Evaluation of combined Pasteurella vaccines in control of sheep pneumonia

Characterisation and pathogenicity of Pasteurella multocida capsular serogroup A isolates from Awassi sheep in Syria

The aim of the present study was to evaluate the prevalence of serogroup A of Pasteurella multocida in Syrian Awassi sheep. Of 1630 samples collected from nasal swabs of healthy and pneumonic sheep (125 herds) and pneumonic sheep lungs, a total of 228 (13.9%) strains were isolated and identified as P. multocida subsp. multocida by phenotypic and biochemical characterisation. However, of them only 117 (51.3%) were identified as serogroup A of P. multocida when PCR assay with specific primers for serogroup A strains was applied. The highest rate of serogroup A isolation was from apparently healthy sheep (49.6%) with consideration that all lung isolates (23 isolates) belonged to serogroup A. Geographical and seasonal distribution showed that about 60% of positively isolated bacteria originated from Syrian desert (29 isolates) and central parts of semi-arid step zone (41 isolates). A significant increase (P≤0.05) in the rate of positive isolates was observed in winter as compared to spring. Pathogenicity tests of 10 isolates with 50 or 10 LD50 values showed that 5 isolates were able to induce symptoms of fowl cholera in challenge-exposed chickens indicating that migratory Awassi sheep might serve as a carrier for serogroup A of P. multocida and that ovine isolates may be virulent for local breed of chickens.

Exploring the importance of mixed autogenous vaccines as a potential determinant of lung consolidation in lambs using Bayesian networks

Bayesian networks are used to evaluate the effectiveness of mixed autogenous vaccines in fattening lambs to prevent the ovine respiratory syndrome. An experiment was performed with 460 fattening lambs, which were clustered into four groups according to the kind of vaccine received (Pasteurella spp., Mycoplasma spp., Mixed Mycoplasma-Pasteurella or placebo). After slaughtering, lungs were collected, and macroscopic and microscopic studies were performed. A microbiological study was carried out to evaluate the presence of Mycoplasma spp. and Pasteurellaceae by conventional culture and identification by nested polymerase chain reaction. To the best of the authors' knowledge, Bayesian networks have not been used to evaluate the effect of vaccines on the absence/presence of lung consolidation. Our results revealed that the use of mixed autogenous vaccines can decrease lung consolidation from 15.75% (12.42-19.08) to 9.24% (6.59-11.89). Therefore, the use of these autogenous vaccines in farms could be considered an effective control tool against ovine respiratory syndrome.

Phylogenetic analysis of Indian isolates of Pasteurella multocida based on partial 16S rRNA gene sequences: Association of caprine isolate with lineage B

Pasteurella multocida is responsible for diseases, which are endemic and economically important in India, still comparative investigations on phylogenetic relations of Indian P. multocida isolates are scarce. Therefore, present study was undertaken to understand the phylogenetic relationship of several isolates belonging to different host, place of isolation and capsular types based on partial 16S rRNA gene sequencing. In the current study, a 838 bp fragment of 16S rRNA gene of 35 field isolates of P. multocida belonging to different capsular types, recovered from cattle, buffalo, sheep, goat, pigs and birds, collected from different states of India sequenced and analyzed. There were 12 unique 16S rRNA types among 35 isolates, which clustered into 2 distinct phylogenetic lineages, viz. A and B. There were strong correlations between the phylogenetic relations and capsular types, with maximum heterogeneity seen among isolates of capsular type A. However, there was no clustering based on the host or place of isolation indicating the potential hazard of interspecies sharing and the possibility of translocation of infected animals across international borders. Moreover, one of the caprine isolates belonged to lineage B. To the best of our knowledge, this is the first report of a caprine isolate in lineage B, since lineage B is reported to be exclusively associated with birds and cats. It may be alarming that the strains of lineage B are becoming adapted to different host species.

Comparative analyses of Pasteurella multocida strains associated with the ovine respiratory and vaginal tracts

Thirty-five isolates of Pasteurella multocida from the vagina and respiratory tract of sheep were compared by analysing their capsular polysaccharide types and outer membrane protein profiles. The phylogenetic relationships of selected isolates with respect to reference strains of P. multocida were also determined by comparative 16S rRNA sequence analysis. Three capsular types, A, D and F, and three major outer membrane protein types were identified, and there were four different combinations of these characteristics which probably marked four individual clones of P. multocida. Strains representing three of these clones were recovered from cases of ovine pneumonia, whereas isolates of the fourth clone were associated exclusively with the vagina of healthy ewes and the liver of a dead septicaemic lamb on the same farm. Analysis of the 16S rRNA sequences showed that there was 100 per cent identity between representative pneumonic isolates and reference strains of P. multocida subspecies galliseptica and P. multocida subspecies multocida. The 16S rRNA genes of representative vaginal and liver isolates from the same farm were identical but differed from the other strains at one nucleotide position, providing strong evidence that the vaginal and liver isolates represent a distinct subpopulation of P. multocida.

Efficacy of intranasal administration of formalin-killed Pasteurella haemolytica A2 against intratracheal challenge in goats

A trial was conducted to compare the efficacy of intranasal vaccination in protecting goats against pneumonic pasteurellosis with intramuscular vaccination using an oil adjuvant vaccine, and a combination of the two methods. Forty goats were divided into four equal groups. Group 1 was vaccinated twice intranasally with formalin-killed Pasteurella haemolytica A2, group 2 was vaccinated twice intramuscularly with an oil adjuvant vaccine containing P haemolytica A7, and group 3 was initially vaccinated intranasally with the formalin-killed P haemolytica A2 followed by intramuscular vaccination with the oil adjuvant vaccine. In each group the two vaccinations were carried out four weeks apart. Group 4 was the unvaccinated control group. All goats were challenged intratracheally with 4 ml of an inoculum containing live P haemolytica A2 at a concentration of 1.3 x 10(7) colony forming units/ml two weeks after the last vaccination and were killed 14 days after the challenge. Although group 2 showed the highest clinical score following the challenge, deaths were observed only in group 3. Three goats in group 1 had pneumonic lung lesions, compared with six goats in group 2 and all the goats in groups 3 and 4. The lung lesions in group 1 were significantly (P < 0.05) less severe than in groups 3 and 4. Similarly, the lesions in group 2 were markedly less severe than in groups 3 and 4, although the differences were not significant. The difference between the extent of the lung lesions in the goats in groups 1 and 2 was not significant. Antibody against P haemolytica A2 in group 1 reached peak levels and was significantly (P < 0.01) higher than in the control group one week after the second vaccination, before declining.

An epidemiological study into risk indicators for Pasteurella haemolytica related 'summer pneumonia' in lambs in the southern Netherlands

Risk indicators for Pasteurella haemolytica related summer pneumonia in lambs in The Netherlands were investigated using a mail questionnaire survey of 860 flocks. The response rate was 64% (n = 550). Multivariate risk analysis indicated that taking sheep to sheep fairs, the purchase of sheep and/or lambs, the lack of possibility for indoor housing, and an increased flock size were associated with increased risk of occurrence of summer pneumonia in lambs of the home flock.