Impact of Q Fever on cattle reproduction

Coxiella burnetii, the causative agent of Q Fever, has an impact on the endometrium and trophoblasts of the placenta in cows. Due to these effects, when a farm experience a Q Fever outbreak, an impact on placental retention, endometritis, fertility, and pregnancy losses may also occur.

Prevalence

C. burnetii infects cattle, with a significant distribution of the infection in cattle in many countries worldwide. The global average prevalence is 20% [0-100%] at animal level, and 38% [4-100%] at herd level [1]. In Spain, there are very high seroprevalences at herd level: in beef cows in pasture systems, 93.7% of farms have at least one positive animal [2], and in dairy cows, 46% of farms have positive bulk tank milk in Galicia and 67.5% in the Basque Country [3].

Impact on reproduction

Thanks to recent research, it is known that C. burnetii infects macrophages in the endometrium, which may explain its association with endometritis and infertility [4]. It has also been demonstrated that C. burnetii infects trophoblasts in the placenta, causing placentitis and abortion [5].

The main impacts of Q Fever on dairy cattle, as confirmed in published studies, are:

1. Retained placenta: an increase in the rate of retained placenta above the reference rate of 8%.
2. Endometritis: an increase in the rate of endometritis at three weeks postpartum, based on a reference rate of 15%.
3. Infertility: a decrease in the conception rate, based on a reference rate of 30%.
4. Pregnancy losses: an increase in the abortion rate, based on a reference rate of 5%.

Retained placenta

Placental membrane retention is a multifactorial situation. However, the association between positive serology for C. burnetii and retained placenta in cows has been known for over 30 years (Vidic et al., 1990). A more recent study in three high-producing dairy cow herds infected with C. burnetii in Spain showed that seropositive cows have twice as much retained placenta as seronegative cows [9], resulting in a placental retention rate of 12.5% in seropositive cows, clearly above what is considered normal (below 8%). Figure 1.

Figure 1. Percentage of cows with retained placenta according to their serological status against C. burnetii.

Endometritis

Two studies have highlighted the effect of Q Fever on the incidence of endometritis: in a first study published in 2014, involving 246 farms in various areas of Italy, it was showed that Q fever positive farms in bulk tank milk were 2.5 times more likely to have a high incidence (>15-17%) of metritis and endometritis [10].

Another study published in 2018 highlighted the relationship between the presence of C. burnetii and chronic endometritis in infertile cows. Diagnostic tests were performed on uterine biopsies from 40 repeat-breeder cows. Biopsies from 30 cows showed no significant lesions, and no pathogens were identified by aerobic bacterial culture or PCR. However, 10 cows exhibited chronic endometritis with fibrosis, and tested positive for C. burnetii while testing negative for other pathogens by aerobic bacterial culture and PCR. Immunohistochemical (IHC) evaluation of C. burnetii from PCR-positive biopsies identified, for the first time, the presence of C. burnetii within the lesions and intracytoplasmically in endometrial macrophages in cattle. According to the authors, the persistence of bacteria-containing macrophages may contribute to the inflammation, the progressive damage and a functional failure of the endometrium [4].

Infertility

The effect of Q Fever on reducing reproductive performance in cattle has been evaluated from two perspectives: the association between Q Fever and reproductive disorders and the comparison of reproductive performance between vaccinated and non-vaccinated cows and heifers.

Association between Q Fever and reproductive problems

An association between the status of cows or farms with reproductive problems and seroconversion has been shown by several studies. A trial carried out in Germany reported a prevalence of antibodies against C. burnetii twice as high in farms experiencing infertility [11]. It has also been reported that the prevalence of antibodies against C. burnetii is higher in dairy cows with reproductive disorders (60%) than in animals without problems (36%) [12].

Similarly, a study was conducted on 262 farms in Galicia [13] and published in 2024. Serology on bulk tank milk was performed by ELISA. It was found that the overall conception rate and first insemination conception rate were significantly lower in positive farms (37.1% and 32.9%, respectively) compared to negative farms (39.8% and 36.1%, respectively). Positive farms also had a significantly higher incidence of endometritis (13.7% vs. 11.2%, p <0.05).

Improvement in reproductive parameters with vaccination

Several studies have shown improvement in various reproductive parameters with Q Fever vaccination:

• Conception rate at first insemination: a study conducted in Spain where pregnant cows were vaccinated at around 6 months of gestation, evaluated the effect in the subsequent lactation. The conception rate at the first postpartum artificial insemination (AI) was higher in vaccinated animals than in non-vaccinated ones (41.9% and 30.1%, p<0.05) [14].
• Percentage of repeat-breeder cows: After two consecutive rounds of vaccination within a whole year, among seronegative cows before vaccination, vaccinated cows were less likely to be "repeat-breeder cows" (requiring >3 inseminations to become pregnant) compared to non-vaccinated ones (14.3% and 28.1%, p=0.01) [15].
•  Reduction of open days: In one of the studies conducted in Spain, a difference of 14 days in calving to conception interval (expressed as “open days”) was observed between non-vaccinated and vaccinated cows (106 and 92, respectively) [14]. In another study carried out in Italy, the number of open days were reduced by 20 (142 in non-vaccinated and 122 in vaccinated) [16].

Pregnancy losses

According to a survey of abortion events conducted in France in 2017 (OSCAR) [7] with data from 434 abortions, 10.4% of abortion were attributable to C. burnetii. Q fever was the second infectious cause of abortion after neosporosis (14.7%). The third cause was BVD (7.6%). Another study also reported the presence of the bacteria by PCR in 9% of aborted fetuses or stillborn calves (Muskens et al., 2012). These abortions appear to be more frequent in the last third of gestation [6]; however, it should be noted that abortions are also more easily detected and consequently, more investigated during this period.

As C. burnetii is commonly detected in the placenta, birth products, and vaginal mucus after normal births, it was important to find confirmation that the organism causes abortion through a solid correlation between lesions and the presence of the pathogen. This correlation has been confirmed using IHC [5]: it has been shown that placenta from aborted cows positive by IHC test were more at risk of being inflamed, having necrosis than negative placenta. Similarly, fetuses with bronchopneumonia lesions (changes frequently associated with infectious placentitis) were more frequent in the IHC positive group than in the IHC negative one. With IHC staining of C. burnetii antigen in placental trophoblasts of cows with abortion, the positivity varies from a few granules of intracytoplasmic material within morphologically normal trophoblasts to massive amounts of antigen within many enlarged trophoblasts (Figure 2).

Figure 2. Immunohistochemical detection of Coxiella burnetii antigen in trophoblasts in the placenta of a cow with Coxiella burnetii abortion.
(From Bidfell et al., 2000).

When there is circulation of C. burnetii on a farm, infected animals may experience a range of disorders related to the bacterium's action at the uterine and placental levels, leading to a higher risk of reproductive disorders. The multifactorial nature of reproductive problems can make them more or less visible, highlighting the essential role of the veterinarian in proper differential diagnosis and data management to assess whether reproductive and health parameters are correct. Once the presence of Q Fever on farms is detected, control measures should be implemented, primarily consisting of biosecurity measures and vaccination.

This content has been developed from the following article: https://ruminants.ceva.pro/es/coxielosis written by Antonio Jimenez.

References

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