Parasite offers key to a longer life

By SIMON COLLINS

New Zealand scientists have discovered a set of genes in a tiny possum parasite that may help humans to live for up to 2400 years.

The genes allow worms in the possum's small intestine to live for up to a year - while the same worms live outside in the soil for only a matter of days if they do not "switch on" the longevity genes.

Similar genes exist in humans. If they could multiply an 80-year human life as many times as in the possum, it could lead to a life of thousands of years.

Scientists at AgResearch's Wallaceville Research Centre near Wellington found the genes when genetically modifying the worms to create a possum contraceptive.

Team leader Warwick Grant said the genetically modified worms could cut the possum population by 80 per cent by sterilising every possum they infect.

An estimated 5 to 10 per cent of New Zealand's 70 million wild possums are infected with tuberculosis. They infect cattle, and while tuberculosis infected only 0.77 per cent of cattle and deer herds in the year to June, it is the country's costliest animal disease.

The Animal Health Board spent $78 million in the latest year on testing five million cows and deer, trapping and poisoning possums and researching new control methods.

Australian researchers have developed viruses to sterilise pests such as mice, rabbits and foxes, but the NZ scientists realised they could do that with the intestine worm.

"If we can release it - which is a big issue - the advantage is that it establishes itself in the possum itself and you have a permanent reduction in the possum's fertility," Dr Grant said.

His team found the worm had two distinct life phases, hatching in the soil and then deciding whether to switch on its longevity genes.

If there was plenty of food the longevity genes stayed off. The worm matured in about 36 hours, mated, and the female laid about 100 eggs in 24 hours. Both mother and father worm died about 24 hours later.

Dr Grant said the short lifecycle was the best way for the species to multiply.

However, once the food runs out, newly hatched worms choose a different strategy.

They switch on the longevity genes, which allow them to survive on a frugal diet in the soil for a few weeks until they can bore their way through the skin of a possum and find their way to its intestine, where they can live in comfort for up to a year. They continue to breed and their eggs get passed out in the possum's droppings.

"It ensures that the species gets distributed as widely as possible and that new worms get a kick-start by being deposited in a very nutrient-rich environment," Dr Grant said.

"We believe one of the keys to that occurring was this ability to have a short-lived phase where you can reproduce rapidly and a long-lived phase where you can survive for a long time, because you need to be able to maximise your use of two completely different environments. It's pretty unusual to find an organism that can do that."

The Royal Society of New Zealand announced yesterday it had given a $200,000 Marsden grant to allow a Canadian scientist in Dr Grant's team, Susan Stasiuk, to work for the next three years on the implications of the worm's longevity genes for other species, including humans.

She will collaborate with United States laboratories and an Australian biotech company.

Dr Grant said the work was still a long-shot. "If you are putting money into this, from a commercial angle a lotto ticket would be a better idea."* Sixty-nine Marsden grants totalling $33.3 million were announced.

RSNZ