Abstract:

In order to study the pathological changes and the etiological agent of the Swine High Fever Syndrome (SHFS) in central region of Shandong province, we diagnosed the clinical symptoms and the pathological changes of 109 cases in 56 pig farms and collected 363 serum samples from Jan. 2011 to Mar. 2012. Three viruses were detected on tissue samples by histopathological, immunohistochemical examination and RT-PCR or PCR, including classical swine fever virus (CSFV)，porcine reproductive and respiratory syndrome virus (PRRSV), porcine circovirus type 2 (PCV-2). Serological tests were used for detecting prevalence of CSFV，PRRS, and PCV- 2 antibody by ELISA. The results showed that all pigs suffering from high fever had been vaccinated by Classical Swine Fever vaccines, part by Porcine Reproductive and Respiratory Syndrome attenuated live vaccines, but none by Circovirus vaccines. However, they had high positive rates of antibody against CSFV，PRRSV, and PCV-2. The pathological changes mainly included acute inflammation in lymphoid tissues, interstitial pneumonia and viral encephalitis, and the occurrences were respectively 92.3%, 76.1% and 66.1%.The pathogenetic rates of CSFV, PRRSV and PCV2 were respectively 30.27%, 66.97% and 41.28%. Co-infection rates of CSFV and PRRSV, CSFV and PCV2, PRRSV and PCV2 were respectively 16.51%, 6.42% and 28.44%. And the triple infection rate was 4.59%. In addition, other pathogenic infections were 8.26%. Sequence analysis showed that the epidemic strains of CSFV were developing towards being far away from the HCLV, PRRSV strains were highly pathogenic ones, and PCV2 strains were mainly the virulent Type-PCV2b. In conclusion, CSFV, PRRSV and PCV2 were the main pathogens which caused the Swine High Fever in central region of Shandong province, and the severe cases were mainly caused by co-infection. What’s more, mixed infection of Mycoplasma and Haemophilus parasuis used to occur in clinical cases. Therefore, the Swine High Fever in the region was due to multiple infection.