Infectious coryza remains an important disease in the poultry industry despite the long-term and widespread
use of vaccines against its causative agent, Haemophilus paragallinarum, in South Africa.
In order to detect antigenic changes between populations of H. paragallinarum isolated before the use
of vaccines against infectious coryza in this country, and field isolates obtained after the introduction of
infectious coryza vaccines, 106 different NAD-dependent isolates (of which 93 were identified as H.
paragallinarum) from 63 different farms, and dating from 1972 to March 1995, were identified by means
of rabbit antisera against serogroups A, B and C. Serogroup C isolates show weaker cross-protection,
requiring the further subdivision of this serogroup into its four different serovars.
The percentages of the different serovars obtained in the 1970s, confirmed previously published data
on South African isolates. A tendency towards a decrease in the number of serogroup A and serovar
C-2 isolates, and an increase in the percentage of serovar C-3 isolates, was noted among isolates of
the 1980s. These changes were markedly enhanced in the isolates obtained from 1990 to March 1995.
The percentage of serogroup A isolates decreased significantly from 34% in the 1970s to only 5% in
the 1990s, and that of serovar C-2 isolates, from 31-18%, while the abundance of serovar C-3 isolates
increased significantly from 31% in the 1970s to 73% in the 1990s. Serogroup B remained more or
less constant and never reached more than 10% of the population.
These results indicate the need for the incorporation of serovar C-3 in a vaccine for use in South Africa,
particularly in those areas of the country from which isolates were collected during this study.
Some of the NAD-dependent isolates obtained from poultry in South Africa between 1970 and 1995,
were biochemically identified as Pasteurella avium and P. volantium. As H. avium has been subdivided
and reclassified into the genus Pasteurella, this represents the first report of the identification of P. avium
and P. volantium in South Africa.
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