Q fever, or query fever, is an uncommon bacterial infection transmitted from animals to humans. It can be acute or chronic, and the chronic type can be fatal.

Sheep, goats, cattle and other livestock are most likely to carry the bacterium, but it has been found in many types of animals including fish, dogs, camels, and guinea pigs.

Q fever can occur anywhere in the world. In 2014, 167 cases of Q fever were reported in the United States (U.S.).

The infection is called Query fever because, when it was first identified, the cause was a mystery. The cause has since been identified, but use of the name has continued.

There are two main types: acute and chronic.

Acute Q fever

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Q fever is carried and spread by livestock.

This type is more common and less serious. Flu-like symptoms occur, including muscle pain and an elevated body temperature, or fever. Rarely, mild pneumonia, hepatitis, or both may develop.

Most patients with acute Q fever make a full recovery within a few weeks without treatment. Antibiotics can help relieve symptoms within a few days.

However, in some people, it can become chronic, especially in people who already have another chronic condition.

Chronic Q fever

Chronic Q fever is far less common but more serious. The inner lining of the heart may become inflamed, known as endocarditis.

This could lead to heart failure if left untreated.

Other complications of chronic Q fever can include:

Chronic Q fever is usually fatal if left untreated.

The outlook for patients with chronic Q fever depends on whether they have access to antibiotics. With timely treatment, the survival rate is 90 percent.

People with chronic Q fever commonly have to take antibiotics for several years to prevent recurrence.

Signs and symptoms develop between 14 and 21 days after the initial infection. This is known as the incubation period.

Signs and symptoms of acute Q fever include:

  • fever, with a body temperature of at least 39.4 degrees Celsius, or 104 degrees Fahrenheit
  • severe headache
  • muscle pain
  • joint pain
  • sweats
  • photophobia, or sensitivity to light
  • weight loss
  • skin rash, although this is rare
  • mild pneumonia
  • hepatitis, or inflammation of the liver, but this is rare

The signs and symptoms of Chronic Q fever appear about 6 months after the acute manifestation.

The most common symptom is endocarditis.

Symptoms of endocarditis include:

  • a high temperature
  • a new heart murmur
  • aching muscles
  • alterations in a heart murmur
  • bleeding under fingernails or toenails
  • broken blood vessels in the eyes
  • broken blood vessels in the skin
  • chest pains
  • coughing
  • headache
  • shortness of breath
  • small lumps on fingers and/or toes
  • shortness of breath
  • sweating including night sweats
  • swelling of the abdomen
  • swelling of limbs
  • tiredness
  • unexpected weight loss
  • weakness

Osteomyelitis, a bone infection, may also occur. Patients typically experience deep pain and muscle spasms in the inflammation area, as well as fever.

The infection is caused by a bacterium, Coxiella burnetii (C. burnettii), which passes from tics to livestock.

People then become infected by inhaling contaminated particles of air, or through contact with the milk, urine, feces, vaginal mucus, or semen of infected animals.

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Working on or near a farm and its animals can lead to an increased risk of contracting Q fever.

People who have frequent contact with livestock face a significantly higher risk of developing Q fever. This includes farmers, veterinarians, stablehands, meat packers, and slaughterhouse workers.

Living near a farm or farming facility may increase the risk. The bacteria can also be airborne.

Geographical location can also be a factor. In the U.S., over a third of the cases in 2014 came from Texas, California, Colorado, or Illinois.

Humans can become infected by either indirect or direct exposure to infected animals:

Direct exposure is most common. The person inhales small particles released by an infected animal, such as when the animal is giving birth or being slaughtered.

Indirect exposure occurs as the bacterium is resilient and may survive outside its environment for up to 10 months, for example in soil.

Contaminated soil, dust, or hay may be spread by the wind over a long distance.

In 2003, a Q fever outbreak in an Italian prison was believed to have been caused by contaminated dust, which 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 infection.

The only way a human can infect another human is either through sexual intercourse or from an infected pregnant mother to her fetus.

Risk factors that increase the likelihood of Q fever turning chronic include:

The doctor will carry out a physical examination and ask the patient about their occupation.

Some blood tests and other tests may be ordered if the doctor suspects acute or chronic Q fever.

Serologic testing: A blood serum test can help diagnose infectious diseases. In this case, it can detect the presence of antibodies to the c. burnetii antigen. A high enough number (titer) of the antibodies will suggest a diagnosis.

A platelet count: This blood test 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 will not confirm it.

Echocardiogram: Sound waves produce images of the parts of the heart, including muscle, valves, and chambers, to test for endocarditis.

The echocardiogram can give a detailed picture of the structure and workings of the heart. It can reveal clumps of bacteria and cells and infected or damaged heart tissue.

Treatment will be different for the two types.

Acute Q fever

Mild or nonsymptomatic cases usually resolve within a couple of weeks without any treatment.

However, antibiotics may be prescribed for 2 to 3 weeks, depending on how severe the infection is. Doxycycline is the standard treatment. The antibiotic is most effective within one week of symptoms appearing, so it is important to start as soon as possible.

The patient may be asked to return in 6 months for further serologic testing, to determine whether the Q fever has returned.

If specific antibodies are present, further antibiotics will be necessary.

Chronic Q fever

Patients with Q fever will take antibiotics for at least 18 months, and sometimes up to 4 years.

More severe manifestations may need more invasive treatment.

A patient with endocarditis may need surgery to remove or graft affected heart valves, or to repair an aneurysm.

An aneurysm occurs when part of a blood vessel or cardiac chamber swells and either damages the blood vessel or causes a weakness in the wall.

As blood pressure builds up, the blood vessel balloons out at its weakest point. The swelling can be small or very large and it can extend along the blood vessel. As the aneurysm grows, the risk of rupture increases. Rupture can lead to severe hemorrhage and other complications, including sudden death.

The patient will need to be monitored for several years in case the infection returns.

Q fever during pregnancy

Most of the antibiotics used to treat Q fever are not recommended during pregnancy. The patient may choose to wait until after giving birth before receiving treatment. However, this involves a further risk, as Q fever can cause complications for the fetus.

Medical staff must explain all the treatment options and their risks to the patient.

Preventive measures must be 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 restricted.

Workers should avoid touching anything that has been in contact with animal urine, feces or blood.

Where possible, those with an underlying condition such as chronic kidney disease, heart valve problems, abnormalities of blood vessels, or a weakened immune system should avoid working with livestock.

Pasteurizing milk destroys the bacterium that causes Q fever.