Hidden cancer threat to wildlife revealed

By Catherine Brahic Cancer poses a serious threat to wild animals. That is the message of two pathologists working for the Wildlife Conservation Society, in New York, who have for the first time reviewed the impacts of cancer on wildlife around the world. Conservationists awoke to the problem in the late 1990s when numbers of Tasmanian devils plummeted as a result of the gruesome and disfiguring devil facial tumour disease. The disease causes tumours to form in and around the marsupials’ mouth and they eventually die of starvation (see image: may upset some readers). In 2008, the World Conservation Union listed the Tasmanian devil as endangered. Despite this, “cancer really isn’t something that’s been on anyone’s radar in a conservation sense”, says Denise McAloose, chief pathologist for the WCS‘s global health programme. McAloose and colleague Alisa Newton have gathered together all the known examples of cancer in animals from those published in the scientific literature. Tasmanian devils are by no means the only affected species, and are not the only species to have become endangered because of the disease. Attwater’s prairie chickens (see image) and western barred bandicoots are also in danger of extinction as a result of cancer. Worryingly, when conservation biologists created a captive breeding programme for the Attwater’s prairie chicken in the 1990s in the hopes of saving the species, they discovered that animals in their programmes harboured the cancer-causing viruses. As a result, reintroducing these animals could now contaminate disease-free wild populations. The trouble, say the researchers, is that most wild animals live and die in anonymity. “I would guess that there are untold numbers of species that are threatened by cancer,” says McAloose. For the vast majority of species, the data simply does not exist to say just how big a problem cancer is. In instances, where the data does exist, it can be very worrying. Long-term monitoring of the beluga population in the Gulf of St Lawrence in Canada has revealed that 18 per cent of deaths in this particular population are caused by cancer – making it the second leading cause of death (see image). A further 27 per cent of adult animals that were found dead had tumours. The numbers are even more concerning when compared to human figures: cancer is the second leading cause of human death in the US and is responsible for 23 per cent of all deaths. “Humans and animals aren’t all that different,” says McAloose. This, she argues, introduces a self-serving reason for monitoring cancer in wild animals. “Anything that affects animals may potentially affect humans.” Many animal cancers are triggered or worsened by environmental pollutants. The clean-up of these pollutants benefits humans as well as animals. And understanding the cancers in animals will help understand them better in humans. The pair list 22 species that suffer from viral cancers. While some of the viruses have only been found in wildlife, others are closely related to human viruses, including papilloma virus, herpes simplex virus and hepatitis virus. Journal reference: Nature Reviews Cancer (DOI: 10.1038/nrc2665) More on these topics:
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