Q fever, also known as Query fever is a bacterial infection caused by the coxiella burnetii bacterium. Animals, most typically sheep, goats, cattle and other livestock infect humans – i.e. humans get it from animals. The organism is uncommon.
People become infected by inhaling contaminated particles of air, or from contact with milk, urine, feces, vaginal mucus or semen of infected animals. The incubation period – time from initial infection to the appearance of symptoms – is from 9 to 40 days.
Experts say Q fever may be considered the most infectious disease in the world, as a human being can be infected by a single bacterium.
The infection is also known as Query fever because when it was initially identified nobody knew what caused it. Even though we now know what the cause is, the term query has continued.
There are two main types of Q fever:
Acute Q fever – the most common and less serious type. The infected individual experiences flu-like symptoms, including muscle pain and an elevated body temperature (fever). In rare cases mild pneumonia may develop, and/or mild hepatitis.
Chronic Q fever – much less common, but more serious. The inner lining of the heart may become inflamed (endocarditis) – this is potentially extremely serious. If left untreated it could lead to heart failure.
According to the National Health Service (NHS), UK, Q fever may occur in many parts of the world, especially in Australia and the south of France. Approximately 70 cases are reported annually in the UK. The figure is probably much higher because people with mild symptoms may not seek medical help. According to the Centers for Disease Control and Prevention (CDC), USA, on average, approximately 50-60 cases of Q fever are reported in the United States each year, and the average annual reported incidence is 0.28 cases per million persons.
People who are in contact with livestock (farm animals) have a significantly higher risk of developing Q fever; these may include farmers, stablehands, meat packers and abattoir workers (slaughterhouse workers).
In the majority of cases, individuals with acute Q fever make a full recovery within a few weeks without treatment. Experts say that antibiotics can help relieve symptoms within a few days. Chronic Q fever is usually fatal if left untreated. Outlook for patients with chronic Q fever depends on whether they have access to antibiotics. Outlook is moderately good if the patient has treatment (NHS: mortality 10%). People with chronic Q fever commonly have to take antibiotics for several years to prevent recurrence.
There is a Q fever vaccine which has been produced in Australia. In some countries, including the UK, it has not been licensed for use. British authorities are still deciding whether to approve the vaccine for high-risk individuals.
According to Medilexicon’s medical dictionary:
Q fever is a disease caused by the rickettsia Coxiella burnetii, which is propagated in sheep and cattle, in which it produces no symptoms; human infections result from contact not only with such animals but also with other infected humans, air and dust, wild reservoir hosts, and other sources.
What are the Signs and Symptoms of Q fever?
A symptom is something the patient senses and describes, while a sign is something other people, such as the doctor notice. For example, drowsiness may be a symptom while dilated pupils may be a sign.
Signs and symptoms develop between 7 and 40 days after the initial infection – this is known as the incubation period.
Acute Q Fever – possible signs and symptoms include:
Fever – a body temperature of at least 39.4C (104F)
Very bad headache
Photophobia – sensitivity to light
Skin rash (rare)
Mild pneumonia (rare) – symptoms here may include a dry cough, sharp chest pain that worsens when the patient breathes deeply, coughs or laughs.
Hepatitis, inflammation of the liver (rare) – symptoms may include yellowing of the skin and whites of the eyes (very rare)
Chronic Q Fever – signs and symptoms generally appear about six months after the acute Q fever. The most common symptom is Endocarditis.
Endocarditis – the heart consists of four chambers and four valves – these have lines around them with a thin layer of cells (a membrane). This membrane is called the endocardium. An infection of the endocardium causes endocarditis. Put simply, endocarditis is inflammation of the inner lining of the heart. Signs and symptoms of endocarditis include:
A high temperature (fever)
A new heart murmur
Aching muscles (sometimes quite painful)
Alterations in heart murmur
Bleeding under fingernails or toenails
Broken blood vessels in the eyes
Broken blood vessels in the skin
Shortness of breath (panting)
Small lumps (nodules) on fingers and/or toes
Sweating (this may include night sweats)
Swelling of abdomen
Swelling of limbs
Unexpected weight loss
Mild pneumonia may also develop.
Osteomyelitis – bone infection. Patients typically experience deep pain and muscle spasms in the inflammation area, as well as fever.
What are the Risk Factors for Q Fever?
A risk factor is something which increases the likelihood of developing a condition or disease. For example, obesity significantly raises the risk of developing diabetes type 2. Therefore, obesity is a risk factor for diabetes type 2.
Occupation – people who are exposed to livestock (farm animals) and animal products have a higher risk of developing Q fever, such as veterinarians, meat processing workers, livestock farmers, those involved in animal research, and abattoir (slaughterhouse) workers.
Geographical location – being near a farm or farming facility may increase the risk of developing Q fever. The bacteria may travel through the air and be inhaled.
Gender – males are much more likely to develop symptomatic acute Q fever.
Medical history – people who have had acute Q fever are at risk of developing the chronic form of the disease, especially individuals with heart valve disease, blood vessel abnormalities, some kidney diseases, as well as patients with a weakened immune system.
What are the Causes of Q Fever?
The bacterium, coxiella burnetii (or c. burnetii) usually spread to animals by infected ticks. C. burnetii samples have been found in nearly all types of animals, even fish. As far as humans are concerned, the animals that pose a risk are:
Pets, such as dogs, guinea pigs and cats
In the majority of cases the infected animal has no signs or symptoms. This makes it hard to know whether an animal is infected. Infected animals are much more likely to have miscarriages.
The infected animal may release the bacteria through its:
Placenta – a birth by-product. The placenta is the organ that connects the fetus to its mother. Birth products contain the highest number of c. burnetii bacteria. According to the NHS, UK, an estimated 1 gram of infected bacteria can infect 100 million guinea pigs with Q fever.
Humans can become infected by either indirect or direct exposure to infected animals:
Direct exposure – most commonly, the human inhales small particles released by an infected animal, such as when the animal is giving birth or being slaughtered.
Indirect exposure – the c. burnetii bacterium is hardy and may survive outside its environment, such as in soil, for up to 10 months. Contaminated soil, dust or hay may be picked up by the wind, spreading the bacteria over a long distance. A 2003 Q fever outbreak in an Italian prison was believed to be caused by contaminated dust that had originated from a nearby field where sheep had been grazing.
Unpasteurized milk from an infected cow, sheep or goat may also be a source of human infection.
Experts say that the only way a human can infect another human is either by sexual intercourse, or by an infected pregnant mother to her fetus (unborn child).
What are the Causes of Chronic Q Fever?
In the majority of cases, chronic Q fever develops in patients with certain pre-existing health conditions, such as:
Heart disease – especially stenosis or other diseases that affect the heart valves
Blood cancer – such as leukemia or lymphoma
Weakened immune systems – patients with weakened immune systems, such as those with HIV/AIDS, or patients receiving chemotherapy or long-term steroids.
How is Q Fever Diagnosed?
The doctor, often a GP (general practitioner, primary care physicians) will carry out a physical examination, and also ask the patient questions about his/her occupation.
Some blood tests may be ordered, and other tests too if the doctor suspects chronic Q fever.
Platelet count – this is a blood test that calculates the number of platelets in a volume of blood. Platelets are the smallest cell-like structures in the blood. This test result may suggest Q fever, but it is not definitive.
Serologic testing – test of blood serum for the diagnosis of infectious diseases. In this case, to determine whether there are any antibodies to the c. burnetii antigen. An antigen is anything that causes an immune response when it enters the body, such as bacteria, foreign blood cells, and the cells of transplanted organs.
Echocardiogram – this may be done if the doctor suspects chronic Q fever. Sound waves produce images of the parts of the heart, including muscle, valves and chambers. This allows the doctor to look at the structure and workings of the patient’s heart in more detail. Clumps of bacteria and cells (vegetations) can be identified with an echocardiogram, as well as infected or damaged heart tissue.
What are the Treatment Options for Q Fever?
Acute Q fever treatment – mild or nonsymptomatic (no symptoms) cases usually resolve within a couple of weeks without any treatment. Even so, doctors will generally recommend treatment, even if there are no clear symptoms, to prevent any subsequent complications.
Antibiotic – doxycycline is the standard treatment for Q fever. In most cases the patient will take it for two or three weeks – course duration depends on the severity of the infection. As the antibiotic is most effective within one week of symptoms onset, it is important to take it as soon as possible.
The doctor may ask the patient to return in six months for serologic testing to determine whether the Q fever has returned. If specific antibodies are detected, another course of antibiotics will be required.
Chromic Q fever treatment – in this case antibiotics are taken for much longer, often for at least 18 months, and in advanced cases perhaps for four years.
Q fever endocarditis – the patient may require surgery to remove or graft affected heart valves, or to repair an aneurysm. An aneurysm occurs when part of a blood vessel (artery) or cardiac chamber swells, – either the blood vessel is damaged or there is a weakness in the wall of the blood vessel. As blood pressure builds up it balloons out at its weakest point. The swelling can be quite small or very large – when large it tends to extend along the blood vessel. As the aneurysm grows there is a greater risk of rupture – this can lead to severe hemorrhage, and other complications, including sudden death.
The patient will need to keep coming back for checkups for several years, in case the infection returns.
Pregnancy – most of the antibiotics used for Q fever treatment are not recommended during pregnancy, treating a pregnant woman is not easy. The patient may chose to wait until after giving birth before receiving treatment – however, this decision carries its own risks; Q fever can cause complications for the baby. It is important that the medical staff explain all the treatment options and their risks clearly to the patient.
What are the Possible Complications of Q Fever?
Q fever has the potential to affect many organs, including the heart, lungs, brain and liver. The following complications are possible:
Acute respiratory distress – the body does not get enough oxygen. This is a medical emergency.
Pregnancy complications – miscarriages, low birth weight, premature birth, stillbirth, and intrauterine growth retardation.
If the patient does not have any underlying disease/condition, has a healthy immune system, and receives treatment, the risk of complications is minimal. Even people at risk of complications have those risks significantly reduced if they receive prompt treatment.
Preventing Q Fever
Occupational hazards – it is important that preventative measures are in place to minimize the risk for people who work with animals and animal products. For example, all animal birth products should be disposed of properly, and access to infected animals should be strictly restricted.
Pasteurizing milk destroys the bacterium that causes Q fever.
Be careful not to touch anything that has been in contact with animal urine, feces or blood.
If you have an underlying disease/condition, such as chronic kidney disease, heart valve problems, abnormalities with blood vessels, or a weakened immune system, try to avoid jobs, such working with livestock, in an abattoir (slaughterhouse), a meat packing factory, or a veterinary center.
Pregnancy – avoid contact with farm animals, especially when they are giving birth, e.g. lambs and sheep during the lambing season. Avoid contact with clothing and footwear worn by people who were in contact with animals, such as ewes and lambs.