Laboratory Diagnosis of Coxiella burnetii
Specimen: Blood, tissues from cardiac valve
- Culture can be performed in tissue culture cells using human embryonic lung fibroblast cell lines, and recently in a cell-free medium; however, culture is rarely performed except in research laboratories licensed to work with these highly contagious organisms.
- Serology is the most commonly used diagnostic test.
- A variety of methods are used to measure antibody production: the microagglutination tests, indirect immunofluorescence antibody (IFA) test, and enzyme-linked immunosorbent assay (ELISA).
- IFA is the test of choice, although ELISA is used in many laboratories and appears to be as sensitive.
- In chronic infections, the antibodies to phase I antigens are elevated whereas in acute Q fever, immunoglobulins IgM and IgG antibodies are developed primarily against phase II antigens.
- Complement fixation test can also be done detecting IgG antibodies to phase II antigens.
- A diagnosis of chronic Q fever is confirmed by the demonstration of antibodies against both phase I and II antigens, with the titers to the phase I antigen typically higher.
- PCR amplification has been used to detect C. burnetii DNA in clinical samples from acute and chronic Q fever patients.
- Strains of C. burnetii differ in their plasmids which they carry.
- QpH1 plasmids are found in acute Q fever isolates; whereas QpRS plasmids are found on the strains isolated from endocarditis patients.
Treatment of Coxiella burnetii
- Most infections resolve without antibiotic treatment, but administration of doxycycline reduces the duration of fever in the acute infection and is definitely recommended in cases of chronic infection.
- Fluoroquinolones (e.g., ofloxacin, pefloxacin) have been used as an alternative to doxycycline but are contraindicated in children and pregnant women.
- The newer macrolides have also been shown to be effective in the treatment of acute pneumonia.
- Chronic Q fever requires prolonged treatment for 18 months or longer with a combination of doxycycline and hydroxychloroquine.
- In Q-fever endocarditis, long-term administration of a combination of two drugs, combination therapy among doxycycline, ciprofloxacin and rifampicin has been suggested to prevent relapse.
Prevention and Control of Coxiella burnetii
- The presently recommended conditions of “high-temperature, short-time” pasteurization at 71.5°C for 15 seconds are adequate to destroy viable Coxiella species.
- Exposure can be reduced by construction of separate facilities for animal parturition, destruction of suspect placental membranes,heat treatment of milk and efforts to reduce the tick population.
- Occupationally exposed persons may reduce their risk of infection with burnetii by wearing respirators that prevent aerosol infections.
- Inactivated whole-cell vaccine (Q-Vax) and partially purified antigen vaccines for Q fever have been developed, and the vaccines prepared from phase I organisms have been shown to provide the best protection and is recommended for occupationally exposed workers.
- Good animal husbandry practices should be followed such as proper disposal of animal excreta and aborted materials, isolation of aborting animals for 14 days.
Laboratory Diagnosis, Treatment and Prevention of Coxiella burnetii
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