From animal to humans: A review of Coxiella burnetii and its role in zoonotic diseases

Introduction

Zoonotic diseases are an important concern in global health, accounting for more than 60% of emerging infectious diseases. Among these, Coxiella burnetii, the causative agent of Q fever, represents a unique challenge due to its ability to infect a broad spectrum of animal hosts and its capacity to transmit through the air to humans. ¹ Zoonotic diseases, which are infections that are transmitted from animals to humans, have become a critical concern in global health, representing more than 60% of emerging infectious diseases. ² The increasing incidence of zoonotic diseases poses a significant challenge to public health systems around the world, as the interfaces between humans, animals, and the environment continue to evolve. Among the multitude of zoonotic pathogens, Coxiella burnetii, the causative agent of Q fever, stands out due to its complex transmission dynamics, wide host range, and remarkable environmental resilience. ³ This obligate intracellular bacterium, which is responsible for Q fever, is a leading example of how pathogens can cross species barriers, with significant implications for human and veterinary health. ⁴ Coxiella burnetii is known for its ability to infect a wide range of animal hosts, including domestic ruminants such as cattle, sheep, and goats, as well as species of wildlife. Although frequently asymptomatic in these animals, the bacterium can cause significant reproductive problems, including spontaneous abortions and stillbirths, resulting in both economic losses and public health risks. ⁵ The pathogen is capable of surviving in harsh environmental conditions, often in the form of highly resistant spore-like structures, which contribute to its persistence in the environment. This environmental resilience, combined with its ability to be transmitted through aerosols, highlights the potential for airborne transmission to humans, a characteristic that sets C. burnetii apart from many other zoonotic pathogens. Humans acquire Q fever through inhalation of contaminated aerosols from infected animals or their excretions, although direct contact with infected animals or consumption of unpasteurized dairy products may also lead to infection. ⁶ The clinical spectrum of Q fever in humans is wide, ranging from acute febrile disease, often presented as a flu-like disease with fever, headaches, and fatigue, to more severe and chronic manifestations, including endocarditis, particularly in individuals with underlying heart conditions. Although most human cases resolve with appropriate antibiotic treatment, a significant proportion of infections progress to chronic forms, which can lead to life-threatening complications if left untreated. Q fever outbreaks have been notably linked to livestock farming, particularly in settings such as abattoirs and dairy farms, where the density of animals and the potential for aerosolization of the pathogen create a conducive environment for human exposure. ⁷ These outbreaks underscore the intricate relationship between human and animal health and the importance of understanding the transmission dynamics that bridges these domains. As such, C. burnetii represents a prime example of the need for a One Health approach, which recognizes the interconnectedness of human, animal, and environmental health, to address the challenges posed by zoonotic diseases. ³ The review also examines current strategies to control and preventing the spread of C. burnetii, including vaccination, surveillance, and biosecurity measures, while addressing emerging issues such as antimicrobial resistance and the influence of environmental factors on the persistence and spread. While Coxiella burnetii is primarily treated with tetracyclines, particularly doxycycline, concerns about antimicrobial resistance (AMR) are emerging. The obligate intracellular nature and its unique developmental cycle contribute to its ability to evade host immune responses and survive prolonged exposure. ⁸ A critical component of this review is the integration of One Health principles, emphasizing the need for a multidisciplinary approach to effectively mitigate the public health risks posed by C. burnetii and Q fever.

Review

The literature search was carried out using electronic databases, including PubMed and Google Scholar, with medical subject headings (MeSH) terms such as Coxiella burnetii, Q fever, Zoonotic diseases, Epidemiology, Animal-to-human transmission, One Health approach. The Boolean operators “AND” and “OR” were used to refine and combine these terms, creating various search strategies to identify the most relevant studies.

The initial search returned 128 articles. After removing duplicates (n = 44), an initial screening of titles and abstracts excluded 84 articles that were not related to C. burnetii or its implications within the One Health framework. A detailed review of the full text of the remaining articles excluded 49 more, resulting in a final selection of 18 articles for review (Figure 1).OPEN IN VIEWER

Conclusion

Coxiella burnetii is a complex zoonotic pathogen with significant implications for public and animal health. Its ability to persist in the environment, infect diverse hosts, and cause severe human disease underscores the need for a multidisciplinary approach to its management. Advances in diagnostics, vaccines, and public health interventions offer hope for improved control, but challenges such as antimicrobial resistance and environmental persistence remain. By adopting a one-health approach that integrates human, animal, and environmental health, we can mitigate the impact of C. burnetii and improve global health security.