A combination of two licensed antiviral drugs could be used to treat the deadly Middle East Respiratory Syndrome (MERS) virus that causes an acute respiratory illness in humans and has killed about half of the individuals known to be infected, a US study said Sunday.

The findings, published in the journal Nature Medicine, showed that the combination of the two drugs, known as interferon alpha- 2b (IFN-2b) and ribavirin, "reduces virus replication and improves clinical outcome" in a recently developed monkey model of the MERS virus infection.

The two drugs are routinely used together to treat viral diseases such as hepatitis C, and its combined use has been reported to inhibit replication of MERS virus in cell culture in a previous study, according to the researchers.

Given the current lack of treatment options, the researchers concluded that the combination "should be considered as an early intervention."

In their study, investigators at the National Institutes of Health infected six rhesus macaques with the MERS virus and, eight hours later, treated half of them with the two-drug regimen.

Compared to the untreated animals, the treatment group showed no breathing difficulties and only minimal X-ray evidence of pneumonia, the researchers said.

They also found that the treated animals had lower amounts of virus and less severe tissue damage in the lungs.

These findings lent support to the potential clinical application of the combination for treatment of the MERS virus infection in humans.

"IFN-2b and ribavirin treatment would be expected to provide the greatest benefit early in infection; however, the prolonged disease course in humans suggests the treatment window may be considerably longer," they wrote in their paper.

The researchers were also quick to point out that the rhesus macaque appears to develop only mild to moderate forms of the MERS disease, making it difficult to extrapolate the outcome of this treatment in severe human cases.

"Thus, it is currently unknown whether initiation of treatment upon progression to severe respiratory illness would have any benefit, a situation faced in many acute infectious diseases," they said.

MERS was first described in September 2012 and continues to spread. So far, more than 110 human cases have been reported worldwide while 52 of them have been killed. Presently, there is no effective cure for it.