Letter to the editor
An original article has recently been published in Transboundary and Emerging Diseases entitled ‘Unravelling animal exposure profiles of human Q fever cases in Queensland, Australia, using natural language processing’ by Clarck and others (https://doi.org/10.1111/tbed.13565; Clark et al., 2020), to which we have some comments.
In this paper, the authors applied natural language processing to an 18-year data set of Q fever notifications in Queensland, Australia, to investigate whether patients belonging to different demographic groups commonly report different potential exposure pathways. Identifying potential exposure pathways is necessary to design effective interventions and aid outbreak prevention.
Q fever is a worldwide zoonosis caused by an obligate intracellular bacterium, Coxiella burnetii (Angelakis and Raoutl, 2011). With only anecdotal reports of human-to-human transmission, the epidemiology of human infections always reflects the circulation of the bacterium in animal (domestic and wild) reservoirs. The prevalence of Q fever is highly variable from one country to another, due to mainly epidemiological and geographical disparities. In areas of endemicity, as Australia and Spain, Q fever occurs as sporadic cases, usually after identifiable at-risk activities (farming, slaughterhouse work, or rural tourism), however, as a rule, it is infected livestock, particularly goats and sheep, the most important sources of zoonotic Q fever outbreaks in humans. Nonetheless the origin of several human Q fever cases continues to be unclear. Besides domestic livestock, a diversity of possible wildlife reservoirs has been identified through molecular and serological surveys, including wild mammals, birds and even ticks (Toledo et al., 2009; Cooper, Stephens, Ketheesan, & Govan, 2013; González-Barrio and Ruiz-Fons, 2019). Throughout history, wildlife has been an important source of infectious diseases transmissible to humans. Today, zoonoses with a wildlife reservoir constitute a major public health problem, affecting all continents, an example is the SARS-CoV 2 that it has been able to cross the inter-species barrier to emerge as the most devastating human pandemic of our time. The total number of zoonoses is unknown, some 1,415 known human pathogens have been catalogued and 62% are of zoonotic origin (Billinis, 2013). Human impacts on habitats, biodiversity and climate could be responsible for changes in the patterns of interaction between domestic animals, wildlife and humans, allowing wild animals to be involved in the epidemiology of most zoonoses and thus serving as important reservoirs for the transmission of zoonotic agents to domestic animals and humans (González-Barrio and Ruiz-Fons, 2019). These changing patterns may also be behind the re-emergence of enzootic zoonoses such as Q fever that, although with a lower pandemic potential, it may become a serious health problem. Within Europe, Spain has reported the highest number of human Q fever cases annually since 2016 (0.8 cases per 100.000 population). In 2018, more than a third of the overall number of cases were notified from Spain (ECDE, 2019). In addition, Spain is the country where more studies in relation to Q fever have been conducted on wildlife and where more reservoirs of the bacteria have been confirmed (González-Barrio and Ruiz-Fons, 2019). In my opinion, these factors combined with the identification of shared genotypes between wildlife and humans in Iberian Peninsula (González-Barrio et al., 2016a,b,c) makes it possible that wild reservoirs, in this case ticks, deer, rabbits and micromammals (Toledo et al., 2009; González-Barrio et al., 2015a,b) among others, may play an important role in the increase of Q fever cases in Spain.