Comparative pathogenesis of type 1 (European genotype) and type 2 (North American genotype) porcine reproductive and respiratory syndrome virus in infected boar

Abstract

Background: Porcine reproductive and respiratory syndrome virus (PRRSV) now has two main genotypes, genotype 1 (European) and genotype 2 (North American). There is a lack of data on the comparison of pathogenicity of the two genotypes in boars. The objectives of the present study were to evaluate the amount of PRRSV present in semen over time and compare the viral distribution and microscopic lesions of type 1 and type 2 PRRSV-infected boars.

Methods: Twenty-four 8-month-old PRRSV-naïve Duroc boars were randomly allocated to 3 treatment groups. The boars in groups 1 (n = 9) and 2 (n = 9) were intranasally inoculated with type 1 or type 2 PRRSV, respectively. The boars in groups 1 (n = 6) served as negative controls. Semen and blood samples were collected up to 35 days post-inoculation (dpi), and necropsies were performed on 14, 21, and 35 dpi.

Results: There were no significant differences in the genomic copy number of PRRSV, microscopic testicular lesion score, number of PRRSV-positive germ cells, or number of apoptotic cells between the type 1 and type 2 PRRSV-infected boars throughout the experiment. Histopathological changes were manifested by the desquamation of spermatocytes and the presence of multinucleated giant cells in seminiferous tubules of both type 1 and type 2 PRRSV-infected boars. The distribution of PRRSV-positive cells was focal; the virus was found in single germ cells or small clusters of germ cells, localized to the spermatogonia, spermatocytes, spermatids, and non-sperm cells in type 1 and type 2 PRRSV-infected boars.

Conclusions: The results of this study demonstrated that two genotypes of PRRSV do not have significantly different virulence toward the male reproductive system of pigs.

Figure 1

Antibody responses of boars experimentally infected with type 1 and type 2 porcine reproductive and respiratory syndrome virus by the enzyme-linked immunosorbent assay (ELISA; type 1 ■; type 2 □).

Figure 2

Mean values of the genomic copy numbers of porcine reproductive and respiratory syndrome virus (PRRSV) cDNA in serum (type 1 PRRSV, ■ and type 2 PRRSV, ●) and semen (type 1 PRRSV, □ and type 2 PRRSV, ○) samples from experimentally infected boars.

Figure 3

In situ hybridization of testicular tissues from boars experimentally infected with porcine reproductive and respiratory syndrome virus (PRRSV) at 14 days post-inoculation. Type 1 (a) and type 2 (b) PRRSV nucleic acids are detected in spermatocyte (arrow) and spermatogonia (arrowheads).

Figure 4

Immunohistochemistry of semen smear from boars experimentally infected with type 2 porcine reproductive and respiratory syndrome virus (PRRSV) at 14 days post-inoculation. PRRSV antigen is detected in the non-sperm cells (arrow) and spermatocyte (arrowhead).

Figure 5

Mean score for immunohistochemistry of semen smear (spermatogonia, ■; spermatocytes, □; spermatids, ●; and non-sperm cells, ○) in pigs experimentally infected with type 1 (a) and type 2 (b) porcine reproductive and respiratory syndrome virus.

Figure 6

Apoptotic signals are detected in spermatocytes (arrow) and spermatogonia (arrowhead) in boras experimentally infected with type 1 porcine reproductive and respiratory syndrome virus at 14 days post-inoculation.

Figure 7

Phylogenetic analysis of open reading frame 5 of porcine reproductive and respiratory syndrome virus (PRRSV) genome. An unrooted neighbor-joining tree was constructed from aligned nucleic acid sequences of several PRRSV found in GenBank.