Chlamydial infections in animals
Chlamydophila abortus : Treatment
and control
Treatment
Chlortetracycline given orally or as low-dose injections
has been shown to be effective against chlamydial abortion provided it was administered prior to the
second chlamydaemia phase of infection (Shewen,
1980). However, this phase cannot be easily predicted, particularly
as the time of onset of infection is usually unknown. At present, a more effective treatment is that of two intramuscular injections of high-dose, long-acting
oxytetracycline (at 20 mg/kg). When given during the later stages of pregnancy, abortion can be prevented
(Rodolakis et al., 1980). The first injection should be given at 95-110 days of gestation,
with the second 2 weeks later (Jones,
1999). Antibiotic therapy of entire flocks in which ewes are aborting,
particularly those experiencing abortion for the first time, can reduce losses. However, antibiotic treatment does not prevent the spread of infection and may
conceivably affect the development of immunity.
Control
Although ovine and bovine chlamydial abortion episodes appear to
be independent, the C. abortus strains causing the disease are very
similar. Control of chlamydial abortion can be attempted by several methods. Pregnant animals can be segregated during
the lambing and calving seasons. Chlamydiae are shed in large numbers from aborting animals in aborted foetuses, diseased
placentae, purulent uterine discharges and faeces. Aborting ewes should be kept
separate until their uterine discharges dry up. Infected materials need to be
carefully disposed of.
In Britain, there are various health schemes
whereby participating flocks are given an annual disease status based on serological monitoring of C. abortus infection.
Flocks with "disease free" status tend to have higher monetary value.
This approach can be combined with vaccination, newly purchased female stock
being vaccinated prior to breeding in the autumn (Dawson,
1990). Clearly there
is a need for careful selection of purchased sheep, preferably from disease-free flocks, as vaccination may be less effective on sheep already infected with C. abortus.
In the case of chlamydial abortions in cattle, which
is more sporadic than in sheep, antibiotic treatment has been considered the most
practical measure for control of the disease (McKercher,
1969).
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