Q is for Q Fever
“What is Q fever?” you ask. Well, let me tell you! Q stands for query. It was a disease of unknown origin when first documented in 1935 Australia and in the United States in the 1940s (although it was found in ticks Montana ticks in 1938). Q Fever was later found to be caused by Coxiella burnetii, an obligate intracellular bacterium (which means it is a bacteria that has to live inside of cells to survive). It can be found worldwide, except in New Zealand.
Q fever does not always cause symptoms and the symptoms are so vague that many cases may be misdiagnosed or never even see a doctor, so the exact number of people infected is unknown.
Symptoms range from fever (generally for 7-14 days) and malaise to chest and/or abdominal pain to chills and muscle aches. Cough, vomiting, and diarrhea can also be seen. Have you had any of these symptoms lately? Sounds like just about everything that is out there during cold and flu season. The majority of people with acute infections recover, but those with complications can develop pneumonia, inflammation of the heart or liver, and even problems with the brain or spinal cord. Pregnant women are at a much higher risk of preterm labor and delivery, as well as miscarriage. Thankfully, the death rate is relatively low, <2% of hospitalized patients. Chronic infections (those infections that never really go away, <5% of the acute infection patients) can show up as early as 6 weeks after an acute infection or as long as many years after. Chronic Q fever is most common in pregnant women, individuals with heart valve defects prior to their acute infection, and those that are immunosuppressed. The fatality rate of these patients is much more significant. In fact, endocarditis (inflammation of the heart valves), the most common form of chronic disease, makes up 60-70% of all reported cases, with untreated fatality rates of 25-60%. In animals, the most common symptom is miscarriage.
Diagnosing and treating Q fever is difficult since treatment is most effective if started within the first 3 days of disease, but most people do not go to the doctor within the first 3 days of disease. Diagnostic tests such as looking for antibodies are not accurate until 7-10 days into the illness. Another test, polymerase chain reaction (PCR), can be done in the first week of illness, but sensitivity decreases over time, especially after antibiotic administration, a positive result is helpful, but a negative result does not rule out disease. Therefore, treatment is often started based on physical examination, symptoms, and history of possible exposure. Risk factors including being a veterinarian or farmer, travel to rural or agricultural areas where infections are present, and ingesting unpasteurized dairy products, including milk. Paired blood samples test via IFA, indirect immunofluorescense assay, taken 2-4 weeks apart are the gold standard for diagnosis. This test looks for a four fold increase in IgG antibody levels. The paired sample is also important because one test alone is not diagnostic. Currently, about 3% of healthy people have antibodies to C. burnetii, and about 20% of high risk individuals (such as veterinarians) have titers from past exposure.
Treatment consists of doxycycline and should be given for 2-3 weeks for acute cases, if the fever does not subside within 3 days it is generally considered to not be Q Fever. For chronic cases, duration of treatment is 18 months with both doxycycline and hydroxychloroquine. Other medications in the same drug class have been found to actually increase the risks of complications, so they are not recommended. Pregnant women should not receive doxycycline due to the risk of complications with the fetus, so there are other recommendations for them. Due to the resent dramatic increase in the cost of doxycycline its use in veterinary medicine is now often cost prohibitive for clients.
A significant concern with C. burnetii is that it is a risk for bioterrorism since it is resistant to heat and drying, can be spread through aerosolization (small particles in the air) to be inhaled, and very few organisms are required to infect a person. According to the CDC website, Q fever also has a history of being developed for use as a biological weapon. It is considered a potential terrorist threat.