Occurrence and characteristics of A. vibacterium paragallinarum in Uganda
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Date
2006
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Sokoine University of Agriculture
Abstract
Investigations were conducted to establish the occurrence and characteristics of Avibacterium paragallinarum in Uganda. Seven hundred and ten bacteriological and serum samples (642 from healthy birds and 68 from chickens with coryza-like signs) were collected from chickens and turkeys for isolation of bacteria and demonstration of antibodies. Isolates were characterised by phenotypic (scrotyping, biotyping and antimicrobial susceptibility) and genotypic methods (enterobacterial repetitive intergenic sequence based polymerase chain reaction, ERIC-PCR and distribution of resistance genes). The potential role of gallinaceous birds in transmission of A.paragallinarum was evaluated experimentally and the efficacy of a commercial vaccine against the disease was assessed. Only five isolates were recovered and all were serotype C and NAD-dependent. Overall seropositivity was 40.5%, with 18%, 0.5% and 22 % against serotypes A, B and C, respectively. No antibodies were demonstrated in turkey sera. Multidrug resistance was demonstrated in three isolates and resistance genes for sulphamethoxazole (sn/2), ampicillin (blaTEM), tetracycline (tetC and tetA) and streptomycin (strA) were demonstrated. Only antimicrobial resistance markers differentiated isolates according to their epidemiological
background. Commercial and local chickens were equally susceptible to challenge while turkeys and guinea fowls showed transient mild signs and did not transmit infection neither did they pick infection from infected chickens. The isolates were resistant in normal chicken scrum at both 3 and 6 hours of incubation but resistant at 3 hours and sensitive at 6 six hours in turkey and guinefowl sera. The susceptibility of the isolates in serum correlated with their pathogenicity in the different poultry. No carrier status was demonstrated in this study using PCR and culture. Vaccinated birds were partially protected. This is the first report of isolation and characterisation of A. paragallinarum from Uganda. Resistance genes in A. paragallinarum are also reported for the first time. Studies based on a wider collection of isolates would be important to elucidate the mechanisms behind their persistence in carrier chickens and the potential exchange of resistance genes among respiratory tract pathogens.
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A. vibacterium paragallinarum, Uganda