Table 4. Interpretation of Coxiella burnetii results by different test methods and in different matrices/samples in relation to abortion in ruminants.
| Technique | Sample | Prove of
causality 1 (-, +/-, +, ++, +++) |
Interpretation and conclusion |
|---|---|---|---|
| MZN Smears | Placenta/fetus | + | Unspecific result on its own; needs
confirmation of presence of Cb by PCR. |
|
Histopathology (HP)
Typical pathological lesions and IHC positive |
Placenta (fetus) 2 | +++ | Lesions compatible with
Cb are not
pathognomonic; needs positive IHC or IHC positivity to prove Cb causality of the abortion. |
|
Real-time PCR
In general, Cb PCR on its own does not prove a relationship between the detection of the pathogen and the abortion, although both the type of sample investigated and the level of positivity influence the likelihood of causality. The higher the level of positivity, the more likely causality. Causality can be proven by HP in combination with immunohistochemistry. | |||
| Fetus | ++ | Can be used to confirm the detection of
Cb, in
association with compatible histopathological findings. In the absence of compatible lesions, PCR positivity makes the relationship between pathogen and abortion more likely if other abortifacients have been ruled out. |
|
| Placenta | ++ | Same interpretation as fetus but only
if Cb PCR positivity level is high; low PCR positivity levels can be the result of sample contamination. |
|
| Vaginal discharge | + | Indication for a putative relationship
between abortion and Cb that needs further confirmation. Shedding of Cb can also occur after normal parturition. |
|
| Bulk tank milk or individual
milk sample (independently of Ct-value) |
- | Detects shedding of
Cb in a herd/flock or
at the individual level. Does not prove a relationship between abortion and pathogen. |
|
| Environmental sample
dust/air/…) (independently of Ct-value) |
- | Detects environmental contamination with
Cb
which may result in human exposure. Does not prove a relationship between abortion and pathogen. Tracing the most likely source of shedding may be advised depending on the context of the result. |
|
| Serology 3 | Maternal serum | - | Seropositivity shows previous contact with
Cb, but no causality with abortion. The relationship between shedding/abortion and serology is poor. |
| Milk | - | ||
Abortion: Abortion, stillbirth, premature birth or weak offspring
MZN: modified Ziehl-Neelsen stained smears (unspecific method)
Cb: Coxiella burnetii
HP: Histopathology
IHC: immunohistochemistry ( Cb specific antibodies are currently unavailable for every routine laboratory).
Ct: Cycle threshold
1 Prove of causality based on expert opinion
2 Placenta is more informative than the fetus
3 Positive serology can be a result of previous infection, vaccination or even cross-reaction