HUMORAL RESPONSE TO DIFFERENT VACCINATION SCHEMES AGAINST CLASSICAL SWINE FEVER (CSF) SUCCESSIVELY APPLIED DURING AN OUTBREAK OF THE DISEASE

摘要

Vaccination against classical swine fever (CSF) is an essential measure for its control in endemic areas, and the Chinese Strain has been used with success in already disease free countries. Nevertheless the complexity of the factors interacting on the epidemiology and control of CSF, when the expected success is not reached with the vaccination of premises, doubts always fall on the vaccine used and the vaccination scheme applied In consecuences, many changes in vaccination scheme by the breeders are frecuently observed whitout positive influence in CSF control. To clarify the CSF recurrence in a herd vaccinated by a different scheme as the one recommended in the national control program, serological samples were taken to different animal groups in three moments. Sample I, to evaluate the response to the vaccination scheme decided by producers (litters on 5 and 40 days); and samples II and III, to know its behaviour after the implementation of the scheme recommended by official veterinary service (litters at weaning, at 33 days). The presence of titres =1:50 in all litters at 3 days of age (Sample I), indicated that primo-vaccination at 5 days is not correct. The absence of protective titres on 22% of the animals (9/41), belonging to the groups with clinical cases of the disease, at only 23-30 days from the second doses, confirmed that the double vaccination scheme at 5 and 40 days was not correct. Although at 33 days of age a risk of vaccinating in the presence of high titres of passive antibodies (=1:50) in 65% of the pigs was present (Sampling II), it was verified that at 37 post-vaccination days all pigs showed high neutralizing antibodies titres (Sampling III). This result, together with the clinical behaviour and humoral response of pigs on pre- fattening demonstrated that primo-vaccination at 33 days was adequate and contributed to the control of clinical manifestation of the diseases in the herd.