| Porcine reproductive and respiratory syndrome(PRRS)is an acute highly contagious disease caused by Porcine reproductive and respiratory syndrome virus(PRRSV),which is characterized by reproductive disorders in sows and respiratory symptoms in piglets.Since1996,when the disease was first reported in China,PRRS has caused huge economic losses to the pig industry in China.In recent years,due to the pressure of prevention and control of African Swine Fever(ASF),some pig farms have reduced or even stopped PRRS vaccination.At the same time,the infection of ASF often leads to frequent empties and recombination of pig herds,and there is a lack of effective monitoring of PRRSV infection status in pig herds.The incidence of PRRS in large-scale pig farms in some areas of Anhui Province has increased.Therefore,understanding the incidence and prevalence pattern of PRRS in large-scale pig farms in the ASF era and mastering the prevalence of strains on the herd will provide theoretical basis and data support for PRRS prevention and control.Based on this,the following work was carried out in this study.1.PRRS serological investigation: In this study,2479 serum samples sent from six PRRS unimmunized pig farms in Bozhou area during 2020-2021 were tested by ELISA and categorized for statistical analysis.The results showed that(1)the PRRS antibody positivity rate in the six pig farms during 2020-2021 ranged from 40% to 93.90%,the antibody level dispersion ranged from 0.54 to 1.23,and the abnormal antibody percentage ranged from 0 to 20.88%.(2)the average PRRS antibody positivity rates from the first quarter to the fourth quarter were 66.99%,64.87%,74.82% and 60.25%,respectively;(3)the average PRRS antibody positivity rates of different litters of sows(first,second,third,fourth and fifth litters and above)were 75.99%,72.22%,48.78%,43.18% and 86.44%respectively;(4)There were some differences in the positive rate of antibody at different stages.The positive rates of sows were the highest in two years(76.06% and 76.25%,respectively),the positive rate of nursery pigs in 2020 was the lowest,and the positive rate of Suckling piglets in 2021 was the lowest(21.93%).2.PRRS pathogenic detection and strain prevalence survey: In order to verify the serological detection results and clarify the prevalence of PRRS infection within each pig farm,fluorescent PCR was used to detect PRRSV antigen in 207 suspected samples which were sent for testing and to sequence and compare the homology of PRRSV ORF5 gene in25 positive samples.The results showed that:(1)in 2020,in total of 58 samples were tested and 9 of them were positive,the annual positivity rate was 15.52%,and the antigen positivity rate of six pig farms ranged from 0 to 21.43%.A total of 149 samples were tested and 44 of them were positive in 2021,the annual positivity rate was 29.53%,and the antigen positivity rate of six pig farms ranged from 0 to 41.30%;(2)There were differences in the detection of antigens in different pig stages,In 2020,the positive antigen detection rate of sows was the highest(19.51%),while no positive antigen was detected in nursery pigs.In 2021,the highest antigen detection rate was 40% in nursery pigs,and no positive antigen was detected in Suckling piglets;(3)The 25 PRRSV strains sequenced were all American variant strains,and the homology with the variant JXA1 strain ranged from 97.2% to 98.4%.The homology between the 25 PRRSV strains was 97.9% to 100%,and the homology between the 25 PRRSV strains was highly homologous.The results showed that:(1)several pig farms under investigation had high and fluctuating antibody levels and a high proportion of abnormal antibodies,indicating the existence of serious PRRS infection;(2)PRRS infection has a certain degree of seasonality,with the lowest infection rate in the second quarter and the highest rate in the third quarter;(3)there were differences in the infection of sows of different gestational ages,with the lowest positive infection rate in sows of low and medium gestational ages and the highest positive infection rate in sows of five litters and above.(4)The sow herd is most susceptible to PRRSV,and the infection status of lactating piglets and nursing piglets is closely related to the sow infection and detoxification status and the PRRS contaminated surface in the farm;(5)The antigen detection results verify the serological findings,and the infection status within each farm is more serious in 2021,and the prevalent strains are all American variant strains and highly homologous to each other.It is presumed that the PRRSV infection in each pig farm is caused by the spread of the same virulent strain. |
PDF Full Text Request