# Smart mathematical model prevents the spread of swine fever

NETHERLANDS - Dutch epidemiologists have calculated that partial vaccination can stop outbreaks of swine fever. What's more, mother sows do not need to be vaccinated.
14 April 2003
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The research was carried out at the Institute for Animal Science and Health, Lelystad, and Utrecht University. PhD student Don Klinkenberg calculated that partial vaccinations do not exceed the limit for the outbreak of an epidemic. If the mother sows are not vaccinated, the spread of the swine fever is limited to transfer to less than one pig production unit. Therefore a partial vaccination can successfully control an epidemic of swine fever.

An epidemic of swine fever is only possible if each pig production unit transfers the swine fever virus to an average of more than one other pig production unit. With complete vaccination the transfer of the virus remains under the limit and the epidemic eventually dies out. A disadvantage of complete vaccination is that the spread of the virus cannot be properly monitored. Virus-carrying piglets continue to be born and these form an infection danger for nearby breeding units. These piglets are scarcely detectable because the virus obtained form the mother sow does not respond to normal detection methods.

One possibility for rendering the piglets infected via the mother 'visible', is not to vaccinate the mother sows. The piglets are then 'normally' ill and can therefore be detected.

The researcher's conclusions are based on the mathematical model he developed. That model is valid for areas with an average pig density, relatively many breeding units and a virus of average virulence. The virus is comparable with that present during the epidemic of 1997 and 1998.

The model has calculated that the vaccination takes effect after about a week. Vaccination reduces the spread of the virus but does not completely prevent it. As a result of this the epidemic can still persist for several months. This will partly depend upon how severe the epidemic is when the vaccination takes place.

The question remains as to whether large-scale vaccination will take place in a future epidemic without the need for preventive slaughtering. Risks such as the transfer of the virus from sows to unborn piglets and the fact that the infection can never be completely excluded in vaccinated animals will probably be seen as too big for the further spread of the virus.

The doctoral thesis will be defended on 24 April 2003. Mr Klinkenberg's supervisors are Prof. M.C.M. de Jong and Prof. J.H.M. Verheijden.

Source: Netherlands Organization for Scientific Research - 11th April 2003

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