Anytime a novel virus infects human populations, scientists focus on tracing its origins. And this time their search led to the humped dromedary.
After a Saudi Arabian national died unexpectedly last September, scientists have been tracking the emergence of a new virus, never before seen in people, that has since been identified as a coronavirus, part of the same family that produced SARS. As of last week, the World Health Organization reported that a total of 94 people have been infected and 46 people have died from the infection. Known as Middle East respiratory syndrome coronavirus (MERS-CoV), it causes severe respiratory illness, pneumonia, fever and coughing. So far, cases have been reported in nine countries, most of them in the Middle East, but international travel may have taken the virus to France, Germany, Italy and the U.K.
While MERS-CoV is part of the same family of viruses as SARS, it is genetically different from that virus, and a recent study comparing the two found that while they can cause similar symptoms, MERS Co-V infections can lead to respiratory failure about five days sooner than SARS infections. MERS Co-V, however, appears to be less infectious than SARS, although there have been some reports of limited person-to-person transmission of the virus.
Because MERS Co-V does not seem to jump readily between people, scientists believe that its natural reservoir may be an animal, as is the case with bird-flu strains that originate in fowl and are picked up by people who come in contact with them. Most coronaviruses are believed to be generated by bats, but since human and bat populations rarely come in direct contact with each other, researchers believe intermediate species, like livestock, or, in the case of SARS, civet cats, are acting as the conduit. Identifying such chains of transmission are critical for controlling spread of the virus and preventing new cases from emerging.
All of the cases of MERS Co-V originated in the Middle East, with patients either residing in the area or traveling to the region before falling ill. Some reported contact with livestock, goats and camels, so an international group of scientists led by Dr. Chantal Reusken, of the National Institute for Public Health and the Environment in Bilthoven, the Netherlands, analyzed a variety of animals for their ability to harbor MERS Co-V. They also tested blood from cattle, goats and camels in Europe to determine if the virus had spread to animal populations there.
All 50 of the camels from Oman, which is adjacent to Saudi Arabia, where the first cases were identified, showed antibodies to MERS Co-V, indicating that the camels were infected with the virus and were able to develop immune cells against it. About 14% of camels in Europe possessed the same antibodies, hinting that the virus has spread to that species, which appears to be fighting off the virus but can spread it to other animals or even people.
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In a statement about the findings, published in the journal Lancet Infectious Diseases, the researchers say: “As new human cases of MERS-CoV continue to emerge, without any clues about the sources of infection except for people who caught it from other patients, these new results suggest that dromedary camels may be one reservoir of the virus that is causing MERS-CoV in humans. Dromedary camels are a popular animal species in the Middle East, where they are used for racing, and also for meat and milk, so there are different types of contact of humans with these animals that could lead to transmission of a virus.”
The scientists go on to speculate why MERS Co-V may have blossomed among Middle Eastern populations of camels and not in other regions, like the Canary Islands, where only 10% of the animals showed signs of the antibodies to the virus. Because countries in Africa, Saudi Arabia and the United Arab Emirates are the world’s leading breeders of camels for racing and consumption, the constrained conditions in which the animals are raised might promote transmission of the virus, as well as provide the evolutionary pressure the virus needs to become more virulent and adaptable to new hosts, including people.
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Because there is some evidence that MERS Co-V can spread between people, especially in a health-care setting, public-health officials are concerned that the virus could mutate to become more adept at hopping from host to host. On its MERS Co-V site, the U.S. Centers for Disease Control and Prevention writes: “CDC recognizes the potential for the virus to spread further and cause more cases and clusters globally, including in the United States.”
Now that a potential animal reservoir for the virus has been identified, scientists will next compare the strains of MERS Co-V taken from infected camels with those obtained from patients, to confirm that the animals are indeed the source of the new infections. The more information that’s available about where the virus comes from, the better equipped health officials will be in controlling and preventing infections.