Bovine viral diarrhoea virus in beef cattle herds of Yucatan, Mexico: seroprevalence and risk factors.

A survey of bovine viral diarrhoea virus (BVDV) infection was carried out from June 2001 to July 2002 in a non-vaccinated beef cattle population from the livestock region of Yucatan, Mexico, to assess seroprevalence and identify risk factors related to seroprevalence. The aim was also to estimate the intra-herd correlation (r(e)) and design effect (D) of BVDV seropositivity. Cattle were selected by a two-stage cluster sampling. Blood samples were collected from 560 animals originating from 40 herds. Sera were tested for antibodies against BVDV using an indirect ELISA test. The sensitivity and specificity of the test was 97.9 and 99.7%, respectively. Risk factors regarding the herd and each animal sampled were recorded through a personal interview at the time of blood sampling. Twenty-four of the 40 herds had at least one seropositive animal. The animal true seroprevalence was estimated as 14%. The marginal logistic regression model used to describe the data found a significant (p<0.05) association of herd size-cow-origin interaction. The interaction was due to a higher risk of seropositivity in the category of herds with <or=100 animals and purchased cows (OR=1) as compared to herds with <or=100 animals and cows born in the farm (OR=0.23). Seropositivity between cows purchased and cows born in the farm was similar for herd sizes of 101-196 and >196 animals. The r(e) and D values were 0.17+/-0.05 and 3.16+/-0.57, respectively.