small mammals are disappearing – are town rats spreading ...€¦ · like most other animals, the...
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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).
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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
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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
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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
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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.
b.
c.
Cage traps to catch rats
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Samples: Parts of each town rat taken for disease analyses
brain
glands
ear tip
heart
liver
spleen
lung
stomach
intestine
faeces
fur
kidney
BLOOD
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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. -200°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
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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.
Dr Bethany Jackson (our Vet) releasing a black-
footed tree-rat (a native mammal in trouble) caught
during trapping for town rats.
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Middle
of gut(lumen)
Lining ofgut
Mu
scle
aro
un
d g
ut
1 mm
Slices through a worm
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.