Medycyna Wet. 63 (12), 1515-1518, 2007
Truszczyński M., Pejsak Z.
Virus properties and immunity against PRRS
Special attention in this review is given to published work on genetic, antigenic and pathogenic variations of the virus of porcine reproductive and respiratory syndrome (PRRS) and the potential implications of these properties for vaccine efficacy. Genomic organization of type 1 and type 2 strains of the PRRS virus is presented: the former being the representative of the European strains and the latter of the North American isolates. Among the European isolates 4 subtypes are differentiated. More homogenous are the strains of the Northern American type. Despite very high differences in antigenic properties of both European and North American isolates, it is possible to differentiate them, using serological methods, particularly the immunofluorescence test. The ELISA test proved to be useful in diagnosis of PRRS. However, antigens of the PRRS virus are of no use in the selection of strains for vaccine production. The high degree of variation among PRRS virus isolates is also demonstrated in pathogenic properties. Generally, the heterogeneity of genetic, antigenic and pathogenic properties, being a continuous process, is the explanation for the persistent infections resulting from the selection of mutants that escape neutralizing antibodies or cytotoxic T lymphocytes. Because of the heterogeneity of the mentioned biological properties of the field strains, the immunoprophylactic value of the available vaccines is not high. Better results are obtained when live, attenuated vaccines are used. In relation to this topic the proposition of Mengeling, called SWINE, is presented. The first letter means sensitization of the pig by vaccine injection; the second letter means waiting for more than several weeks until the level of neutralizing antibodies reaches low values; the letter I means immunization; N means neutralization of the virus; the letter E means eradication, in other words the elimination of PRRS. The last step must be supported by biosecurity and additional veterinary measures. Another method of immunoprophylaxis is the vaccination of pigs introduced to a herd using viremic serum of pigs of the same herd, which provides the best homogeneity of immunity and the highest efficacy.
Keywords: PRRSV, viruses