Q fever

Overview

Q fever is a disease caused by infection with Coxiella burnetii, a bacterium that affects humans and other animals. This organism is uncommon, but may be found in cattle, sheep, goats and other domestic mammals, including cats and dogs. The infection results from inhalation of a spore-like small cell variant, and from contact with the milk, urine, feces, vaginal mucus, or semen of infected animals. Rarely, the disease is tick borne. The incubation period is 9–40 days. Humans are vulnerable to Q fever, and infection can result from even a few organisms. The bacterium is an obligate intracellular pathogenic parasite.

Symptoms

Incubation period is usually two to three weeks. The most common manifestation is flu-like symptoms with abrupt onset of fever, malaise, profuse perspiration, severe headache, muscle pain, joint pain, loss of appetite, upper respiratory problems, dry cough, pleuritic pain, chills, confusion and gastrointestinal symptoms, such as nausea, vomiting, and diarrhea.

Approximately half of infected individuals exhibit no symptoms.

During its 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 four to five days of infection.

Less often, Q fever causes (granulomatous) hepatitis, which may be asymptomatic or becomes symptomatic with malaise, fever, liver enlargement, and pain in the right upper quadrant of the abdomen. Whereas transaminase values are often elevated, jaundice is uncommon. Retinal vasculitis is a rare manifestation of Q fever.

The chronic form of Q fever is virtually identical to inflammation of the inner lining of the heart (endocarditis),[6] which can occur months or decades following the infection. It is usually fatal if untreated. However, with appropriate treatment, the mortality falls to around 10%.

Causes

Q fever is caused by a type of bacteria called Coxiella burnetii, most commonly found in sheep, goats and cattle. It also can infect pets, such as cats, dogs and rabbits.

These animals transmit the bacteria through their urine, feces, milk and birthing products — such as the placenta and amniotic fluid. When these substances dry, the bacteria in them become part of the barnyard dust that floats in the air. The infection is usually transmitted to humans through their lungs, when they inhale contaminated barnyard dust.

Prevention

Protection is offered by Q-Vax, a whole-cell, inactivated vaccine developed by an Australian vaccine manufacturing company, CSL. The intradermal vaccination is composed of killed Coxiella burnetii organisms. Skin and blood tests should be done before vaccination to identify pre-existing immunity, because vaccinating subjects who already have an immunity can result in a severe local reaction. After a single dose of vaccine, protective immunity lasts for many years. Revaccination is not generally required. Annual screening is typically recommended.

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

The Soviet Union had earlier developed a killed vaccine, but its side effects prevented its licensing abroad.

Preliminary results suggest vaccination of animals may be a method of control. Published trials proved that use of a registered Phase I vaccine (Coxevac) in infected farms is a tool of major interest to manage or prevent early or late abortion, repeat breeding, anoestrus, silent oestrus, metritis and decreases in milk yield when C. burnetii is the major cause of these problems

Diagnosis

Diagnosis is usually based on serology (looking for an antibody response) rather than looking for the organism itself. Serology allows the detection of chronic infection by the appearance of high levels of the antibody 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.

Prognosis

Prognosis for Q fever: In general, most patients will recover to good health within several months without any treatment. Only 1%-2% of people with acute Q fever die of the disease

Treatment

Treatment of acute Q fever with antibiotics is very effective and should be given in consultation with an infectious diseases specialist. Commonly used antibiotics include doxycycline, tetracycline, chloramphenicol, ciprofloxacin, ofloxacin, and hydroxychloroquine. Chronic Q fever is more difficult to treat and can require up to four years of treatment with doxycycline and quinolones or doxycycline with hydroxychloroquine.

Q fever in pregnancy is especially difficult to treat because doxycycline and ciprofloxacin are contraindicated in pregnancy. The preferred treatment is five weeks of co-trimoxazole.