Study on Virulence of PRRS Virus Strain Hua 02 Isolated in North Vietnam in Piglets

Abstract

      In this study, we investigated the virulence and pathogenicity of porcine reproductive and respiratory syndrome virus (PRRSV) strain HUA 02 in 8-weeks old PRRSV antibody-negative pigs. Experimental pigs were intranasally inoculated with a dose of TCID₅₀ 1,74x10⁶/25 μl (2 ml/pig). After inoculation, the pigs were recorded for clinical signs,

virus replication in the blood, and macroscopic and microscopic lesions of some tissues for 21 days post inoculation. The results demonstrated that pigs infected with PRRS HUA 02 virus strain had clinical signs and symptoms of moodiness, fatigue, anorexia, high fever, rapid breathing, dyspnea, skin rash and constipation. Reverse transcription PCR (RT-PCR) results revealed the presence of PRRS HUA 02 virus strain in the blood and nasal swabs of infected pigs at 3 and 5 days post inoculation, respectively. Similarly, the viral load in serum quantified by Realtime PCR showed that the PRRSV loads were recorded in the serum at 3 days post infection, and reached highest level in all infected pigs at 9 days post infection. Macroscopic lesions consistently observed included lung inflammation, congestion, hemorrhage and interstitial pneumonia and kidneys with spotting hemorrhage. In lung the lymph nodes were characterized by swelling and hematoma, and in pericardium with hydropericarditis of pigs infected with PRRS HUA 02 virus strain. The microscopic lesions were observed mainly in lungs with bronchoalveolar inflammation, haemorrhagic lymph nodes, and hemorrhagic glomeruli. The results of our study showed that the PRRSV HUA 02 is capable of causing severe disease in pigs with clinical signs, symptoms, macroscopic and microscopic lesions similar to those of highly-pathogenic PRRS virus strain observed previously in North Vietnam.