BackgroundMass vaccination of dogs is considered fundamental for national rabies control programmes in Sri Lanka, as dog is the main reservoir and transmitter of the disease.MethodsDogs were followed to determine the sero-prevalence of antibodies to the rabies virus. Altogether 510 previously vaccinated and unvaccinated dogs with owners (domestic dogs) and dogs without owners (stray dogs) of the local guard dog breed in different age groups recruited from Kalutara District, Sri Lanka. The dogs were vaccinated with a monovalent inactivated vaccine intramuscularly and serum antibody titres on days 0, 30, 180 and 360 were determined by the Rapid Fluorescent Focus Inhibition Test (RFFIT).ResultsThe results indicated, a single dose of anti-rabies vaccination fails to generate a protective level of immunity (0.5 IU/ml) which lasts until 1 year in 40.42% of dogs without owners and 57.14% of previously unvaccinated juvenile (age: 3 months to 1 year) dogs with owners. More than one vaccination would help to maintain antibody titres above the protective level in the majority of dogs. The pattern of antibody titre development in annually vaccinated and irregularly vaccinated (not annual) adult dogs with owners is closely similar irrespective of regularity in vaccination. Previously vaccinated animals have higher (2 IU/ml) antibody titres to begin with and have a higher antibody titre on day 360 too. They show a very good antibody titre by day 180. Unvaccinated animals start with low antibody titre and return to low titres by day 360, but have a satisfactory antibody titre by day 180.ConclusionsA single dose of anti-rabies vaccination is not sufficient for the maintenance of antibody titres for a period of 1 year in puppies, juvenile dogs with owners and in dogs without owners. Maternal antibodies do not provide adequate protection to puppies of previously vaccinated dams and puppies of previously unvaccinated dams. Immunity development after vaccination seems to be closely similar in both the groups of puppies.
In Sri Lanka, the first dose of pre-exposure antirabies vaccine is given to puppies at the age of 3 months with annual boosters. There have been many instances where puppies of less than 3 months have been affected with rabies. Antirabies vaccination failures have also been reported. Therefore, it is important to know the duration of protection in dogs following antirabies immunization.Animals for this study were divided into two main groups (adult dogs and puppies) and further sub divided into 4 groups (adult dogs with a past immunization history against rabies, adult dogs without a past immunization history, puppies of immunized bitches and puppies of unimmunized bitches). In this study, neutralizing antibody titres in puppies and adult dogs following pre and post anti-rabies immunization were determined by the rapid fluorescent focus inhibition test.All animals were bled on days 0 (D 0 preimmunization), 30 (D J0 ), 180 (D |g0 ) and 360 (t> 3 J. Titres were less than 0.5 IU/mL (protective antibody titre against rabies) in D Q samples of all puppies recruited for this study, in 26.7% of D J0 samples of puppies of unimmunized bitches, in 89.5% of D |80 samples of puppies and in all D J60 samples of puppies. Antibody titres in 50% of D J60 samples of adult dogs without a previous immunization history were also less than 0.5 IU/ mL. Antibody titres of all dogs with a past immunization history against rabies, were maintained above the protective level 1 year after immunization.Based on the results of this study, it is recom mended that puppies should be immunized against rabies before the age of 3 months with a booster at a suitable interval. Thereafter, annual revaccination should be done. Adult dogs without a past immunization history also should be given two anti-rabies vaccines in the first year at a suitable interval in order to maintain a protective antibody titre until the annual booster.
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