A new study suggests that the wolves reintroduced in Yellowstone National Park are facing health risks from mange and viral diseases, thus causing their population decline.

Researchers from Pennsylvania State University studied the wolves pack that were reintroduced in the native habitat in Yellowstone to find out how parasites invade the native species that were introduced again and the impact of the diseases on the animals.

As part of restoring the ecosystem, conservationists across the United States have been indulging in establishing the endangered and threatened native mammals in their natural habitat again in order to increase their population growth. The grey wolves also known as Canis lupus which were removed from at least 48 states in the North American continent during the beginning of the twentieth century, were re-established in the  Northern Rockies in the years 1995 and 1996, according to the study report. 

The research team collected blood samples of the wolves in Yellowstone to monitor if any parasites have invaded the animals and caused deaths. They found that 100 percent of the wolves had at least one infection, except for mange infection which did not spread until 2007, according to a report in phys.org. Mange is a skin infection which makes wolves scratch their back and lose their fur.

Most of the infections that spread first among the wolves were all viral like the contagious virus - canine parvovirus. In 2007, Mange virus caused by scabies mites started infecting the wolves in packs while contacting other mite-infected animals or contacting the mites themselves, according to the researchers.  

"Many invasive species flourish because they lack their native predators and pathogens, but in Yellowstone we restored a native predator to an ecosystem that had other canids (Any of various widely distributed carnivorous mammals of the family canidae, which includes foxes, wolves, dogs, jackals and coyotes) present that were capable of sustaining a lot of infections in their absence," Emily S. Almberg, graduate student in ecology from the Penn State university, said in a statement from the university, according to phys.org.

"It's not terribly surprising that we were able to witness and confirm that there was a relatively short window in which the reintroduced wolves stayed disease-free," she said.

Experts noticed that mange infected one pack of wolves known as Mollie's pack in the park in 2007, but they recovered in 2011. The other pack known as the Druid pack were infected with mange in 2009. However, the Druid pack could not recover as they were infected right during winter, when the wolves lost their fur due to the infection. The infected wolves were exposed to cold temperatures and they froze to death.

According to the researchers, the population of wolves in Yellowstone Park has been seeing several changes. While their population was rapidly increasing between 1995 and 2003, it remained stable from 2003 to 2007.However, data collected from 2007 to 2010 showed a steady decline in the wolves' population.

While the main purpose of restoring the animals to their natives was to increase their population growth, experts involved in this study revealed that the population of wolves is not as stable as it was previously thought. 

The findings of the study are published in the journal Philosophical Transactions of the Royal Society B .