Q fever is an infectious disease that is spread by the inhalation or ingestion of a bacterium known as Coxiella burnetii, which belongs to the order of Legionellales. C. burnetii is spread mainly by breathing contaminated air or eating or drinking a contaminated food. Farm workers, especially those who work with animals, people who work in slaughterhouses and veterinarians are especially vulnerable to this disease. Because infection can occur as a result of airborne transmission and the agent is very resistant to environmental conditions, it was included on the list of possible bacteriological weapons. Q fever causes highly variable diseases ranging from acute (often self-limited) infection to fatal chronic infection. Infections that do not cause outward symptoms (subclinical) or no symptoms (asymptomatic) are also common.
The symptoms of Q fever can vary dramatically from one person to another. Infection can result in no apparent symptoms (asymptomatic); an acute form of disease characterized by a flu-like illness that may go away on its own (self-limited) or can cause other more serious symptoms; or a chronic, long-lasting form that can be associated with serious complications. Researchers believe that a variety of factors may influence the severity of Q fever including age, gender, and a person’s general health, including the existence of previous medical conditions (e.g., heart disease).
Acute Q Fever
The acute form of Q fever usually starts approximately two to three weeks after exposure to the bacterium. Acute Q fever is usually characterized by flu-like symptoms such as high fevers, chills, muscle pain (myalgia), and headaches. In some cases, fevers do not occur. Additional nonspecific symptoms can potentially occur including a cough, chest pain, sore throat, a skin rash or gastrointestinal symptoms.
Two other conditions are commonly associated with acute Q fever to varying degrees – pneumonia and inflammation of the liver (hepatitis). Pneumonia is often mild, but potentially can progress to cause acute respiratory distress syndrome (ARDS). Hepatitis may cause abnormal enlargement of the liver (hepatomegaly). More rarely, it can cause yellowing of the skin and the whites of the eyes (jaundice).
Cases of acute Q fever are usually self-limited. However, other symptoms can occur in some affected individuals including inflammation of the muscular wall of the heart (myocarditis), inflammation of the sac-like membrane that surrounds the heart (pericarditis), and the development of a purple skin rash caused by bleeding (hemorrhaging) from tiny blood vessels just below the surface of the skin.
Sometimes acute Q fever presents as neurological disease such as inflammation of the thin membrane covering the brain and spinal cord and the brain itself (meningoencephalitis). In some individuals, acute Q fever can affect the kidneys, thyroids or genitals.
Chronic Q Fever
Chronic Q fever may occur months to years after acute disease or may occur without a previous history of acute Q fever. Most cases of chronic Q fever occur in individuals with predisposing conditions such as existing heart valve or blood vessel (vascular) abnormalities or a compromised immune system.
The most common manifestation of chronic Q fever is inflammation the thin membrane lining the inside of the heart and heart valves (infective endocarditis), potentially damaging the heart valves or heart tissue. Affected individuals can develop congestive heart failure, a serious complication in which a limited ability to circulate blood to the lungs and the rest of the body results in fluid buildup in the heart, lungs and various body tissues.
Less commonly, chronic Q fever can present as infection of the bones and joints (osteoarticular infection) such as osteomyelitis or osteoarthritis, vascular infections, chronic hepatitis or chronic pulmonary disease. Osteoarticular infection can cause bone and joint pain. Chronic hepatitis can cause enlargement of the liver or jaundice. Chronic pulmonary disease can cause difficulty breathing (dyspnea) and other respiratory abnormalities.
Individuals with chronic Q fever may also experience a variety of nonspecific symptoms including prolonged fevers (although fevers are often absent), joint pain (arthralgia), muscle pain (myalgia), night sweats, chills, fatigue, and unintended weight loss.
Some individuals with Q fever develop long-term complications (long-term sequelae) such as chronic, persistent fatigue. Some researchers believe that infection with Q fever increases an individual’s risk of developing cardiovascular disease later in life.
Q fever is caused by inhalation or ingestion of the bacterium Coxiella burnetii. People are most often exposed to the bacterium from the milk, urine and feces of infected animals (for example, by inhaling contaminated air in a barnyard). Also, when an infected animal gives birth, the bacteria may be present in high numbers in the amniotic fluid and placenta. Q fever bacterium primarily infects farm animals such as cattle sheep and goats. However, it has been reported in a wide variety of animals including domesticated animals such as dogs and cats.
The C. burnetii bacterium is highly infectious and only a tiny amount is needed to cause disease. The bacterium can survive in the environment for lengthy periods of time because it is resistant to environmental conditions such heat and pressure. It is also resistant to many common disinfectants.
Less common modes of transmission to humans include working in a slaughterhouse, drinking unpasteurized milk, and hunting, slaughtering or dressing infected animals. According to the medical literature, in extremely rare cases, human-to-human transmission has been reported.
The mode of transmission in wild and domestic animals is different from the mode of transmission in humans. Animals become infected with C. burnetii from infected ticks. Originally, Q fever was classified as a rickettsial disease, a group of infectious diseases most often spread to humans from ticks. However, based on DNA-DNA hybridization studies and genome sequencing C. burnetii was placed to the order of Legionellales, which also contains Legionella pneumophila, the bacterium that causes Legionnaire’s disease.
Q fever is a zoonosis, a disease that can be transmitted from animals to humans. C. burnetii is a small, obligate intracellular gram-negative bacterium that can only reproduce within the living cells though the recent findings indicate the possibility of growing C. burnetii also in axenic media. Gimenez staining is very sensitive procedure and often used for visualization of Coxiella and Rickettsia.
Q fever first became a reportable disease in the United States in 1999. In the ensuing five years, the mean annual incidence of reported cases in the United States was approximately 50. In recent years, cases have been reported in U.S. military personnel serving in Iraq and Afghanistan.
Q fever occurs worldwide and can affect individuals of every racial and ethnic background. The incidence of Q fever is unknown because in many countries it is not a reportable disease. Researchers believe that the infection is underreported. Certain countries have higher incidence rates than other countries, e.g. infections involving hundreds to thousands of human cases occurred recently in the Netherlands.
Q fever has occurred more often in men than women, although researchers attribute this to the fact that more men work in occupations where exposure to C. burnetii bacterium is more likely to occur. Q fever can affect individuals of any age. Although children with Q fever are rarely reported, the diagnosis is probably often missed and the actual incidence of Q fever in children is unknown. Some researchers have speculated that children develop symptoms less often than adults and generally have more mild disease than adults when symptoms do develop.
Q fever was first reported in the medical literature in 1937 by Edward Derrick who named the infection Query Fever.
The signs and symptoms of Q fever are nonspecific and can be associated with a wide variety of diseases. A diagnosis of Q fever usually requires serological examination, which measures and characterizes antibodies. Q fever has two antibody-producing (antigenic) phases called phase I and phase II. These phases can help confirm a diagnosis and can help distinguish acute Q fever infection from chronic Q fever infection. Infected individuals develop specific antibodies against Q fever including immunoglobulin G (IgG), immunoglobulin A (IgA) and immunoglobulin M (IgM). Measuring the levels of these classes of antibodies can help confirm a diagnosis of Q fever. During the acute phase of Q fever, IgG and IgM antibodies may be detected. In chronic Q fever, IgG or IgA levels may be detected.
In acute Q fever, the levels of antibodies to phase II antigen of C. burnetii are higher than those to the phase I antigen and, in general, the formers are first detected during the second week of the illness.
In chronic Q fever, a high level of phase I antibodies with a constant or falling level of phase II antibodies together with other signs of inflammatory disease are common.
The three most common serological tests for Q fever are indirect immunofluorescence, complement fixation and enzyme-linked immunosorbent assay (ELISA). Indirect immunofluorescence is a test that enables physicians to detect the presence of specific antibodies in the blood or other fluids. The antibodies are tagged with a substance that causes them to glow when exposed to ultraviolet light. Complement fixation and ELISA tests can also detect the presence of specific antibodies or antigens.
Isolation of the infectious agent in cell cultures, embryonated hens eggs and laboratory animals is also possible, but required special laboratory with biosafety level three (BSL3).
A newer test that has been used to aid in the diagnosis of Q fever in some cases is a polymerase chain reaction (PCR) test. A PCR test is a highly sensitive test that amplifies a specific segment or sample of DNA, creating billions of copies that particular segment. This amplified segment can then be studied to detect the presence of C. burnetii infection. It has been employed successfully to detect C. burnetii DNA in cell cultures and biological samples.
The first nucleic acid amplification in vitro diagnostic (IVD) test by Idaho Technology, Inc. (ITI) was approved by the FDA in 2011 to detect Coxiella burnetii, the bacteria that causes Q fever. It will be used to test military personnel suspected of contracting the disease and run on the Joint Biological Agent Identification and Diagnostics System (JBAIDS), utilized across all branches of the military for diagnostic testing. Use of the test is limited to designated Department of Defense laboratories equipped with the JBAIDS.
Antibiotic therapy is used to treat individuals with Q fever. Some mild cases of Q fever may improve without treatment, although antibiotic therapy usually reduces the duration of the infection. Physicians recommend that all individuals in whom Q fever is detected receive antibiotic therapy, even those with no recognizable clinical findings (subclinical disease).
Doxycycline is currently the most commonly used antibiotic therapy for the treatment of individuals with Q fever and is most effective when started within three days of infection. Anti-inflammatory drugs may be used if individuals do not respond to antibiotics. Hydroxychloroquine, which is often used to treat malaria, has also been used to treat Q fever.
Chronic Q fever is more difficult to treat. Endocarditis may require prolonged antibiotic treatment which usually involves treatment with multiple drugs such as a combination of doxycycline and hydroxychloroquine whic. drastically reduces lethality. The optimal duration of therapy is unknown and may vary from one person to another.
In some individuals with damage to the heart valves or evidence of heart failure, surgery may be necessary. Decisions concerning the use of particular interventions such as surgery should be made by physicians (e.g., cardiologist, infectious disease specialist) and other members of the healthcare team in careful consultation with the patient, based upon the specifics of his or her case; a thorough discussion of the potential benefits and risks; patient preference; and other appropriate factors.
There is no vaccine approved by the U.S. Food and Drug Administration (FDA) for Q fever. However, other countries have developed vaccines. In 1989, Australia licensed a vaccine against Q fever.
Fluoroquinolones, which are antibiotics that kill bacteria or prevent their growth (antimicrobials), have also been used to treat individuals with Q fever. These drugs include ofloxacin, pefloxacin, and ciprofloxacin. Additional antibiotics that have been used to treat individuals with Q fever include chloramphenicol, co-trimoxazole and rifampin. More research is necessary to determine the long-term safety and effectiveness of these potential therapies.
Macrolides are a class of antibiotics that have been used to treat individuals with Q fever. A common macrolide is erythromycin. However, macrolides have generally been unreliable. Newer macrolides such as clarithromycin, azithromycin and roxithromycin have shown greater promise as potential therapies for Q fever. More research is necessary to determine the long-term safety and effectiveness of newer macrolides as potential treatments for individuals with Q fever.
The treatment of women who are pregnant has proven difficult because most standard therapies are unsafe for use during pregnancy. Pregnant women with Q fever are usually treated with a drug called co-trimoxazole until delivery because it lowers the risk of pregnancy complications. However, the drug is usually not curative and women may experience a new outbreak of infection following a disease-free or inactive period (recrudescence). After giving birth, a woman with Q fever infection can be treated as discussed above in standard therapies.
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