The immune response in Q fever.

Abstract

Q fever is an infection caused by the bacterium Coxiella burnetii. A large outbreak of Q fever occurred in the Netherlands between 2007 and 2010, in which infected goats and sheep were the source of human infections. In some people, so-called ‘chronic Q fever’ develops, which mainly manifests as endocarditis, infection of vascular prosthesis or aortic aneurysms, or both. We studied the immune response against C. burnetii in blood of healthy individuals, chronic Q fever patients and people with a past Q fever infection. Immune cells of chronic Q fever patients showed an increased production of ‘interferon-gamma’, a key signalling molecule. We concluded that, in contrast to what had generally been assumed, the interferon-gamma mediated immune response is not defect in chronic Q fever. Subsequently, we used the measurement of interferon-gamma production and other cell-signalling molecules (‘cytokines’) in blood in-vitro for diagnostic purposes. We found that these kind of blood tests can accurately detect a past or chronic Q fever infection. This valuable new diagnostic tool is currently being developed to a commercial blood test for Q fever infection. In a screening-study among patients with rheumatoid arthritis (RA) with immunomodulating drugs, we studied the risk for chronic Q fever. We found that RA patients are at increased risk for chronic Q fever compared to the general population. We advised to carefully check for chronic Q fever in these patients when they have been exposed to C. burnetii. We alse studied the unique Q fever vaccination campaign in the Netherlands in 2011, in which 1370 people with increased risk for chronic Q fever were vaccinated. This was the first time worldwide that such a large population at risk was being vaccinated against Q fever. We could conclude that vaccination was safe, but many vaccinees reported local skin reactions. We measured the immune response in blood of vaccinees 6 and 12 months after vaccination and found overall only a limited immune reaction to C. burnetii. We calculated retrospectively that only 11% of people at risk have been vaccinated in this 2011 campaign.