Coxiella burnetii in pregnant goats

Coxiella burnetii is an intracellular bacterium and the causative agent of Q fever. The zoonotic impact of Q fever was recently underlined by the Dutch Q fever outbreak, which emerged from an endemic state. In this outbreak dairy goats and dairy sheep were deemed responsible for the human cases, although information about the genetic background of human and animal isolates was lacking. Also tissue dissemination, excretion pathways and immune responses in C. burnetii-infected goats are still poorly understood. The aim of this thesis is to investigate the epidemiology and pathogenesis of C. burnetii infection in goats in the recent large outbreak of Q fever in the Netherlands. The epidemiology of C. burnetii was studied by characterising outbreak isolates from infected goats, sheep and humans using multiple locus variable number tandem repeats analysis (MLVA) and multispacer sequence typing (MST). In addition, potential presence of the Q fever agent in roe deer, cats, dogs, pigs, horses and cattle was investigated. Pathogenesis, excretion patterns and immune responses were investigated during experimental infections in pregnant goats inoculated with a Dutch outbreak isolate. Genotypic characterisation revealed that one unique genotype of C. burnetii was predominantly present in dairy goat herds representing 60% of all dairy goat herds with abortion problems, and in two sheep herds in the human Q fever outbreak area in the south of the Netherlands. This genotype was also present in human outbreak samples. In roe deer, dogs, horses and cattle samples C. burnetii DNA was detected. Genotyping results suggest species-specific genotypes for roe deer and cattle that are unrelated to the Dutch outbreak genotype, although the outbreak genotype was detected in one bovine placenta. In experimental infections, pregnant goats were successfully inoculated via the intranasal route. C. burnetii showed a strong tropism towards the placenta. Bacterial replication seemed to occur predominantly in the trophoblasts of the placenta and not in other organs of goats or kids. High numbers of C. burnetii were excreted during abortion, but also during parturition of liveborn kids. C. burnetii was not detected in faeces or vaginal mucus before parturition. Two weeks post-inoculation a strong anti-C. burnetii Phase 2 IgM and IgG antibody response was observed, succeeded by an anti-Phase 1 response. Four weeks before parturition, the number of IFN-γ producing cells in peripheral blood increased and reached high levels during the first week after parturition. These results confirm dairy goats and sheep as the source of the Dutch Q fever outbreak, while in cattle a specific cluster of C. burnetii genotypes was found, unrelated to the outbreak genotype. C. burnetii has a strong tropism for the trophoblasts of the placenta and is not excreted before parturition; pathogen excretion occurs during birth of dead as well as live, healthy kids. Upon C. burnetii infection a strong phase-specific antibody response is detected. This may be useful in the early detection of C. burnetii-infected pregnant goats. These animals should be considered as a major zoonotic risk via abortions, but also via normal deliveries