Coxiella burnetii (Q-Fever) Phase 1 IgG

The Rickettsia Coxiella burnetii, a worldwide distributed pathogen, is responsible for the disease known as Q fever. The small gram-negative, obligate intracellular bacterium reproduces in the digestive system of ticks (Dermacentor marginatus) and placental trophoblasts. As a result tick faeces and afterbirths of infected mammals (particularly sheep) are highly infectious. Occupational groups with direct contact to farm animals are at particular risk of infection. In this group, antibodies against Coxiella burnetii can be detected in 30 to 70 %. Infection usually results from inhalation of contaminated aerosols, especially during dry summer months. The incubation time is around two to four weeks. Clinical symptoms are developed in 30 to 50 %; the remaining individuals (50 to 70 %) reveal subclinical or non-specific symptoms. Influenza-like symptoms are often evident. In about 50 % of cases an atypical, interstitial pneumonia develops. Less frequently, the infection results in a hepatitis. In a few cases, the acute phase may be complicated by meningoencephalitis, myocarditis or pericarditis. If not treated the pathogen persists in 1 to 11 % of all cases in a variety of organs, which ends after months or years, in a chronic infection. Chronic courses often lead to an endocarditis (especially patients with heart valve disease) and/or granulomatous hepatitis. About 65 % of chronic Q-fever cases are lethal. Following a primary infection antibodies directed against the phase 2 antigen are produced during the acute phase of Q fever disease. IgM antibodies appear approximately after two weeks followed by IgG with in two months post infection. While IgM antibodies can be detected up to three months post infection, IgG is frequently detectable for up to five years. Only when an infection enters the chronic stage IgA and IgG directed against the C. burnetii phase 1 antigen appear. These antibodies are particularly significant when diagnosing Q fever endocarditis. Due to the fact, that IgM antibodies directed against phase 1 antigen are not present after a longer time period, there is no sense of IgM detection during a chronic course. Rheumatoid factors are significantly increased in the chronic phase. Due to the lack of characteristic clinical symptoms of acute and chronic Q fever infection, diagnosis is based primarily on serologic techniques. The use of ELISA test systems is recommended by the WHO due to its high sensitivity and specificity and the possibility to perform a differential analysis of the antibody response. Following diseases should be considered for differential diagnosis: Chlamydia infections, Mycoplasma pneumoniae-infections, Legionella pneumophila- and Legionella micdadeiinfections, Virus-pneumonias and Leptospirosis.

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