Everybody loves giant pandas. But did you know they require special attention to be preserved?
While the Giant panda Saving Program has been very effective (from 2004, the population in the wild and in the captivity increased by 17% and 50%, respectively), another threat became a concern aside from the loss of bamboo habitat due to climate change: a canine distemper virus (CDV).
In 2015, five captive giant pandas died in Shanxi Rare Wildlife Rescue and Breeding Research Center due to CDV. The outbreak started with one panda having convulsions. Over the course of time, four pandas, housed in proximity to the first one, got sick as well, and all five animals turned out to be CDV positive. CDV causes systemic infection with a broad range of symptoms: from respiratory to neurological damage, and viral genome was detected throughout the body (heart, liver, spleen, lungs, kidneys, intestine, and brain). Like measles, which belongs to same virus family, CDV is also highly contagious, since it spreads through aerosol and contact with all body fluids including nasal and ocular secretions, urine, and feces. There is no antiviral treatment available, so quarantine and vaccination are the most important measures to prevent the spread.
Was there a reason for this virus to be that deadly to giant pandas? CDV is known to have a wide host-range (dogs, foxes, raccoons, bears, non-human primates, and large cats). The main viral protein allowing CDV to enter the host cell is hemagglutinin (H) protein also used by the flu. Scientists isolated virus from infected pandas in 2015 and compared it to the isolates from different animals. They found 6 mutations in H protein and suggested one particular mutation that CDV needs to cross the species barrier and to become infectious to not only dogs. This mutation was previously found in CDV infected ferrets, minks, foxes and raccoon dogs and now giant pandas.
Besides the common symptoms of CDV, CDV-infected pandas displayed diarrhea without any specific hints of enteric pathogens. The scientists found a significant change of microbiota composition upon CDV infection: the quantity of symbiotic bacteria normally present in the gut decreased and other bacteria including opportunistic pathogens replaced them. This explained the additional intestinal disorder in CDV-infected pandas. Thus, combining therapeutics to restore the microbiome balance and attenuate the progression of intestinal diseases with antivirals against CDV infection would be the best strategy to cure infected animals.
Even though CDV antivirals are not yet developed, there is one good news: CDV vaccines are available. Nevertheless, the attenuated vaccine used for dogs is considered to be risky, because it contains the infectious virus, but there is a canarypox-vectored CDV vaccine, which only contains some parts of the CDV, and proved to be safe, and has already been introduced in many panda conservation centers. The efficacy of this vaccine proved once more in 2015 outbreak since the only survived panda was previously vaccinated against CDV.
The best approach to safe pandas seems to be the broad vaccination in all the captivity centers but if the pandas get infected, the best treatment could be the combination of antivirals against CDV together with probiotics which maintain the microbiota and thus, prevent other gut-linked diseases.