WildLife Group
of the SAVA
detectable in fetal tissues, highlighting the importance
of always submitting placental tissue from an abortion
investigation. Diagnostics.
Histopathology is also fairly unique and diagnostic
characterized by a severe suppurative placentitis,
involving both the intercotyledonary and cotyledonary
placenta, but in the absence of vasculitis (which
distinguishes it from chlamydia). Organisms
are usually present in high numbers and have a
characteristic foamy appearance, with multiple
unstained vacuoles within a pale blue cytoplasm. Immunohistochemistry is a highly specific and
extremely useful diagnostic procedure for the
confirmation of Coxiella burnetti as the cause of an
abortion. This is because IHC staining of formalin fixed
placental tissue enables observation of positively
labelled bacteria within the diagnostic placental or
fetal lesions providing confidence in the diagnosis.
A. Immunohistochemistry (IHC).
B. Polymerize chain reaction (PCR).
PCR tests can be utilized to identify Coxiella burnetti
in tissues, however high levels of immunoglobulin
interfere with the test and therefore the incidence
of false negatives can be high, especially if testing is
performed more than 2 weeks after acute infection.
In addition, seasonal variability in shedding of the
organism hinders the interpretation of a single PCR
test. Even in persistently infected animals, levels of
shedding may drop below detectable levels, especially
outside the peri-parturient period and this is further
complicated by the presence of antibodies.
Figure 3: placenta histopathology revealing marked hyperplasia
of trophoblastic cells (arrows) containing Coxiella burnetti organisms
C. Serology.
Acute and convalescent paired sera taken 2 weeks
apart can be used to detect recent infection. However,
one should appreciate this merely indicates exposure
and does not confirm that Coxiella was the cause. In
addition, shedding of Coxiella burnetti may occur in
the absence of measurable serum antibody titer in up
to 20% of infected animals. Therefore, serology has its
limitations as a diagnostic procedure.
Placental histopathology at higher magnification demonstrating
numerous Coxiella burnetti organisms having characteristic foamy
appearance, with multiple unstained vacuoles within a pale blue
cytoplasm (arrows)
6
Care must be taken in attributing the simple presence
of Coxiella as sufficient evidence for the cause of
abortion. Animals may carry the organism for a
prolonged period and, although they appear to
abort only once, there may be large numbers of
organisms in the placenta in subsequent pregnancies.
Assessment of the extent of the placental lesion is
therefore important, as the placenta has characteristic
pathology both grossly and histologically, while
the fetus may have nonspecific or no lesions and