Makindo Medical Notes

Coxiella endocarditis can be difficult to diagnose due to intermittent fever, absence of vegetations on echocardiogram, and negative cultures. Always maintain a low threshold for culture or PCR testing. Serology for phase I and II antigens can aid in diagnosis. A key clue is contact with animals, as well as fever, low platelets, endocarditis, raised ESR, and WCC.

About

• Known as Q (Query) fever, first described in Queensland in the 1950s by Derrick and colleagues.
• A worldwide zoonotic infection. Primarily a disease of humans and animals, with a significant public health impact in endemic areas.
• Can cause culture-negative endocarditis. The heart valve involvement can be silent or subtle, leading to delays in diagnosis.
• The disease can present in both acute and chronic forms, with chronic Q fever associated with persistent infections.

Characteristics

• A gram-negative obligate intracellular coccobacillus. This bacterium requires a host cell to replicate and cannot be cultured easily from blood samples.
• Resistant to drying and capable of surviving in the environment, making it a highly infectious pathogen in contaminated animal products and dust.
• It is a member of the Rickettsia family, exhibiting the same intracellular survival mechanism as other pathogens in this group.

Source

• Primarily domestic livestock. Cattle, sheep, goats, and camels are common carriers of the pathogen.
• Infection occurs via tick bites or direct inhalation. Ticks are the primary vector in many animal species.
• High titres are present in pregnant animals, with high concentrations of the pathogen found in their placental tissues.
• Transmission can occur through dust inhalation, aerosols of urine, faeces, amniotic fluid, or placenta from infected animals.
• Unpasteurised milk or cheese from infected animals is another source of transmission, especially in rural or underdeveloped regions.
• Human-to-human transmission is rare but can occur through close contact with infected bodily fluids.

Pathogenicity

• Pyrexia of unknown origin is a hallmark of acute Q fever.
• Endocarditis and myocarditis. Chronic Q fever is often characterized by persistent low-grade infection, with endocarditis being a significant complication.
• Pneumonia, hepatitis, erythema nodosum are also common manifestations of the infection.
• Fever during pregnancy and fetal loss. In pregnant women, Q fever can lead to miscarriage, stillbirth, or preterm labor.
• Can also cause Guillain-Barré Syndrome. Some cases present with neurological complications like neuropathy and encephalitis, especially in immunocompromised individuals.
• Chronic Q fever is associated with prolonged, low-grade fever and persistent infection. It may also lead to organ damage such as hepatic fibrosis or chronic heart disease.

Investigations

• Often culture-negative; diagnosis is typically made with serology tests, as Coxiella is difficult to culture from blood or tissue samples.
• Acute Q fever shows a raised phase II antigen and IgG >200, indicating recent infection.
• Chronic Q fever is indicated by a raised phase I antigen and IgG >800, often suggesting persistent infection.
• Infection during the first trimester can cause abortion or congenital complications, including liver damage and fetal cardiac defects.
• Infected individuals may exhibit elevated liver enzymes (ALT/AST) and abnormal coagulation markers.
• Polymerase chain reaction (PCR) testing for Q fever DNA in blood, tissue, or fluids may be helpful in diagnosing acute or chronic infection.

Management

• Tetracycline 500 mg three times daily for 10 days is the standard treatment for acute infection.
• Alternatives include doxycycline for 2 weeks and hydroxychloroquine in certain cases.
• For chronic Q fever or severe cases, prolonged therapy with long-term doxycycline and/or hydroxychloroquine may be required for several months.
• In patients with endocarditis or severe infections, intravenous antibiotics such as doxycycline or ciprofloxacin are often necessary.
• Chronic Q fever endocarditis may require surgical intervention (e.g., valve replacement) if antibiotic therapy fails to resolve the infection.

Prevention

• Vaccination is not currently available for Q fever, so prevention relies on reducing exposure to infected animals.
• Proper hygiene, including wearing protective clothing and using face masks, can help reduce the risk of transmission in endemic areas.
• Avoiding unpasteurized dairy products, especially in pregnant women, is essential for reducing the risk of infection.