There's bad news for city dwellers. Rats are on the move. They're swimming through the sewers and climbing into your ceilings. The creeks where these scientists from Australia's science organisation, CSIRO, are laying traps aren't in the bush or in the back streets of a city they are in suburban Melbourne.

Australia has over 50 species of native rodents, like the Hydromy, a native water rat with its distinctive white bobbed tail. It has webbed feet, making it unlikely to scale your fence and it rarely carries disease. However the introduced Black and Norwegian rats, which travel through the storm water drains and sewers, just love to get into your roof, where they pee and poo, increasing the chance of spreading disease.

"The diseases we are talking is a full range from the parasites, the round worm that occur in the lungs for example, that transfer to humans through to the viruses."

Up till now, only one virus, known to spread from rats to humans has been found in Australia, the LCMV, and it's only been found in mice. According to CSIRO's Dr. Grant Singleton, no other rodent borne viral diseases, found overseas have been detected, but that doesn't mean they're not here. However, there are a number of rodent borne bacterial diseases that have caused health problems in Australia. And his team of rat catchers has been trapping rats in the inner suburbs of Melbourne, to see if they carry any of these diseases.

"If we know the diseases are here then it can help medicos diagnose early and to treat early."

In parts of Asia, the locals face an added problem. There, the rats destroy rice crops. And rice is not only their major food source it's also their livelihood. And the problem doesn't stop after the harvest. There is also the problem of the rats getting into the stored grain.

"In Indonesia annually they lead to seventeen per cent loss of crop production. And if you work out how much rice that is, if we were able to control those rats then there would be enough rice to feed 25 million people."

Dr. Singleton's team has been working with the local farmers to find new ways of dealing with the rats, many of which are different to those found in Australia.

"The farmers cannot afford to spend money on poisons and often they don't know how to use the poisons effectively. So we're trying to develop methods which are extending what farmers do anyway, and using information that we know about the ecology of the species to develop a simple, but effective, and also environmentally friendly methods of control."

One method is to wrap plastic sheeting around a field. The rats get in and can't find their way out again. Inside the field are traps with food in them. Up to 30 rats are sometimes found in the one trap.

So far, by using this method, up to 20 thousand rats have been caught in 2 months. In one area of Indonesia alone, this has meant an increase in crop yields of 12 to 15 per cent.

Controlling rat populations can help prevent the threat of disease in Australia, but in Asia, it could mean the difference between survival and devastation for many communities.

Dr. Grant Singleton
CSIRO Sustainable Ecosystems
P.O. Box 284
Canberra ACT 2601

grant.singleton@csiro.au