What do the Micro Rabies Screen Testing (MRS) results mean?

Dr. Mike Moore, Rolan Davis and Dr. Susan Moore

The MRS test is a serum neutralization assay based on the RFFIT designed to give a rapid screening for evaluating the need for rabies boosters. Work done at Kansas State Veterinary Diagnostic Laboratory (KSVDL), indicates dogs and cats that have been vaccinated for rabies in the past but are not current on their rabies vaccination status respond similarly to a booster as animals that are current on their rabies vaccination. We (KSVDL) suggest that both groups (non-current and current) can now be
referred to as “pre-exposure” vaccinated animals.

Although revaccinating dogs and cats that have been exposed to rabies is effective for disease management, the concern is how to protect our pets from unknown exposures. In human medicine, titers are recommended on a periodic basis to confirm adequate response to rabies vaccination. The level defined as an adequate response is 0.5 IU/ml. This titer level is also recognized by OIE as protective in dogs and cats based on challenge studies.

A review of rabies challenge-studies indicates that there is a positive correlation between rabies virus neutralizing antibody (RVNA) titers and the level of protection after virus challenge.

Pre-exposure vaccination coupled with a RVNA titer at or above 0.5 IU/mL indicates greater assurance of protection than does current vaccination status. The MRS test measures RVNA.

Using the MRS test results, if the RVNA value is <0.5IU/ml, KSVDL recommends administering a rabies booster. If the value is >0.5IU/ml we would not recommend a rabies booster, but instead rechecking the RVNA in year.

Currently whether an animal requires a rabies booster vaccination is not determined by the level of RVNA in the serum, but by local regulations. The Compendium of Rabies Prevention and Control recommendations, which are routinely used as guidance for local regulations, are routinely under review with consideration of new information. KSVDL is part of this process and is working to influence change that will provide the best guidelines for rabies booster requirements.

For more information or to order biopsy mailers please contact Client Care at 866-512-5650 or clientcare@vet.ksu.edu.

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