Comparison of anamnestic responses to rabies vaccination in dogs and cats with current and out-of-date vaccination status

Abstract

Each year in the United States there are thousands of dogs and cats exposed to the rabies virus, primarily through bites of infected wildlife. Rabies vaccination laws for domesticated animals vary from state to state, however the recommended public health response to a domestic animal exposed to rabid animals is described in the Compendium of Animal Rabies Prevention and Control (Compendium). Based on Compendium guidelines, it is recommended that dogs and cats that are current on rabies vaccination and that are exposed to the rabies virus should receive a rabies vaccine booster and a 45 day observation period at home. The recommendation for dogs and cats that have never been vaccinated for rabies and that are exposed to a rabid animal is euthanasia or quarantine for 6 months. However, dogs and cats with a history of rabies vaccination that is out-of-date must be assessed on an individual basis. In these cases the public health official must consider the number of prior rabies vaccinations received, the time since last vaccination, the type of rabies exposure encountered, local rabies epidemiology and any relevant diagnostic test results when determining the need for euthanasia or immediate revaccination and observation or isolation .1 The results of this study indicate that there are no differences in neutralizing titers between dogs considered current on rabies vaccination compared to those considered out-of-date. The major question we hoped to address was whether or not current and overdue dogs and cats responded to a rabies booster with equal robustness. Our results demonstrate that anamnestically, out-of-date dogs are not inferior in their response. This suggests that out-of-date animals can perform similar to current vaccinates following a booster. This is compatible with the protocol for human rabies post exposure recommendations for previously vaccinated individuals. In humans the protocol for pre-exposure vaccinated individuals exposed to rabies is 2 boosters at day 0 and day 3 regardless of what time has passed since initial vaccination. To date there are no known individuals who have succumbed to rabies using this protocol. In the spirit of One Health it should follow that a rabies vaccine booster could be trusted to protect dogs and cats in the same manner. If public health officials are concerned with dogs and cats priming vaccinations, a day 0 and day 5-7 titer could be done to make sure an anamnestic response occurs. The compendium states “because a rapid anamnestic response is expected, an animal is considered currently vaccinated immediately after a booster vaccination.” This statement coupled with the results of this study should warrant a policy change to booster healthy dogs and cats, which are overdue and exposed to rabies, and observe for 45 days instead of euthanasia or 6 month quarantine. Four potential ways to handle this policy change would be: 1. Allow out-of-date animals and current animals to go home after a booster for a 45 day observation. 2. Do day 0 and day 5-7 titers on all exposed dogs and cats to determine if they reach an endpoint of pre-determined acceptance. If they do not, booster again and proceed with a 6 month quarantine. 3. Do day 0 and day 5-7 titers on biologically out-of-date animals to determine if they reach an endpoint of pre-determined acceptance. If they do not, booster again and proceed with a 6 month quarantine. 4. Do day 0 and day 5-7 titers on by label out-of-date animals to determine if they reach an endpoint of pre-determined acceptance. If they do not, booster again and proceed with a 6 month quarantine.