Pathogenicity Studies of NADC34-like Porcine Reproductive and Respiratory Syndrome Virus LNSY-GY and NADC30-like Porcine Reproductive and Respiratory Syndrome Virus GXGG-8011 in Piglets

Abstract

The porcine reproductive and respiratory syndrome virus (PRRSV) has caused significant economic losses to the swine industry. The U.S., China, and Peru have reported NADC30-like or NADC34-like PRRSV-infected piglets, which have been identified as the cause of a significant number of abortions in clinics. Although the pathogenicity of NADC30-like PRRSV and NADC34-like PRRSV in piglets exhibits significant variability globally, studies on their pathogenicity in China are limited. In this study, the animal experiments showed that within 8-14 days post-infection, both piglets infected with NADC30-like PRRSV GXGG-8011 and those infected with NADC34-like PRRSV LNSY-GY exhibited significant weight loss compared to the control piglets. Additionally, the viremia of the LNSY-GY persisted for 28 days, while the viremia of piglets infected with the GXGG-8011 lasted for 17 days. Similarly, the duration of viral shedding through the fecal-oral route after the LNSY-GY infection was longer than that observed after the GXGG-8011 infection. Furthermore, post-infection, both the LNSY-GY and GXGG-8011 led to pronounced histopathological lesions in the lungs of piglets, including interstitial pneumonia and notable viral colonization. However, the antibody production in the LNSY-GY-infected group occurred earlier than that in the GXGG-8011-infected group. Our research findings indicate that LNSY-GY is a mildly pathogenic strain in piglets, whereas we speculate that the GXGG-8011 might be a highly pathogenic strain.

Keywords: NADC30-like; NADC34-like; PRRSV; pathogenicity.

Figure 1

(A) The viral kinetics of the two PRRSV strains used in this study. Sequence alignment and phylogenetic analysis of the PRRSV. Phylogenetic analysis PRRSV based on the Nsp2 (B) and the ORF5 (C) gene. GXGG-8011 labeled with belongs to sublineage 1.8 (NADC30-like), while LNSY-GY labeled with belongs to sublineage 1.5 (NADC34-like).

Figure 2

Sequence alignment of NSP2 proteins. The GXGG-8011 exhibits an identical deletion pattern, as observed in the NADC30-like strains, which encompass 131 amino acids, ranging from aa320–430, aa483, and aa503 to aa521 (111 + 1 + 19), labeled with a red box. The LNSY-GY and NADC34-like PRRSV shared the same 100-aa deletion, labeled with a blue box, corresponding to positions 330–429 in the VR2332 NSP2 protein.

Figure 3

Rectal temperatures, average daily body weights, and oral–fecal detoxification in the experimental piglets. (A) Body temperature changes in piglets infected with the PRRSV. A rectal temperature ≥ 39.5 °C was defined as fever. The mean ± SD (error bars) of temperatures is shown. (B) Mean clinical score during the PRRSV infection. (C) Body weight changes during the PRRSV infection. The body weight gain of piglets was calculated at 7, 14, 21, and 28 dpi. The mean ± SD (error bars) of body weight gain is shown. *, p < 0.05, **, p < 0.01, ***, p < 0.001. ns, no significant difference. (D,E) Virus shedding patterns after the PRRSV infection. PRRSV RNA copies in oral–nasal (D) and fecal of (E) piglets were detected using real-time qPCR.

Figure 4

Viremia examination and serological test analysis. (A) Dynamics of viremia were detected using qPCR. (B) Pig serum was analyzed for PRRSV-specific antibodies. The threshold for seroconversion was set at a sample-to-positive (S/P) ratio of 0.4. (C) Pig serum was analyzed for PRRSV neutralization antibodies. The bars represent the average S/P of one group of piglets. The mean ± SD (error bars) of the specific antibodies is shown.

Figure 5

The pathogenicity of the PRRSV in piglets. Viremia (A) and viral loads in tissues (B) were measured using qPCR. Each bar represents the average for one group of piglets ± SD.

Figure 6

Gross, histological lesions and immunohistochemistry of lungs from the three groups of piglets. (A) Consolidation and ecchymosis in the lungs were compared with those of controls (left panels). Infiltration of inflammatory cells around bronchiole, alveolar septa, and alveolar spaces (middle panels); extensive serous and interstitial pneumonia in the lungs were compared with that of the control (middle panels). Positive brown-red macrophages in the lungs were compared with those of the control (right panels). (B) The difference in average lung gross scores between the lungs of the control and the PRRSV-infected animals was presented. (C) The difference in average interstitial pneumonia scores between the lungs of the control and the PRRSV-infected animals was presented, **, p < 0.01, ***, p < 0.001, ****, p < 0.0001. ns, no significant difference.