The snake harmers

August 13, 1999

A primitive, single-celled blood parasite could be the answer to a Pacific island's prayers, potentially ridding it of a snake plague.

Scientists at the University of Queensland in Brisbane have found a parasite that they believe may be an effective biological control for brown tree snakes, which, since their accidental introduction some 50 years ago, have turned the Pacific island of Guam into a snake hotspot. The snake population, estimated at 5,000 per square kilometre, has decimated the native bird population, bitten humans, frightened tourists and caused electricity blackouts by winding themselves around power lines.

Fears that they may now spread from Guam to other islands such as Hawaii mean the race is on to find an effective control. Currently, the best eradication programme is chopping off the snakes' heads with machetes.

A grant from the US Department of Agriculture has enabled Australian researchers to survey the blood and faecal parasites infecting brown tree snakes in their native ranges in Australia, Papua New Guinea and the Solomon Islands, comparing them with those parasites found in the snakes on Guam. While researchers found that brown tree snakes had a relatively high incidence of parasitic infection in native habitats, those on Guam had few parasites or pathogens.

The Queensland researchers found that several non-Guam snakes in very poor health had high levels of parasites in their red blood cells. They identified the invaders as primitive haemo-gregarine parasites, which spend several sexual stages in the blood, from where they can be transported from one host to another by blood-sucking invertebrates.

Peter O'Donoghue, senior lecturer in the microbiology and parasitology department of Queensland University, says that before moving to the blood, the parasites "go beserk, reproducing in the lungs and liver and appearing to cause hepatitis and pneumonia-like diseases in the snakes". For some snakes, the infections are fatal.

The scientists have not found a similar parasite in Guam snakes, but are yet to determine whether the parasites are species-specific, only occurring in native-range brown tree snakes.

"The last thing we want is for a non--species-specific parasite to infect other reptiles on Guam and cause a biological disaster," explains Dr O'Donoghue. He and his co-researcher Joan Whittier are DNA sequencing the parasite found in native-range brown tree snakes to check it is a different species to parasites found in other reptiles. If it is, the next stage will be to try to find out how the parasite is transmitted from one snake to another.

"Then we will have to start looking at invertebrate vectors, such as mosquitoes and ticks, to see if they are carrying parasite DNA," explains Dr O' Donoghue, stressing that the research is still in its early days.

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