Small mammals are disappearing are town rats spreading disease? Final Report.

Transcription

1 Small mammals are disappearing are town rats spreading disease? Final Report. A report for Kakadu National Park Ref no: K2010/0030 December 2010 Bethany Jackson*, Simon Ward, Stuart Young and John Woinarski Biodiversity Conservation Division, NRETAS, PO Box 496 Palmerston 0831, NT. * Murdoch University (WA) and Auckland Zoo (New Zealand).

2 Summary Small native mammals are disappearing in northern Australia, and we don t know why. At the same time, town rats (also called black rats) are spreading out in the Top End. Town rats came to Australia with Europeans in the last 200 years, and we know they can carry diseases that are new and deadly to Australian animals. Is it possible that the decline of native mammals is because town rats are spreading diseases? This project looked at this question. We caught and tested a total of 97 rats; 23 from Kakadu, 69 from Darwin and 5 from Adelaide River. We killed them and took samples of blood, parasites, genetics and tissue. We chose 6 diseases we thought might be the biggest problems (for people or native mammals) if town rats are carrying them and we sent out samples from all the rats to special laboratories around Australia for analysis. All the tests were negative, which means that none of the town rats were carrying these diseases. This is good news, but disease and town rats may still be problems for Kakadu. Diseases we didn t test for could still be spread by rats to native mammals or people, or these diseases could be spread in other ways. Like most other animals, the rats carried parasites; lice were the most common, and worms in the gut. These can carry new diseases which could be spread when parasites jump from rats to native mammals. We also caught rats in places many 1

3 kilometres from buildings or communities, in native bush. They shouldn t be there and we need action to stop them spreading. The Problem Native small mammals are declining across northern Australia National Parks, Indigenous lands, grazing properties, coastal and inland plains, rocky country and islands. Numbers trapped in 1996, 2001 & 2008 Decline is happening across the north of Australia 2

4 Why are they disappearing? Maybe grazing (cattle, buffalo, horses, donkeys), fire regimes, and feral cats. Maybe disease, but no studies before this one. Town rats carry diseases and may spread them to native animals (and people). Rat diseases that might cause problems: Leishmania skin disease that causes ulcers Hantavirus viral disease that causes fever and nausea, leading to kidney failure Angiostrongylus cantonensis lungworm, also attacks the brain Encephalomyocarditis viral disease that attacks the heart and causes sudden death Trypanosomes parasites that get into your blood and cause various types of diseases Leptospirosis a bacterium that attacks the liver, kidneys and brain 3

5 The Project We trapped for town rats in Kakadu, Darwin, Adelaide River and Kabulwarnamyo. All the town rats we caught were killed and cut open to get samples for disease testing. Places we trapped for town rats a. c. b. Cage traps to catch rats 4

6 Samples: Parts of each town rat taken for disease analyses intestine lung faeces stomach ear tip brain fur kidney spleen liver heart BLOOD glands 5

7 Rats and disease tests Taking a blood sample from a rat under anaesthesia, searching for lice, ticks and mites (orange dots are mites), post-mortem of a rat to take samples from organs, and storage of samples in liquid Nitrogen (c C). We trapped 23 town rats from 2091 trap nights in Kakadu, 5 in Adelaide River (140 trap nights) and 69 in Darwin (747 trap nights) total = 97 rats. The Kakadu rats came from the Mary River area and Black Jungle Springs (see maps page 5). We didn t catch any rats at Kabulwarnamyo (200 trap nights). Samples were sent out to 5 specialist laboratories around Australia for testing. None of the diseases were found in any of the rats. So town rats are probably not currently important in spreading these diseases to native animals or people in the Top End. This is good news! However, other diseases we didn t test for may be contributing to the decline, and rats may still be important carriers if new diseases arrive. The rats we caught were mostly healthy and in good condition. Like most animals they had parasites like lice in the fur and worms in the gut, but not in large numbers likely to cause sickness or death. But these parasites can carry diseases which can spread from rats to native mammals or people. More 6

8 studies of disease in small mammals in northern Australia are needed to look at these questions further. We are concerned that we caught town rats in near-natural bush at Black Jungle Springs, and there are more records of rats in other places in Kakadu. They are obviously spreading. Even if they don t carry diseases they can kill native animals and their eggs or drive them out of these places. We need to control town rats around communities and towns and make sure they don t travel to new areas in our cars, trucks, boats or other gear. Thanks to all the rangers who helped us on this project, and to the TOs for permission to trap on their country. Special thanks to Anne O Dea at HQ for help organising our trapping trips, and to Mick at Mary River Roadhouse and the managers of the tip, Golf Club, ERA Mess, Sports Club, Gagadju Hotel in Jabiru for letting us trap around their properties. Thanks also to the people of Kabulwarnamyo, and everyone who trapped for rats around their houses in Darwin. 7 Dr Bethany Jackson (our Vet) releasing a blackfooted tree-rat (a native mammal in trouble) caught during trapping for town rats.

9 Muscle around gut Middle of gut (lumen) Slices through a worm Lining of gut 1 mm Photo taken with a microscope of a very thin section of the food pipe of a town rat. The 4 round shapes are slices through a parasite worm living in the lining of the food pipe. A near-natural place where town rats should not be, but now live. 8