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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.
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