Q Fever Diagnosis and Control in Domestic Ruminants

Abstract

Q fever is a zoonosis caused by the bacterium Coxiella burnetii, a highly infectious agent that can survive in the environment. Therefore, Q fever has a major public health impact when outbreaks occur. Small ruminants are identified as the source in the majority of outbreaks in humans. Accurate diagnosis and effective control strategies are necessary to limit the zoonotic and veterinary impact of Q fever. For this, knowledge of the pathogenesis of Q fever and excretion routes of C. burnetii from infected animals is crucial. Abortions as well as normal parturitions in infected small ruminants are the most important excretion routes of C. burnetii. Excretion of C. burnetii via faeces and vaginal mucus has also been suggested. However, contamination of these samples by bacteria present in the environment may influence the results. This hampers the accurate identification of infected animals by these samples; however, the detection of C. burnetii in milk samples seems not to be influenced by environmental contamination. Q fever in animals can be detected by direct (immunohistochemistry and PCR) and indirect (complement fixation test (CFT), enzyme- linked immunosorbent assay (ELISA) and indirect immunofluorescence assay (IFA) methods. A combination of both direct and indirect methods is recommended in current protocols to detect Q fever on herd level. For the control of Q fever in domestic animals, vaccination with a phase 1 C. burnetii whole cell inactivated vaccine is reported to be effective in preventing abortion and reducing bacterial shedding, especially after several years of administration. Vaccination might not be effective in already infected animals nor in pregnant animals. Furthermore, the complicated vaccine production process, requiring biosafety level 3 facilities, could hamper vaccine availability. Future challenges include the development of improved, easier to produce Q fever vaccines.