Q fever
Q fever is an infection people catch from animals. It is caused by the bacterium Coxiella burnetii, which lives mainly in sheep, goats and cattle.
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Medicines commonly prescribed for Q fever
For informational purposes only. Always consult a doctor before using any medicine.
Dosage form: TABLET, 100 mgActive substance: doxycyclineManufacturer: Pierre Fabre Iberica S.A.Prescription requiredDosage form: ORAL SOLUTION/SUSPENSION, 60 mlActive substance: doxycyclineManufacturer: Hospira Invicta S.A.Prescription requiredDosage form: CAPSULE, 100 mgActive substance: doxycyclineManufacturer: Industrial Farmaceutica Cantabria S.A.Prescription required
Q fever is an infection people catch from animals. It is caused by the bacterium Coxiella burnetii, which lives mainly in sheep, goats and cattle. For most people it means a week or two of flu-like illness that settles on its own. In a minority, though, the infection can lie hidden and return months or years later wearing a different face: damage to a heart valve. It is that second, late part of the story that usually goes untold.
How people catch it
The main route is breathing it in. The bacterium is shed in enormous quantities in the amniotic fluid and placenta when animals give birth, and also in droppings and urine. As it dries it takes on a hardy form that survives for months in dust, straw, manure, wool and clothing, and that the wind carries. Inhaling a very small quantity is enough to become infected, so it is not only people who have handled animals who fall ill: being downwind of a farm, or walking past a barn during the lambing and kidding season, can be enough.
Hence the profile of those most at risk: farm and abattoir workers, vets, shearers, stable staff, laboratory workers and people living in the countryside near sheep and goat holdings. Outbreaks that affect whole districts usually coincide with the period when most animals are giving birth.
The second route is unpasteurised milk and cheeses made from it. It is real, but it accounts for far fewer infections than the air does. Transmission is also possible through ticks carried by animals and, rarely, through blood transfusion or from mother to baby. Person-to-person spread is virtually unknown, so there is no need to isolate someone who is ill.
How the first, acute illness runs
About half of those infected have no symptoms at all and find out much later, by chance, from a blood test. In the rest, fever starts abruptly two to three weeks after contact.
The picture is fairly recognisable:
- a high temperature with chills and drenching sweats;
- a severe headache, often felt as pressure behind the eyes;
- aching muscles and joints, and marked weakness;
- a dry cough and sometimes chest pain on breathing;
- loss of appetite, nausea, abdominal pain;
- occasionally yellowing of the skin and the whites of the eyes.
Unlike many other infections, there is usually no rash. Two organs bear the brunt: the lungs, where pneumonia develops, and the liver, where inflammation sets in — and it is sometimes the liver that brings the person to a doctor. All of this lasts a week or two, rarely longer, and in most people ends in recovery.
After recovery some people complain for months of tiredness, sweating and difficulty concentrating while every blood test comes back normal. This is not a sign that the infection is still going, and antibiotics do not help, but it is not imagined either: the state is well described and deserves follow-up rather than a shrug.
Who is most at risk from it
Most people get through Q fever easily. Certain groups, though, should see a doctor even for an apparently mild illness — and should mention any possible contact with animals:
- pregnant women. The infection usually causes no symptoms at all in pregnancy, yet it can lead to miscarriage, premature birth and low birth weight. Where contact is known, the question is settled by a blood test rather than by how well someone feels;
- people with an abnormal or artificial heart valve: valve disease, a valve replacement, a bicuspid aortic valve;
- people with a vascular graft or an aortic aneurysm;
- people whose immune system is suppressed: after a transplant, on chemotherapy, or on medicines that damp down immunity.
In these groups the infection is not simply treated but followed up afterwards, with blood tests repeated over two years so that a shift to the chronic form is not missed. Everyone else needs no such follow-up.
See a doctor the same day if a high temperature lasts more than a week, if breathlessness becomes marked, if jaundice appears, or if there is confusion or a severe headache with vomiting.
The chronic form: endocarditis months and years later
This is the most important thing to know about Q fever, and the part that is usually left out. In a small proportion of those infected the bacterium does not clear: it settles in one place and lives there quietly for years. It may surface at six months, at two years, sometimes later. This form arises almost exclusively in the risk groups listed above, and above all in people with a diseased or replaced valve.
Its main expression is endocarditis, inflammation of the inner lining of the heart and of a valve. Less often the bacterium lodges in the wall of an aortic aneurysm or in a vascular graft, in bone, or in the liver.
What makes it treacherous is that it begins insidiously and without any obvious infection. The warning signs are:
- a low-grade temperature that drags on — and sometimes no fever at all;
- night sweats and weight loss;
- growing weakness, breathlessness and swelling, in other words signs of heart failure;
- an enlarged spleen and changes in the blood tests;
- sudden weakness in an arm or leg, or pain in a limb, if a fragment has broken away from the valve.
If you have valve disease or a valve replacement and have felt unwell without explanation for months, tell your doctor that you have been around sheep, goats or cattle, or that you have drunk raw milk. That sentence sometimes settles the diagnosis.
Why an ordinary blood culture misses it
Coxiella burnetii lives inside cells and does not grow on the usual culture media. As a result the blood culture — the first test ordered when endocarditis is suspected — comes back negative. Q fever belongs on the short list of causes of so-called culture-negative endocarditis, and unless it is looked for deliberately, someone can spend months with an infected valve and no diagnosis.
It is found in other ways:
- serology, a blood test for antibodies, which is the main method. Antibodies against two phases of the bacterium are distinguished, and the balance between them separates recent infection from chronic infection. A single result says little: it usually has to be repeated two or three weeks later to see the trend;
- PCR, which detects the bacterium itself in blood during the first few days, before antibodies appear; later it becomes useless, so the two methods complement each other;
- echocardiography, often the transoesophageal kind where endocarditis is suspected, because it examines the valve at close range;
- CT and positron emission tomography, when the focus is being sought in the aorta, a vascular graft or bone.
How it is treated
Symptomatic acute illness is treated with an antibiotic from the tetracycline group for two to three weeks. It is best started in the first days: later on the benefit falls off noticeably. A mild illness in a healthy person often resolves without treatment, but with a high fever, pneumonia or liver involvement the antibiotic is given. Finish the whole course even if you feel better after three days.
These drugs are unsuitable in pregnancy, so a different antibiotic is chosen and taken long-term until delivery, under supervision; blood tests are checked afterwards.
The chronic form is treated in a completely different way. It calls for a combination of two drugs — an antibiotic from the tetracycline group together with an antimalarial that makes the bacterium vulnerable inside the cell — taken not for weeks but for eighteen months to two years, longer with an artificial valve. Throughout that time antibody levels are repeated and side effects are monitored, including the condition of the eyes. Some people also need valve surgery.
What lowers the risk
- Do not drink unpasteurised milk or eat cheeses made from it, particularly during pregnancy and if you have valve disease.
- Pregnant women should not help animals give birth, and should stay away from them altogether during the birthing season, which falls in different months from country to country. The same precaution also guards against toxoplasmosis and ovine chlamydial infection.
- Anyone working with animals should use gloves, a close-fitting mask and eye protection, especially when assisting births, clearing bedding and shearing.
- Placentas and stillborn animals should be cleared away at once and disposed of safely rather than left in the open.
- Do not eat or drink where animals are kept; wash work clothes and boots separately and do not bring them into the house.
- Clean and cover cuts as soon as they happen.
- A human vaccine exists, but it is licensed only in a few countries and given to occupational risk groups after prior screening; in most of Europe it is not available. Vaccinating livestock is used in some regions to reduce infection in herds and flocks.
Online consultation
Q fever is one of those conditions where the diagnosis comes not from a test but from a question asked in good time: where have you been, and which animals were you near. An online consultation is a good place to go through that carefully.
It is worth booking if a high temperature with a severe headache follows a stay in the countryside or work with animals; if you are pregnant and there has been contact with sheep, goats or cattle; if you have valve disease or a valve replacement and have been unwell without explanation; or if the antibody test has already been done and the two-phase figures mean nothing to you.
The doctor will advise which tests are needed and when to repeat them, explain why a negative blood culture rules nothing out, help you make sense of a long treatment course and its side effects, and say whether you need monitoring over the next two years. If anything you describe points to an emergency, you will be directed there straight away.
This material is for information only and does not replace medical advice.
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