Q Fever
Dima Youssef
James W. Myers
INTRODUCTION
Coxiella burnetii is a gram-negative intracellular, pleomorphic coccobacillus that undergoes phase variation. This variation is associated with changes in the lipopoly-saccharide of the outer membrane.
The virulent phase I exists in nature, but the avirulent phase II form is found following repeated passage of phase I bacteria in embryonated chicken eggs.
C. burnetii can be found in arthropods (ticks) rodents, birds, and fish.
The infected ticks can transmit it to sheep, goats, and cattle.
Acute Q fever, which develops after an incubation period of a few weeks, is usually characterized by a nonspecific febrile illness, pneumonitis, or hepatitis. On the other hand, chronic Q fever may present months to years after initial infection, usually manifesting as culture-negative endocarditis.
EPIDEMIOLOGY
Sources of Human Infection
Milk
The pasteurization process of commercial milk may reduce transmission of C. burnetii from cattle to humans.
Placental products
Dried feces in inhaled dust
Not by tick exposure
Occupational risk
Hunters
Farmers
Abattoir workers
Veterinarians
US military personnel recently deployed to Iraq and Afghanistan
France and Australia cases outnumber those from the USA.
CLINICAL MANIFESTATIONS
The incubation period is usually about 4 weeks. Many patients appear to be asymptomatically infected.
A self-limited, flu-like illness appears to be the most common infection.
A “chronic fatigue” syndrome has been reported in patients after infection with acute Q fever. This may have a genetic predisposition.
Pulmonary
May present as an atypical pneumonia, often with fever, pleurisy, myalgias, diarrhea, and a severe headache
Cough is nonproductive and may be absent despite the presence of pneumonia.
Usually, Coxiella pneumonia is of mild-to-moderate severity, but it can be rapidly progressive and cause respiratory failure.
Multiple rounded opacities may be seen.
Pleural effusions in 1/3 of patients
Hilar lymphadenopathy
Thirty days is the average resolution time for the radiographs.
If an lumbar puncture (LP) is performed for the headache, it is usually normal at this time.
Liver
“Doughnut granulomas” on liver biopsy in patients with an fever of unknown origin (FUO)
Q fever hepatitis
Fever, abdominal pain, anorexia, nausea, vomiting, and diarrhea
Alkaline phosphatase, AST, and ALT levels are usually elevated to two to three times the normal level.
Autoantibodies are often present.
Central nervous involvement
Meningoencephalitis occurs in 1% of cases.
Lumbar puncture will primarily show mononuclear cells, elevated protein, and normal glucose.
Patients with CNS involvement do not demonstrate differences in predisposing conditions but more frequently have occupational exposure to goats than patients with acute Q fever but no neurologic involvement.
Headache is the most common symptom, but Q fever can manifest in a variety of neurologic syndromes including aseptic meningitis and radiculitis.
Pregnancy
Obstetric complications, such as spontaneous abortion, intrauterine growth retardation, intrauterine fetal death, and premature delivery, occur.
Pregnant women are at risk of developing of chronic Q fever.
A review suggested that the outcome was found to depend on the trimester.
Abortions occurred in 7 of 7 insufficiently treated patients infected during the first trimester as opposed to 1 of 5 patients infected later.
Co-trimoxazole given until delivery protected against abortion (0/4) but not against the development of chronic infections and did not significantly reduce the colonization of the placenta (2/4 vs. 4/4) in one study.
Endocarditis was not observed among any of the patients who received long-term co-trimoxazole therapy in another study.
Heart
Myocarditis
One percent of Q fever cases
T-wave changes
Tachycardia, respiratory failure, and cardiac failure
May lead to death of the patient
Diagnosis by serology to phase II antigen, culture, and biopsy
Pericarditis
One percent of cases
Often associated with endocarditis or myocarditis
Effusions and T-wave changes are noted.
Chest pain
Endocarditis
One of the causes of “culture-negative” endocarditis
Seventy percent of all chronic Q fever cases
More common in Europe than in the United States
Abnormal native valves (congenital, rheumatic, degenerative, or syphilitic)
Prosthetic valves can also be infected.
Mostly males
Age >40
Immunosuppression is a risk factor.
Organ transplant recipients
Cancer
Lymphoma
Rare in HIV patients
Symptoms are often related to heart failure.
Fever, often low-grade or remittent
Weight loss, chills, anorexia, and night sweats
Malaise
Hepatosplenomegaly
Marked clubbing
Purpuric rash
Embolic phenomena in 20%
Immune complex glomerulonephritis and microscopic hematuria
LVH on EKG can be seen.
Elevated erythrocyte sedimentation rate
Polyclonal increase in IgG, IgM, and IgA levels
Anemia and thrombocytopenia are often seen.
Most patients present with abnormal LFTs.
Lactate dehydrogenase and creatine phosphokinase levels may be abnormal.
Rheumatoid factor, circulating immune complexes, and cryoglobulin abnormalities can be found.
Anti—smooth muscle antibodies, circulating anticoagulant antibodies, antimito-chondrial antibodies, antinuclear antibodies, and a positive Coombs test have also been reported.
Histologically, one may see significant fibrosis and calcifications, slight inflammation and vascularization, and small or absent vegetations.
These pathologic features might be confused with noninfectious valvular degenerative damage.
These histologic features are very similar to that observed with other blood culture —negative types of endocarditis, such as bartonellosis and Whipple disease. Meaning that the histologic features of Q fever endocarditis may be confused with degenerative damage.
Usually, Q fever endocarditis is diagnosed serologically.
High levels of anti—phase I antibodies are found in chronic Q fever, whereas anti—phase II antibodies predominate during acute Q fever.
Note that the diagnosis of Q fever endocarditis can also be made by other means including C. burnetii isolation in cell culture, polymerase chain reaction (PCR), or immunohistochemical examination.
Patients should be serologically monitored for at least 5 years because of the risk of relapse.
Vascular infections
Aortic aneurysms
Vascular grafts
Mortality (25%)
Surgery helpful
DIAGNOSIS
Liver function tests are usually abnormal, the WBC count is normal to elevated, and the ESR may be high, but these findings are nonspecific.
Lab workers must handle specimens by wearing gloves and masks and only then in biosafety level 3 laboratories.
Tissue biopsy specimens
Can be tested either fresh, or following formalin fixation and paraffin embedding
Immunodetection may be performed by the immunoperoxidase technique, capture ELISA/ELIFA systems, or immunofluorescence with polyclonal or monoclonal antibodies.
Fibrin rings or “doughnut” granulomas can be seen.
Human embryonic lung fibroblasts (HEL cells) grown in shell vials are often used to culture the organism.
Blood, cerebrospinal fluid, bone marrow, cardiac valve, vascular aneurysm or graft, bone biopsy, liver biopsy, milk, placenta, and fetal specimens after abortion are suitable for culture.Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
