Chlamydial infections in animals
Chlamydophila abortus : Clinical
signs
C. abortus infections
are endemic among ruminant species and can colonise the placenta efficiently (Rodolakis et al.,
1989).
Although C. abortus infection is primarily associated with abortion, stillbirth or the delivery of weak, full-term neonates,
apparently normal lambs may also be infected.
The clinical signs and pathogenesis of chlamydial abortion disease in sheep and cattle have been described in detail
(Storz 1971; 1988). In experimentally infected ewes, a fever,
lasting for 3 - 5 days, develops 1 - 2 days following experimental inoculation (Storz,
1969).
During the initial, blood-borne phase, the infection becomes established in the
main organs of the
ewe, with the liver, spleen, kidneys, lung, thymus, brain, regional lymph nodes and intestine of foetal
lambs involved as early as 3 - 5 days after inoculation (Storz,
1969). However, there are no overt signs of disease until abortion occurs.
A secondary chlamydiaemia then arises involving the placenta . Chlamydial
infection is subsequently eliminated from most of the bodily organs (Storz,
1968), except in the placenta. There the infection becomes established in the chorionic epithelial cells, causing epithelial ulceration.
The periplacentome of affected cotyledons is often thickened (Storz ,
1988) with an opaque, yellow to pink colour. The surface of the intercotyledonary chorion has a tough, granular consistency, and
contains yellow, flaky material. The margins of affected cotyledons show small foci of soft necrosis
(Storz and Whiteman, 1981). The chorionic arterioles and cores of affected
villi
are infiltrated by inflammatory cells.
This acute placentitis is the major pathological change in ewes (Stamp et al.,
1950; Kwapien et al., 1970). Immunohistological
examination of placental tissues from aborted foetuses showed that cells
expressing the macrophage-associated molecule CD 14 were numerous, as were cells
expressing major histocompatibility complex class II (MHC II) molecules. Many
cells expressed messenger RNA encoding tumour necrosis factor-alpha (TNF-alpha),
but few cells expressing interferon gamma mRNA and none expressing interleukin-4
mRNA were detected. The foetal immune response included small numbers of CD4+
and CD8+ cells, gamma delta T cells and B cells. It was concluded that abortion
was the result of several factors, including destruction of tissue by C.
abortus, vascular thrombosis, and an inflammatory response by the foetus. It
was considered that production of TNF-alpha by foetal macrophages expressing MHC
II molecules may be of considerable significance in the pathogenesis of abortion
[Buxton et al., 2003].
Infection of foetal organs with systemic involvement may play a significant role in foetal death and subsequent abortion. The livers of aborted lambs are congested and swollen, with pinpoint white foci
(Studdert, 1963). The lymph nodes are also enlarged and
swollen. When lambs abort near term, they are usually well preserved and clean in appearance. Numerous
petechiae
are seen mostly in the skin of limbs, hip, head and neck, and in thymus and salivary glands
(Studdert, 1963). Foetal livers may be congested and slightly swollen. Affected ewes show signs of malaise in the 2-5 days preceding abortion. Aborting ewes
may also have a purulent
uterine discharge, in which chlamydiae may be excreted for up to two weeks post-abortion.
Shedding of chlamydiae varies with the oestrous cycle, being particularly high
around ovulation (Papp et al.,
1996; 1998). Thus transmission is particularly likely to be favoured
at breeding time.
The majority of aborting ewes make uneventful
recoveries. Subsequent fertility is usually not affected. Some three to six months after abortion, the uterine mucosa of affected ewes does not demonstrate chlamydiae. A few infected pregnant ewes retain their placentae after
abortion and a few may die of complications, such as secondary bacterial infection. Experimental infections have revealed that significantly more multiparous than uniparous ewes abort, which suggests
that abortion may paradoxically have a higher impact in flocks with high lambing percentages
(Tan et al., 1990). A
review article suggests that the persistent genital tract infection which
follows pregnancy failure in ewes may be a useful paradigm for persistent human
genital tract infection with C. trachomatis (Papp
& Shewen, 1997).
In cattle, chlamydial abortions tend to be sudden and sporadic, occurring near or at
term in the seventh to ninth month of gestation. Prior to abortion, there is no overt evidence of clinical disease, although a serous uterine discharge may be present.
Cattle in the second trimester of gestation, inoculated intravenously with a bovine abortion
chlamydial strain developed fever and leukopaenia for 3-5 days afterwards (Storz and
McKercher, 1962). Some animals developed diarrhoea and an intermittent, mucoid, vulvar discharge. Abortions occurred within 5-36 days,
whereas in cows inoculated during the second trimester by other routes (i.e. intramuscularly,
subcutaneously, intradermally), abortions or the delivery of weak calves
occurred 33-126 days later. In field conditions, chlamydial abortions have been detected as early as the fifth month of gestation, but most occur during the third trimester.
Infection sometimes results in the birth of dead calves at term, or weak calves which may die later. Cows that abort during the later stages of gestation demonstrated placental lesions and necrotic foci in foetuses similar to chlamydial abortions of ewes. As with sheep and goats, necrotic placentitis is the major pathological feature. However, in cattle the distribution of lesions may be more patchy
(Storz, 1968). The gross pathology of aborted foetuses is more variable. Foetuses commonly display a pot-bellied appearance due to
ascites. Subcutaneous oedema may be present, and petechial haemorrhages of the mouth, tongue, thymus, lymph nodes
or elsewhere may be seen (Storz, 1971). The liver tends to be yellowish-red and mottled. Other gross lesions may include subcapsular haemorrahage in the kidneys,
an enlarged spleen, and constriction of blood vessels in the brain. Chlamydiae have been isolated from a number of affected organs in aborting cattle
(Storz and McKercher, 1962; Reed et al.,
1975). Abortion causes little adverse effect on dams, which appear normal, but placentae may be retained in both natural and experimental infections. In dairy cows there may be a drop in milk production and sterility may occur.
Bulls infected with C. abortus may be affected by seminal
vesiculitis. In such cases, inflammation of the seminal vesicles and the epididymis may be apparent, the testes may be atrophic and semen quality affected. The bulls may transmit chlamydiae to cows as a venereal disease in semen. Chlamydiae may be naturally shed in semen,
to replicate in endometrial cells of the cow, possibly leading to embryonic death
(Bowen et al., 1978). Infertility may
also result.
Chlamydiae have been isolated from milk samples and mammary tissues from dairy cows affected by naturally occurring mastitis. The chlamydiae involved were thought to be of intestinal origin. In experimentally infected cases, cows developed a high fever of 41°
C / 105.8°
F. During the febrile period, cows were lethargic and off feed, and their milk production decreased sharply. Body temperature returned to normal after about six days, and milk production recovered but never returned to pre-inoculation levels
(Ronsholt and Basse, 1981).
[PG] Updated [MEW] July 2003
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