Doctored gene is new weapon against cholera

Press, 10 January 1983, Page 16

Doctored gene is new weapon against cholera

Cholera affects a quarter of a million people a year and vaccines provide only limited protection.

From

THOMAS LAND

in London

A genetically engineered live vaccine for cholera control is being developed at the London School of Hygiene and Tropical Medicine. The vaccine promises three years immunity to the disease, which is endemic in the Middle East and East Africa. Cholera is a disease of poverty and squalor, 'affecting a quarter of a million people a year and, in the absence of prompt medical treatment, killing up to 90 per cent of the youngest and oldest victims. Cholera outbreaks have been reported recently in the Middle East, Africa, Asia, Central America, Australia and Europe, but public health administrators in many places euphemistically describe the disease as gas-tro-enteritis because of the shame and fear associated with it. Present vaccines provide limited protection. The World Health Organisation considers that mass vaccination programmes are not at present cost-effective. It hopes to attain long-

term protection from the disease through the provision of proper sanitation standards everywhere. That is one of the big objectives of the United Nations current Water Supply and Sanitation Decade.

In the meantime, emphasis is being placed on treatment of the disease, the main danger of which comes from dehydration. Simply replacing lost fluid can save lives.

Genetic engineering in vaccine development, applied by scientists at the London school in association with colleagues at Britain’s Microbiological Research Establishment at Porton Down, Wiltshire, may open an alternative approach. The new vaccine, developed with financial assistance from the Wellcome Foundation and Britain s Medical Research Council, may well be ready within a year. Like a real cholera infection, it would give a

three-year immunity. The mechanism of the disease is still not properly understood. The bacteria produce a two-stage toxin, one of which causes diarrhoea leading to dehydration. Research workers have succeeded in splitting the toxinproducing gene. The next step is to place the doctored gene into the cholera bacterium, inducing it to produce only the harmless part of the toxin, ensuring immunity without ill effects.

That would be a huge improvement on the existing vaccines based on dead bacteria. They provide up to six months protection, but to only about half the people treated.

The new vaccine may take years to develop for largescale application, so improvements in sanitation remain urgently necessary. Copyright — London Observer Service.