A SEROLOGICAL STUDY ON INFECTION PATTERNS, CONTROL AND PERSISTENCE OFCLASSICAL SWINE FEVER IN INFECTED FARMS IN THE PHILIPPINES

In 3 farrow-to-finish farms with enzootic classical swine fever (CSF) all sick pigs were culled and an intensive vaccination programme was i ntroduced. Boars and sows were vaccinated every 6 months and piglets a t the age of 6 and 8 weeks. The infection was monitored on clinical gr ounds and by means of serological examination of the farms. Serologica l results reflected well the clinical situation in the farms. High tit ers and a high percentage of animals with positive titers were observe d in infected farms, compared to lower titers in a clinically ''free'' farm, which were interpreted as titers due to vaccination. Although c linical improvement was noticed, the rigid vaccination regime was not able to control CSF in none of the farms. In all cases, a small percen tage of pigs in the finishing stage was still affected. Since these pi gs seemed not to have responded to vaccination at 6 and 8 weeks of age , the programme was questioned. Additionally, very high titers were re corded in sows from infected farms, which would automatically extend t he period of passive protection in offspring and postpone the age at w hich piglets could be vaccinated. More intensive programmes, which inc lude also vaccination beyond the age of 8 weeks, were suggested to bri ng enzootic infections under control.