Q fever overview
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
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Overview
Q fever is caused by infection with Coxiella burnetii. This organism is uncommon but may be found in cattle, sheep, goats and other domestic mammals, including cats and dogs. The infection results from inhalation of contaminated particles in the air, and from contact with the vaginal mucus, milk, feces, urine or semen of infected animals. The incubation time is 9-40 days. It is considered possibly the most infectious disease in the world, as a human being can be infected by a single bacterium [1].
Historical prespective
The disease was first described by Edward Holbrook Derrick in Australia while the pathogen was first described in 1937 by Frank Macfarlane Burnet.
Classification
According to the onset of symptoms, Q fever can be classified into acute and chronic.
Pathophysiology
Q fever is a disease caused by C. brutenii, an intracellular gram-negative proteobacterium. The disease can have a wide range of clinical presentations and affect many organ systems due to the unique virulence factors of the organism.
Causes
Q fever is caused by the bacteria Coxiella burnetii, which lives in domestic animals such as cattle, sheep, goats, birds, and cats. Some wild animals and ticks also carry the bacteria. Q fever may be contracted through drinking raw (unpasteurized) milk, or after inhaling dust or droplets in the air that are contaminated with animal feces, blood, or birth products.
Differential diagnosis
Q fever must be differentiated from other diseases that cause atypical pneumonia such as mycoplasma pneumonia and legionella pneumonia.
Epidemiology and demographics
C.brutenii is found everywhere except Antarctica and New Zealand.The disease is slightly more prevalent in elder people and in males.
Risk factors
The organism is present mainly in the secretions of cattle and sheep. Any occupation that involves contact with cattle and sheep increases the risk of the disease.
Natural history, complications, and prognosis
Acute Q fever has a good prognosis even without treatment. Chronic Q fever has a less favorable prognosis.
History and symptoms
Acute Q fever presents with flu-like symptoms, pneumonia, and hepatitis. Chronic Q fever almost always presents with endocarditis and sometimes gives musculoskeletal and vascular manifestations.
Physical examination
Patients with Q fever usually appear ill. Physical examination of patients with Q fever is usually remarkable for fever, pneumonia, and hepatomegaly.
Laboratory Findings
Laboratory findings consistent with the diagnosis of Q fever include positive serology for antibodies (especially Indirect immunofluorescence (IIF), positive PCR, and elevated liver enzymes.
Chest X Ray
On chest X-ray, Q fever is characterized by either signs of atypical pneumonia (hazy nonlocalized airspace opacities) or it may show signs of typical pneumonia (lobar consolidation and occasional pleural effusions) in few patients.
CT
Chest CT scan may be helpful in the diagnosis of Q fever. Findings on CT scan suggestive of Q fever include scattered consolidation and opacities or lobar consolidation in one specific lobe.
MRI
There are no additional MRI findings associated with Q fever. Chest X-ray and CT are usually sufficient.
Other imaging findings
There are no other specific imaging findings for Q fever.
Other diagnostic studies
There are no additional diagnostic findings for Q fever.
Medical Therapy
The mainstay of therapy for Q fever is doxycycline. The chronic form is more difficult to treat and can require up to two years of treatment with doxycycline and Hydroxychloroquine. Q fever in pregnancy is especially difficult to treat because doxycycline is contraindicated in pregnancy and so preferred treatment is Trimethoprim/Sulfamethoxazole.
Surgery
Surgical intervention is not recommended for the management of Q fever.
Primary prevention
Effective measures for the primary prevention of Q fever include educating the public on sources of infection, appropriate disposal of the placenta, birth products, fetal membranes, and aborted fetuses at facilities housing sheep and goats and restricting access to barns and laboratories used in housing potentially infected animals.
Secondary prevention
There are no secondary preventive measures available for Q fever.