La fièvre Q, une maladie qui peut passer des ruminants à l’être humain

Q fever, a disease that can be passed from ruminants to humans

Q fever is often misunderstood, even though this disease is widespread throughout the world and was discovered almost a century ago. It can cause reproductive problems in ewes, female goats and cows and be transmitted to humans. Although the disease is generally not serious, it can nevertheless lead to complications, and sometimes takes months or even years to develop after initial infection.

What is Q fever?

Q fever (Q meaning query) is caused by the bacterium Coxiella burnetii. It can infect most domestic and wild animal species. In the majority of cases the bacterium does not give rise to symptoms in infected animals, but it can cause abortions and stillbirths in sheep, goats and cattle. Problems such as uterine infections and infertility have been suggested, but no direct evidence has been reported. It is a zoonosis, meaning that it can be transmitted to humans.

What are the symptoms in humans?

It is estimated that around 40% of human infections cause symptoms. In most cases, these take the form of a flu-like illness. In addition to fever, complications may include hepatitis or pneumonia. These depend partly on the bacterial strain of Coxiella burnetii. The "Guiana" strain is associated with severe lung infections.

The bacterium can also cause premature birth or miscarriage in pregnant women, but the exact incidence is difficult to estimate.

There is a lack of knowledge about the proportion of people who eliminate the bacterium after infection and those who remain carriers. In around 1 to 5% of people infected, Coxiella burnetii can cause chronic clinical forms that persist for several months or years after infection. Such conditions can generally be highly disabling. The most serious forms are endocarditis and chronic fatigue syndrome. More rarely, clinical symptoms may be expressed as neurological or rheumatological disorders.

How is the disease transmitted to humans?

Sheep and goat farms are the main source of human contamination. Transmission of Q fever between humans is anecdotal, and they are considered to be epidemiological dead ends.

Infected animals can shed bacteria through vaginal secretions, the placenta, milk and faeces, even if they show no symptoms. The main route of infection is respiratory: bacteria can be re-suspended in the air, alone or with dust, and then inhaled.

Coxiella burnetii is unique in its ability to develop resistant spore-like forms, which can survive in the open air for several weeks or months and then be spread. Transmission to humans therefore depends on a combination of factors favouring the airborne spread of bacterial spores from infected farms (wind, topography, humidity, etc.), or their re-suspension in the air (spreading of manure, etc.). Transport of animals or animal products can also contribute to the spread of bacteria.

The risk of infection following ingestion of contaminated food is still the subject of discussion. In a 2010 opinion, ANSES concluded that current knowledge indicates that consumption of raw dairy products from infected animals may result in an immune response but no clinical manifestations.

What is the epidemiological situation on French livestock farms?

A programme was carried out in France between 2012 and 2015 to obtain epidemiological information on Q fever in ruminants for the very first time on a national scale. The study showed that there was considerable variability between geographical areas. Overall, many herds were seropositive, meaning that they had been exposed to the bacterium (36% of cattle, 56% of sheep and 61% of goats), and goat farms were the most affected by abortive episodes due to Q fever (2.7% for cattle, 6.2% for sheep and 15.8% for goats). Following on from this programme, the Observatory for monitoring the causes of abortions in ruminants (OSCAR) was set up in 2017. This prototype scheme monitors abortions of infectious origin, including Q fever, in volunteer départements.

Is there any monitoring of cases of animals infected with Q fever?

Animal Q fever has been subject to mandatory reporting and monitoring in the European Union since 2021, under the "Animal Health Law" (Regulation (EU) 2016/429 on transmissible animal diseases). This requirement covers four species of ruminants: goats, sheep, cows and buffalo. However, the existing surveillance schemes are still imperfect, and animal monitoring methods are still being developed in certain countries like France.

Do we know how many human cases of Q fever there are each year?

As reporting of human cases in France is not mandatory, the number is underestimated. The human aspect of Q fever is monitored by the Méditerranée-Infection institute in Marseille, which is the National Reference Centre (NRC) for the disease. It identifies some of the sporadic human cases through its own diagnostic and clinical monitoring activities. Between 100 and 300 cases are confirmed each year.

Cases are often sporadic. Q fever seems to be widespread throughout the country, and is very prevalent in certain regions such as French Guiana.

Human cases sometimes occur in clusters, whose precise origin is not always identified. Sheep have most often been associated with the origin of clustered cases in France.

Which people are most at risk?

A distinction is made between the "risk of exposure" and the "risk of developing disease". The people most exposed are those working in the livestock sector or living near farms. However, people who occasionally enter a contaminated environment seem to be most at risk of developing disease.

Certain factors are well documented: the transition to endocarditis or vascular infections is more common in patients with valvular heart disease or vascular aneurysms, or those wearing vascular prostheses.

What control methods are available?

There is an effective antibiotic treatment for patients with Q fever, but it may need to be taken for several years and often causes intense fatigue. In addition, early diagnosis is important to guarantee its effectiveness. Furthermore, no vaccine against human Q fever has been authorised in France due to uncertainties about side effects.

Disease prevention is therefore crucial. It is based primarily on limiting the spread of the bacterium among animals and in the environment. Veterinary measures can help reduce the pressure of infection on farms, particularly after an abortive episode causing massive shedding of bacteria into the environment. A combination of vaccination of young animals for at least three years, destruction of placentas and aborted foetal material, appropriate manure management, and cleaning of equipment and vehicles has been proposed. Studies are still needed to clarify the various arrangements for these measures, depending on the epidemiological situation. Personal protection measures, such as mask wearing, are also recommended to protect workers and visitors.

Eradicating the infection in livestock does not seem feasible, given the airborne circulation of the bacteria and the many different animal species that can be carriers, including rodents, dogs, cats and birds.

What is ANSES's role regarding Q fever?

The Animal Q Fever Unit at the ANSES Sophia Antipolis laboratory has two reference mandates for Q fever: at national level (NRL) and for the World Organisation for Animal Health (WOAH). Its role is to provide independent scientific advice and assistance. It regularly takes part in expert appraisal work and provides support to animal health stakeholders.

Its main activities focus on assessing diagnostic and epidemiological tests, including commercially available ones, to ensure reliable and comparable results across a network of local diagnostic laboratories.

At the request of the European Food Safety Authority and the European Centre for Disease Prevention and Control, the unit is responsible for improving the quality and harmonisation of animal Q fever surveillance data compiled in the annual European report on zoonoses. This work is carried out with the Italian organisations Istituto Zooprofilattico Sperimentale (IZS) and Istituto Superiore di Sanità (ISS).

The team also participates in epidemiological investigations following alerts of clustered human cases, in order to trace the origin of contamination and advise on the measures to be put in place to prevent new infections, by supporting the Q fever monitoring group of the epidemiological surveillance platform for animal health.

With its partners, the unit's research efforts are focused on three areas:

  • Strain characterisation: improvements in strain isolation methods, studies of degrees of virulence and resistance in the environment, development of more powerful genetic tools to identify certain strains that are more dangerous.
  • Epidemiological description in ruminants, particularly regarding environmental contamination. The aim is to gain a clearer understanding of the wide variability of epidemiological configurations and to define risk indicators for airborne exposure or the impact on human and animal health.
  • Improving preventive measures or action taken during human clusters: coordination with animal and human health stakeholders and livestock farmers, veterinary management options tailored to the risks and while taking account of the protective microbiological balance on farms.