Anticorpos neutralizantes contra o vírus da raiva em cães com e sem histórico de vacinação em Santa Maria – RS - Brasil

Abstract

Rabies virus (RabV) belongs to the family Rhabdoviridae, genus Lyssavirus and is the agent of a severe zoonotic disease that courses with neurological signs and inevitably leads to death. Urban rabies, with is maintained through transmission cycles involving dogs and cats is under control or virtually eradicated in most Brazilian states. Regardless, massive vaccination of urban canine and feline populations is still being performed in many cities as to maintain the population immunity. Considering the recent outbreaks of bovine rabies in Rio Grande do Sul state (RS) and the potential risk of introduction of the virus in the urban populations of dogs and cats, it is relevant to evaluate the levels and coverage of humoral immune response induced by rabies vaccination in these populations. Thus, the present study aimed at: 1. To determine the magnitude of the serological response in dogs with recent history of rabies vaccination; 2. To investigate the frequency and level of antibodies to RabV in dogs with unknown history of vaccination against rabies. The first study included 440 serum samples from dogs with recent historic of vaccination against rabies, collected during the 2015 Rabies Vaccination Campaign in Santa Maria, RS. The second study used 300 samples from dogs submitted to the University Veterinary Hospital (HVU) of the Federal University of Santa Maria in 2015. These dogs have been submitted to HVU for varied clinical and surgical procedures and, thus, rabies vaccination history was unknown. Serum samples were submitted to the rapid inhibition of fluorescent foci test (RIFFT) which detects neutralizing antibodies do RabV. Out of the 440 samples collected from vaccinated animals, 70.4% (330/440) harbored neutralizing antibody titers ≥ 0.5 UI/mL, considered an indicative of protection to rabies by the World Health Organization (WHO). However, approximately 30% of the animals did not contain antibodies in adequate levels. Among the animals with titers below 0.5 UI/mL, 57.4% (74 amostras) had been subjected to two or more vaccinations, indicating failure in the immunization strategies and/or poor vaccine quality. Among the samples collected from dogs with unknown historic of rabies vaccination, 42.3% (127/300) contained neutralizing antibody titers ≥ 0.5 UI/mL. Thus, 57.7% (173/300) of the sampled animals did not contain levels of protective antibodies against rabies. Considering that these samples were collected from a selected dog population, these coverage levels should not be considered representative of the vaccine coverage of the total dog population. However, these numbers are indicative of a low rabies vaccine coverage in the urban dog population of Santa Maria, RS. In summary, our results demonstrated that an important proportion of dogs vaccinated against rabies have not developed adequate antibody levels against RabV, indicating the need of reformulation of the vaccination strategies. On the other hand, the levels of vaccine coverage detected in a selected sampling no history of vaccination indicates the need to extend the rabies vaccination campaigns as obtain a wider vaccine coverage.