During last 2000 decade, an evaluation of anti Rabies post-vaccinal immunity in domestic carnivores (cats/dogs) showed a satisfactory rate of immunization of 74.75% for dogs and 95.8% for cats (titre ≥ 0.5 EU/ml). In addition, 84.870% of cats had antibodies titer greater than 4 EU/ml (≥ 4 EU/ml). Only 14.46% of dogs have reached such titers. Anamnestic immune response observed during this study for cat (84.870%) and for some multivaccinated dogs (14.46%) are consistent with results obtained by Derbyshire and co-workers  and Cliquet and collaborators . This hyperimmunisation of cats was probably linked to the ratio of the antigen to the animal weight . Our study had revealed that 25.25% and 4.2% respectively of dogs and cats were seronegative. In France, a rate of seroconversion failure estimated to 7.4% and 1.9% has been reported in dog and cat, respectively . Also, we had found especially adults dogs, which did not seroconvert. Mainly, dogs older than 4 years and multivaccined represented the most important (62.25%) seronegative dog population . This result probably could be explained by a deficiency of the immune system of old dogs. We also observed that 21.52% of seroconversion failure occurred during prime vaccination of puppies and juvenile dogs. It was likely due to maternal antibodies interference leading to inhibition of post vaccinal immunity [9–11]. Due to the increasing number of puppies affected by rabies, vaccination is promoted for puppies aged above 8 weeks with an attenuated vaccine . Therefore, many reasons had to be considered in case of vaccination failure such as the health status, immunization protocol and the race of the animal. But also, poor quality of sera due to collection and transportation conditions to the laboratory could affect the ELISA result. Sometimes, dogs are bled just after vaccination. Normally, animals should be sampled after thirty post vaccination days at least to enable the immune response to reach a detectable level [2, 6].
In Ivory Coast, regards to the failure rate of seroconversion, exposure to dog though vaccinated might be harmful. Therefore, the role of vaccinated dogs in transmission of Rabies should widely be investigated to assess the real risk they represent. In addition, this may help to estimate optimal vaccination coverage for the control of rabies in the country.
In conclusion, it was estimated a rate of seroconversion failure around 28% by Platelia ELISA for dog.This result suggested to pay attention to dog vaccination pratice. Findings may suggest reschedule of immunisation protocol. Subsequently, sustainable management of old dogs population should be implemented. ELISA is a versatile tool for the titration of antibody to Rabies virus in low resources countries such as in Ivory Coast. It is easier to be performed than gold standard FAVN or RFFIT. Recent developments had prompted out others ELISA kits with satisfactory performance .
Our study may present limitations. Indeed, it has been also reported the Platelia ELISA has a weak sensitivity in quantifying antibody in sera which had low titer . Titers obtained by Platelia Elisa were regarded as underestimated . The use of this kit was abandoned due to controverses on its performance and validation process . Today, OIE stated that Virus neutralisation and enzyme-linked immunosorbent (ELISA) assays are suitable tests for monitoring the antibody response of vaccinated animals in sight of rabies control. For the purposes of measuring antibody responses to vaccination prior to international animal movement or trade, only viral seroneutralisation methods (FAVN test and RFFIT) are acceptable. ELISA does not fit for this purpose anymore.