• The technology centre is analysing the prevalence, epidemiology and genetic diversity of the bacterium Coxiella burnetii in order to improve strategies for the surveillance and control of this zoonosis

Zoonotic diseases, which are transmitted between animals and humans, pose a public health challenge that goes beyond clinical care or the control of infected animals. Furthermore, in the case of pathogens capable of persisting in the environment and spreading through it, it is particularly important to study the conditions that favour their spread.

Q fever is an example of this problem. It is caused by the bacterium Coxiella burnetii, whose main reservoirs are domestic ruminants, particularly sheep, goats and cows. Although infected animals may show no symptoms, in small ruminants the infection can lead to abortions, premature births and the birth of weak offspring. In humans, the infection can cause symptoms ranging from flu-like illness to more serious complications.

NEIKER has been researching the presence, epidemiology and genetic diversity of this bacterium on local livestock farms for more than two decades, with the aim of developing surveillance and control strategies designed to reduce its presence in herds and the risk of transmission to humans.

“One of the most important steps in investigating and controlling human outbreaks of Q fever is to identify its possible animal source. To do this, we need to gain a better understanding of the bacterium and have access to high-resolution genotyping tools that enable us to compare C. burnetii in human, animal and environmental samples. A coordinated approach based on the One Health framework is also essential,” explains Ana Hurtado, a researcher in NEIKER’s Department of Animal Science.

 

Routes of transmission and clinical signs of Q fever

During parturition and abortion, infected animals can shed large quantities of Coxiella burnetii via the placenta, vaginal fluids and other biological waste. These materials contaminate the environment, where the bacterium can remain viable for long periods in dust, manure and organic matter. Furthermore, it can be dispersed through the air over distances of several kilometres. In humans, infection is mainly acquired through the inhalation of contaminated aerosols or dust.

“Although Q fever has traditionally been regarded as an occupational disease associated with livestock farming or veterinary work, it can also affect the general population without direct contact with animals, as C. burnetii can be transmitted through the air from livestock farms to urban areas,” says the researcher. Around 60 per cent of human infections with C. burnetii are asymptomatic, but when symptoms do appear, they are usually similar to those of flu, with fever, headache, tiredness and general malaise. In some cases, more severe forms of the disease develop, such as pneumonia or acute febrile hepatitis and, less frequently, neurological complications. Between 1% and 5% of infected people may develop a severe chronic infection, such as endocarditis or vascular infections.

 

Research based on the One Health approach

The bacterium’s ability to spread amongst animals, people and the environment makes it necessary to coordinate research using the One Health approach, which integrates these three dimensions of health. In the Basque Country, since 2014, the Basque Government’s Public Health Department, Osakidetza, OSALAN, the provincial councils and NEIKER have been collaborating on research into human outbreaks of Q fever by analysing human, animal and environmental samples to identify the source of the infection and the routes of transmission.

“In our region, research has linked the majority of human outbreaks to small ruminants, particularly goats. It has also been confirmed that transmission can occur via the environment in places seemingly far removed from direct contact with animals, such as those recorded at a waste treatment plant, a machine tool factory and a natural cave where the largest outbreak of Q fever ever recorded in Spain took place, affecting 108 people,” says Hurtado.

However, determining the source of the infection is not always straightforward. In order to link human cases to an animal or environmental source, tools are needed to compare the bacteria detected in the various samples. To this end, NEIKER has taken part in the European Q-NET-ASSESS project, alongside institutions from five other countries.

The project is investigating the genetic diversity of the bacterium through genomic sequencing to gain a better understanding of the relationship between the bacterium’s different genetic variants, its ability to infect different animal species and its potential virulence. Furthermore, within this framework, protocols for diagnosing the causes of abortion in ruminants have been compared with procedures for investigating human outbreaks. Data collected between 2022 and 2024 confirmed that C. burnetii is one of the main causes of abortion in small ruminants.

The most effective measure for reducing the risk of infection in humans is the early detection and control of the disease in ruminant herds. To detect the disease, reported abortions on livestock farms are investigated (active surveillance) and serological tests and tank milk tests are carried out in herds with no apparent clinical signs (active surveillance). When a human outbreak is identified, the farms linked to the cases are also investigated to identify a possible source of infection.

Detecting the bacterium enables control measures on farms to be targeted effectively. These include the proper management of birthing waste and manure, the cleaning and disinfection of premises, and the control of animal movements. Vaccinating livestock is another option that can help eradicate the bacterium, although it requires programmes to be maintained over several years.

“As there is no authorised human vaccine in Europe, reducing the circulation of C. burnetii in animals is one way of lowering the risk of transmission to humans,” concludes the researcher.