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Effects of differences in virulence of different serovars of Haemophilus paragallinarum on perceived vaccine efficacy.

Abstract

The virulence of four South African field isolates of NAD-dependent Haemophilus paragallinarum and two field isolates of NAD-independent H. paragallinarum has previously been tested in unvaccinated chickens. In this study, the disease profiles caused by the NAD-dependent isolates of H. paragallinarum in vaccinated chickens were studied. It was shown that the clinical signs induced in the vaccinated chickens were substantially less severe than were those in unvaccinated chickens, as was expected. However, due to the high virulence of the serovar C-3 isolates, clinical signs in the vaccinated chickens challenged with this isolate were still detected. These were as severe as those occurring in unvaccinated chickens challenged with serovar B-1 isolates. Although the clinical signs induced in unvaccinated birds challenged with serovar A-1 were more severe than those occurring when vaccinated birds were challenged with serovar C-3, the overall disease profiles were similar. Substantial clinical signs were recorded in vaccinated birds challenged with serovar C-3. This could be interpreted as vaccination failure if the disease profile obtained in unvaccinated birds is not considered. It was found that a high level of protection was provided by this vaccine against challenge by serovar C-3. The high virulence of this serovar resulted in the development of clinical signs in vaccinated birds. These findings could possibly explain the large number of so-called vaccination failures that are reported in South Africa.

Authors+Show Affiliations

Department of Microbial, Biochemical and Food Biotechnology, University of the Free State, P.O. Box 339, Bloemfontein, 9300, South Africa. BraggRR.sci@mail.uovs.ac.za

Source

MeSH

Animals
Bacterial Vaccines
Chickens
Female
Haemophilus Infections
Haemophilus paragallinarum
NAD
Poultry Diseases
Random Allocation
Serotyping
Treatment Outcome
Virulence

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

15991700

Citation

Bragg, R R.. "Effects of Differences in Virulence of Different Serovars of Haemophilus Paragallinarum On Perceived Vaccine Efficacy." The Onderstepoort Journal of Veterinary Research, vol. 72, no. 1, 2005, pp. 1-6.
Bragg RR. Effects of differences in virulence of different serovars of Haemophilus paragallinarum on perceived vaccine efficacy. Onderstepoort J Vet Res. 2005;72(1):1-6.
Bragg, R. R. (2005). Effects of differences in virulence of different serovars of Haemophilus paragallinarum on perceived vaccine efficacy. The Onderstepoort Journal of Veterinary Research, 72(1), pp. 1-6.
Bragg RR. Effects of Differences in Virulence of Different Serovars of Haemophilus Paragallinarum On Perceived Vaccine Efficacy. Onderstepoort J Vet Res. 2005;72(1):1-6. PubMed PMID: 15991700.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Effects of differences in virulence of different serovars of Haemophilus paragallinarum on perceived vaccine efficacy. A1 - Bragg,R R, PY - 2005/7/5/pubmed PY - 2005/9/9/medline PY - 2005/7/5/entrez SP - 1 EP - 6 JF - The Onderstepoort journal of veterinary research JO - Onderstepoort J. Vet. Res. VL - 72 IS - 1 N2 - The virulence of four South African field isolates of NAD-dependent Haemophilus paragallinarum and two field isolates of NAD-independent H. paragallinarum has previously been tested in unvaccinated chickens. In this study, the disease profiles caused by the NAD-dependent isolates of H. paragallinarum in vaccinated chickens were studied. It was shown that the clinical signs induced in the vaccinated chickens were substantially less severe than were those in unvaccinated chickens, as was expected. However, due to the high virulence of the serovar C-3 isolates, clinical signs in the vaccinated chickens challenged with this isolate were still detected. These were as severe as those occurring in unvaccinated chickens challenged with serovar B-1 isolates. Although the clinical signs induced in unvaccinated birds challenged with serovar A-1 were more severe than those occurring when vaccinated birds were challenged with serovar C-3, the overall disease profiles were similar. Substantial clinical signs were recorded in vaccinated birds challenged with serovar C-3. This could be interpreted as vaccination failure if the disease profile obtained in unvaccinated birds is not considered. It was found that a high level of protection was provided by this vaccine against challenge by serovar C-3. The high virulence of this serovar resulted in the development of clinical signs in vaccinated birds. These findings could possibly explain the large number of so-called vaccination failures that are reported in South Africa. SN - 0030-2465 UR - https://www.unboundmedicine.com/medline/citation/15991700/Effects_of_differences_in_virulence_of_different_serovars_of_Haemophilus_paragallinarum_on_perceived_vaccine_efficacy_ L2 - https://medlineplus.gov/haemophilusinfections.html DB - PRIME DP - Unbound Medicine ER -