الفهرس 
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Abstract
A total of 500 samples were collected from infected as well as apparently healthy ducks, turkeys and chickens, of different ages irrespective of sex and bread. All samples were examined bacteriologically for isolation of Pasteurella multocida either by direct cultivation on 5% defibrinated sheep blood agar and modified Das selective media or by injection of 0.1 ml suspension of 8 hours old broth, cultivated by the samples from internal organs or nasopharyngeal swabs, into swiss mice for isolation, purification and reisolation of the organism. Out of 500 samples examined, 45 (9.0%) isolates of Past. multocida were recovered. Samples from internal organs from infected birds yielded 41 (14.64%) isolates while nasopharyngeal swabs from apparently healthy birds yielded 4(1.81%) Past. multocida isolates. Ducks showed the highest frequency of isolation where the incidence was 12% followed by turkeys (10%) and chickens (3.3%). The isolated Past. multocida were identified on the basis of colonial morphology, pathogenicity to mice, microscopical examination and biochemical reactions. Biochemically the isolated strains of Past. Multocida showed the same biochemical behaviour. These strains were shown to ferment arabinose, mannose, mannitol, sucrose and glucose but they have not the ability to ferment dulcitol, xylose, salicin, maltose and lactose. All strains were indole and oxidase positive, while MR, VP, urease, citrate, gelatin and hydrogen sulphide reactions were negative. Capsular typing of all the avian isolates put them within types A (91.11%) and D (8.88%) Carter, with the incidence of the type D among ducks only (13.3%). However Somatic typing revealed the presence of four 0 groups: 0-group 5, 0-group 8, 0-group 9 and 0—group 2. The results obtained by determining both the capsular and somatic antigens, showed that, the 45 Past. multocida strains isolated from ducks., turkeys and chickens were classified into: 5:A(23) isolates, 8:A(lO) isolates, 9:A(8) isolates and 2:D(4) isolates. The distribution of Past. multocida serovars among different bird species were as follows: out of 30 isolates from ducks, the following serovars were identified 5:A(15), 8:A(8), 9:A(3) and 2:D(4) isolates in an incidence of 50%, 26.6%, 10% and 13.3% respectively. In turkeys 5:A(6), 8:A(1) and 9:A(3) isolates in an incidence of 60%, 10% and 30% respectively. In chickens 5:A(2), 8:A(1) and 9:A(2) in an incidence of 40%, 20% and 40% respectively. The susceptibility of different Past. Multocida serovars to 20 different chemotherapeutic agents revealed that all isolates were sensitive to ampicillin, amoxicillin, colistine sulphate, doxycycline, fluineguine, furadantin, gentamicin, kanamycin, nalidixic acid, neomycine, oxytetra—cycline, polymyxin B, streptomycin, and trimethoprim. While these isolates were resistant to bacitracin, chloram—phenicol, erythromycine, lincomycine, penicillin C and tetracycline. The pathogenicity of the isolated serovars of Past. multocida were tested by inoculation of virulent strains isolated from different avian species through intramuscular and nasal cleft swabbing in chickens, ducks and turkeys of two age groups representing young and adult birds. The recorded mortality rate was 100% in all experimental birds within 18 to 120 hours indicating that the isolated serovars were pathogenic in such birds. The clinical signs observed among infected birds, included sudden death without the development of any premonitory characteristic symptoms, in cases inoculated within 18 to 24 hours. In cases which inoculated within 48 to 120 hours showed rapid breathing through the open beak, ruffled feathers and dullness. The post—mortem lesions included enlargement of the liver and spleen, hyperaemia and dark red in colour of internal organs. There was a peritonitis, and petechial haemorrhages on the serous surface. Past. multocida serovars 5:A, 8:A, 9:A and 2:D were proved to be pathogenic for different bird species. Mature age groups were found to be more susceptable to infection than young age. The route of inoculation showed also the influence on the mortality pattern of inoculated birds.