Foreign or emerging animal diseases: The practical role of the swine veterinarian and the veterinary diagnostic laboratory
David H. Zeman, DVM, PhD, Diplomate ACVP
DHZ: Animal Disease Research and Diagnostic Laboratory, South Dakota State University, Brookings, SD 57007. E-mail: email@example.com.
Zeman DH. Foreign or emerging animal diseases: The practical role of the swine veterinarian and the veterinary diagnostic laboratory. J Swine Health Prod. 2002;10(3):129-131.
The previous four Diagnostic notes columns featured in-depth articles on foreign swine diseases. Two featured foreign animal diseases (FADs) have been long-time scourges of the swine industry worldwide: foot-and-mouth disease (FMD) and hog cholera (commonly referred to as classical swine fever outside the United States). Two other featured diseases are newly emerging, but, as yet, are foreign to swine in North America: Nipah virus disease and porcine epidemic diarrhea. AlthoughUS and Canadian swine veterinarians hope never to see these diseases, the risks for introduction have never been higher.
The Office International des Epizooties (OIE) in Paris, France, is recognized by the World Trade Organization as the official body for determining animal health standards relative to international trade. The OIE, which has 155 member countries, attempts to track and report disease status of select diseases around the world, and maintains two lists of diseases for reporting purposes. List A diseases are highly contagious, serious diseases (Table 1) that have a major impact on the trading of animals and animal products. Consequences include exportation embargos, which rapidly exert negative effects on industries with no warning, quickly escalating into multimillion-dollar losses that have the greatest impact on producers. In this concluding articleof the foreign disease series, I will focus on some themes common to FADs and discuss the practical role of the swine practitioner and the veterinary diagnostic laboratory in preventing an FAD incursion.
How will foreign swine diseases enter your practice area?
The accidental introduction of FAD could occur as a result of introduction of live animals,contaminated animal products, or appropriate insect vectors from infected parts of the world, or humans returning from these areas. Live animal introductions include breeding stock, zoo and exotic animal collections, pets, or wildlife that are free to roam across international boundaries. Live animals are especially of concern because of the common potential to harbor infections silently or shed infectious agents sporadically. Imported contaminated animal products (such as meat, semen, embryos, fiber, and leather) provide another potential mechanism for FAD entry. Contaminated human food products may find their way back into the animal food chain (for example, through garbage feeding) and have been blamed for many FAD outbreaks worldwide. The increased volume of air-passenger traffic in recent decades has increasedthe opportunity for visitors or returning citizens to bring contaminated animal products in their luggage. Currently, ports of entry do not have the manpower to search every piece of luggage to detect banned products. Likewise, mail, parcel services, and air or water freight representopportunities for large volumes of animal products to enter the country.
The potential malicious introduction of a foreign animal disease presents even more challenges for the practitioner. Malicious opportunities are limited only by the imaginations of those who wish to harm American agricultural production. Therefore, listing multiple ways that this might occur will serve no purpose and may fuel ideas for agricultural adversaries. In this current climate of increased potential for malicious activity, practitioners must be as vigilant as possible and should assume that any disease is possible on any farm at any time.
"Red flags" regarding FAD entry potential
- The client has recently imported animals (swine or other species).
- The client has recently imported animal products (semen, embryos).
- The client or farm workers have recently visited other countries.
- The client feeds garbage or other waste or by-product feeds.
- Suspicious people or activities are reported around farm sites.
What will FAD look like in your client's herd?
Foreign animal diseases may present in a variety of ways and, of course, the clinical presentation and lesions will be highly dependenton the agent or agents involved. First, FAD may clinically mimic some commonly occurring diseases. Peracute and acute viremic or bacteremic diseases often present with sudden death and minimal clinical signs. It would be natural to initially suspect common endemic diseases in these situations, such as salmonellosis or erysipelas, or even a toxicosis. Likewise, postmortem examinations may reveal lesions,but very few postmortem lesions are pathognomonic. The FAD may be one that does not immediately cause death or primary lesions, but instead promotes the opportunityfor common secondary infections. An excellent example was the increased incidence of bacterial pneumonia due to Streptococcus suis and Haemophilus parasuis that occurred in nursery pigs when porcine reproductive and respiratory virus (PRRSV) first appeared in North America. It was not until producers and practitioners recognized that the incidence of those common bacterial pneumonias was unusual that a potential underlying new agent was considered as the primary cause. Hence, the potential for delay before consideration of an FAD may be great. Therefore, the key to early detection is to be alert for any unexplained situation that is unusualfor the client's operation.
Alternatively, the FAD may be one that presents unique clinical signs and lesions. For example, any vesicular disease should be an immediate cause for concern and, of course, demands immediate action (Table 2). Likewise, unexplained high morbidity and high mortality should be investigated further. Foreign diseases with unique clinical signs and lesions will tend to automatically trigger suspicion and will most likely be thoroughly and promptly investigated.
"Red flags" regarding FAD clinical or pathological expression
- Unexplained abnormalities for an individual herd.
- Similar unexplained abnormalities in multiple herds in the same area.
- Unexplained high morbidity and high mortality outbreaks.
- Unique clinical or pathological lesions, such as vesicular lesions.
What should the swine practitioner do when an FAD is suspected?
State Veterinarians in each state and the Federal Area Veterinarian in Charge (AVIC) are responsible for managing disease outbreaks in states and specific regions of the country, respectively. These regulatory health officials have the authority to monitor, interpret, and act when necessary. This authority includes ordering additional testing or prohibiting animal movement and establishing quarantine zones. Working closely and precisely with these regulatory officials is crucial to the nation's ability to quickly detect a potential FAD outbreak. If there is strong suspicion of an FAD outbreak in a client's herd, your first calls should be to the State Veterinarian and the AVIC. They will then guide you through the appropriate protocols for confirming or disproving the suspected FAD. This ideal sequence of events is attainable for diseases with unique clinical or pathological presentations (such as the vesiculardiseases) or for diseases with suddenonset of high morbidity and high mortality.
Unfortunately, from a practical perspective, an FAD may first be confused with a common endemic disease, or with an unusual manifestation of a common disease (eg, a syndrome caused by a particularly severe strain of a common domestic disease). In these situations, it is highly likely that the field veterinarian has already sent diagnostic specimens to the state veterinary diagnostic laboratory for routine diagnostic test procedures. Since many diagnostic tests are highly disease specific (eg, fluorescent antibody, serology, molecular diagnostics, and immunohistochemistry), there is no guarantee that the veterinary diagnostic laboratory will identify the FAD at this stage of the investigation. In fact, secondary diseases may be detected first, producing a false sense of assurance that the problem has been correctly diagnosed and categorized as an unusual domestic disease event. This is even more likely to happen when samples are submitted with poor descriptions of clinical and epidemiological findings. Therefore, it is crucial that detailed and accurate histories, clinical syndromes, and necropsy findings be clearly communicated on the submission form. Even better, a telephone call to the diagnostic laboratory before the samples are collected may serve multiple purposes by sensitizing the diagnostician to your client's unusual clinical disease syndrome. This may result in more specific recommendations for ruling out unusual diseases. It may also be necessary for the field veterinarian to make additional visits to the premise to compile more in-depth histories or to collect environmental specimens. Furthermore,if the samples submitted do not result in a diagnosis that satisfactorily explains the syndrome, close communication is more likely to stimulate the laboratory diagnosticians to recommend submission of additional specimens or live animals, or to prompt a decision for an FAD-diagnostician site visit.
High quality communication efforts will hopefully result in a faster diagnosis. When several submissions arrive at the laboratory over several days or weeks with inadequate submission data, they may be assigned to different diagnosticians who are not aware that they are dealing with an unusual disease outbreak. The animal owner must communicate well with the practitioner, and the practitioner must communicate well with the diagnostician, if the outbreak investigation is failing to provide a diagnosis.
To summarize, whenever highly suspicious of FAD, the swine practitioner should immediately contact the State Veterinarian and the federal AVIC. Whenever, a disease investigation is not resulting in satisfactory test results (satisfactory relative to readily explaining the clinical syndrome), the veterinary practitioner should begin a dialogue with laboratory diagnosticians, regulators, or both, and aggressively pursue additional testing until the case is satisfactorily explained by definitive diagnostic results.
"Red flags" during a diagnostic investigation
- Highly unusual clinical syndrome and clinical signs.
- Highly unusual pathological lesions.
- Diagnostic results that do not satisfactorily explain the clinical syndrome.
- Similar syndromes are seen in other client herds in the same area.
What can the swine practitioner and producer do to be proactive relative to FAD?
The efforts of the United States Department of Agriculture to keep FAD out of the United States have recently been evaluated via a process called the Animal Health Safeguarding Review. This effort utilized a broad variety of national experts, was coordinated by the National Association of State Departments of Agriculture, and can be seen at www.nasda-hq.org. Many recommendations of the safeguarding review are already being implemented, but many others will take years to initiate and even more time to become effective. Initiatives such as this are very important, but must be complemented by individual proactive preventative measures tailored to each individual production system.
Swine practitioners have been promoting biosecurity for prevention of many economically important swine diseases for decades.The importance of biosecurity today is magnified to new heights. Biosecurity is no longer just an optional management practice to be considered for adoption by progressive producers, but is now an absolute necessity for every serious swine producer. Furthermore, the intensity and sophistication of our biosecurity protocols must match the changes in modern production systems. Biosecurity efforts are confounded by the complexity of many integrated units and the sheer numbers of animals involved. Although this may seem daunting, there is also good news, since diagnostic technologies continue to improve test sensitivity, specificity, and time to results. Many excellent articles have been written on the subject since the recent FMD outbreak in Great Britain. Designing farm-specific standard operating procedures (SOPs) for biosecurity should be a high priority for every producer and is best accomplished in conjunction with the herd veterinarian. Biosecurity SOPs must also include provisions to test effectiveness of the protocols, to assure that farm managers are following the plan and that the plans are accomplishing their goals.
Routine monitoring and surveillance tests are also useful tools for the early detection of FAD. Swine operations that routinely conduct ante mortem tests (eg, serological profiles and (or) PCR surveillance for selected economically important diseases) are exercising and perfecting the same protocols that would be necessary should FAD occur in their area, with mandatory implementation of surveillance. Likewise, swine operations that routinely conduct necropsies and submit specimens for diagnostic evaluations are much more likely to be aware of new disease syndromes. Negative diagnostic findings may be as valuable as positive resultsin these instances, by providing a background disease baseline from which the herd veterinarian can detect variations.
In addition, many state veterinarians, veterinary associations, and diagnostic laboratories are providing opportunities for continuing education relative to emerging and foreign diseases. This is an important time to be professionally ready and prepared. Some states have organized teams of field veterinarians for state emergency preparedness plans. Volunteering to be a crisis volunteer will require training effort and time, but this may be an excellent means to developexpertise in these crucial areas-expertisethat may be used in other aspects of your professional practice.
- Maximize biosecurity efforts on every premise.
- Establish, evaluate, and continually upgrade biosecurity SOPs.
- Establish domestic disease baselines through routine ante mortem and post mortem monitoring and surveillance.
- Maintain a high degree of suspicion and vigilance.
- Practice potential outbreak situations and protocols with your clients.
- Keep current on national and international disease issues.
- Volunteer to be a member of your state emergency preparedness team.
Foreign animal disease, agricultural bioterrorism, emerging diseases, larger productionunits, and more complex management schemes have increased disease pressures in our nation's swine herds. In the midst of a serious conflict, a strong defense and strong offense are both necessary. Vigilance, proactive effort, and FAD diagnosis and response protocol exercises will best prepare the swine veterinarian and his clientfor the unknown. The costs involved with conducting these activities are necessary and in the long run, it is money well spent.