08/21/2014 02:04 EDT | Updated 10/21/2014 05:59 EDT

Scientists finally find a good MERS animal model, but marmosets a mixed blessing

TORONTO - Scientists working to solve the mysteries of the MERS coronavirus have finally filled a gaping hole — with a very tiny animal.

U.S. researchers have reported that marmosets are a good animal model for the infection, suffering from the same symptoms humans do when they contract the Middle East respiratory syndrome virus.

The researchers reported their work Thursday in the journal PLoS Pathogens. (PLoS is short for Public Library of Science.)

"At the moment it's the best disease model that we have for MERS," one of the senior authors, Dr. Heinz Feldmann, said in an interview.

Animal models are crucial in research, helping scientists tease out how diseases attack the body and chart the damage they do. They are also critical in efforts to develop drugs or treatments for disease, which must be tried on animals before they are tested in people.

But in order for an animal model to work, the animal in question must experience the same type of illness as humans do. And that has been a problem with the MERS virus.

Though it is known the virus infects camels — and they probably infect people — the dromedaries don't get noticeably sick when they are infected. Even if they did, the animals are too large to work with easily in high containment laboratories.

Rhesus macaques can be infected with the virus, but they don't experience the severe disease people get. Hamsters and ferrets, which are commonly used in animal studies, also don't work for MERS.

Researchers at the University of Iowa and elsewhere have been working on developing a mouse model for the disease. But work reported earlier this year suggested the first effort also experienced a similar problem; the mice didn't become sick or lose weight.

Now scientists from the U.S. National Institute of Allergy and Infectious Diseases's facility in Hamilton, Mont., say their work with marmosets show the tiny primates do develop illness that mirrors what is seen in humans infected with MERS.

Still, Feldmann — who runs a virology lab at the Hamilton facility — acknowledged there are things about marmosets that make them less than ideal as an animal model.

For one thing, the animals are hard to come by. During the time the lab was doing this research, the price per animal doubled to $5,000. And the primates — which weigh between 250 and 500 grams, on average — are so small the techniques normally used to anesthetize animals before inoculating them don't work.

"They're a little bit ... I wouldn't say dangerous, but they're a little bit tricky to handle in high containment because you ... basically have to catch them unanesthetized. But that's all workable," Feldmann said.

Their small size means as well that it's not feasible to take multiple blood samples, which can be done with a larger animal.

As a result, the research team is suggesting that scientists trying to develop MERS vaccines — work which requires repeated blood analyses — continue to use the rhesus monkeys.

"We're proposing this model for antivirals and drug treatment studies, but the vaccine studies we think are better in the rhesus macaque model because you don't have the issue with the multiple blood samples, which you need," Feldmann said.

Meanwhile, work continues on other options. Next up are pigs, which the group believes will be both a good model for human disease and much cheaper than marmosets.

Since the MERS virus was first discovered in 2012 there have been about 850 cases diagnosed and more than 300 people have died from the disease. All cases have either occurred in or had links to several Middle Eastern countries.