Prevalence of different OmpH-types among Pasteurella multocida isolated from lungs of calves with respiratory problems.

Pasteurella multocida is among the most important respiratory pathogens of cattle. Outer-membrane protein (OmpH) constitutes an essential bacterial antigen and is well studied in avian bacterial strains. Studies on isolates from cattle with signs of respiratory disease caused by Pasteurella multocida serotypes A and D have not yet been covered in the literature. The objective of this study was a comparative analysis of the ompH gene sequences from 83 isolates and four Russian reference strains of P. multocida to assign them to the allelic variants of the gene (OmpH-types). In addition, the above P. multocida strains have been characterized on the basis of capsular serotypes and virulence-associated genes. The isolates were classified into the OmpH -types based on allele specific PCR and gene fragment sequencing. The isolates of capsular serotype A have been subdivided into 6 OmpH -types, of which the most common types identified were A1 and A2. All capsular serotype D isolates belong to the same OmpH-type (D1). On 16 of a total of 23 farms all isolates belong to only one OmpH-type, on 4 farms - to 2, and on 3 farms - to three OmpH-types. The tbpA and pfhA genes were found more often in the isolates of capsular group А as compared to capsular group D (p ≤ 0.05). OmpH-types of serogroup А differ significantly (p ≤ 0.05) among themselves by the prevalence of the pfhA and hgbB genes.

Virulent Properties of Russian Bovine Viral Diarrhea Virus Strains in Experimentally Infected Calves.

The results of experimental study of three noncytopathic and two cytopathic bovine viral diarrhea virus (BVDV) strains isolated from cattle in the Siberian region and belonging to the type 1 (subtypes 1a, 1b, and 1d) have been presented. All investigated strains caused the development of infectious process in the seronegative 4-6-month-old calves after aerosol challenge with the dose of 6 log10 TCID50. The greatest virulence had noncytopathic strain and cytopathic strain related to the subtypes 1d and 1b, respectively. All strains in infected calves caused some signs of moderate acute respiratory disease and diarrhea: depression 3-5 days postinfection (p.i.), refusal to food, severe hyperthermia to 41.9°Ð¡, serous exudate discharges from the nasal cavity and eyes, transient diarrhea with blood, leukopenia (up to 2700 cells/mm(3)), and macroscopic changes in the respiratory organs and intestine. The infected animals recovered from 12 to 15 days p.i. and in 90% cases formed humoral immune response 25 days p.i. (antibody titers to BVDV: 1 : 4-1 : 16). Our results confirmed the presence of virulent BVDV1 strains and showed the need for researches on the molecular epidemiology of the disease, development of more effective diagnostic systems, and optimization of control programs with use of vaccines.