Experimental Inoculation of Male Rats with Coxiella burnetii: Successful Infection but No Transmission to Cage Mates
ABSTRACTBeginning in 2007, the largest human Q fever outbreak ever described occurred in the Netherlands. Dairy goats from intensive farms were identified as the source, amplifyingCoxiella burnetiiduring gestation and shedding large quantities during abortions. It has been postulated that wild rodents are reservoir hosts from whichC. burnetiican be transmitted to domestic animals and humans. However, little is known about the infection dynamics ofC. burnetiiin wild rodents. The aim of this study was to investigate whether brown rats (Rattus norvegicus) can be experimentally infected withC. burnetiiand whether transmission to a cage mates occurs. Fourteen male brown rats (wild type) were intratracheally or intranasally inoculated with a DutchC. burnetiiisolate obtained from a goat. At 3 days postinoculation, a contact rat was placed with each inoculated rat. The pairs were monitored using blood samples and rectal and throat swabs for 8 weeks, and after euthanasia the spleens were collected. Rats became infected by both inoculation routes, and detection ofC. burnetiiDNA in swabs suggests that excretion occurred. However, based on the negative spleens in PCR and the lack of seroconversion, none of the contact animals was considered infected; thus, no transmission was observed. The reproduction ratioR0was estimated to be 0 (95% confidence interval = 0 to 0.6), indicating that it is unlikely that rats act as reservoir host ofC. burnetiithrough sustained transmission between male rats. Future research should focus on other transmission routes, such as vertical transmission or bacterial shedding during parturition.