Confronting a Suspicious Foreign Animal Disease Case
The capability of a laboratory to confirm the diagnosis of a suspected exotic animal disease is directly related to the types, amounts, and conditions of the specimens submitted. The field diagnostician must select, aseptically procure, and properly preserve specimens for the isolation or demonstration of a causative agent. In addition, an adequate number of specimens must be taken from the appropriate tissues, at the proper stage of the disease, to maximize the chances of isolating the pathogen. The herd or flock owner, private practitioner, and diagnostic laboratory comprise a front-line defense and will, most likely, be confronted with the initial case of an exotic disease. It is vitally important that these people contact the State Veterinarian or Federal Veterinarian in Charge (FVIC) as soon as possible if a foreign animal disease (FAD) is suspected. The State or Federal official will, in turn, assign the suspicious case to a FAD diagnostician for immediate investigation.
A cadre of trained FAD diagnosticians exists throughout the country. These diagnosticians are on call at all times and are trained to investigate suspicious cases of exotic diseases of livestock and poultry. The FAD diagnostician is responsible for collecting and couriering specimens to a reference laboratory such as the National Veterinary Services Laboratories on Plum Island in New York or in Ames, Iowa, for a laboratory assessment.
Speed and efficiency in detecting, reporting, and diagnosing a newly introduced livestock or poultry disease are essential in preventing the disease from becoming widespread in the United States.
When the existence of a FAD is suspected, no animal or specimen should be removed from the premises of origin unless in the custody of an officially designated FAD diagnostician. Animals should not be moved from the premise until a diagnosis is obtained.
Specimen Preparation
The following general suggestions are presented as a guide for preparing diagnostic specimens for submission to a diagnostic laboratory. Developmental studies on new diagnostic procedures are in progress for certain diseases; therefore, it is wise to contact the diagnostic laboratory (see address at end of the appendix) in addition to the State Veterinarian or Federal Veterinarian for information on special handling that may be necessary.
An initial incursion of an exotic disease will, in most cases, only be confirmed in a reference laboratory through the isolation and identification of the etiologic agent. Thus, specimens to be submitted for agent identification should be collected as aseptically and completely as possible.
Disease investigation and specimen collection must be done thoroughly and properly to avoid a return visit and a need to repeat specimen collection and submission, which would only delay the laboratory diagnosis.
Prenecropsy Procedures
1. Obtain and record a complete herd history. Information should be submitted on proper forms (VS 12-27 or APHIS Form 8004) when possible; the following information should be included:
- (a) Name and address of owner.
- (b) Name, address, and phone number of submitter.
- (c) A description of animal: breed, sex, peculiarities, etc.
- (d) Suspected disease or examinations requested, or both.
- (e) Number of animals showing signs and their ages.
- (f) Number of animals dead.
- (g) Vaccines administered to the animal(s) from which specimens were collected-especially important when examinations for antibodies will be conducted.
- (h) Dates of the first losses and of subsequent losses.
- (i) The disease signs and their duration.
- (j) Ration fed.
- (k) The condition of the animal.
- (l) A description of the spread of the infection, if in a flock or herd. A diagram of the area is often useful.
- (m) Treatment, if any.
- (n) Type of housing.
- (o) Accessory information; the type of preservative used for specimens.
- (p) An epidemiological assessment, including recent movements into and out of the flock or herd.
- (q) Any exposures of the affected poultry or livestock to persons having traveled abroad or foreign visitors.
2. Be objective and approach the investigation without a preconceived diagnosis.
3. Be alert to safety hazards in handling livestock and consider zoonotic potentials. As an example, the possibility of rabies as a differential diagnosis should be considered where appropriate.
4. Ensure that prelabeled specimen containers and tubes are available for collection and are scrupulously clean and sterile. The label must include proper identification of the animal and type of specimen.
5. Examine and collect specimens from live animals or poultry in various stages of clinical disease. Serum, vesicular fluid or tissue, or both, swabs of exudates or lesions, or both, can be secured from live animals. Serum from apparently healthy exposed animals or poultry can also be helpful. Animals sampled should be permanently identified because it is possible that convalescent serums or samples will be taken in the future for comparative purposes.
6. Blood smears should be prepared on clean glass slides. A thin blood film should be made, rapidly dried, and fixed in absolute methanol for 5 minutes. Slides having a frosted end should be used and should be identified using a lead pencil.
Unstained films should be protected from dust, insects, and abrasion and should not be refrigerated.
Obtaining Specimens at Necropsy
1. Necropsy and collect specimens from animals that have died and have undergone minimal putrefaction.
2. If it is possible to select several live animals for necropsy, try to select animals in various stages of clinical disease.
3. Be aware of any safety or biological hazards that necropsy might impose on you and the owner. Availability of a proper and safe disposal site should be considered before beginning necropsies.
4. Do not conduct necropsies while wearing street clothes. Wear rubber boots, gloves, overalls, etc., that can be disinfected or that are disposable. A mask and goggles may be used at the discretion of the diagnostician.
5. Prelabeled specimen containers will help ensure that recommended specimens will be collected.
- (a) Use a label that cannot be easily destroyed. For instance, surgical tape should go entirely around the vial so that it will not be dislodged by moisture.
- (b) Writing should be with pencil or ink that will not smudge or blur when wet.
- (c) Use plastic screw-capped containers instead of glass containers where practical.
- (d) Tape the lids of containers. Tape should be wound around the cap in the same direction as the screw-cap is applied.
- (e) Use disposable equipment such as cardboard trays, disposable syringes, etc.
6. Have a systematic plan for the necropsy and know what specimens are to be collected before starting the proceedure. Be certain to include all lesions for laboratory examination. Body fluids and contents of cysts, abscesses, or skin lesions can be collected using a sterile swab. If an animal is presented for euthanasia, collect all blood samples before euthanizing. If the animal or bird is presented dead, collect blood from the heart. Make blood smears as previously discussed. Ectoparasites should be noted and collected, if pertinent. The collection of specimens based on species rather than a specific disease will be most useful in providing a diagnosis. The specimens listed in the Table of Specimen Collection are the minimum recommended and are not intended to replace the field diagnostician's judgment concerning the collection of additional specimens. In addition to the listed specimens, samples of all lesions should be collected for histologic examination. Toxicology-related problems have not been given consideration in these recommendations.
7. Fluid from any enlarged joints should be aspirated aseptically.
8. Any excess body cavity fluids should be collected aseptically via a syringe.
Other Considerations in Specimen Collection
1. Two sets of tissues are to be collected.
a. Fresh tissue for microbiological examination: Any tissue that is to be preserved in a refrigerated or frozen state should be placed in a separate container.
b. Preserved tissue for histological examination: The recommended preservative is 10 percent neutral buffered formalin. All tissues can be placed in one container, but allow no more than 1 volume of tissue to 10 volumes of formalin. Tissues from organs should be cut perpendicularly to the surface to expose their anatomic structure. The specimen should include affected and surrounding normal tissue. To provide adequate fixation, tissues except for the brain, should be sliced no more than 3 to 6 mm thick. Any lymph nodes collected should be incised.
Specimens should not be folded or bent by the container in which they are fixed. Only wide-mouthed containers should be used in this procedure.
2. The initial piece of each organ or lesion should be collected aseptically for microbiology. Tissues for formalin fixation can be collected during the necropsy.
3. Swabs should be sent in appropriate transport medium (e.g., Tris-buffered typtose broth). The laboratory can assist in the proceedure for obtaining this media.
4. Materials submitted for possible virus isolation should be obtained from animals that died and have minimal putrefaction and from animals in the early, acute, febrile phase of illness. A reliable overnight delivery service should be used (the laboratory can recommend a service that has been effective in providing this service). Specimens shipped for virology and bacteriology should be shipped refrigerated. If at all possible, the use of dry ice should be avoided because the CO2 will produce acid conditions that will inactivate many viruses. If there is no way to get the specimens to the laboratory within 48 hours, dry ice must be used. In this case, the specimens must be completely sealed so that there is no contact of the gas emitted by the dry ice with the specimens.
Postnecropsy Considerations
1. Clean and decontaminate instruments.
2. Clean and disinfect all work surfaces and dispose of, or clean and disinfect, personal effects.
3. Record necropsy findings.
4. Dispose of carcasses and body parts so as to avoid exposure of other animals and contamination of environment.
Considerations for Shipping Diagnostic Specimens
Regulations require that diagnostic specimens transported in interstate traffic must be packaged and labeled properly. Improper packaging and labeling of diagnostic specimens and other hazardous materials can result in unnecessary exposure to postal, shipping, and laboratory personnel.
1. The specimens must be in securely closed, watertight primary enclosures such as a screw-cap container or sealed vial. Be certain that exterior surfaces of the primary containers are decontaminated before shipment.
2. Each primary container should be wrapped in sufficient dry absorbent cotton or paper towels to absorb the material in case of breakage. Ideally, the wrapped container should be placed in sealed plastic bags.
3. Pint-, quart-, or half- gallon-sized paint cans should be used as secondary containers. These cans should have friction-type lids and be watertight when hammered closed. The primary container should be padded with more cotton or paper to prevent jarring. A tertiary container, such as a larger-sized version of the secondary container, should be considered if a zoonotic or highly infectious FAD is suspected.
4. The sealed secondary or tertiary container should be placed in a shipping container and again packed with material such as paper. The shipping container should be an insulated box with a lid that can be taped shut. A corrugated shipping box, affixed with the proper labels and shipper's certification, is the final enclosure and contains all other containers.
5. If specimens can be in transit for less than 48 hours, ice packs may be used for cold storage. Frozen "foam ice," "blue ice" picnic packs, or water frozen in sealed containers may be used. Wet ice, even when wrapped in plastic bags, should be avoided to eliminate the possibility of leakage.
6. Dry ice is the only suitable refrigerant to keep specimens frozen. Shippers must be aware of dry ice restrictions imposed by certain airlines and plan according.
7. Regular mail or airmail shipment should not be used when a FAD is suspected. Courier service is the appropriate method of shipment. If FMD is considered as a possible diagnosis, a responsible individual should handcarry the specimen to the reference laboratory.
8. It is not desirable to have the submission form, with the history and other information, within the container. It is preferable to enclose the submission form between the shipping container and the cover of the outside corrugated box.
9. The shipper is responsible for notifying the intended recipient of all information relative to transportation arrangements in order to expedite package pickup and delivery to the laboratory.
10. Care must be taken to ensure that a FAD-suspicious package is only opened within the confines of a biosecure facility.
Reference Laboratory Contacts
1. Foreign Animal Disease Diagnostic Laboratory, P.O. Box 848, Greenport, Ll, NY 11944-0848, Phone: (516) 323-2500, Ext. 256.
2. National Veterinary Services Laboratories, P.O. Box 844, Ames, IA 50010, Phone: (515) 239-8266.
L.M. Siegfried, D.V.M., USDA, APHIS, VS. Area Veterinarian in Charge. 2301 N. Cameron St. Rm. #412, Harrisburg, PA 17110
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