Prevalence, epidemiology, and virulence of Pasteurella multocida and related organisms obtained from poultry and their animal contacts
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Date
2000
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The Royal Veterinary and Agricultural University
Abstract
This thesis is divided into two sections. The first section presents six reviewing chapters in relation to work performed and a chapter detailing conclusions from the study. The second part contains four papers referred to as Appendix 1-1V, which detail the work in the thesis. The articles I and II present prevalence and epidemiological investigations of P. multocida in commercial poultry flocks in Denmark, and free range village chickens and their contact animals in Tanzania. Article 111 discusses phenotypic, molecular and epidemiological investigations of Pasteurella species obtained from Tanzania. The last article presents the study on correlation between serum resistance, outer-membrane proteins and virulence of P. multocida.
The prevalence of P. multocida carriers in the flocks with a history of fowl cholera was shown to be significantly higher than that of the flocks without a history of fowl cholera in commercial flocks in Denmark (Appendix I). These findings underline the importance of surviving birds in the epidemiology of fowl cholera. The carriers in flocks without history of fowl cholera were also demonstrated, but their role in fowl cholera is still uncertain. All three subspecies of P. multocida, namely ssp. Multocida, ssp. septica and ssp. gallicida were demonstrated, but the subspecies gallicida was obtained exclusively from Pekin ducks from a farm with a history of fowl cholera. A single clone affected each of the investigated flocks, but some clones appealed in more than a single flock. Investigations into strains of P. multocida from one of the farms in four consecutive outbreaks demonstrated a different clone in each outbreak. This indicates that outbreaks are clonal, and the disease can be eliminated from the infected farms. Isolation of P. multocida from the cloacal mucosa of earners was reported for the first time, however, the significance of cloacal earners in spreading infection is not known.
Occurrence of P. multocida and related species in free ranging chickens and ducks, dogs and pigs (Appendix II) was investigated in three subclimatic zones; hot, warm viand cool, in rural Morogoro district, Tanzania. The strains obtained included P. multocida ssp. multocida from chickens, ducks, cats and dogs, /< multocida ssp. septica from dogs and cats, gallinarum from a duck, P. canis and P. dagmatis from dogs, and P. slomatis from dogs and cats. Other strains included organisms with uncertain taxonomic affiliation named taxon 16, and unclassified strains with Pasteurella like features. P. multocida was obtained from two chickens (2%) and 11 ducks (22%) of warm zone. No isolates were obtained from poultry in the remaining zones. Cats had the highest prevalence of P. multocida ssp. multocida, while P. canis and taxon 16 were predominant in dogs. Mouse inoculation was more sensitive in etecting P. multocida ssp. multocida than blood agar and selective medium. Direct culture on blood agar recovered most of the other Pasteurella spp.. These findings demonstrated the existence of P. multocida carriers in the free ranging village poultry, cats and dogs, and underline the potential of exchange of strains between the different animal species. Surveillance of diseases in free ranging village chickens to gauge the clinical importance of fowl cholera and other diseases was recommended.
One hundred and forty-three Pasteurella spp. strains and ten unclassified strains obtained from free ranging poultry, dogs and cats were investigated by extended phenotypic characterization (Appendix III). One hundred and forty-nine of these strains were selected for further studies using ribotyping and REA-typing to evaluate the role of dogs and cats in P. multocida transmission to poultry. Seven and six-type strains were included for comparison in phenotyping and genotyping, respectively. Eleven clusters and six unclustered strains were revealed by phenotyping. Ribotyping outlined twelve clusters and six unclustered strains. A correlation between clusters obtained by phenotyping and ribotyping was demonstrated which indicated that a genetic basis exists for clusters outlined by quantitative evaluation of phenotypic data. Similarities and differences in hosts, phenotype, ribotype, and zone of isolation were demonstrated among Pasteurella strains investigated. Isolates of P. multocida from ducks were shown to be clonal by both phenotyping and ribotyping. These strains were identical to one of the chicken strains. REA-typing, however, showed that the chicken strain was different underlining that exchange of clones of P. multocida viibetween avian species seems to be rarely happening under village conditions. Management practices in the villages suggest the potential for exchange of P. multocida between poultry and animals kept in contact. Tire present findings, however, did not indicate that clones of P. multocida are widely exchanged between poultry and other animal species even though close contact exists. In the present investigation, exchange of clones of P. multocida was only demonstrated among animals belonging to the same species. Caution is drawn to the use of ribotyping alone for epidemiological typing and tracing of P. multocida. The present results also underline the importance of proper phenotyping in the identification of P. multocida and related species.
Serum resistance of P. multocida in the sera from chickens, turkeys, ducks and pigs was determined and correlated with in-vitro and in-vivo outer-membrane proteins expression and virulence in chickens. Eighty-seven field strains of Pastcurella and nine reference strains representing different clones were grown in sera from chickens, ducks, turkeys and pigs. Serum activity of each strain was measured by changes in the optical density of the serum after inoculation and incubation at 41 °C for chicken, turkey and duck serum and 39 "C for pig serum. The strains were classified into High serum resistant (R), moderate serum resistance (M), and serum sensitive (S) by comparing with strains of known serum activity. Strains of identical genotype by Restriction endonuclease analysis were found to have identical growth curves and the same maximum OD values, when cultured in serum from the same host species. Turkey serum was shown to be less inhibitory to a wide range of P. multocida strains than chicken, duck and pig sera. Serum resistant strains were demonstrated among avian as well as mammalian strains, with the proportion of serum resistant strains being higher in fowl cholera outbreak strains than in non-outbreak avian strains. A range of minor and major outer-membrane proteins were common among the selected serum resistant and serum sensitive strains, when cultured in BHI, in-vivo and in chicken serum. However, no specific OMP expressed in vitro or in vivo was consistent with serum resistance or sensitivity among the strains investigated. Although most severe lesions in experimentally infected chickens were produced by a serum resistant strain, lesions were also found in chickens infected by scrum sensitive strains, indicating the involvement of multiple factors in the virulence of P. multocida. Further investigations on scrum resistance should also relate other host and bacterial factors responsible development of fowl cholera.
Description
PhD Thesis
Keywords
Pasteurella multocida, Poultry