SALMONELLA ENTERICA SEROVAR DUBLIN INFECTION IN DAIRY CATTLE: A CASE STUDY ON THE MANAGEMENT OF AN OUTBREAK IN VENETO REGION

Salmonella enterica, subsp. enterica serovar Dublin (S. Dublin), is a serovar adapted to cattle, causing both intestinal and systemic infections. The introduction of the bacterium leads to serious economic losses due to abortions, high mortality in calves and persistent infections, also representing a major health problem as zoonotic agent. This case study describes an outbreak of S. Dublin on a farm of 210 Holstein-Friesian lactating cows. Clinical signs were observed in calves younger than 6 months; deaths occurred in animals younger than 30 days. Following the conferral at the IZSVe of a newborn calf that died from enteric syndrome, S. Dublin was diagnosed. At the autoptic exam pathological findings were observed in gut, liver, pericardium, lungs, joints, lymph nodes and abomasum. Considering the pathogenesis of S. Dublin, authors decided to apply a protocol prepared by the IZSVe based both on direct and indirect prophylaxis. Screening tests were performed both on fecal and milk samples. Feces were collected from 80 animals (dry-off cows and calves), in 7 times; 25 milk samples were collected from bulk tank milk (BTM). 2 environmental swabs were also collected from lactating and dry cows’ boxes. All lactating cows were tested with fecal swabs 2 times for a total of 220 and 223 dairy cows. Considering the difficulty to find an effective commercial vaccine against S. Dublin, an autogenous vaccine prepared by the Istituto Zooprofilattico Sperimentale della Sardegna (IZS Sardegna) was administered. A pre and post-vaccination screening was performed to assess the immunization of cows and the effectiveness of the protocol itself. A total of 52 cattle randomly selected among cows and heifers were enrolled for a 3-time sampling (T0, T1, T2), the first 1 day prior immunization, the second and the third 2 and 11 months later respectively, both on feces and serum, collecting blood samples from the coccygeal vein. 25 BTM samples were also weekly bacteriologically analyzed. Serological examination identified 13/52 (25%), 49/49 (100%) and 32/44 (73%) positive animals at T0, T1 and T2 respectively. No fecal sample in all time-points was found positive. After vaccination only 1 milk sample turned out positive. Considering the pathogenesis of S. Dublin, the negativity of the bacteriological exams suggests a positive effect of the protocol in the reduction of clinical cases, circulation of the etiological agent and biocontainment of the infection.