Kangaroo disease may hop to humans
5 May 2004
Australia's iconic marsupial,
the kangaroo, has a skin disease that could spread to humans, says a team of
experts.
While the parasitic disease is not severe, it causes kangaroos to develop
skin ulcers, particularly on the ears and tail.
And while the disease in unlikely to be transmitted directly to humans, the
researchers say it may be transmitted via sandflies.
Dr Kerry Rose from the Australian Registry of Wildlife Health at Sydney's
Taronga Zoo led the research, which was published in the latest issue of the
International Journal for Parasitology.
The research, which was a collaboration between Australian and Swiss
scientists, found that red kangaroos were the first animals in Australia to
have this particular type of skin disease, known as cutaneous leishmaniasis.
The disease is caused by a parasite that belongs to a yet-to-be identified
species of the genus Leishmania, a genus that causes a range of diseases in
more than 80 countries around the world.
"This is the first demonstration that this type of [skin disease] parasite
exists in Australia at all," said co-author Dr Emanuela Handman from
Melbourne's Walter and Eliza Hall Institute of Medical Research.
In other countries the disease is passed on by sandflies, she said, and
expects sandflies in Australia could do the same.
Humans could become infected when a sandfly takes a bloody meal from a
kangaroo infected with the parasite. The parasites then develop in the
sandfly's gut. And if the sandfly takes a bite of a second kangaroo, or a
human, they too could be infected.
While rare cases of leishmaniasis have been reported in Australia, these
were from people infected outside the country.
Handman said the researchers had not yet found out if the Leishmania
parasite was native to Australia.
"Whether it's imported or if it has been here for a very long time we don't
know, we are trying to get a grant to find out," she said.
Other forms of leishmaniasis in humans can cause severe illness including
vomiting, fever and diarrhoea, and eventually be fatal. But the skin disease
form, if passed on to humans, would be restricted to ulcers forming around
the site of infection, said Handman.
An ulcer on the tail of a red kangaroo (Walter and Eliza Hall Institute of
Medical Research)
"While normally the Leishmania would infect other animals, if humans happen
to be that area with infected sandflies, then humans may become infected,"
Handman said.
In other parts of the world some species of mammalian Leishmania could
infect humans, while other species, found in guinea pigs, gerbils and
lizards, could not, she said.
To gauge the parasite's potential for infecting other mammals, the
researchers infected mouse cells with the parasites in vitro.
They found that the parasites infected the cells, but only at 33ºC and not
at the normal human body temperature of 37ºC, which surprised the
researchers.
But this did not necessarily rule out infection in humans as human skin
temperature could be less than 37ºC, Handman said.
Handman said the researchers would contact dermatologists to find out if
they had seen ulcers on humans similar to those found on the kangaroos.
But Handman stressed that there was no evidence so far that humans could
become infected.
"At the moment we cannot tell if the parasites from kangaroos are or are not
infectious. Based on what we know in other countries, humans will develop an
ulcer at the site if the parasite is infectious to humans," she said. "But
that's a big if."