New swine fever culling study undertaken
According to the study, CSF outbreaks can cause enormous losses in smaller pig herds, and finding a way minimise the economic damage and the number of animals culled is essential.
Experts said the baseline of the CSF control strategy in the European Union and Switzerland consists of culling all animals in infected herds. The countries also implement movement restrictions for animals, material and people within a given distance to the infected herd and start epidemiological tracing of transmission contacts.
However, the research revealed that additional disease control measures, such as vaccination or pre-emptive culling, could be a solution to a mass cull in certain scenarios.
The model simulated transmission both within-herds and between-herds and looked at direct and indirect contacts, as well as local area spread. It did this by varying four parameters — control measures, index herd type, detection delay and contact tracing probability — which created 112 “distinct” simulation scenarios.
“Additionally, we studied the influence of initial outbreak conditions on outbreak severity to improve the efficiency of disease prevention and surveillance. A spatial, stochastic, individual-animal-based simulation model, using all registered Swiss pig premises in 2009 (n=9770), was implemented to quantify these relationships,” said the study’s authors.
To assess the impact of scenarios on outbreak severity, daily transmission rates were compared between scenarios. When the results were compared with the current strategy of culling and restricting movement, it was shown that pre-emptive culling and vaccination did not reduce the size of the outbreak or lower the duration.
Researchers said: “Outbreaks starting in a herd with weaning piglets or fattening pigs caused higher losses regarding to the number of culled premises and were longer-lasting than those starting in the two other index herd types. Similarly, larger transmission rates were estimated for these index herd type outbreaks.
“A longer detection delay resulted in more culled premises and longer duration and better transmission tracing increased the number of short outbreaks. Based on the simulation results, baseline control strategies seem sufficient to control CSF in low to medium animal-dense areas. Early detection of outbreaks is crucial and risk-based surveillance should be focused on weaning piglet and fattening pig premises.”