Which samples should be taken in case of abortion in cattle suspected of Q Fever (Coxiella burnetii infection)?
In cattle, C. burnetii infection may be associated with abortion and other reproductive disorders. In the event of repeated abortions in a herd, coxiellosis should be investigated in first instance, together with other major diseases causing abortion, such as neosporosis, bovine viral diarrhoea (BVD), leptospirosis, infectious bovine rhinotracheitis (IBR), brucellosis and other viral/bacterial/fungal infections depending on the clinical and epidemiological context, where applicable.
For more details on Q Fever in cattle, please refer to the Q-Fact “When to suspect Q Fever (Coxiella burnetii infection) in cattle?” here.
Which samples should be taken in case of abortion in cattle suspected of Q Fever (Coxiella burnetii infection)?
In cattle, C. burnetii infection may be associated with abortion and other reproductive disorders. In the event of repeated abortions in a herd, coxiellosis should be investigated in first instance, together with other major diseases causing abortion, such as neosporosis, bovine viral diarrhoea (BVD), leptospirosis, infectious bovine rhinotracheitis (IBR), brucellosis and other viral/bacterial/fungal infections depending on the clinical and epidemiological context, where applicable.
For more details on Q Fever in cattle, please refer to the Q-Fact “When to suspect Q Fever (Coxiella burnetii infection) in cattle?” here.
PURPOSE OF THIS FACTSHEET
To review the diagnostic approach to Q Fever/coxiellosis in the event of abortions in cattle, and to answer four practical questions: Which animals should be sampled? Which samples should be taken? Which tests should be requested? How should the results be interpreted?
COORDINATORS OF THIS FACTSHEET
DVM, PhD, MSc, DIRECTOR OF THE PERIPHERAL LABORATORIES OF PADOVA, VICENZA AND ROVIGO – ISTITUTO ZOOPROFILATTICO SPERIMENTALE DELLE VENEZIE, ITALY.
“Coxiellosis is a very common infection in cattle farms, too often underestimated and underdiagnosed. Clinical signs can be subtle, sometimes with few to no abortions and more signs of sub-optimal fertility. Only when control measures are implemented and the pressure of the infection is reduced, the improvement in farm productivity becomes obvious.”
DVM, MSc, PhD FELLOW, MANAGER OF THE HEALTH ADMINISTRATION SERVICE OF ARSIA (BELGIUM).
“In the context of Q Fever, an abortion should never be dismissed as just one isolated loss. It can be the first sign of disease circulation within the herd, and every abortion cluster starts with a single case. That is why early surveillance matters so much: it turns one event into useful knowledge and allows farmers to act quickly with the right control measures, from biosecurity and management to vaccination when needed. With Q Fever, individual diagnosis has its value, but herd diagnosis comes first. What matters most is determining whether the herd has been exposed and whether the bacterium is circulating, because that is what should guide surveillance and control.”
Early PCR and herd surveillance are key to controlling Q fever in cattle farms.
Which animals should be sampled? What kind of samples? For which tests?
Which samples should be taken in case of abortion?
Whenever feasible, direct detection of the pathogen by PCR remains the preferred option, as it provides the most robust basis for interpretation. From the cow(s) that aborted, samples should ideally be collected within 24 hours after abortion and no later than 7 days afterwards to maximize the likelihood to detect C. burnetii. It is also important to minimise contamination of the foetus and placenta with manure from the environment during collection. Because laboratory preferences may vary, it is advisable to contact the laboratory in advance to confirm which sample type they prefer.
The preferred samples are:
- The entire aborted foetus. This remains the best option, not specifically for the diagnosis of Q Fever, but because the laboratory can investigate other possible causes of abortion, select the most appropriate tissues and, if needed, perform a necropsy in addition to Q Fever testing.
- If the whole foetus cannot be submitted, collect abomasal (stomach) fluid from the fresh aborted foetus.
- Placental tissue is always useful, whenever available. Sampling whole cotyledons is preferable, as the laboratory can then perform the most suitable swabbing procedure, although even a part of placenta can still be submitted. Placental submission increases the sensitivity of Q Fever detection compared with relying on a foetal sample alone, because the placenta is the primary site of entry and colonization for C. burnetii (causing placentitis), and abortion may occur even when the foetus itself is not detectably infected.
- If placental tissue is not available, collect an endocervical swab as soon as possible after the abortion.
- A blood sample of the aborted cow. Although serology cannot by itself prove that C. burnetii caused the abortion, it can demonstrate exposure of the aborted cow to C. burnetii. Vaccination status must always be taken into account, as vaccination may interfere with the interpretation of serology. Any seropositive result in an aborted cow, especially if the intensity of the test reaction is high, should be considered an alert signal and should prompt additional herd-level investigations.
All samples to be PCR tested, should be stored and sent cooled (+4°C) as quickly as possible, ideally within 24 hours.
Why combine PCR and ELISA?
Studies conducted in herds with coxiellosis-related abortion episodes show that cows positive by PCR may still be seronegative at the time of abortion, and only seroconvert later. Even if ELISA carries a substantial risk of false-negative results at the individual level, it remains useful as a low-cost alert test because a seropositive result indicates exposure of the animal. For this reason, the most informative approach is to combine direct detection by PCR with ELISA-based serological screening in a selected group of animals from the herd.
- PCR is recommended on samples from aborted cows, especially vaginal swabs collected within 7 days after abortion, and ideally as soon as possible after abortion (placental swabs are possible, but within 24h from birth).
- Serology (ELISA) should be performed on at least six cows with reproductive problems, including the one(s) that aborted. Suitable animals include cows with retained placenta, endometritis or fertility disorders.
When should serology be preferred over PCR?
PCR should be preferred during the first days after abortion, because PCR positivity on genital swabs decreases rapidly over time. Fewer than one third of animals that are PCR-positive on the day of abortion may still test positive 7 days later. In practice, swabs or placenta for PCR should therefore be collected up to 7 days post-abortion, and preferably as soon as possible after abortion.
When this time window has been missed, serology becomes more useful than PCR as an individual-level support tool, because the likelihood of underdiagnosis increases substantially as infected cases may no longer be detected by PCR. Serology may therefore be preferred over PCR when sampling is delayed, while remaining complementary to PCR in the overall diagnostic approach.
What about bulk tank milk?
In dairy cattle, bulk tank milk should not be considered an appropriate sample for diagnosing the cause of an abortion event; neither PCR on bulk tank milk nor ELISA antibody testing on bulk tank milk is relevant for that purpose. However, it may still be useful at herd level to highlight the circulation of C. burnetii and should be interpreted in that context only.
NOTE: For more details, please refer to the Q-Fact “Guideline for the interpretation of the results of C. burnetii (Q Fever) bulk tank milk analysis in ruminants” here.
How should the results be interpreted?
A meaningful interpretation is only possible when the recommended sampling strategy has been complied with. Because Q Fever is primarily a herd-level issue, results must be interpreted collectively rather than on the basis of a single animal.
The interpretation grid below is adapted for routine veterinary practice, where PCR results are often reported qualitatively (detected/not detected) rather than as fully quantified bacterial loads. Whenever available, quantitative PCR may provide useful additional information, but routine diagnosis can rely on standard PCR combined with herd serology. This interpretation framework is based on EFSA recommendations.
Table: Causative interpretation of PCR and ELISA results linking abortions to C. burnetii, simplified for routine use, adapted from the French OSCAR protocol.
Practical considerations regarding PCR and qPCR
Quantitative PCR (qPCR) can be helpful because a high bacterial load strengthens the suspicion that C. burnetii played a causal role in the abortion event. However, in routine veterinary practice, laboratories often report standard PCR results simply as ‘detected’ or ‘not detected’. This remains suitable for field diagnosis, provided the result is interpreted together with the type of sample collected, the delay between abortion and sampling, and the herd serology results.
- A negative PCR result does not exclude coxiellosis if sampling was delayed, if storage or shipping conditions were suboptimal, or if inappropriate samples were submitted.
- A positive PCR result remains highly informative, especially on foetus or placental or genital samples collected promptly after abortion.
- When only one PCR result is positive and herd serology is not yet available, coxiellosis should not be dismissed. Additional serology, repeat sampling in the event of further abortions, or both, may be needed.
- In practice, combining PCR and ELISA – and repeating testing when necessary – is more useful than relying on a single isolated result.
KEY MESSAGE: Determining whether C. burnetii is the sole cause of an abortion series is informative, but the main point is to establish that the herd has been exposed to the pathogenic agent, C. burnetii. Once seropositive animals are identified and C. burnetii is detected by PCR in one or more abortion cases, herd diagnosis takes precedence over individual diagnosis. In Q Fever, the priority is therefore to document herd exposure and bacterial circulation, so that appropriate surveillance, biosecurity and control measures can be implemented.
REFERENCES
- WOAH. Manual of Diagnostic Tests and Vaccines for Terrestrial Animals, Chapter 3.1.17 Q Fever. 2018/2023 online version. https://www.woah.org/fileadmin/Home/eng/Health_standards/tahm/3.01.18_Q_FEVER.pdf
- doi: 10.1016/j.tvjl.2011.08.033 – https://www.sciencedirect.com/science/article/abs/pii/S1090023311003315?via%3Dihub
- doi: 10.1016/j.vetmic.2011.09.026 – https://www.sciencedirect.com/science/article/abs/pii/S0378113511005360?via%3Dihub
- Guérineau S. et al. Valeur informative de la qPCR dans le diagnostic des avortements répétés chez les bovins : retour sur le choix d’un seuil d’interprétation pour le diagnostic de la fièvre Q. in Proceedings, Journées Nationales des GTV. Nantes, 2018. [in French].
- Observatoire et suivi des causes d’avortements chez les ruminants (Oscar). 2025 [In French]. https://plateforme-esa.fr/fr/observatoire-et-suivi-des-causes-davortements-chez-les-ruminants-oscar