Summary about Disease
Q fever endocarditis is a severe and chronic manifestation of Q fever, an infection caused by the bacterium Coxiella burnetii. Unlike acute Q fever, which is often a self-limiting flu-like illness, Q fever endocarditis is a serious infection of the inner lining of the heart (endocardium) and heart valves. It develops in a small percentage of people infected with *C. burnetii*, often years after the initial infection. It is characterized by a slow and insidious onset, making diagnosis challenging. If left untreated, Q fever endocarditis is almost always fatal.
Symptoms
Q fever endocarditis often presents with subtle and non-specific symptoms that can develop gradually over months or even years. These may include:
Fatigue: Persistent and unexplained tiredness.
Night sweats: Excessive sweating during sleep.
Weight loss: Unintentional loss of weight.
Fever: Low-grade fever that may come and go.
Heart murmur: New or changed heart murmur detected during a physical exam.
Splenomegaly: Enlargement of the spleen.
Hepatomegaly: Enlargement of the liver.
Arthralgia: Joint pain.
Digital clubbing: Widening and thickening of the fingertips and toes.
Embolic events: Stroke, limb ischemia, or other organ damage due to blood clots breaking off from the infected heart valve.
Skin lesions: Less common, but may include splinter hemorrhages (thin, red-brown lines under the nails).
Causes
Q fever endocarditis is caused by infection of the heart valves with the bacterium Coxiella burnetii. The bacteria typically enter the bloodstream during an initial acute Q fever infection, which may be asymptomatic or cause mild flu-like symptoms. *C. burnetii* has the ability to survive within cells for long periods (persistence). In susceptible individuals, the bacteria can then infect the heart valves, leading to chronic inflammation and damage. Predisposing factors for developing Q fever endocarditis include:
Pre-existing valvular heart disease: Damaged heart valves are more susceptible to infection.
Prosthetic heart valves: Artificial heart valves provide a surface for bacteria to adhere to.
Immunosuppression: Weakened immune systems (due to conditions like HIV/AIDS or immunosuppressive medications) increase the risk.
Vascular aneurysms: Pre-existing conditions with aneurysm.
Medicine Used
The standard treatment for Q fever endocarditis involves a prolonged course of antibiotics. The most commonly used regimen is a combination of:
Doxycycline: A tetracycline antibiotic, typically administered for at least 18 months, and often longer (sometimes lifelong) in patients with prosthetic valves.
Hydroxychloroquine: An antimalarial drug, also given for a prolonged duration in combination with doxycycline. The combination of doxycycline and hydroxychloroquine is synergistic, meaning they work together to enhance the effectiveness of the treatment. In some cases, surgery may be necessary to replace damaged heart valves.
Is Communicable
While acute Q fever is communicable, Q fever endocarditis itself is not directly communicable from person to person. The infection is acquired through exposure to infected animals, primarily livestock (cattle, sheep, goats), or their products (milk, wool, contaminated soil, birthing fluids). People with Q fever endocarditis do not typically shed the bacteria in a way that would easily transmit the infection to others. However, proper precautions should still be taken to prevent the spread of C. burnetii from potential sources like blood or tissue samples during medical procedures.
Precautions
To prevent Q fever infection (and, consequently, the risk of developing Q fever endocarditis), the following precautions are recommended:
Avoid contact with livestock birthing fluids: This is the most common route of transmission.
Pasteurize milk and dairy products: Pasteurization kills C. burnetii.
Use protective equipment: Wear gloves, masks, and eye protection when handling livestock or their products, especially during birthing.
Vaccination: A Q fever vaccine is available in some countries (e.g., Australia) for high-risk individuals, such as abattoir workers, farmers, and veterinarians.
Proper hygiene: Wash hands thoroughly after contact with animals or potentially contaminated materials.
Control dust: C. burnetii can survive in dust and soil, so efforts to control dust in agricultural settings can help reduce the risk of exposure.
Safe disposal of animal waste: Dispose of animal placentas and other birthing materials properly.
How long does an outbreak last?
The duration of a Q fever outbreak can vary depending on several factors, including the source of the infection, the number of people exposed, and the public health response. Outbreaks can last from several weeks to several months. Sporadic cases can occur year-round. Control measures, such as identifying and eliminating the source of infection, implementing hygiene practices, and vaccinating at-risk populations (where available), can help shorten the duration of an outbreak.
How is it diagnosed?
Diagnosing Q fever endocarditis can be challenging due to its insidious onset and non-specific symptoms. The diagnosis typically involves a combination of:
Clinical suspicion: Considering Q fever endocarditis in patients with suggestive symptoms and risk factors (e.g., history of valvular heart disease, exposure to livestock).
Blood cultures: Blood cultures are often negative in Q fever endocarditis, making them unreliable for diagnosis.
Serological testing: Detecting antibodies against C. burnetii in the blood is the mainstay of diagnosis. Elevated IgG antibody titers against phase I antigen of *C. burnetii* are highly suggestive of chronic Q fever, including endocarditis. Serial testing may be necessary to confirm a rising antibody titer.
Echocardiography: To assess the heart valves for vegetations or other signs of endocarditis. Transesophageal echocardiography (TEE) is more sensitive than transthoracic echocardiography (TTE) for detecting valve abnormalities.
PCR (Polymerase Chain Reaction): PCR testing of valve tissue (obtained during surgery or autopsy) can detect C. burnetii DNA.
Valve Pathology: Examination of the excised valve tissue, when available, typically reveals chronic inflammation. The modified Duke criteria, used for diagnosing infective endocarditis, may be used to aid in the diagnosis of Q fever endocarditis, incorporating serological evidence of C. burnetii infection.
Timeline of Symptoms
The timeline of symptoms in Q fever endocarditis is typically chronic and insidious:
Initial Infection: Many people don't recall or notice the initial acute Q fever infection. It can be asymptomatic or cause mild, flu-like symptoms that resolve without specific treatment. This phase might occur months or years before the onset of endocarditis symptoms.
Latent Period: A period of latency follows the initial infection, during which C. burnetii persists in the body, often without causing noticeable symptoms. This phase can last for months to years.
Onset of Endocarditis Symptoms: The symptoms of endocarditis develop gradually and subtly. Initial symptoms may include fatigue, night sweats, and low-grade fever.
Progression: Over time (months to years), the symptoms become more pronounced, and complications such as heart murmur, weight loss, splenomegaly, arthralgia, embolic events, and heart failure may develop.
Important Considerations
High Index of Suspicion: Clinicians should maintain a high index of suspicion for Q fever endocarditis in patients with unexplained heart valve abnormalities, especially those with a history of livestock exposure or suggestive symptoms.
Prompt Diagnosis: Early diagnosis and treatment are crucial to improve outcomes and prevent complications.
Prolonged Treatment: Treatment with antibiotics must be prolonged (at least 18 months, often longer) to eradicate the infection.
Valve Replacement: Surgical valve replacement may be necessary in severe cases or when antibiotic therapy fails.
Monitoring: Patients with Q fever endocarditis require close monitoring for complications and relapse. Regular follow-up with a cardiologist and infectious disease specialist is essential.
Serological Testing: Serial serological testing is important to monitor treatment response and detect relapse.
Prognosis: Untreated Q fever endocarditis is almost always fatal. With appropriate treatment, the prognosis is significantly improved, but complications and relapse can still occur.
Public Health Importance: Q fever is a zoonotic disease with public health implications. Prompt reporting of cases and implementation of preventive measures are important to control the spread of infection.