The relevance of the wild reservoir in zoonotic multi-host pathogens: The links between Iberian wild mammals and Coxiella burnetii

Abstract

Q fever is a worldwide zoonosis caused by an obligate intracellular bacterium, Coxiella burnetii, with only anecdotal reports of human-to-human transmission. The cause of human Q fever infections is the circulation of C. burnetii in animal reservoirs. Infected livestock, particularly goats and sheep, may cause Q fever outbreaks in humans. However, wildlife is the origin of several human Q fever cases. Human impacts on habitats, biodiversity and climate are responsible for changes in the patterns of interaction between domestic animals, wildlife and humans, allowing wild animals to play an increasingly relevant role as Q fever reservoirs. In the Iberian Peninsula, human impacts on the environment combined with a high biodiversity, which could maintain high transmission rates of this multi-host pathogen, make wild reservoirs an important piece in Q fever epidemiology. In this study, we review the reporting of C. burnetii infections and exposure in Iberian wild mammals and analyse the link between the diversity of wild mammals and the frequency of C. burnetii notifications in wildlife. For it, the number of wild mammal species per UTM 10 × 10-km grid in mainland Spain and Portugal was estimated as a potential predictor of C. burnetii transmission. The results of non-linear regression analysis showed a quadratic relationship between the number of wild mammal species per grid and the presence of C. burnetii cases reported in the literature both by serology (R² = 0.86) and polymerase chain reaction (R² = 0.83). Increasing wild mammal diversity was linked to increasing C. burnetii transmission until an intermediate level when the relationship was inverted. Thus, at high levels of wild mammal diversity, the risk of C. burnetii transmission was lower. These observations show a role of wild mammal biodiversity in C. burnetii ecology that needs to be further explored to better prevent the negative impact of Q fever in livestock and human health in Iberia.

Keywords: Coxiella burnetii; Iberian Peninsula; Q fever; host richness; wildlife.