File photo: A six-month old giant panda cub eats bamboo in an enclosure in Chimelong Safari Park in Guangzhou, China.
(CNN)—A deadly virus has claimed the lives of two of China's beloved giant pandas and left a third in critical condition.
Chinese state media reported this week that veterinarians are using antiviral therapy to treat five-year-old Feng Feng, after medical tests showed serious damage to the panda's heart, liver, kidney and lungs.
Two other pandas -- Chengcheng and Dabao -- have passed away from the canine distemper virus since early December, according to Han Xueli, spokesperson at the Shaanxi Province Rare Wildlife Rescue and Breeding Research Center.
The virus is often fatal for pandas, killing up to 80% of those infected. The research center says it does not know how the infections occurred.
Uphill battle
The caretakers face an uphill battle against the virus, since there often aren't adequate tools available when it comes to treating and preventing panda diseases.
"It's hard on giant pandas, because no companies or research institutions at home produce vaccines that are specially designed for giant pandas. In other words, we can hardly find a vaccine that can give effective protection," Jin Yipeng, associate professor of Veterinary Medicine at China Agriculture University told CCTV, China's state broadcaster.
The Shaanxi center said it's doing what it can to prevent the disease from spreading.
Chinese state media reported that panda breeding centers in neighboring Sichuan province have instituted emergency measures, including enhanced disinfection of panda enclosures and limits on public contact.
China has devoted considerable resources to saving the giant panda, an endangered species that is considered a national treasure.
Scientists have made headway in recent years getting the pandas to breed in captivity and a serious disease outbreak could undermine those efforts.