Among the lessons learned by the pig breeding and respiratory syndrome virus (PRRSV) to pig farmers and veterinarians, viruses that continue to evolve and produce multiple lineages and have huge differences are one of them. But better understanding of this genetic diversity - how this virus evolves, spreads and maintains itself in the pigs is the next step in fighting the disease.
" Pig Reproductive and Respiratory Syndrome Virus (PRRSV) is one of the most diverse viruses at present," Kim VanderWaal, PhD, assistant professor in the Department of Population Veterinary Medicine at the University of Minnesota, told Pig Health Today. " The diversity of this virus is a result of recombination and genetic drift. The latter is just the slow accumulation of mutations in the virus and the selection pressure to change so that it can spread more smoothly in the pig herd."
Since the virus was first discovered in the United States in the late 1980s, VanderWaal said that the genetic diversity of PRRSV type 2 (PRRSV North American version) has increased by about 20%. In fact, PRRSV follows a common model, that is, an important new type or strain will appear in every 3 to 5 years. The most recent happened in 2014.
To further study PRRSV, researchers from the University of Minnesota School of Veterinary Medicine and the University of Edinburgh Roslin Institute launched a four-year collaborative project (project funding reached $3 million), with Vander Waal as the project leader.
"PRRS is not a problem unique to the United States," she said. Although PRRSV causes more than $560 million to the U.S. pork industry every year, it is also dragging down pork production areas in Europe and Asia. Having two university scientists’ broad foundation in viral expertise and experience can bring special advantages.
"We will continue to analyze the changing trends at the industry's herd level through in vitro and in vivo experimental studies, and respond to the evolutionary problems of PRRSV through different dimensions," Vander Waal said.
Explore new concept
Among the tools that researchers will use, there is a concept named Multi-strain Kinetics . This concept has been used in medicine to deal with problems such as human influenza, but the exploration of this concept in the field of veterinary medicine is still very limited. However, as abundant data have been accumulated in the pig production system, it is possible to better understand the possibility of multi-strain dynamics through pig research, VanderWaal pointed out.
For example, researchers can identify the location of the farm and track how animals move between farms. However, as important virus sequencing has been completed, scientists have mastered information on when and where PRRSV occurs.
For researchers at the University of Minnesota, the Morrison Swine Health Monitoring Program (MSHMP) database (tracking PRRSVs in about 50% of pig breeding populations in the United States) and the Veterinary Diagnostic Laboratory (VDL) (which can trace genetic data of the prevalent virus to more than 20 years ago) are obvious advantages. Cesar Corzo, coordinator of Morrison’s swine health monitoring program, and Albert Rovira, assistant director of the Veterinary Diagnostic Laboratory, are members of the project team.
Although some of the research is to evaluate how viruses adapt, evolve and spread, another part of the research is to further understand the role played by host immunity. In theory, the most influential PRRSV strain at any given time point is determined by the immunity of the host population, VanderWaal said. Therefore, viruses with significantly different viruses encountered by and pig herds may experience more successful transmission.
"We want to examine the behavioral changes of these different viral lineages over a period of time. Understanding how different viral lineages interact and how they compete with each other may help us recognize and be able to better predict the next steps of the virus," she added.
End-up Battle
The genetic data generated by this cooperative research can be used to guide further vaccine development. It is also expected to bring benefits in diagnostic aspects.Declan Schroeder, a virology expert at the University of Minnesota, is also a member of the research team of this project. A new technology has been developed by the laboratory he led to can draw a complete map of a genomic strain of PRRSV within 24 hours of sampling. This will provide veterinarians with an effective tool to quickly detect PRRSV infection in pigs.
When the project ended its four-year period, VanderWaal hoped to better understand how PRRSV evolved and adapted to immunity at the individual host and population levels. "We want to know how these factors interact and predict the susceptibility of the herd to different PRRSV strains and develop corresponding coping strategies," she said.
Finally, our final battle is to help pig manufacturers and veterinarians defeat PRRSV.
