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Rabies Diagnostic Testing



DEFINITION


Evaluation of presence or absence of rabies virus infection



TYPICAL NORMAL RANGE


Results are reported as positive or negative.



PHYSIOLOGY


Rabies is an acute encephalitis caused by an RNA virus of the rhabdovirus family. Virus localizes to central nervous system. Direct IFA testing of brain tissue is the method used for definitive diagnosis. Submission of appropriate specimens requires necropsy examination. The test detects viral antigen in the neural tissue of infected animals.



CLINICAL APPLICATIONS


CAUSES OF ABNORMALLY HIGH LEVELS: Viral infection


NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS HIGH: Exposed personnel should consult their physicians immediately. Exposed animals should be quarantined and observed for development of clinical signs (see p. 961).



SPECIMEN AND PROCESSING CONSIDERATIONS


SPECIMEN: Fresh brain tissue. Note: Aerosolization of rabies virus is possible during craniotomy portion of necropsy or during removal of head (exposure of spinal cord). Therefore, removal of head or brain should be reserved for qualified personnel (e.g., pathologist or state veterinarian). Body of rabies suspect should be chilled (refrigerated), not frozen. Cut brain in sagittal (longitudinal) section. Submit half in clean, dry double bag for IFA test. Clearly label as rabies suspect.


RELATIVE COST: $$—$$$$ (charges vary widely among state labs)



PEARLS



• Most testing is done at state diagnostic laboratories.

• Half the brain should be submitted in formalin to assess for other diseases if rabies testing is negative.

• Brain tissue is the only suitable specimen; other tissue such as whiskers or peripheral nerve are not.

• Dogs and cats that have an implanted microchip, are currently vaccinated for rabies, and have a protective titer certified by the FVNA Laboratory at Kansas State University or the Veterinary Command Food and Diagnostic Laboratory, Fort Sam Houston, Texas may avoid quarantine when traveling from the continental United States to Hawaii or the United Kingdom if they meet other criteria. For more details regarding pet travel, refer to http://www.aphis.usda.gov/animal_welfare/pet_travel/pet_travel.shtml.

AUTHOR: LOIS ROTH-JOHNSON



Relaxin



DEFINITION


Peptide hormone produced by the reproductive tract of many species during pregnancy



TYPICAL NORMAL RANGE


Relaxin is measured by a commercially available assay (Witness Relaxin, Synbiotics). Positive/negative result; negative (undetectable) in nonpregnant (diestral) bitches.



PHYSIOLOGY


The tissue source of relaxin varies with species and stage of the reproductive cycle. It may be produced by the corpus luteum (CL), placenta, or uterus. In pregnant dogs, relaxin is initially produced by the CL, followed by the placenta. The primary effects of relaxin occur during implantation and later during parturition. Relaxin promotes uterine, cervical, and vaginal growth during pregnancy. It may also play an important role in mammary development in some species. Additionally, relaxin is involved in nonreproductive processes such as fibrosis, wound healing, and protection against myocardial ischemia.



CLINICAL APPLICATIONS


CAUSES OF ABNORMALLY HIGH LEVELS: Pregnancy. High concentration may persist following abortion. Nonpregnant cats with ovarian cysts have been reported to have high serum concentrations of relaxin.


NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS HIGH: Evaluate for pregnancy (abdominal radiographs, ultrasound).


IMPORTANT INTERSPECIES DIFFERENCES: Relaxin is of value for diagnosing pregnancy in both wild and domestic canids. Small studies have shown it to accurately detect pregnancy in cats.



SPECIMEN AND PROCESSING CONSIDERATIONS


LAB ARTIFACTS THAT MAY INTERFERE: Hemolysis must be avoided; hemolyzed samples should not be used, as they may cause a false negative.


SPECIMEN: Plasma or serum. Collect blood in EDTA (lavender-top tube), citrate (blue-top tube), or heparin (green-top tube) or serum (red-top tube). Spin down, collect plasma or serum, and transfer to a clean tube without additives.


Do not use whole blood or hemolyzed samples.


RELATIVE COST: $$$

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Jul 24, 2016 | Posted by in SMALL ANIMAL | Comments Off on R

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