Coxiella burnetii seroprevalence of shepherds and their flocks in the lower Saint-Lawrence River region of Quebec,Canada

OBJECTIVE:

To determine the seroprevalence of Coxiella burnetii among the shepherds and their sheep in the lower Saint-Lawrence River region (LSLRR) of Quebec, Canada.

DESIGN:

A prospective human-animal comparative study was conducted with 81 shepherds from 46 farms and a control group matched for sex and age. All participants answered a standardized questionnaire to evaluate their risk factors for Q fever, including a specific section on the work practices of the shepherds. All human subjects had a blood sample taken for serology to phase I and phase II antigens of C burnetii performed by indirect immunofluorescence assay. At each participating farm, seven to nine sheep had blood samples taken for C burnetii serology to be assessed by the complement fixation test.

RESULTS:

The seroprevalence to C burnetii was higher in the group of shepherds (28.4%) than the control group (1.2%) (P<0.005). Among the group of shepherds, spending more than 5 h/week in the sheep barn (P=0.06) and buying and/or trading sheep within the past six months (P=0.004) were associated with positive C burnetii serology. A total of 137 of 334 sheep (41%) were seropositive for C burnetii. These positive sheep were distributed in 41 of the 46 flocks (89%). No correlation could be demonstrated between a serology for C burnetii in the herds and the shepherds.

CONCLUSION:

Q fever is highly prevalent in the LSLRR of Quebec, affecting 89% of the flocks and 28% of the shepherds. Shepherds in this region are at increased risk for C burnetii infection in comparison to the general population.Key Words: Coxiella burnetii, Flock, Q fever, Quebec, Serology, Seroprevalence, Sheep, ShepherdQ fever is a worldwide zoonosis caused by an intracellular rickettsial agent, Coxiella burnetii. This bacteria shows a characteristic phase conversion: the virulent phase I is directly isolated from infected animals, and the avirulent phase II is obtained after successive passages on cellular cultures of embryonated eggs (1,2). Q fever is predominantly transmitted to humans by inhalation of contaminated aerosols from infected animal litters (3-5). The parturition products and the feces and urine of sheep, cats, goats and dogs are the more common sources of transmission of the bacteria (6-9). Although these animals rarely show any symptoms of the infection (10,11), abortions in sheep, goats and cattle can be seen in some cases (5,6,12-14).Human Q fever is often asymptomatic or manifests as a mild illness. Atypical pneumonia and hepatitis are the principal clinical manifestations of the acute symptomatic infection, while endocarditis is the most frequent presentation of chronic Q fever (1,3,15,16). Very few studies in North America have addressed the issues of prevention of Q fever. In Australia, a highly effective vaccine (Q-Vax, Commonwealth Serum Laboratories, USA) is available for workers with occupational exposition to C burnetii (17,18).Seroprevalence studies conducted in Canada have shown that 5% to 36% of blood donors (19,20), 20% of slaughterhouse workers of the Mauricie region of Quebec (12), 25% of personnel of the animal pathology laboratory in Rimouski in the lower Saint-Lawrence River region (LSLRR) (M Rochette, unpublished data) and 49% of veterinarians in Nova Scotia (21) were positive for C burnetii.Epizootiological studies have also been done on animal populations in Canada. A seroprevalence study in the Mauricie region of Quebec showed that C burnetii had infected 26.7% of the cats, 11.5% of the cattle and 7.7% of the sheep (22). Cats were reported as important vectors of transmission of C burnetii to humans in the Mauricie region of Quebec and in Nova Scotia (23,24). In Ontario, a seroprevalence study demonstrated that 21.3% of the sheep were positive for antibodies to C burnetii (25).Q fever is a notifiable disease in Quebec. From January 1990 to December 1998, 43 (36.1%) of 119 reported cases were from the LSLRR, which had the highest incidence rate of the province, although it represents only 5% of the population. A review of the cases of Q fever from the LSLRR between 1991 and 1999 showed that 67% of the Q fever cases were related to exposure to sheep (P Jutras, unpublished data). It is noteworthy that an important rise in the number of sheep was observed in LSLRR, with an increase from 11,000 animals distributed in 110 flocks in 1983, to more than 33,000 in 180 flocks in 1999 (Union des producteurs agricoles of Quebec, personal communication).To evaluate the association between Q fever and exposure to ovine in the LSLRR, a prospective human-animal seroprevalence study was undertaken to compare the seroprevalence of C burnetii between the shepherds, their flocks and the general population. The work practices of the shepherds were also evaluated.