Q fever seroprevalence and risk factors in sheep and goats in northwest Italy

Abstract

Q fever is a zoonosis caused by the bacterium Coxiella burnetii; domestic ruminants, mainly goats and sheep, are the main source of Q fever outbreaks in humans. From both a public and an animal health perspective, providing reliable prevalence data is extremely relevant for the decision processes by policymakers and food producer organizations. Information on Q fever seroprevalence in small ruminants in Italy is currently incomplete and largely based on reports of reproductive disorders in livestock farms. To estimate animal and flock seroprevalence of C. burnetii in small ruminants (sheep, goats and mixed flocks), a cross-sectional study with a two-stage design was carried out in northwest Italy. Between January and December 2012, sera from 5738 animals (2553 sheep and 3185 goats) belonging to 411 flocks (206 goats, 111 sheep, and 94 mixed flocks) were examined for specific anti-C. burnetii IgG antibodies by a commercial ELISA kit. A questionnaire investigating possible associations between farm management and C. burnetii seropositivity was administered. At the flock level, the overall true seroprevalence adjusted for test sensitivity and specificity was 31.2% (95% confidence interval [CI]: 24.8-37.7). Sheep-farm and goat-farm true seroprevalence was 38.7% (95% CI 25.5-51.9) and 19.5% (95% CI 11.5-27.6), respectively. Interestingly, the true seroprevalence (48.5%; 95% CI 34.7-62.3) was higher in the mixed flocks (sheep and goats). At the animal level, the overall true seroprevalence was 15.9% (95% CI 15.4-16.4). No difference was found between the two species, but the true seroprevalence was significantly higher (χ(2)=7.49; p<0.007) among the goats in mixed flocks (25.7%; 95% CI 24.4-27.1) than the sheep (16.3%; 95% CI 15.1-17.4), suggesting a potential difference in susceptibility between the two species or the result of factors affecting their immune response or related to the livestock management system as the period of exposure to C. burnetii. A multivariable logistic model that controlled for farm-level clustering identified five main risk factors associated with farm seropositivity (p≤0.05): flock size of more than 12 animals (odds ratio [OR] 4.2; 95% CI 2.6-6.7), contact with other flocks (OR 2.1; 95% CI 1.2-3.6), mixed flock type (OR 2.4; 95% CI 1.4-4.2), farms located in the western area (OR 2.4; 95% CI 1.4-4.2), and infertility during the previous year (OR 2.6; 95% CI 1.2-5.2). The results of this study yielded baseline information that may be useful to set up future epidemiologic, flock management, and public health policies for the prevention and control of Q fever in Italy.

Keywords: Coxiella burnetii; Goats; Q fever; Risk factors; Seroprevalence; Sheep; Small ruminants.