September

• Top publications | September
• Jason A. Galvis, Cesar Corzo, Gustavo Machado

Porcine reproductive and respiratory syndrome virus (PRRSV) continues to cause substantial economic losses for the North American pork industry. Here we developed and parameterized a mathematical model for transmission of PRRSV amongst the swine farms of one U.S. state. The model is tailored by eight modes of between-farm transmission pathways including: farm-to-farm proximity (local transmission), networks comprised of different layers contacts here considered the number of batches of pigs transferred between-farm (pig movements), transportation vehicles used for feed delivery, transferring live pigs to farms and to markets, and personnel (crew), in addition to the quantity of feed with animal by-products within feed ingredients, and finally we also accounted for re-break probabilities for farms with previous PRRSV outbreaks. The model was calibrated on weekly PRRSV outbreaks data. We assessed the role of each transmission pathway considering the dynamics of specific types of production. Our results estimated that the networks formed by transportation vehicles were more densely connected than the actual network of pigs moved between-farms. The model estimated that pig movements and farm proximity were the main route of transmission in the spread of PRRSV regardless of production types, but vehicles transporting pigs to farms explained a large proportion of infections (sow = 17.2%; nursery = 11.7%; and finisher = 29.5%). Animal by-products delivered via feed contributed principally to finisher farms, with a significant impact on PRRSV outbreaks on sow farms. Thus, our results support the consideration of transport vehicles and feed meals in order better to understand the transmission dynamic of PRRSV and establish more robust control strategies.

• Top publications | September
• K. David, K. Dittmar, K. Heenemann, G. Reiner, K. Donat

Saliva samples from chewing ropes are a reliable diagnostic of porcine reproductive and respiratory syndrome virus (PRRSV) infections. The aim of this study was to test whether saliva samples taken with saliva swabs (cotton swabs and GenoTube Livestock) or with chewing ropes are suitable for monitoring PRRSV in unsuspicious farms, this means to detect a prevalence of 20% infected animals with a 95% probability. Saliva samples were collected from 12-16 pens in five pig farms by using a chewing rope for collective samples and by individual saliva swaps from five randomly selected animals per pen. A total of 291 animals from 58 pens in four study farms and 60 animals from 12 pens in one control farm were collected. The samples were taken from all age categories. According to the current monitoring system the analysis of five individual serum samples from the same pens served as the reference method for the relative sensitivity of the saliva samples. Serum and chewing rope samples were tested by ELISA for antibodies. Two different systems were used for the serum samples. Chewing ropes, saliva swabs (GenoTube Livestock) and serum samples were examined for virus genomes using a nested reverse-transcriptase PCR and a commercial real-time reverse-transcriptase PCR kit. Cohen's Kappa was used as a measure of agreement. PRRSV antibodies were detected in the chewing ropes of 44 pens and in the serum samples of only 34 pens. Viral RNA was found in 13 (chewing ropes), respectively 16 pens (serum samples). Saliva swabs (GenoTube Livestock) showed a lower relative sensitivity of 20.00% compared to serum samples. The agreement of the two serum analysis was very good for the ELISAs (κ = 0,911), and moderate for the PCR (κ = 0,706). The comparison of the chewing rope method with the analysis of the serum samples advocates this method as a suitable supplementary monitoring tool in PRRSV unsuspicious pig farms. Easy handling and lower examination costs of the chewing rope method allow higher testing frequency and would therefore improve the monitoring system. However, they are not an alternative to serum samples. Sampling with saliva swabs is unsuitable.

• Top publications | September
• Dengshuai Zhao, Bo Yang, Xingguo Yuan, Chaochao Shen, Dajun Zhang, Xijuan Shi, Ting Zhang, Huimei Cui, Jinke Yang, Xuehui Chen, Yu Hao, Haixue Zheng, Keshan Zhang and Xiangtao Liu

The porcine reproductive and respiratory syndrome virus (PRRSV) is the pathogen causing epidemics of porcine reproductive and respiratory syndrome (PRRS), and is present in every major swine-farming country in the world. Previous studies have demonstrated that PRRSV infection leads to a range of consequences, such as persistent infection, secondary infection, and co-infection, and is common among pigs in the field. In recent years, coinfection of PRRSV and other porcine pathogens has occurred often, making it more difficult to define and diagnose PRRSV-related diseases. The study of coinfections may be extremely suitable for the current prevention and control in the field. However, there is a limited understanding of coinfection. Therefore, in this review, we have focused on the epidemiology of PRRSV coinfection with other pathogens in swine, both in vivo and in vitro.