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Use of clinical indicators of Q fever (Coxiella burnetii) exposure in dairy herds as an example of syndromic surveillance

Abstract:

Q fever is a zoonosis occurring worldwide in livestock. Although it is often ignored in differential diagnosis, Q fever can persist in herds of ruminants and generate major financial losses in the long run. Well-known pleomorphic manifestations of Q fever include abortions, stillbirths, delivery of weak offspring and premature delivery. In cattle, Q fever is frequently asymptomatic and/or under-reported. Syndromic surveillance of cattle herds using health related data (clinical signs or other) is frequently cited because it may precede or replace formal diagnosis using laboratory complementary analysis. Resorting to new methodologies in the epidemiological surveillance, gives a chance to identify early ndicators of Coxiella burnetii exposure. A random cross-sectional survey was conducted to estimate the seroprevalence of Q fever in southern Belgium by means of an ELISA test on bulk tank milk (n = 206 herds). Herds giving a positive result were regarded as herds potentially exposed to the risk. At the same time a questionnaire was sent out separately allowing the investigation of presumptive clinical signs over the previous twelve months in prime- and multiparous cows. A multivariate logistic regression analysis was used to identify irregular repeated matings and stillbirths or weak calves as risk factors in first primi- and multiparous cows respectively. In addition, a boostrapped quantile regression revealed that the average score of putative clinical signs related to Q fever was significantly higher than other factors in both sub-groups. A classification and regression tree analysis confirmed the importance of an average clinical score as the main splitter and additionally infertility as second splitter, irrespective of the sub-group. The use of more advanced epidemiological methods permits to propose syndromic surveillance as a tool permitting the early identification of dairy herds exposed to Q fever. Syndromic surveillance permits the focusing of complementary investigations in dairy herds presenting altered clinical indicators.