Genetic Diversity (orf5) of Prrsv Isolates from a Herd with Sams

Introduction Severe epidemic of sow abortion and sow mortality firstly appeared in the USA in the last quarter of 1996 (1). Clinical episodes (first referred to as sow abortion and mortality syndrome [SAMS]) typically lasted 1 to 5 weeks and were characterized by an high rate of abortion and a sow mortality. The severity of acute PRRS episodes raised the suspicion that a new disease had emerged in the US swine population. It was soon discovered, however, that the sydrome was actually a severe form of PRRS caused by a highly virulent North American strain of PRRS virus (PRRSV). Two viral genotype have been described for PRRS: American and European. The PRRS genome is about 15 kb in length and contains 8 ORFs. Six PRRSV structural proteins, designed GP2, GP3, GP4, GP5, M and N, have been identified and found to be encoded by ORF2 to ORF7. The major viral glycoprotein, GP5, contains immunologically important domains associated with virus neutralisation (2). Several studies have described a high degree of antigenic and genetic diversity between American and European PRRSV isolates. GP5 has been found to be the most variable protein, with only 51-55% aminoacid sequence identity between American and European isolates (3). ORF5 also shows the highest degree of diversity within one gentotype (4). Different clusters of EU strains can coexist in the same herd (5). This fact is of major relevance for the design of vaccines, as these variations could potentially affect their efficacy under field conditions. In this paper, we present the results of ORF5 genetic analysis of PRRSV isolated from a herd affected by SAMS.