Epidemiological situation of vesicular stomatitis virus infection in cattle in the state of Paraíba, semiarid region of Brazil

The aim of this survey was to estimate the apparent herd-level and animal-level prevalences, as well as to identify risk factors and spatial clustering of vesicular stomatitis virus (VSV) positive herds in the state of Paraíba, semiarid of Brazil. The state was divided into three sampling strata: Sertão, Borborema and Zona da Mata/Agreste. For each sampling stratum, herd-level and animal-level prevalences were estimated by a two-stage sampling survey. First, a pre-established number of herds (primary sampling units) were randomly selected; second, within each herd, a pre-established number of cows aged ≥ 24 months were systematically selected (secondary sampling units). In total, 2279 animals were sampled from 468 herds. Serum samples were submitted to virus neutralization (VN) test for detection of antibodies to VSV using three viral strains: VSIV-3 2013SaoBento/Paraiba E, strain Indiana (VSIV-1) and VSNJV. A herd was considered positive for VSV if it included at least one positive animal in herds of up to 10 females, two positive animals in herds of 11-99 females, and three positive in herds with more than 99 females. The spatial clustering was assessed using the Cuzick-Edwards' k-nearest neighbor method and spatial scan statistics. The apparent herd-level prevalence in the state of Paraíba was 38.5% (95% CI = 35.5-41.6%), 80.6% (95% CI = 73.6-86.2%) in the region of Sertão, 7.0% (95% CI = 3.9-12.2%) in Borborema, and 2.6% (95% CI = 1.0-6.7%) in Agreste/Zona da Mata. The apparent animal-level prevalence was 26.2% (95% CI = 20.6-32.8%) in the state of Paraíba, 48.2% (95% CI = 41.5-54.9%) in Sertão, 6.3% (95% CI = 2.7-14%) in Borborema, and 3.2% 1.9% (95% CI = 0.4-8.4%) in Agreste/Zona da Mata. The risk factors identified were as follows: mixed production (milk/beef) (OR = 4.54), herd size > 23 animals (OR = 3.57), presence of cervids (OR = 15.24), rental of pastures (OR = 3.02), sharing of water sources (OR = 2.57) and presence of horses (OR = 1.69). Two significant clusters of positive herds were detected: the primary cluster covered the Sertão region and the secondary cluster covered part of the Sertão and Borborema regions. Our results suggest high VSV circulation in the bovine population of the state of Paraíba, semiarid region of Brazil, mainly in the Sertão mesoregion, and based on risk factor analysis it was possible to identify important associations that deserve more investigation on causal factors.