Role of the Private Veterinarian in the Diagnosis of Foreign Animal Diseases
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Foreign Animal Disease Relevance
Canada is one of a few countries that remain free from a number of serious epizootic diseases of animals. It is a high priority of the Canadian Food Inspection Agency (CFIA) that foreign animal diseases (FADs), especially a rapidly spreading disease such as foot-and-mouth disease (FMD), be recognized and then eradicated as soon as possible. The consequences will depend on the size and nature of the outbreak, and can be greatly minimized by early identification, containment, and elimination.
According to a study conducted in 1998 an occurrence of FMD would result in an embargo on Canadian red meat and products of animal origin that would translate into a devaluation of the livestock industry of between 950 million and 1.9 billion dollars. If no measures were put into place to halt the disease, it is believed that one outbreak could cost the cattle industry up to $34 million per day.
Veterinary practitioners are most likely to be the first to encounter and recognize an FAD once it has gained entry into Canada. Early recognition by veterinarians may prevent widespread transmission and great expense to the Canadian public.
When should you suspect a Foreign Animal Disease?
FADs of concern to the CFIA are those which would have severe economic consequences in Canada, primarily associated with the loss of our export markets. Thus, it is essential to be aware of the possibility of FADs. The spectrum of pathogenicity of FADs has changed significantly. Traditional expectations of dramatic clinical manifestations of FADs in our highly susceptible livestock must be discarded. Changes in pathogenicity induced by accidental release of modified strains, or alterations included by passage through partially immune hosts, has resulted in a generation of agents whose clinical signs closely mimic common diseases of Canadian livestock.
The challenge for the clinician then becomes - when do I refer a case to the District Veterinarian? This must remain the judgement of the attending clinician. However, there are a couple of guidelines that may be useful. Firstly, a history of a possible recent contact, such as visitors or people or livestock returning from abroad, should raise suspicions. This should be a key factor in the decision to refer. Secondly, a syndrome which does not follow expected clinical or treatment and response patterns should also be questioned. During the last 30 years, outbreaks of hog cholera (classical swine fever), anaplasmosis, avian pneumoencephalitis (Newcastle disease), and bluetongue have all occurred in Canada. Although clinicians are unlikely to encounter such diseases, you should be aware that they exist.
The following examples may be a useful reminder of some of these:
- Hemolytic anemia with no hemoglobinuria, affecting adult cattle—consider anaplasmosis.
- Mature cattle affected with oral lesions and diarrhea; morbidity and mortality high or low—consider rinderpest.
- Pigs with severe systemic illness; morbidity high, or low and increasing (insidious)—possibility of African swine fever and hog cholera. History and gross necropsy may be most useful.
- Reproductive problems in sows—always include pseudorabies, hog cholera, and African swine fever, at least in the initial diagnostic diseases list.
- Horse with vesicles or papules on tongue—definitely call the CFIA on suspicion of vesicular stomatitis.
- Several bred mares return to heat with mucopurulent vaginal discharge; cultures are negative—search in breeding/travel history for possibility of contagious equine metritis.
- Sheep with stomatitis, lameness—suspect bluetongue, vesicular diseases.
- depression, neurological signs, head edema, diarrhea, variable morbidity and mortality, hemorrhagic enteritis—consider Newcastle disease, highly pathogenic avian influenza (HPAI), possibly fowl typhoid
- if restricted to chicks and poults—consider pullorum disease
- Cattle over 3 years of age exhibiting a progressive neurological disease of two to three months duration, consider bovine spongiform encephalopathy (BSE).
You are encouraged to request printed material from your District Office to keep updated on clinical signs and post-mortem findings of serious FADs.
The Practitioner's Role
Veterinarians are required by law (see Health of Animals Act Sec.5(1)(2)) to immediately notify the District Veterinarian of reasonable suspicion of any serious FAD, regardless of whether it is reportable.
Once a firm suspicion is established, it is important that the practitioner remain on the suspect premises until relieved by the CFIA Veterinarian.
If the District Veterinarian believes that an FAD is a serious possibility, the clinician must consider very carefully the risks associated with continued contact with livestock on other premises without extensive personal and equipment decontamination. Many FAD agents are resistant and spread readily by fomites. The danger of transmission by veterinarians from premises to premises is real and must be recognized, along with the potentially tragic consequences and possible liability to the veterinarian, should such an incident occur.
Individuals should maintain a list of alternative contacts, in case you are unable to reach local District Veterinarians (e.g. neighbouring district veterinarian, area office personnel). Be discreet when discussing a tentative diagnosis with clients especially on party telephones lines. For example, use the term "possible exotic disease," rather than "FMD." If confirmed, eradication measures would involve at least the quarantine of the premises and an epidemiologic investigation (e.g. origin of vesicular stomatitis confined to horses at one stable). Further action would depend on other factors, such as extent of spread (e.g. involvement of wildlife), legal mandate, and industry support, and could extend to movement controls on an entire area and involve depopulation of affected premises.
In the case of an outbreak of an FAD, a designated emergency response team would be mobilized to a Field Emergency Operations Centre (FEOC) to control the spread and eradicate the disease. Operationally, this Team is made up of units with specific tasks: diagnostic, trace-out, movement control, evaluation, destruction and disposal, and cleaning and disinfection. Veterinary practitioners could be requested to provide assistance in one of these areas.
The control and eradication activities would begin by controlling movements of animals and people in zones where the disease has been diagnosed. There would be one Infected Zone (or more) containing the infected premises. Depending upon the disease, the perimeter of the Infected Zones(s) would extend a finite distance beyond all known infected premises and would this limit, when possible, would follow natural barriers and roadways to facilitate implementation of disease control procedures. Surrounding this (these) Infected Zone(s) would be a Restricted Zone, extending from the perimeter of the Infected Zone(s) to a certain distance, which could vary according to the disease. A Security Zone would extend from the outer limit of the Restricted Zone to the limit of the Control Area. The three zones would constitute a Control Area where certain measures would be applied according to a pre-approved disease control/eradication strategy. During an outbreak, practitioners receiving information, which is suggestive of the FAD in question, would notify the FEOC in the outbreak area. In the case of an FAD emergency, appropriate information concerning the location and the telephone number(s) of the FEOC, the limits of the Control Area, the movement restrictions, disinfection procedures, etc., would be made available at that time to all practitioners through the appropriate channels.
Disinfectants routinely used by a practitioner may not be effective against the agent of a suspected disease. The veterinary practitioner should consult with a District Veterinarian to determine what products are acceptable in the disinfection of himself, his equipment, and his vehicle.
Client education is an integral part of the practising veterinarian's role in FAD prevention and control. Owners will turn to their veterinarian as a primary source of information in the event of an outbreak. Control procedures, such as disease reporting, quarantine, and disinfection, will be effective only with the element of owner cooperation and participation. This results from an understanding of the procedures and their rationale.
The involvement of practising veterinarians with respect to FAD may be summarized as follows:
- Maintain current knowledge of the FADs most likely to enter Canada. These include anaplasmosis, HPAI, bluetongue, velogenic Newcastle disease, pseudorabies, vesicular stomatitis, FMD, hog cholera, and African swine fever, and BSE. The District Veterinarian has information on such diseases.
- Be aware of clinical/necropsy findings, which should alert suspicion. Routinely include FAD in differential diagnoses.
- Immediately report any suspicion of the existence of an FAD to the nearest District Veterinarian.
- If you have been physically present on the farm, stay on-site until the District Veterinarian arrives, and encourage others not to leave the premises.
- During an outbreak, continue to refer suspicious calls.
- Communication with livestock owner:
- Inform the owner of your suspicions of an exotic animal disease without specifying the disease.
- Owners will be more willing to comply with regulatory requirements when they are kept informed.
- Date modified: