Q fever
Q fever Is an acute or chronic disease caused by rickettsial-like , Coxiella burnetii.
Symptoms of acute disease are sudden onset of fever, headache, malaise, and interstitial pneumonitis.
Chronic disease manifestations reflect the organ system affected.
Diagnosis is confirmed by several serologic techniques, isolation of the organism, or chloramphenicol.
Coxiella burnetii is a small, intracellular,pleomorphic bacillus that is no longer classified with the rickettsia. Molecular studies have reclassified a proteobacteria in the same group as Lagionella
Etiology and Epidemiology
Worldwide in its distribution. Q fever is maintained as an in apparent infection in domestic or farm animals. Sheep ,cattle,and goats are principals reservoirs for human infections.
C.bunetii persist in stool,urine,milk, and tissues especially the placenta, so that fomites and infective aerosols form easily.
C.brunetii is also maintained in nature through an animal-tick cycle.
Cases occur among workers whose occupation brings them in close contact with farm animals or their products.
Transmission is usually by inhalation of infected aerosols, but the disease can also be contracted by ingesting infective raw milk.
C.burnetii is very virulent, resists inactivation, and remains viable in dust and stool for months, even a single organism can cause infection.
Q fever can be acute or chronic . Acute disease produces a febrile illness that often affects the respiratory system,although sometimes the liver is involved .
Chronic Q fever is usually manifested by endocarditis or hepatitis, however osteomyelitis may occur.
Symptoms and Signs
The incubation period averages 18 to 21 days (range 9 to 28 days). Some infections are minimally symptomatic, usually, however patient shave influenza – like symptoms.
Onset is abrupt, with fever, severe headache, chills, severe malaise,myalgia,anorexia, and sweats.
Fever may rise to 40° Centigrade and persist 1 > 3 wk. Respiratory symptoms, dry non productive cough pleuritic chest pain appear 4 to 5 days after onset of illness.
Lung symptoms may be particularly severe in elderly or debilitated patients.
On examination, lung crackles are common,and findings suggestive of consolidation may be present .
Unlike the rickettsial diseases, acute Q fever does not produce rash.
Acute hepatic involvement occurring in some patients resembles viral hepatitis, with fever, malaise, hepatomegaly with right upper abdominal pain and possibly jaundice. Headaches and respiratory signs are frequently absent.
Chronic Q fever hepatitis may present as FUO and must be differentiated from other causes of liver granulomas ( eg Tuberculosis,sarcoidosis,histoplasmosis,brucellosis,tularemia,syphilis) by laboratory testing.
Endocarditis resembles viridians group subacute bacterial endocarditis, aortic valve involvement is more common, but vegetation may occur on any valve. Marked finger clubbing , arterial emboli,hepatomegally and splenomegaly and purpuric rash may occur.
Q fever is fatal in only 1 % of untreated patients. However some patients with neurologic involvement have residual impairment.
Diagnosis
Early on, Q fever resembles many infections (eg influenza, other viral infections,salmonellosis, malaria, hepatitis,brucellosis). Later it resembles many forms of bacterial, viral, and mycoplasmal pneumonias.
Contact with animals or animal products are an important clue.
Immunofluorescence assay (IFA) is the diagnostic method of choice,enzyme-linked immunosorbent assay (ELISA) is also available.
Acute and convalescent serology (typically complement fixation) may be used.
PCR can identify the organism in biopsy specimens.
C.burnetii may be isolated from clinical specimens, but only by special research laboratories, routine blood and sputum cultures are negative.
Patients with respiratory signs or symptoms require chest X-ray, findings may include atelectasis, pleural-based opacities,pleural effusion, and lobar consolidation.
The gross appearance of the lungs may resemble bacterial pneumonia, but histologically more resembles psittacosis and some viral pneumonia.
In acute Q fever. CBC may be normal, but about 30 % of patients have an elevated WBC count.
Alkaline phosphatase , AST and ALT levels are mildly elevated to 2 to 3 times the normal level in typical cases.
If obtained, liver biopsy specimens show diffuse granulomatous changes.
Treatment and Prevention
Primary treatment is doxycycline 200mg po once followed by 100mg po bid until the patient improves and has been afebrile for about 5 days but continued for at least 7 days.
Chloramphenicol 500mg po or IV qid for 7 days in 2nd line treatment .
Fluoroquinolones and macrolides are also effective.
In endocarditis, treatments need to be prolonged > = 4 wk, tetracycline is preferred.
When antibiotic treatment is only partially effective, damaged valves must be replaced surgically, although some cures without surgery have occurred.
Clear-cut regimens for chronic hepatitis have not been determined.
The patient is isolated. Vaccines are effective and should be used to protect slaughter-house and dairy workers, rendering plant workers, herders, wool sorters, farmers and other at risk.
These vaccines are not available commercially but may be obtained from special laboratories eg in the US Army Medical Research Institute of Infectious Diseases in Fort Detrick, Maryland
0 comments :
Post a Comment