Dr. Hamish Spencer, a geneticist at the University of Otago, believes some parasites can be beneficial for their hosts. Previous research shows that people infected with internal parasites may suffer less of arthritis and other diseases, as exposure to parasites moderates the immune system - stopping it from attacking beneficial bacteria within our body.
Captive animals are often treated for internal parasites, which, according to Dr. Spencer, may be a mistake, especially if there are plans to reintroduce those animals into the wild.
Some parasites can only be found in one species, or closely-related species. Deparasiting a species may result in the extiction of those parasites. Colpocephalum californici, a feather louse, was driven to extinction when all Californian condors were brought to captivity and deparasited.
Two captive kakapos (Strigops habroptila), critically endangered, flightless birds from New Zealand, were dewormed after they were found to be infected with tapeworms. Although this was done with the best interest of the birds in mind, Dr. Spencer thinks that could have been a mistake, as they could have driven a parasitic species to extinction.
We should, according to Dr. Spencer, stop medicating captive animals without any restrictions, as this may weaken their immune system and jeopardise their chances of survival, if they are ever reintroduced to the wild.