A breakthrough study by the University of Hong Kong has found two existing drugs offer the best hope of beating the Middle East respiratory syndrome (Mers) coronavirus that has claimed hundreds of lives globally since its emergence three years ago. The two medicines, which are now being used to treat HIV and sclerosis, have proven to be effective in curing Mers-infected marmosets, palm-size monkeys that are considered the best animal models to study the virus. The research is the first in the world to use the monkeys to confirm the efficacy of these two drugs against Mers, with no other viable treatments immediately available. "We would recommend doctors to start using both drugs immediately to treat Mers patients if they are critical," said Jasper Chan Fuk-woo, clinical assistant professor in microbiology at HKU. "The evidence in this study is quite strong in proving the effectiveness of these two drugs." Also in Chan's team was Professor Yuen Kwok-yung, head of the microbiology department, who is well known for his work in fighting the outbreak of severe acute respiratory syndrome (Sars) in 2003. Although a number of commercially available drugs were previously proven to be highly effective against Mers in cell culture, they were never tested on animals as it was difficult to find a mammal that would suffer a similar severity of infection as humans. Mice, hamsters and other types of monkeys were either not infected by Mers or recovered very quickly from the virus, making it difficult for researchers to advance their studies, Chan said. Last year a US study identified the marmoset as the best animal model to carry out the research as cases closely mimicked Mers infections in humans. READ MORE: South Korea declares Mers outbreak is over as last patient undergoes treatment for deadly virus The species, which is one of the smallest monkeys in the world, is hard to come by and very delicate to handle. But the HKU team, with the help of the Chinese Academy of Medical Sciences, was able to obtain 12 marmosets from the mainland. Yuen said his team found that those animals treated with the two drugs, namely lopinavir with ritonavir and a type of interferon, had much better outcomes than the untreated animals. Marmosets that were treated with either medicine were much less symptomatic and had fewer chest X-ray abnormalities, lower viral loads and better survival rates, Yuen said. "Our future work includes evaluating combination treatment of these drugs in representative animal models and developing other new specific antiviral drugs for Mers," he said. "Both drugs are currently commercially available and have well-known side-effect profiles and dosing regimens. These properties would facilitate their use in patients with Mers." The paper explained the study aimed to find immediately available treatment for Mers before methods that were currently under research - namely, novel agents and convalescent-phase plasma therapy - became available. Mild side effects such as gastrointestinal upsets, hypersensitivity and liver dysfunction had been observed in patients who took the two drugs to treat other diseases. Chan believed the two medicines could now be used together to treat Mers patients as an experimental drug as long as the doctor gained the patient's consent. As of Monday, South Korea had not reported any new Mers cases for 22 consecutive days, and no deaths for 16 days. Only one suspected case was reported in Hong Kong yesterday, but the patient tested negative for the virus.