Chlamydial infections
Chlamydophila psittaci : Typing
C. psittaci strains isolated from different avian species
consist of many different serovars which may be differentiated by experimental host range and
their ability to cause disease (Schachter and Caldwell,
1980). Currently, there are eight established serovars from a variety of avian hosts which
can be differentiated by serovar-specific monoclonal antibodies
(Andersen, 1997; Vanrompay
et al., 1993). These serovars are as follows:
| Serovar |
Comment / Distribution |
A
|
psittacine birds; endemic; often systemic but can be
inapparent; sporadic zoonotic disease in humans |
B
|
pigeons; endemic; also from turkeys; also caused abortion in dairy
cattle |
C
|
duck, turkey, partridge; specific avian host not identified; zoonotic risk to poultry workers and people in
contact |
D
|
turkeys, seagull, budgerigar, humans; zoonotic risk to poultry workers and people in
contact |
E
|
ducks, pigeons, ostriches and rheas; specific avian reservoir not identified; first isolated from cases of pneumonitis in
humans |
F
|
parakeets; single isolate in this
serovar
|
G
|
isolated from a disease outbreak in muskrats and
hares
|
H
|
isolated from enteritis in
cattle
|
Some C. psittaci strains carry an extrachromosomal
plasmid
[see: chlamydial plasmids], and several strains are infected with bacteriophages
(Storey et al., 1992; see: chlamydial
phages). Monoclonal antibodies against the chlamydial lipopolysaccharide (LPS) and major outer membrane protein
(MOMP) antigens have been used to distinguish between avian C. psittaci and mammalian chlamydial strains
(Fukushi et al., 1987). C. psittaci isolates from birds have also been differentiated in restriction mapping of
gene encoding chlamydial MOMP (Sayada et al.,
1995). In an analysis of 65 avian isolates, seven groups were found which did not correspond to host or geographic specificity. Again, these groups were all distinguishable from mammalian chlamydial strains.
Phylogenetic analyses have also been carried out on avian chlamydial strains based on 16S rRNA gene sequences
(Takahashi
et al., 1997). This study identified four genetic groups among a range of avian and mammalian
isolates within the previous
C. psittaci taxon. These authors concluded that the 16S-23S intergenic spacer regions, which are more variable than 16S
rDNA, could be used for more precise identification / differentiation. In a further development, which led to the proposed reclassification of the order
Chlamydiales, Everett et al., (1999) reported
phylogenetic analyses of 16S and 23S rRNA chlamydial
genes [see taxonomy]. All avian chlamydial strains were placed in the Chlamydophila psittaci
taxon, for which the type strain is 6BC (ATCC
VR125).
NEXT: C. psittaci: Treatment
and control
|
