Spread of Q fever within dairy cattle herds: key parameters inferred using a Bayesian approach

Q fever is a worldwide zoonosis caused by Coxiella burnetii. Although ruminants are recognized as the most important source of human infection, no previous studies have focused on assessing the characteristics of the bacterial spread within a cattle herd and no epidemic model has been proposed in this context. We assess the key epidemiological parameters from field data in a Bayesian framework that takes into account the available knowledge, missing data and the uncertainty of the observation process owing to the imperfection of diagnostic tests. We propose an original individual-based Markovian model in discrete time describing the evolution of the infection for each animal. Markov chain Monte Carlo methodology is used to estimate parameters of interest from data consisting of individual health states of 217 cows of five chronically infected dairy herds sampled every week for a four-week period. Outputs are the posterior distributions of the probabilities of transition between health states and of the environmental bacterial load. Our findings show that some herds are characterized by a very low infection risk while others have a mild infection risk and a non-negligible intermittent shedding probability. Moreover, the antibody status seems to be a key point in the bacterial spread (shedders with antibodies shed for a longer period of time than shedders without antibodies). In addition to the biological insights, these estimates also provide information for calibrating simulation models to assess control strategies for C. burnetii infection.     

An outbreak of Q fever in the Basque country.

The main clinical manifestations of 42 cases of Q fever occurring in an outbreak in Valmaseda, Spain during March, April and May 1982 are described in this paper. The benign character of the acute disease is emphasized. Further epidemiologic studies must be done to determine the incidence of Q fever in the Basque country.     

Assessment of vaccination by a phase I Coxiella burnetii-inactivated vaccine in goat herds in clinical Q fever situation

A study was carried out to assess the efficacy of vaccination, using a phase I Coxiella burnetii-inactivated vaccine (Coxevac?; CEVA), within three goat herds experiencing Q fever abortions waves. The stratification of the population (n = 905) was based on parity and on infection status related to both serological and qPCR vaginal shedding results. Control (n = 443) and vaccinated (n = 462) groups were established in each farm. Vaccination was administered to does before mating and to kids after active immunity acquisition (at least 3–4 months old). The vaccine effectiveness was analyzed at subsequent farrowing on both clinical incidence and vaginal shedding at the delivery day. Among the 231 animals considered as susceptible, that is, seronegative nonshedders, about 90% were infected whatever the group, showing that vaccination did not prevent infection under high infection exposure. Fortunately, vaccination induced an overall decrease in shedding levels. A significant average difference between groups was estimated to 1.16 log(10) bacteria per swab for primiparous and even higher (1.81 log(10)) for initially susceptible ones. Thus, in a clinical context, vaccination should be implemented first in renewal animals. Indeed, young animals are those which best respond to vaccination by significantly reducing C. burnetii burden and, conversely, which excrete bacteria most massively if not vaccinated.     

Coxiella burnetii vaginal shedding and antibody responses in dairy goat herds in a context of clinical Q fever outbreaks

This study, carried out in three goat herds, was aimed at describing individual responses to Q fever infection in an abortive context, focusing on both antibody and shedding levels. Seroprevalence of Coxiella burnetii (Cb) infection and vaginal shedding of 1083 goats were investigated using ELISA and realtime qPCR assays, respectively. At the end of the outbreaks, a seroprevalence of 45.0% was found, and vaginal shedding appeared massive with levels above 10(4) Cb per swab in 42.3% of the whole population and above 10(6) Cb per swab for 90.9% of aborted goats. Susceptible animals (i.e. seronegative nonshedders) were unfrequent (31.2%), most of them being kids (94.7%). Seronegative females were predominant among nonshedders and conversely seropositive ones, predominant among high shedders (above 10(6) Cb per swab). Nevertheless, at least 43.3% of seronegative goats shed bacteria confirming the need of interpreting serology on a herd scale. The subsequent farrowing period was characterized by a significant reduction in the number of clinical cases. Females that had already aborted were more often involved than others. Shedding quantities remained high, particularly for primiparous does, mainly when facing infection for the first time. Thus, Q fever control must be based on both preventive measures directed to the preherd and environmental precautions.     

Q fever in the Ukraine

Q fever occurs in all geographical landscape zones and in most administrative regions of the Ukrainian SSR. The disease was diagnosed in those areas where no such cases had ever been registered. In the Kharkov region the examination of 425 fever patients with unclear diagnosis resulted in diagnosing 5 cases of Q fever. The proportion of seropositive persons among different professional groups of the population in the eastern part of the republic was determined (6.9% among workers of meat-packing factories, 8.7% among workers of fur- and wool-treating establishments, 5.2% among stock breeders). At the farms of the Kharkov, Poltava and Sumy regions the spread of infection among large cattle was 2.3% and among small cattle 5.6%. Rickettsial carriership revealed in hard ticks collected in the Kharkov region indicated the possibility of the existence of the natural focus of Q fever in this zone and increased the available information on the presence of the territories with the natural foci of this infection in the Ukraine.