Urban Possum: Friend or Foe?

By Daniela Binder

Brush-tailed possums are now common in Australian urban areas and researchers are looking at whether they could be spreading diseases to humans and livestock.

Brush-tailed possums used to be a common site in the Australian bush. Recently, their populations in the wild have been declining and many are now found in urban areas, showing a remarkable ability to adapt to city life and breed successfully. But for many humans who live close to the possums, they are not the cute and cuddly creatures they appear to be. Rather, they prove to be destructive pests who damage property, trees and vegetable patches. Even more troubling are the claims that possums are spreading disease to humans and livestock. Are possums in fact transmitting diseases to other species?

Disease carriers?

At Macquarie University, in Sydney, Australia, doctoral student Nichola Hill and a team of researchers in the department of marsupial immunology are investigating whether brush-tailed possums could be carrying zoonotic pathogens - disease producing agents that are infectious to both animals and humans. They are studying possums living in the grounds of Sydney’s Taronga Zoo and are screening the possums for a range of these pathogens. There are growing concerns that the increasing urbanisation of wild habitats may facilitate the exchange of diseases between humans and the wildlife that live near urban boundaries.

On four days out of every month, the researchers trap several of the zoo’s 150-180 resident possums. They are scanned to see if they have already been microchipped, and thus previously examined, and faecal samples are collected at the site for later analysis.

The possums are then driven to the veterinary clinic for examination. With the help of a veterinary nurse, they are anaesthetized and their temperature, heart rate, and respiratory rate are noted. Hill also records their weight and size and checks the state of their teeth, often a good indicator of the animal's age.

The possums are then inspected from the outside for injuries and illnesses and hair, blood and faecal samples are collected. Hill delights in finding fleas, ticks, and other parasites on the possums’ coats which she studies under her microscope. Once the animals are examined, they recuperate in separate cages, a necessary condition since possums are very territorial. They are fed apples, bananas, and home-made muesli bars before being released later in the evening in the same place that they were found.

Tracking the diseases

Back in the lab, Hill analyses the data she has collected. By identifying antibodies in the possums’ blood plasma, she can find out which diseases they could be carrying. Hair and faecal samples are viewed under the microscope to identify other potentially harmful microorganisms and external parasites.

Hill has found that possums do carry a range of parasites and pathogens. However, most of them exhibit host-adaptation, which means that the diseases have become suited to possum hosts and would not be able to thrive in humans. The evolutionary divergence of marsupials and humans has left few pathogens that are able to swap hosts and survive. ‘At this stage of my research, I would say that possums are unlikely to act as a reservoir for zoonotic disease in urban areas,’ says Hill.

Sick possums

Ironically, research has shown that possums themselves are prone to catching fatal infections like toxoplasma from domestic cats. ‘Possums have adapted their biology to exploit the higher concentration of resources in urban areas, but there is a flip side in that they have to live in an environment where there is a range of introduced pathogens,’ explains Hill. As the possums have not co-evolved with these pathogens, they often have not developed immune protection, and can die from the infections.

In the future, Hill will track possums with Global Positioning System (GPS) collars to determine the extent of their movement into urban areas. She also hopes to find out how dependent these animals are on human resources of food and shelter. Although possums seem to be at home in urban areas, there is still ground to cover to ensure they survive in the long term. ‘We need to limit the interaction of domestic pets and native fauna by restricting the ranging behaviour of pets at night and doubling our efforts to control feral cat and dog populations,’ Hill says.

About the author:

As part of the World-Wide Day in Science Project 2006, the author, Daniela Binder, an undergraduate in zoology at the University of New South Wales, spent a day with doctoral student Nichola Hill. Binder followed Hill as she trapped and collected data and samples from urban possums living in the grounds of Sydney’s Taronga Zoo.

SOURCE : http://www.firstscience.com