Q fever: the contribution of cattle as a reservoir of human infection should not be overlooked

Context and issues

Q fever, caused by Coxiella burnetii, is a zoonosis whose main reservoirs are domestic ruminants (cattle, sheep, goats). Most studies of seroprevalence and risk factors in humans have been conducted in areas where both cattle and small ruminants are present, the latter being systematically involved in human epidemics of Q fever. Therefore, the specific contribution of cattle to the risk of transmission to humans remains uncertain. Furthermore, in these same areas, the positive serological status of part of the population could be the result of determinants linked to goats, which questions the validity of the risk factors for seropositivity reported in the literature for humans living in contact with or near cattle alone.

In order to specifically assess the role of cattle, and to identify specific preventive actions that could be advised to these human populations, we conducted a cross-sectional study in areas where C. burnetii infection in cattle was endemic, and where the density of cattle and small ruminants was respectively high and very low. The objectives were to estimate seroprevalence and to explore risk factors for seropositivity among occupational (farmers and veterinarians) and non-occupational (general adult population) risk groups.

Results

Sera were collected from 176 dairy farmers, 45 veterinarians and 347 blood donors (representing the general population), and tested for phase I and II antibodies using IFA. Seroprevalence rates were 56.3% in cattle farmers, 88.9% in veterinarians and 12.7% in blood donors. The risk factors identified were: in the general population, working with ruminants compared to any other activity; in farmers, managing an infected cattle herd. No other controllable risk factors (lifestyle, outdoor activities, proximity to pets and production animals, professional and biosecurity practices) were identified.

Perspectives

In areas where Q fever is endemic in cattle, human exposure to C. burnetii is to some extent unavoidable, given the high dispersal potential of this bacterium, its ubiquity and its high resistance in the environment. However, exposure does not always imply infection or disease. Moreover, most infections remain asymptomatic or result in a mild flu-like syndrome. However, severe acute forms as well as complications (endocarditis, abortions, ...) can occur. Raising awareness among doctors of the symptoms of Q fever and the importance of adopting general biosecurity measures is crucial and must be reinforced, particularly for at-risk groups, in all livestock areas, including those without small ruminants.

Valorisation

2 scientific publications

Newsletters to participants

Confidential written feedback to each participant on their serological status

Bibliographical references

Pouquet et al., 2020. Doi: 10.1017/S0950268820001880

Beaudeau et al., 2021. Doi: 10.1111/zph.12803