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When cryptosporidium gives us the runs


Cryptosporidium oocyst: dead or alive? (Image: Lawrence Berkeley Natl Lab/C Petersen, UCSF)

Scientists will be better able to tell when water contaminated with the cryptosporidium parasite is really a hazard to health, new Australian research suggests.

A simpler way of growing cryptosporidium in the laboratory means that parasitologists can rapidly culture its oocysts and if they hatch, scientists can test which species is involved to see if it is harmful.

Dr Nawal Hijjawi, a post-doctoral research fellow at Murdoch University in Perth, published her work in the current issue of the International Journal for Parasitology.

The new method will allow scientists to more easily distinguish between live cryptosporidium oocysts, which causes diarrhoea and can kill people with a weak immune system, and dead oocysts, which don't.

The ability to quickly and accurately distinguish between live and dead oocysts was an issue in Sydney in 1998, when residents were advised to boil drinking water after oocysts were found in the water supply.

But no-one was infected and an inquiry concluded that many of the oocysts that prompted the public health scare may in fact have been dead.

Hijjawi's team was the first to grow the microscopic protozoan in the lab without using host cells, a difficult method that doesn't produce many parasites.

Scientists may one-day also test candidate drugs against cryptosporidium cultured in the lab using her new method.

Vaccinating cattle against crypto

Co-author Professor Andrew Thompson said cryptosporidium was a major cause of diarrhoeal disease, particularly in humans and livestock.

So, he said another outcome from the research may be the development of a vaccine to protect cattle from the parasite.

Thompson said the research also questioned what we know of cryptosporidium's lifecycle.

Hijjawi found cryptosporidium has several additional phases when it can live outside the host cell and may infect water. Because the parasite can spend its entire lifecycle outside of cells, she said its classification should be revised.

The research, which was funded by the Australian Research Council and Sydney Water, has attracted interest from the UK, China, India, Iran, Egypt and other countries.

The UK and US are among countries whose water supplies have been contaminated by cryptosporidium. The largest outbreak left 400,000 people ill in Milwaukee in 1993.

Tags: environment, health, zoology