What is Q fever?
Q fever is a bacterial infection caused by Coxiella burnetii that is transmitted from animals to humans. It is a zoontic infection that is primarily contracted through inhalation of the bacteria. Although rare, human-to-human transmission of Coxiella burnetii is possible. Q fever is a very mild disease, similar to the flu (influenza), in most people and some may not have any symptoms at all. It is an acute self limiting infection although chronic Q fever is possible. Q fever may cause complications such as pneumonia or carditis in some individuals and it is these complications that are the more likely to lead to severe health implications associated with the infection.
How common is Q fever?
Q fever is uncommon in the United States. It is more frequently seen in countries such as Australia, New Zealand, Netherlands, Spain and southern France and is endemic in the Middle East possibly due to the hot and dusty environment. Farm workers are naturally at a higher risk fo contracting the infection as livestock is the primary reservoir. It is estimated that about 3 out of 100 Americans may have had Q fever in the past and the disease could have gone unnoticed. The incidence can be as high as 20% amongst farm workers and veterinarians.
Infection with Coxiella Bacteria
Coxiella burnetii can spread through several different ways but in most cases it gains entry into the lung when it is inhaled. Macrophages, a type of immune cell that normally consumes invaders, actually serves as a means of transport for the bacteria. The Coxiella burnetii bacteria can fuse with lysosomes, tiny enzyme filled sacs, and multiply within the macrohpages. The acidic enzymes within the lysosomes are not able to destroy the bacteria. Eventually the proliferation of the bacteria within the host cell causes it to rupture and the bacteria can spread within the body. By traveling within macrophages, the bacteria tend to heavily infect organs like the liver, spleen and bone marrow.
Q Fever Granulomas
The presence of the bacteria in large amounts within these organs triggers the local immune responses and inflammation ensues. This causes the formation of granulomas. These granulomas are the body’s ways of walling of an inflamed and infected area from surrounding healthy tissue. In Q fever, the granulomas are referred to as doughnut granulomas because it has a thin outer fibrin wall with a central accumulation of fat. This effective immune response ensures that the bacteria do not severely damage the organ where it is deposited. Therefore Q fever is usually mild in most people. However, people with weakened immune systems are at risk of severe disease.
Signs and Symptoms
Q fever may be acute or chronic. Most people will experience only acute Q fever, the symptoms are mild and the disease is self limiting. Chronic Q fever is uncommon. It is believed to be a result of activation of a previous infection and people with weakened immune systems are at a greater risk. The incubation period of Q fever is around 2 to 3 weeks but can be as long as 6 weeks. This means during this time period after contracting the infection, a person may not exhibit any signs or symptoms.
Chronic Q fever can arise as soon as 6 weeks after the initial infection or arise several years later. The symptoms of Q fever largely resemble common viral infections like the flu (influenza). These symptoms may include :
- Malaise – a feeling of being unwell
- High fever as high as 40 degrees Celsius (104F)
- Sweating (sometimes)
- Chills (sometimes)
- Muscle pains throughout the body
- Severe headaches
- Non-productive cough (dry)
- Chest pain
- Nausea with or without vomiting
- Abdominal pain
Overall complications are rare in Q fever but when it occurs it can present as pneumonia (lung), hepatitis (liver), carditis (heart) and meningoencephalitis (brain and meninges surrounding it). The disease can also affect the skin, ovaries and testes, kidney, blood vessels, bones and joints. Pregnant women may experience a miscarriage (spontaneous abortion) or go into premature labor.
Causes of Q Fever
Q fever is caused by the coccobacillus, Coxiella burnetii. The primary reservoirs for these bacteria are cattle, goats and sheep but it may also be found in pets like cats and rabbits. These animals pass out the bacteria in their milk, urine or feces. The bacteria are highly resilient and can switch to a dormant spore-like state where it can remain in soil, straw or manure for long periods of time. Humans can be infected by :
- ingesting foods that are contaminated with the bacteria.
- skin contact with infected body fluids and tissue from these animals.
- bites of ticks that have previously fed on infected animals.
- inhaling dust contaminated with the bacteria.
- transfusion of blood or blood products from infected individuals.
The most common way in which humans contract the Q fever bacteria is through inhalation of the bacteria. Since the bacteria are so hardy, it can survive for long periods in and on inanimate objects (fomites). Therefore a person may still contract the infection after coming into contact with dust that was contaminated long before with the tissue, blood or excreta of infected animals.
Tests and Diagnosis
The symptoms of Q fever are not sufficient to diagnose the condition but may raise the suspicion of the condition along with the patient’s medical history. In fact the clinical presentation may vary meaning that the collective symptoms may differ from one patient to the next. Laboratory tests and imaging studies are therefore necessary.
- Blood tests are the most definitive way of diagnosing Q fever. These tests will be able to confirm the presence of antibodies produced against the bacterial antigens. However, these antibodies may not be detectable in the blood in the first 7 to 10 days. Polymerase chain reaction (PCR) tests are more sensitive but are not accurate if antibiotics have already been administered.
- Imaging studies like an X-ray, computed tomography (CT) scan and ultrasound may help identify the extent of complications. The characteristic doughnut granulomas seen in Q fever may also occur with Epstein-Barr virus (EBV) and cytomegalovirus (CMV) infection. It is therefore not a conclusive indicator of Q fever.
Q Fever Treatment
Most patients with Q fever will overcome the infection without the need for any treatment. Supportive measures may be all that is needed until the infection resolves spontaneously. Bed rest, a nutritious diet and plenty of fluids may be sufficient.
Doxycycline is the antibiotic of choice in the treatment of Q fever. Alternative antibiotics include ofloxacin, rifampin, sulfamethoxazole and trimethoprim, tetracycline and ciprofloxacin. Doxycycline may be sufficient in acute cases although a combination of antibiotics are considered for chronic cases. In Q fever, antibiotics are used for longer periods than in most bacterial infections. With acute Q fever, antibiotics may be continued for 2 to 3 weeks while in chronic Q fever, antibiotics may be used for as long as 18 months.
Various other drugs are utilized in the treatment of Q fever solely for symptomatic relief.
- Ibuprofen and acetaminophen are useful for treating the fever and to relieve the malaise.
- Aspirin is useful for the treatment of headaches but should not be used by children.
- Cough suppressants (antitussives) may be helpful in relieving the cough.