Q fever

Q fever is an acute or chronic disease caused by the rickettsia-like bacterium Coxiella burnetii. Symptoms of acute disease include sudden onset of fever, headache, weakness, and interstitial pneumonitis. Manifestations of chronic disease depend on the organ affected. Diagnosis is confirmed by multiple serologic tests, culture of the murine membrane, or PCR testing. Treatment of Q fever is with doxycycline and chloramphenicol.

Coxiella burnetii is a small intracellular pleomorphic bacillus that is no longer classified as a Rickettsia. Molecular studies have allowed it to be classified as a Proteobacteria, the same group as Legionella.

ICD 10 code

A78. Q fever.

Epidemiology of Q fever

Q fever is a natural focal zoonotic infection. There are two types of foci of the disease: primary natural and secondary agricultural (anthropurgic). In natural foci, the pathogen circulates between carriers (ticks) and their warm-blooded hosts: ticks → warm-blooded animals → ticks.

The reservoir of the pathogen in natural foci is ixodid, partially gamasid and argasid ticks (more than seventy species), in which transphase and transovarial transmission of rickettsia is observed, as well as wild birds (47 species) and wild mammals - carriers of rickettsia (more than eighty species). The existence of a stable natural source of infection contributes to the infection of various types of domestic animals (cattle and small cattle, horses, camels, dogs, donkeys, mules, poultry, etc.).

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What causes Q fever?

Q fever is considered an asymptomatic infection of domestic and farm animals worldwide. Sheep and cattle are the main reservoirs of human infection. C. burnetii is found in feces, urine, milk and tissues (especially the placenta). This organism also persists in nature, in the animal-tick cycle.

Cases of the disease occur in people whose work involves close contact with farm animals or their products. Transmission usually occurs through inhalation of infected aerosols, but the disease can also occur through consumption of contaminated raw milk. Coxiella burnetii is highly virulent, resistant to inactivation, and remains viable in dust and faeces for months. Even 1 of this organism can cause disease.

Q fever can be acute or chronic. Acute disease is a febrile infection that often affects the respiratory system, but in some cases liver damage may occur. Chronic Q fever usually presents with endocarditis or hepatitis. Osteomyelitis may also develop.

Pathogenesis of Q fever

Q fever is a cyclic benign rickettsial reticuloendotheliosis. Due to the lack of tropism of the pathogen to the vascular endothelium, panvasculitis does not develop, so the disease is not characterized by rash and other symptoms of vascular damage. Unlike other rickettsioses, coxiella multiply mainly in histiocytes and macrophages.

What are the symptoms of Q fever?

Q fever has an incubation period that ranges from 18 to 21 days (extreme periods are 9 to 28 days). Some infections are accompanied by minimal symptoms, but in most cases, patients develop flu-like symptoms. The onset of the disease is sudden, with fever, severe headache, chills, severe weakness, myalgia, anorexia, and profuse sweating. Fever can reach 40 C, and the febrile period can last from 1 week to 3 or more. Respiratory symptoms, dry nonproductive cough, and pleuritic pain appear on the 4th to 5th day after the onset of the disease. Pulmonary symptoms may be particularly severe in elderly and debilitated patients. Wheezing is common on physical examination, and signs of lung consolidation may also be present. Unlike diseases caused by rickettsiae, there is no rash with this infection.

Acute liver disease, which develops in some patients, resembles viral hepatitis. It is characterized by fever, weakness, hepatomegaly accompanied by pain in the right hypochondrium, and possibly jaundice. Headache and respiratory symptoms are often absent. Chronic Q fever may present with fever of unknown origin. This disease must be differentiated from other causes of liver granulomas (e.g., tuberculosis, sarcoidosis, histoplasmosis, brucellosis, tularemia, syphilis) by performing laboratory tests.

The endocarditis in this disease resembles subacute infective endocarditis caused by viridans group bacteria; the aortic valve is most commonly affected, but vegetations may be found on any valve. Clubbing of the fingers, arterial emboli, hepatomegaly, and splenomegaly, and a purpuric rash may occur.

Q fever is fatal in only 1% of untreated patients. Some patients develop residual effects with nervous system damage.

The most severe forms of the disease occur with airborne infection, however, it is a cyclical infection, during which the following periods are distinguished: incubation, initial (3-5 days), peak (4-8 days) and recovery. The following forms of the disease are distinguished:

• acute (disease duration 2-4 weeks) - in 75-80% of patients;
• subacute or protracted (1-3 months) - in 15-20% of patients:
• chronic (from several months to one year or more) - in 2-30% of patients;
• erased.

How is Q fever diagnosed?

Laboratory diagnostics of Q fever consists of serological reactions: RA, RSK, RNIF, the results of which are analyzed taking into account the phase variations of Coxiella, which allows differentiating between patients and those who have recovered (standard diagnostics).

At the beginning of its course, Q fever resembles many infections (for example, influenza, other viral infections, salmonellosis, malaria, hepatitis, brucellosis). In later stages, it resembles many forms of bacterial, viral and mycoplasmal pneumonia. Important diagnostic information is contact with animals or their products.

The immunofluorescence method is the diagnostic method of choice. ELISA can also be used. Serological tests (usually paired sera in the complement fixation reaction) can also be used for diagnosis. PCR testing can identify the microorganism in biopsy material. C. burnetii can be cultured from clinical samples, but this is only possible in specialized laboratories. Routine blood and sputum cultures are negative.

Chest radiography is indicated for patients with respiratory signs and symptoms. Radiographic features may include pleural opacities, pleural effusion, and lobar consolidation. The gross appearance of the lungs may resemble bacterial pneumonia, but histologically it is more similar to psittacosis and some viral pneumonias.

In acute Q fever, the complete blood count may be normal, but approximately 30% of patients have elevated white blood cell counts. Typically, alkaline phosphatase, AST, and ALT levels are moderately elevated (2-3 times). Liver biopsy reveals diffuse granulomatous changes in histological examination.

How is Q fever treated?

Primary treatment for Q fever involves doxycycline 200 mg orally once, followed by 100 mg twice daily until clinical improvement and afebrile illness for 5 days. Doxycycline therapy is continued for at least 7 days. Second-line treatment is chloramphenicol 500 mg orally or intravenously 4 times daily for 7 days. Fluoroquinolones and macrolides are also effective.

In case of endocarditis, treatment should be at least 4 weeks. In this case, the most preferred drugs are tetracyclines. In cases where antibiotic treatment is only partially effective, damaged valves should be replaced surgically, but sometimes recovery occurs without surgery. Clear treatment measures for chronic hepatitis are not defined.

The patient should be isolated. Effective vaccinations against Q fever are available. These vaccines should be used to protect workers in slaughterhouses, dairies, raw material handlers, shepherds, wool sorters, farmers, and other high-risk individuals. These vaccines are not commercially available but can be obtained from special laboratories such as the Army Medical Research Institute of Infectious Diseases at Fort Detrick, Maryland.

What is the prognosis for Q fever?

Q fever has a favorable prognosis with timely and comprehensive treatment, although the recovery period in some patients is longer than with other rickettsioses and is accompanied by asthenoapatoabular syndrome, autonomic and vestibular disorders.

Fatalities are rare and are usually due to the development of endocarditis, the main syndrome of chronic Q fever.