Q fever

Q Fever: An Introduction

Q fever, also known as Q fever pneumonia, Coxiella Burnetii fever, and Query fever, is a globally prevalent infectious disease caused by the bacterium Coxiella burnetii. Originating from certain animals, the disease manifests in both acute and chronic stages in humans.

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Microscopic view of Coxiella burnetii, the causative agent of Q fever.

Source and Transmission

Reservoir Animals

• Goats: A primary reservoir for C. burnetii.
• Sheep: Another significant carrier of the bacterium.
• Cattle: Less frequently implicated, but still a potential source of the disease.

Transmission to Humans

Humans typically acquire Q fever through:

• Inhalation of airborne particles contaminated with the bacteria.
• Contact with the birth products of infected animals, such as placenta and amniotic fluid.
• Handling or consuming contaminated milk, urine, or feces from infected animals.

Clinical Presentation

While many infected individuals may remain asymptomatic, others may experience symptoms including:

• High fever
• Fatigue
• Headache
• Chest pain
• Dry cough

The disease can progress from an acute to a chronic phase, especially if not treated timely.

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Diagnosis and Treatment

Diagnosis

• Blood Tests: Detection of antibodies against C. burnetii.
• PCR Testing: Identification of bacterial DNA in blood samples.

Treatment

• Antibiotics, especially doxycycline, are effective during the acute phase.
• Chronic Q fever may necessitate longer treatment durations and a combination of medications.

Transmission

People get infected by breathing in dust that has been contaminated by infected animal feces, urine, milk, and birth products that contain Coxiella burnetii. Direct contact (e.g. touching, being licked) with an animal is not required to become sick with Q fever. People may also get sick with Q fever by eating contaminated, unpasteurized dairy products. Rarely, Q fever has been spread through blood transfusion, from a pregnant woman to her fetus, or through sex.

Riskfactors

Certain professions are at increased risk for exposure to C. burnetii, including veterinarians, meat processing plant workers, dairy workers, livestock farmers, and researchers at facilities housing sheep and goats. People working in these areas may need to take extra precautions

Signs and Symptoms

About 5 out of 10 people infected with Coxiella burnetii will get sick. Illness typically develops 2-3 weeks after being exposed to the bacteria. Signs and symptoms of Q fever may include:

• Fever
• Chills or sweats
• Fatigue (tiredness)
• Headache
• Muscle aches
• Nausea, vomiting, or diarrhea
• Chest pain
• Stomach pain
• Weight loss
• Non-productive cough

Symptoms can be mild or severe. People who develop severe disease may experience infection of the lungs (pneumonia) or liver (hepatitis). Women who are infected during pregnancy may be at risk for miscarriage, stillbirth, pre-term delivery, or low infant birth weight.

Chronic Q fever A very small percentage of people (less than 5 out of 100) who become infected with C. burnetii bacteria develop a more serious infection called chronic Q fever. Chronic Q fever develops months or years following initial Q fever infection. People with chronic Q fever often develop an infection of one or more heart valves (called endocarditis). People with endocarditis may experience night sweats, fatigue, shortness of breath, weight loss, or swelling of their limbs. A healthcare provider will need to perform a series of tests to diagnose endocarditis.

Diagnosis

Diagnosis is usually based on serology(looking for an antibody response) rather than looking for the organism itself. Serology allows the detection of chronic infection by the appearance of high levels of the antibody against the virulent form of the bacterium. Molecular detection of bacterial DNA is increasingly used. Culture is technically difficult and not routinely available in most microbiology laboratories.

Q fever can cause endocarditis (infection of the heart valves) which may require transoesophageal echocardiography to diagnose. Q fever hepatitis manifests as an elevation of alanine transaminase and aspartate transaminase, but a definitive diagnosis is only possible on liver biopsy, which shows the characteristic fibrin ring granulomas.

Treatment

Most people who are sick with Q fever will recover without antibiotic treatment. However, for people who develop Q fever disease, treatment with 2 weeks of doxycycline antibiotic is recommended. Chronic Q fever A life-threatening infection, requiring several months of antibiotic treatment. Treated with a combination of antibiotics including doxycycline and hydroxychloroquine for several months.

Prevention

• Protection is offered by Q-Vax, a whole-cell, inactivated vaccine developed by an Australian vaccine manufacturing company, CSL Limited. The intradermal vaccination is composed of killed C. burnetii organisms. Skin and blood tests should be done before vaccination to identify pre-existing immunity, because vaccinating people who already have an immunity can result in a severe local reaction. After a single dose of vaccine, protective immunity lasts for many years. Revaccination is not generally required. Annual screening is typically recommended.

• Q fever vaccines are not available in the United States.

• Reduce your risk of getting Q fever by avoiding contact with animals, especially while animals are giving birth. Animals can be infected with Coxiella burnetii and appear healthy.

• Do not consume raw milk or raw milk products.

• If you have been diagnosed with Q fever and have a history of heart valve disease, blood vessel abnormalities, a weakened immune system, or are pregnant, talk to your healthcare provider about your risk for developing chronic Q fever.

Epidemiology

Q fever was first recognized as a human disease in Australia in 1935 and in the United States in the early 1940s. The “Q” stands for “query” and was applied at a time when the cause was unknown. C. burnetii can survive for long periods of time in the environment and may be carried long distances by wind.

Q fever was made a nationally notifiable disease in the United States in 1999. The number of Q fever cases reported to CDC increased, from 19 cases reported in 2000, to 173 cases reported in 2007. In 2008, the Q fever case definition was changed to allow for the reporting of chronic and acute Q fever separately. During 2008–2013 the number of reported cases decreased slightly, relative to 2007, returning to high levels in 2014. In 2017, 153 acute Q fever cases were reported, as well as 40 chronic Q fever cases.

Prevention

• Avoiding contact with potentially infected animals.
• Drinking pasteurized milk and dairy products.
• Using appropriate protective equipment in occupational settings involving animals.

Conclusion

Q fever, although a zoonotic disease primarily affecting animals, can have serious health implications for humans. Awareness, timely diagnosis, and proper treatment are essential in managing and controlling the spread of this disease.

Q fever Resources
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