July and August, 1999

PRRS collaborative investigative study

Joseph F. Connor, DVM

This report is not refereed.

In the fall of 1996, producers and veterinarians began to note severe abortion storms, sow death loss, and increased preweaning mortality in herds. The early clinical diagnosis was suggestive of porcine reproductive and respiratory syndrome (PRRS). However, the severity of the clinical episodes and the occurrence in herds that were already positive to PRRS made practitioners wonder whether this was PRRS or a new agent. If this was PRRS, then either a more virulent strain had evolved or confounding agents or conditions had changed that exacerbated the clinical outbreaks. The acute clinical episodes were initially identified in southeast Iowa, but soon reports of episodes came from other areas. These outbreaks motivated a collaborative study involving the AASP, National Pork Producers Council (NPPC), herd veterinarians, USDA:APHIS, university researchers, diagnostic laboratories, and allied industry. The AASP and NPPC agreed to partially fund the private herd veterinarians who participated on a herd-by-herd basis. The USDA participated in the funding by providing personnel and supporting diagnostics.

The objectives of the project were to:

  • complete an epidemiological study that would identify the agent or agents,
  • complete an epidemiological study that would evaluate risk factors contributing to a clinical outbreak,
  • involve herd veterinarians as part of the information collecting body,
  • use the epidemiological study to educate herd veterinarians in proper disease investigation, and
  • analyze the results and disseminate the data to participants in the pork industry.

What have we learned for the future?

  • An investigative study requires cooperation and coordination by many parties, including producers, herd veterinarians, the AASP, the NPPC, USDA:APHIS, diagnostic laboratories, and university researchers.
  • A working group must be convened immediately and delegation of responsibilities completed. Time delays can critically sabotage defining the problem and identifying control interventions.
  • An epidemiological study must be developed. Establishing selection criteria is difficult, but critical. Selection criteria that are too sensitive will exhaust the system, whereas selection criteria that are insensitive will delay the entire process.
  • Technical teams must direct selection of the most appropriate diagnostic method based on preliminary diagnostics. Numerous techniques must be used to rule out new agents. Diagnostic teams and/or herd veterinarians must be directed in proper sample collection, packaging, and submission.
  • Good initial sample collection and the initial investigation may be more critical than the summary study and diagnostics.
  • Herd veterinarians are in a unique situation to help the producer understand and correctly respond to an epidemiological survey. Herd veterinarians need compensation.
  • Information has to be collected from the database and disseminated electronically to participants. A person or persons needs to be identified to update this information in real time. The investigative group must analyze the preliminary information in real time and adjust the investigation.
  • Anonymity of both the practitioner and producer is crucial to participation.
  • Information dissemination must be timely and accurate in the context of solving the immediate problem. Information will affect markets and movement of animals. An initial, intermediate, and final report should be completed.
  • Financial reserves need to be in place to pay for an immediate investigative study.
  • Financial resources must be available to implement control measures or eliminate livestock, including depopulation if needed.
  • The epidemiological study of risk factors should be completed even if conclusive identification of an agent is completed early in the study.
  • Emergency management modeling of disease threats should be ongoing.

A perfect example of disease impact on the pork industry occurred recently. There was a disease outbreak in Malaysia in pigs and people associated with pigs. The disease, which was originally thought to be Japanese B encephalitis, was later identified as a Hendra-like virus and is now named Nipah virus.
To date, nearly 100 people have died and over 900,000 pigs have been destroyed.

In summary, the acute PRRS project provided an excellent blueprint for cooperation in investigating a field disease outbreak. The investigation allowed herd veterinarians to participate and resulted in an excellent opportunity for education and training in an epidemiological study. This education will be vital for the pork industry, because we will have an outbreak of a new disease in the United States. The participants are to be highly commended for their efforts and persistence.