Pathological study of the selected thai isolates of porcine reproductive and respiratory syndrome virus and restriction fragment length polymorphism analysis of open reading farme 5

Abstract

The 10 selected Thai isolates of porcine reproductive and respiratory syndrome virus (PRRSV) were amplified at the open reading frame 5 by reverse transcriptase polymerase chain reaction (RT-PCR) and cut with restriction enzymes; M/ul, Hincll, Sacll and Haelll for the US genotype and with Pstl, Haell and Clal in the EU genotype . None of the field isolates had similar cutting pattern to the MLV vaccines. However, several cutting patterns were obtained from those study. The results suggested that genetic variation occurred among the Thai isolates, even within the same genotypes. The variation may cause by the introduction of a new variant into the area or by local evolution. In order to study of the pathogenesis of the Thai isolates , twenty-one PRRSV-free pigs were randomly divided into 3 groups, 3 pigs for negative control group, 9 pigs for 01NP1(US genotype)-infected group and 9 pigs for 02SB3 (EU genotype)-i nfected group. Pigs-infected with the US genotype had more severe clinical signs and lung lesions than those infected with the EU genotype. The lung lesions were observed as early as 5 day post inoculation (dpi) and persisted until 15 dpi. Lymphadenopathy characterized by enlargement of lymph node (2-4x) was seen at all necropsied date but greater at 15 dpi . The non-suppurative encephalitis and non-suppurative myocarditis were seen at 15 dpi only in the US group. Petechial hemorrhage on the renal cortex may be induced by PRRSV. No evidence of classical swine ever or pseudorabies virus was found in those study with virus isolation , PCR or Neutralization test.