Characterisation of experimental Q fever infection and the detection of Coxiella burnetii antigens in urine

Abstract

Coxiella burnetii, the aetiological agent of Q fever, causes acute, chronic or asymptomatic disease in humans. Routine clinical diagnosis of acute and chronic Q fever primarily relies on serodiagnosis. Isolation of the organism is rarely attempted, as C. burnetii is known to be amongst the most infectious of bacteria. This thesis aims to define and characterise a relevant experimental model of Q fever and establish whether C. burnetii-specific antigens appear in the urine of experimental animals. It is further intended to characterise any antigens excreted and assess urinary antigen detection as a method for the laboratory diagnosis of Q fever. Experimental C. burnetii infection was established in the guinea pig using Lane strain (a previously uncharacterised British isolate from heart tissue of a patient suffering from Q fever endocarditis). The aerosol route of delivery resulted in a more severe disease compared to delivery by the intraperitoneal route and C. burnetii organisms were shown to persist in heart tissues for at least thirteen weeks following aerosol infection. A capture ELISA assay was developed with a detection limit of 80 ng antigen ml-1 (equating to approximately 800 organisms ml-1). C. burnetii-specific antigens appeared in the urine of animals, infected by aerosol with approximately 1000 organisms and 1-10 organisms, at 1 and 10 days post-infection, respectively. During subsequent characterisation of the urinary antigens in severely diseased guinea pigs, viable C. burnetii organisms were detected and a C. burnetii-specific immunoreactive protein with an approximate molecular weight of 62 kDa was demonstrated. Evidence also suggested that LPS was present in the urine. The appearance of antigen in the urine was used as a marker of infection to assess the efficacy of doxycycline and ciprofloxacin in the treatment of experimental Q fever.. Preliminary studies supported other data (febrile response, serology and PCR) which suggested that doxycycline was more effective than ciprofloxacin in the treatment of acute experimental Q fever.