Identification of risk factors on rabies vaccine efficacy from censored data: Pre-travel tests for dogs and cats from Yaounde (2005-2015)

Authors: NTSAMA, FRANÇOIS - World Organization For Animal Health; Noh, Susan; TIZZANI, PAOLO - World Organization For Animal Health; AYANGMA NTSAMA, CHANTAL - Centre Pasteur Du Cameroun; NTEME ELLA, GUALBERT - National Laboratory For Animal Husbandry And Veterinary Research (LNERV); AWADA, LINA - World Organization For Animal Health; DJATCHE TIDJOU, GWLADYS SORELLE - Centre Pasteur Du Cameroun

Submitted to: Research in Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2024
Publication Date: 5/1/2024
Citation: Ntsama, F., Noh, S.M., Tizzani, P., Ayangma Ntsama, C.F., Nteme Ella, G.S., Awada, L., Djatche Tidjou, G. 2024. Identification of risk factors on rabies vaccine efficacy from censored data: Pre-travel tests for dogs and cats from Yaounde (2005-2015). Research in Veterinary Science. 174. Article 105278. https://doi.org/10.1016/j.rvsc.2024.105278.
DOI: https://doi.org/10.1016/j.rvsc.2024.105278

Interpretive Summary: Dog-mediated rabies is a highly neglected and under-reported zoonotic disease that is estimated to kill at least 59,000 people worldwide each year, of which, an estimate of 24,000 of these deaths occur in Africa and mainly in children in rural areas and in poor populations. In the absence of immediate, post-exposure prophylaxis, the virus inevitably causes death. Importantly, prevention of rabies in humans can be achieved by vaccination of the canine population. However, achieving protective immunity relies on adherence to vaccination guidelines, including minimum vaccination age, administration of boosters, appropriate vaccine storage and handling. Data regarding these factors and successful vaccination is sparse and difficult to obtain in much of Africa. The aim of this study was to assess the effect of different risk factors on rabies vaccine efficacy under Cameroonian field conditions. Overall, 85.7% of dogs and 100% of cats had titres greater than or equal to 0.5 IU/ml, which are considered protective. For each additional year of age, the value of the rabies-neutralizing serum titre, on average, increases by approximately 0.14 IU/mL. Finally, for each 30 additional days of time between the date of the last rabies vaccination and the date of the sampling, the value the rabies-neutralizing serum titre, on average, decreases by approximately 0.10 IU/mL. These results are useful to determine risk and improve surveillance in preventing the introduction of rabies into a country due to international movements of animals.

Technical Abstract: Little research is available on acquired immunity to rabies in dogs and cats from Central Africa, particularly regarding the legal movements of pets. Movement of domestic animals from rabies-endemic countries like Cameroon to rabies free areas poses one of the main risks for rabies introduction into rabies-free areas. Thus, the aim of this study was to assess the effect of various risk factors on rabies vaccine efficacy in Cameroonian. Since the dependent variable, rabies neutralizing titres, were censored from above (right-censoring), Generalized Additive Model for Location, Scale and Shape (GAMLSS) was used in the analysis. Overall, 85.7% of dogs and 100% of cats had titres greater than or equal to 0.5 IU/mL, which is considered protective. Additionally, compared to cats, the value of the rabies-neutralizing serum titres in dogs was on average smaller by 2.3 IU/mL. For each additional year of age, the value of the rabies-neutralizing serum titre, on average, increased by approximately 0.14 IU/mL. Finally, for each 30 additional days between the date of the last rabies vaccination and the date of the sampling, the value the rabies neutralizing titre, on average, decreased by approximately 0.10 IU/mL, given the species and age at sampling were equivalent. These results are useful for assessing risk and improving surveillance to prevent the introduction of rabies into a country via the international movement of animals.