Chlamydial infections in animals
Infections in pigs
Chlamydial infections in pigs have been
described as the cause of several different clinical syndromes including
pneumonia, conjunctivitis, polyarthritis ,
and polyserositis.
In addition, infection has also been associated with reproductive disorders,
notably abortion in sows and orchitis
in boars (Bohac and Menzik, 1965; Popovici
et al., 1972 Surdan et al.,
1965). The distribution of chlamydial infections of pigs appears to be
worldwide, the majority probably occurring in large breeding complexes.
In early reports, chlamydiae were isolated
from an outbreak of enzootic pneumonia of pigs (Sorodoc et al.,
1961), and from piglets with pneumonia and pericarditis (Guenov,
1961). After experimental exposure of young piglets to chlamydial agents, Pavlov et al.
(1963) described an infectious keratoconjunctivitis. The affected piglets
developed fever, became anorectic and depressed. Chlamydiae have also been
isolated from inapparent intestinal infections in apparently healthy pigs (Kolbl,
1969). Antibodies to chlamydial agents were also
demonstrated in pigs with inapparent infection (Wilson
and Plummer, 1966) suggesting that subclinical infections may be prevalent (Harris,
1976). Chlamydiae in pigs have also been associated with arthritis (Kazemba et al.,1978), intestinal infection (Pospischil
and Wood, 1987) and pneumonia. There may be systemic spread to other organs.
Disturbances of gait and general weakness may be associated with polyarthritis,
while in sows infected by the transmission of chlamydiae in boar semen, abortion
and stillbirth may occur. Piglets born to infected sows may themselves be
infected, occasionally fatally. The infected sows continuing to shed chlamydiae
for a considerable time.
Laboratory diagnosis
Sachse et
al., 2003 examined 109 clinical samples (organ tissue, nasal, and faecal
swabs) from pigs experimentally infected with Chlamydia suis by cell
culture, nested PCR in the ompA gene region, and by two different antigen
enzyme-linked immunosorbent assays (ELISAs). Culture and PCR produced the
highest proportion of concordant results (kappa coefficient 0.712). Among 99
samples, 34 were positive in both assays, 51 were negative in both assays, 12
culture-negatives were positive in PCR, and only 2 culture-positives were
negative in PCR. The sensitivity and specificity of PCR versus culture as
standard were 94.4% and 81.0%, respectively. The corresponding values for the
converse, culture versus PCR as standard were 73.9% and 96.2%, respectively.
Both ELISA tests were less satisfactory. These data underline the potential of
PCR as a detection method for C. suis infection in pigs.
Typing
Chlamydial isolates from pigs with abortion or
pneumonia, previously classified as Chlamydia psittaci, were placed
in immunotype 6 (Spears and Storz 1979;
Perez-Martinez and Storz, 1985).
These strains are now reclassified as Chlamydophila pecorum (Everett et al.,
1999). Isolates from cases of polyarthritis, originally classified as Chlamydia pecorum
are now reclassified as Chlamydophila pecorum (Everett et al.,
1999).
The occurence in pigs of a C. trachomatis-like
agent, closely related to the former mouse pneumonitis biovar [C.
muridarum], but subsequently reclassified as Chlamydia suis
[Everett et al., 1999], has already been described [see: C.
suis]
C. abortus, identified by PCR,
has also been associated with orchitis and abortion (Welchman et al.,
1999). In a PCR-based study of the genital tracts of 101 breeding sows (Busch et al.,
2000) C. abortus was found in 10 cases and avian C. psittaci
in one case. C. trachomatis [C. suis?]
was also detected by PCR in several cases. However the overall results were
inconclusive because faecal contamination of samples may have occurred. A
PCR-based study by Schiller et al.
(1997), suggested an association between abortion and mixed infections with C. pecorum
and C. suis. However C. abortus was also detected. Hoezle
et al., (2000) found a high prevalence of mixed infections with C. abortus
and C. suis in the pig lung and intestine [see: C.
suis]. Reproductive tract
disease in sows was strongly associated with the presence of C. abortus.
The possible presence of mixed chlamydial
infections involving up to three chlamydial species causing both symptomatic and
inapparent infection is an important consideration for the xenotransplantation
of pig organs to humans. Although specific pathogen-free pigs may be used for
this purpose, screening methods will need to cover chlamydiae in order to
eliminate the possibility of zoonotic infection. Worryingly, although antibiotic
resistance has been uncommon among chlamydiae, Lenart et al.,
(2001) have described two C. suis strains that are resistant to
tetracycline, one of the main planks of anti-chlamydial chemotherapy. The
potential for antibiotic resistance among animal chlamydiae to transfer to human
chlamydial species is unknown, but C. suis is closely related to C.
trachomatis.
[PG] Updated [MEW] June 2003
Bibliography
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