Haemophilus paragallinarum causes an acute respiratory disease of chickens known as
infectious coryza (IC), a disease first recognized as a distinct entity in the late 1920's.
Since the disease proved to be infectious and primarily affected nasal passages, the name
"infectious coryza" was adopted (Blackall, 1989). Infectious coryza may occur in both
growing chickens and layers. The major economic effect of the disease is an increased
culling rate in meat chickens and a reduction in egg production (10-40%) in laying and
breeding hens. The disease is limited primarily to chickens and has no public health
significance (Yamamoto, 1991). The most common clinical signs are a nasal discharge,
conjunctivitis, and swelling of the sinuses and face. Various sulfonamides and antibiotics
are useful in alleviating the severity and course of infectious coryza; however, none of
the therapeutic agents has been found to be bactericidal. Relapse often occurs after
treatment is discontinued, and the carrier state is not eliminated (Yamamoto, 1991). All
the commercially available bacterins against IC, consist of inactivated broth cultures of a
combination of two or three different serotypes. Although vaccines against IC have been
used in South Afr ica since 1975, it became apparent in the 1980s that the vaccines were
becoming less effective in controlling the disease (Bragg et al., 1996). This could have
been due to the emergence of a previously unknown serovar, or even serogroup and the
possibility of changes in the population dynamics. Vaccine efficiency is therefore a
problem and an alternative to available vaccines is needed.
Capsules have long been associated with virulence properties of bacteria. The
role that the capsule play in the virulence of bacterial species related to H.
paragallinarum has been investigated by several workers (Kroll et al., 1988; Inzana et
al., 1993; Boyce and Adler, 2000). Mutation, deletion or allelic exchange of gene/s
involved in the transport of capsule polysaccharides in related species like Haemophilus
influenza, Actinobacillus pleuropneumoniae and Pasteurella multocida, resulted in
organisms with reduced virulence. The noncapsulated mutants of Actinobacillus
pleuropneumoniae reported by Inzana et al. (1993) showed extreme stability and induceda protective immune response without any symptoms of disease. This not only proves
the capsule�s involvement in virulence of bacteria but also offers the opportunity to
investigate the possibility of producing live vaccines.
The aim of this study was an attempt to understand the genetic organization of the
capsular genes of H. paragallinarum in comparison to related HAP organisms and the
possibility of producing a mutant lacking the capsule.
The goals were:
1. Isolation and cloning of the capsule transport gene locus.
2. Sequencing and characterization of the locus
3. Transplacement of a gene/s to produce a noncapsulated mutant of
H. paragallinarum.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-09202002-150943 |
| Date | 20 September 2002 |
| Creators | de Smidt, Olga |
| Contributors | Dr. J Albertyn, DR. RR Bragg, Dr. E van Heerden |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://lourie.uovs.ac.za//theses/available/etd-09202002-150943/restricted/ |
| Rights | mixed, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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