported.

Scientists had reported nearly two months ago that the virus was found in camels, but could not confirm it was the original source. Then, one month ago, a team published a study confirming bats in Saudi Arabia were the first source of MERS.

Health experts are beginning to worry about MERS (Middle Eastern respiratory syndrome) because it bears resemblance to SARS (severe acute respiratory syndrome). In 2003 SARS caused a world epidemic, infecting around 8,000 and killing 800, or one in every 10.

Since Sept. 2012, the World Health Organization (WHO) reported at least 90 infections and 44 deaths, or one in every two. The United Nations was originally hesitant for fear of causing panic and only said it could cause a pandemic.

MERS appeared about a year ago and, while not much is known about it, scientists have noticed it has killed mostly people who are already weakened by diseases. MERS still has killed perfectly healthy people, however.

"All cases have been directly or indirectly linked to one of four countries in the Middle East (Saudi Arabia, Jordan, Qatar, and the United Arab Emirates), with most cases (90 cases and 44 deaths) reported from Saudi Arabia," said the report, led by Matthew Cotton, of Britain's Wellcome Trust Sanger Institute and Ziad Memish of the Saudi health ministry.

The study was published the medical journal the Lancet.

"Human-to-human transmission of MERS has been documented in England, France, Tunisia, Italy, and Saudi Arabia," read the report.

Although scientists know where the original source came from, it is still unclear how people became infected, or when. Camels have been discovered to carry the virus and the bats that originally carried MERS could have also infected other animals, as could have the camels.

Some patients showed signs of being infected more than once from different sources, further complicating how people can contract the virus.

Causing concern for Saudi officials is the upcoming Hajj from Oct. 13-18. It is a mass pilgrimage to the Saudi city of Mecca by Muslims from all over. The Saudi government has asked the elderly, pregnant women, children under 12 and those with chronic illnesses not to make the trip. The U.S. government has made similar warnings to American Muslims.