Coxiella burnetii associated reproductive disorders in domestic animals--a critical review

Abstract

The bacterium Coxiella burnetii has been detected in the fetal membranes, birth fluids and vaginal mucus, as well as in the milk and other excretions of several domestic mammals. The finding of C. burnetii in association with abortion, parturition and in the postpartum period has led to the hypothesis that C. burnetii causes a range of reproductive diseases. This review critically evaluates the scientific basis for this hypothesis in domestic mammals.The review demonstrates a solid evidence for the association between C. burnetii infection and sporadic cases of abortion, premature delivery, stillbirth and weak offspring in cattle, sheep and goats. C. burnetii induced in-herd epidemics of this complete expression of reproductive failure have been reported for sheep and goats, but not for cattle. The single entities occur only as part of the complex and not as single events such as generally increased stillbirth rate. Studies show that C. burnetii initially infects the placenta and that subsequent spread to the fetus may occur either haematogenous or by the amniotic-oral route. The consequences for the equine, porcine, canine and feline conceptus remains to the elucidated but that infection of the conceptus may occur is documented for most species. There is no solid evidence to support a hypothesis of C. burnetii causing disorders such as subfertility, endometritis/metritis, or retained fetal membranes in any kind of domestic animal species.There is a strong need to validate non-pathology based methods such as polymerase chain reaction for their use in diagnostic and research in relation to establishing C. burnetii as the cause of abortion and to adapt an appropriate study design and include adequate control animals when linking epidemiological findings to C. burnetii or when evaluating effects of vaccination in production herds.

Figure 1

Schematic outcomes of an intrauterine infection with Coxiella burnetii in a pregnant animal. Little knowledge on the intrauterine spread of C. burnetii is present, but data indicates that the infection may follow one of two routes after an initial localization in the placenta (indicated by red and greens arrows). A latent infection (green arrows) that either remains localized in the placenta or spreads to the fetus (still latent) is probably the most common outcome, at least in cattle. This situation is characterised by normal offspring that may or may not be congenitally infected and vaginal excretion of organisms in association with parturition and in the postpartum period. An active infection (red arrows) that may remain limited to the placenta, although being widespread, or may spread to the fetus by the haematogenous or the amniotic-oral route will most likely compromise the fetus and cause abortion, premature delivery, stillbirth and weak offspring (APSW Complex) although normal but probably congenitally infected offspring may also be found.

Figure 2

Trophoblasts infected by Coxiella burnetii. Huge amounts of C. burnetii DNA are seen as green fluorescence within distended trophoblasts. Fluorescence in situ hybridization, placenta, goat. Courtesy of TK Jensen, Danish Veterinary Institute, Technical University of Denmark.