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Q fever
Classification & external resources

ICD-10	A78.
ICD-9	083.0
eMedicine	med/1982  ped/1973
MeSH	C01.252.400.755

The infectious organism is commonly found in cattle, sheep, goats and other domestic mammals, including cats and dogs. The infection results from inhalation of contaminated particles in the air, and from contact with the vaginal mucus, milk, feces, urine or semen of infected animals. The incubation time is 9-40 days. It is considered possibly the most infectious disease in the world, as a human being can be infected by a single bacterium.

Contents 1 History 2 Manifestations 3 Appearance and incidence 4 Diagnosis 5 Treatment 6 Prevention 7 Other 8 Literature 9 External links

It was first described by Edward Holbrook Derrick in abattoir workers in Brisbane, Queensland, Australia. The "Q" stands for “query” and was applied historically at a time when the causative agent was unknown.

In 1937 the bacterium was isolated by Frank Macfarlane Burnet and Freeman from one of Derrick’s patients for the first time and identified as Rickettsia-species. H.R. Cox and Davis isolated the pathogen from ticks in Montana, USA in 1938, called it Rickettsia diasporica, it was considered nonpathogenic until laboratory investigators were infected; it was officially named Coxiella burnetii the same year. Coxiella burnetii is no longer regarded as closely related to Rickettsiae.

The most common manifestation is flu-like symptoms with abrupt onset of fever, malaise, severe headache, myalgia (muscle pain), loss of appetite, dry cough, pleuritic pain, chills, confusion and gastro-intestinal symptoms such as nausea, vomiting and diarrhoea. The fever lasts approximately 7-14 days.

During the course, the disease can progress to an atypical pneumonia, which can result in a life threatening acute respiratory distress syndrome (ARDS), whereby such symptoms usually occur during the first 4-5 days of infection.

Less often the Q fever causes (granulomatous) hepatitis which becomes symptomatic with malaise, fever, liver enlargement (hepatomegaly), pain in the right upper quadrant of the abdomen and jaundice (icterus).

The chronic form of the Q fever is virtually identical with the inflammation of the inner lining of the heart (endocarditis), which can occur after months or decades following the infection. It is usually deadly if untreated. However, with appropriate treatment this lethality is around 10%.

The pathogenic agent is to be found everywhere except Antarctica and New Zealand. In Europe it appears as hepatitis rather than pneumonia as in the United States. The bacterium is extremely sustainable and infectious: a single organism is able to cause an infection. The common way of infection is inhalation of contaminated dust, contact with contaminated milk, meat, wool and particularly birthing products. Ticks can transfer the pathogenic agent to other animals. Transfer between humans seems extremely rare and has so far been described in very few cases.

Men are slightly more often affected than women, which most likely is attributed to different employment rates in typical professions.

"At risk" occupations include:

• veterinary personnel
• stockyard workers
• farmers
• shearers
• animal transporters
• laboratory workers handling potentially infected veterinary samples or visiting abattoirs
• people who cull and process kangaroos
• hide (tannery) workers.

Diagnosis is usually based on serology (looking for an antibody response) rather than looking for the organism itself. Serology allows to detect chronic infection as high antibody levels are found against the virulent form of the bacterium.Molecular detection of bacterial DNA is increasingly used. Culture is technically difficult and not routinely available in most microbiology laboratories.

Q-fever can cause endocarditis (infection of the heart valves) which may require transoesophageal echocardiography to diagnose. Q-fever hepatitis manifests as an elevation of ALT and AST, but a definitive diagnosis is only possible on liver biopsy which shows the characteristic fibrin ring granulomas.^[1]

Treatment of the acute Q fever with antibiotics is very effective and should take place in consultation with the infectiologist. Commonly used are doxycycline, tetracycline, chloramphenicol, ciprofloxacin, ofloxacin, and hydroxychloroquine. The chronic form is more difficult to treat and can require up to four years of treatment with doxycycline and quinolones or doxycycline with hydroxychloroquine.

Q fever is effectively prevented by intradermal vaccination using a vaccine composed of killed Coxiella burnetii organisms. A skin and blood test, prior to vaccination must be undertaken in order to establish whether there is pre-existing immunity, as vaccination of immune subjects can result in a severe local reaction. After a single dose of vaccine, protective immunity lasts for many years and revaccination is not generally required.

In 2001, Australia introduced a national Q fever vaccination program for people working in "at risk" occupations.

Because of its route of infection it can be used as biological warfare agent. See also bioterrorism.

M Maurin, D Raoult.Q Fever, "Clinical Microbiology Reviews", Oct. 1999, 518 - 583

• National Center for Infectious diseases
• WHO-site: Immunization, Vaccines and Biologicals
• Johns Hopkins University Antibiotic Guide
• EMedicine - Free medical knowledge base
• The Cochrane Collaboration
• Encyclopaedia Britannica, Q fever
• CSL Limited - Q fever vaccine manufacturer.