A vaccine for leptospirosis

Press, 26 September 1980, Page 15

A vaccine for leptospirosis

More than one million doses of a new leptospirosis vaccine have been administered to New Zealand sheep and cattle since the animal remedy was launched on the local market a year ago.

The vaccine was developed in England, but all the fieldwork ' before licensing was done over six years bv research workers at Massey University.

Working mainly with cattle, the researchers showed that the vaccine provided considerable protection against the two

most serious strains of leptospirosis in this country. ■ These strains, hardjo and pomona, claim nearly all the human victims of the disease. In the early ■ stages leptospirosis is similar to a bad dose of influenza, but it can develop into severe jaundice. Leptospirosis is most commonly transmitted to humans through disease organisms shed in animal urine — so it was vital to develop a vaccine that prevented this source of infection. Mr Graham Wallace, veterinary services manager for Wellcome NZ, Ltd, distributors of the

vaccine, says the Massey trials showed the vaccine’s effectiveness in eliminating leptospiraes from animal urine.

These trials basically involved exposing vaccinated and non-vaccinated animals to naturally occuring infection.

In one experiment nineteen calves were exposed to infection seven, months after nine had been vaccinated. Organisms of the hardjo strain were isolated from the urine of six out of the ten non-vaccinated animals on eight occasions. No trace of the disease. was found in the vaccinated animals. In another trial it was shown that eight vaccinated cattle, exposed to infection, were still free of the disease up to 42 weeks after their injections.

Mr Wallace s .id the trials also showed that the vaccine causes no side ef-’ fects in animals. This is

because the bacteria cultures used in producing the vaccine are grown on a protein-free medium. Previous vaccines, which have used cultures grown in a protein serum from other animals, have caused allergic reactions.

But Graham Wallace does not hail the vaccine as an overnight saviour for farmers with infected stock. If disease organisms are already being shed, there is no method of suddenly stopping them. But he says. that herds can be effectively immunised if farmers begin treating their younger animals before they pick up any infection.

The recommended dosage is a 2ml sensitiser followed by a 2ml booster a month later. The vaccine is currently produced in a laboratory near London, solely for New Zealand use. It is airfreighted to Auckland in sterile 30-litre containers.

From these containers it is “bulked” in 500-litre tanks in Wellcome’s 1300 sq. m. vaccine unit, ready for packing in 200 ml vac-uum-sealed packs. Samples .are taken for sterility and safety tests to ensure that each batch of the vaccine is safe under New Zealand conditions.

Mr Wallace said it is possible the vaccine will be produced here if the demand is sustained. “It was only envisaged that England keep us going for a limited time.” he said. "But to begin producing the vaccine we would have to make changes at the unit to ensure no risk of con-* lamination to staff handling the disease bacteria.” Even if the vaccine is produced locally it would still have to be sent to Britain for potency testing. “This sophisticated testing is done on hamsters in England,” said Mr Wallace. “They have had years of experience with leptospirosis vaccines over there.” The vaccine is not licensed for use on pigs as yet. but trials are in progress at Massey.

The accompanying article is th’ second in a series supplied by the Tlealth Department on the disease called leptospirosis. which is a hazard for people who work with cattie on dairy farms. In the first article an experiment which is b*>ng carried out this milking season on the Hanraki , Plains was mentioned. It -is looking into how a new vaccine against the disease administered to cattle affects the incidence of the diseas° in human beings. Today’s article talks about the vaccine itself.