Chlamydial infections in animals
Chlamydophila abortus in ruminants:
Epidemiology
In Britain, C. abortus [formerly
C. psittaci serogroup 1] continues to be the major
genital tract infection affecting sheep flocks. It is estimated to cost the sheep industry more than £20 million a year
(Aitken et al., 1990). Flocks or herds
become affected by the introduction of asymptomatic carrier animals harbouring chlamydial infection. The movement of sheep through markets and across country is likely to contribute to the spread of disease.
The increased movement of animals in recent years and improved diagnosis
may explain why the disease is apparently increasing. In general, chlamydial abortion is most common in lowland sheep flocks, and occurs mainly where sheep are closely confined.
In Switzerland,
Chanton-Greutmann et al 2002
investigated the aetiology of abortion in 144 goats and 86 sheep over two
lambing seasons (1996/1997, 1997/1998). Macroscopic inspection of the foetus and
placenta was complemented by histopathology, by immunohistology for
Toxoplasma gondii, Neospora caninum, C. abortus and Border
Disease Virus, or by bacteriological culture. C. abortus was the most
commonly identified agent of infection-associated abortion, being found in
39% of sheep and 23% of goats), followed by T. gondii (sheep 19%, goats
15%) and Coxiella burnetti (sheep 1%, goats 10%). All other agents were
of minor importance. A seroprevalence study by competitive ELISA on 639 sheep
flocks in eight cantons of Switzerland representative of 60% of the Swiss sheep
population found that almost 19% (118) of the examined flocks were seropositive
for chlamydiae [Borel et al.,
2002].
Infection is most likely to be contracted by uninfected sheep at lambing time by ingestion of C. abortus.
This is excreted by infected and aborting ewes in huge numbers in diseased
placenta, uterine discharges, and faeces. In colder climates, lambing and handling of pregnant and
post-partum ewes may occur in barns, where exposure of humans to the infectious agent may be greater than in open pastures. In sheep, the infection remains present at a subclinical (clinically and serologically undetectable) level until the last four weeks of the next pregnancy. The major outbreak of disease in a flock tends to occur in the second lambing season after C. abortus infection was acquired. It has also been reported that sheep can acquire C. abortus infection and abort in one lambing season
(Storz, 1971). Most affected sheep abort in the last month of gestation. The majority of aborting ewes are young animals, although sheep of all ages are susceptible to infection
(Young et al., 1958). In a flock experiencing C. abortus
infection for the first time, up to 30% of pregnant ewes may abort. In subsequent years, as the infection becomes established as an enzootic disease, between 5-10% of pregnant ewes abort annually. C. abortus infection resulting in abortion leads to
effective immunity in affected ewes.
Chlamydial abortion in goats has been described in several countries around the world including the U.S.A.
(McCauley and Tieken, 1968), India
(Jain et al., 1975) and the U.K.
(Appleyard et al., 1983). Chlamydial strains causing abortion in goats are thought to be similar to abortion strains in sheep. A cycle of infection, which is similar to that seen in sheep, has been described for chlamydial abortion in goats
(Brown et al., 1988). Human infection resulting from contact with infected goats has been reported
(Villemonteix et al., 1990). It is likely that chlamydial abortion in goats should be treated as a similar threat to human health as infection in sheep.
In cattle, chlamydial abortion is believed to have a worldwide distribution. The disease has been diagnosed in several states in the U.S.A.
(Storz, 1971) and in countries around the world, such as France
(Giroud, 1957), Germany (Schoop
et al., 1965), Spain (Blanco,
1969), the U.K. (Holliman et al.,
1994) and the Indian subcontinent (Nanda
et al., 1992). Chlamydial abortion in cattle has not been considered as a major threat to the cattle industry, and as a result has been less well researched than ovine chlamydial abortion. Although the disease is similar to enzootic abortion in sheep, chlamydial abortion in cattle and in other species such as pigs is much more
sporadic
and less common than the disease in sheep and goats.
C. abortus isolates have also been recovered or implicated in cases of abortion in the horse, rabbit, guinea pig and mouse
(Everett
et al., 1999). In chlamydial abortion in cattle, up to 20% of pregnant cows may abort
(Storz and McKercher, 1962). It is likely that transmission of
the disease in cattle occurs as in sheep, by
the ingestion of infected tissues. In the U.S.A. a 53% prevalence of vaginal
C. abortus or C. pecorum infection has been detected in virgin
heifers by quantitative PCR, suggesting that transmission may be predominantly
extragenital [DeGraves et al.,
2003a; 2003b]. In some states of the U.S.A., seasonally related episodes of abortion have been observed, which are most likely due to breeding practices. Chlamydial abortion in cattle is usually associated with C. abortus infection
(Kwapien et al., 1970; Holliman et al.,
1994). However, C. pecorum infection is also associated with metritis,
salpingitis and infertility in cattle, and may cause sporadic abortion
(Bowen et al., 1978; Wittenbrink et al.,
1993; Magnino et al., 2000).
Experimental intrauterine infection of cattle with C. psittaci resulted in lesser pathological changes to the uterus
than C. pecorum, and was thought to be an unlikely cause of infertility.
By contrast C. pecorum infection resulted in a severe metritis which would have resulted in at least temporary infertility
(Jones, 1999). Infertility problems have occurred in dairy cows following abortions
(Reed et al., 1975), and it is possible that sporadic abortions, which may be due to C. pecorum, are
either undiagnosed or are mis-diagnosed as C. abortus. This might arise because of the
limited recognition of the metritis / infertility disease syndrome in cattle caused by C. pecorum.
There are a number of reports of pregnant women who have had spontaneous abortions following exposure to sheep infected with
chlamydiae [see human infections a little
later]. Genetic analysis of the isolates associated with sporadic abortion in
women who had contact with infected sheep, identified the strains as C. abortus
(Herring et al., 1987; Jorgensen,
1997). Organisms were recovered from the placental tissues and, in rare
fatal cases, from additional organs. The incidence of this animal-acquired infection is not known, but sheep infected with C. abortus strains represent an important
potential risk to pregnant women
(McKinlay et al., 1985).
Furthermore, inhalation of infected material from sheep might also result in chlamydial respiratory disease in non-pregnant humans.
[PG, Updated MEW June 2003]
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