What is Q fever?
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Hello and welcome to the Medical Fun Facts Podcast.
It’s Monday 13 November 2017. My name is Gary and the Medical Fun Facts Podcast is a weekly show with a few facts and hopefully one or two funny lines. Don’t expect too much and everything will be okay.
Last week, in episode 91, I spoke about “P is for Pathology”, I also described the various subspecialties in the discipline of pathology.
Tonight, I’m speaking about Q is for Q fever.
What is Q fever?
Q fever was first described by Ed Derrick in Queensland in 1935. He named it Q fever not for Queensland, but for query. At the time, no one wanted a negative connotation associated with the state of Queensland which for readers of my other blogs know is the greatest state in the federation of the Commonwealth of Australia. Whereas the greatest territory is the Northern Territory of Australia which has the friendliest people and the Top End has the best weather and climatic conditions of any place in the world.
Q fever is an acute febrile disease characterised by chills, headache, malaise, sore muscles, and sweats. Infections may be unapparent or present as a fever of unknown origin. A pneumonitis, as opposed to a consolidating pneumonia, may be seen on chest X-rays, although patterns are nonspecific and cannot differentiate from other ætiologies.
Chronic Q fever manifests primarily as culture-negative endocarditis and often occurs in patients with valvular or vascular defects.
Other rare forms have been described. The case-fatality rate in untreated acute cases is usually <1%. However, Q fever endocarditis is fatal if untreated, whereas with treatment the 10-year mortality rate is 19%. So, you have one in five chances of dying from Q fever if you get a heart valve infection.
A post-Q fever fatigue syndrome has been described. Given Q fever can be transmitted by ticks, this could be a cause of tick-borne chronic fatigue or systemic exertion intolerance.
Q fever is caused by Coxiella burnetii. The organism can be found in urine, faeces, and milk of infected animals, with the highest numbers of bacteria shed in birth products like the placenta and amniotic fluid. The bacterium is resistant to quite a few disinfectants and environmental conditions.
The diagnosis uses two antigenic preparations: phase I, represents an infectious agent which can be isolated from humans and animals, while phase II, is a laboratory-generated attenuated noninfectious form of the agent. For acute Q fever, a demonstration of a 4-fold rise in phase II IgG between acute and convalescent serum taken 3 to 6 weeks apart is the standard for confirmed diagnosis.
A single high serum phase II IgG titre probably reflects acute infection in a patient with clinical signs and symptoms.
Laboratory diagnosis by polymerase chain reaction (PCR) of blood or serum can also be used in the first 2 weeks after symptom onset and prior to antibiotic administration.
Diagnosis of chronic Q fever requires a phase I IgG antibody titre ≥1:1024 and a compatible clinical presentation.
When using sensitive immunofluorescence, antibodies to C. burnetii can be detected for up to 10 to 15 years.
Q fever is found globally and it is endemic in areas where reservoir animals are present. Outbreaks have occurred among workers in abattoirs, in laboratories, and research.
The Netherlands experienced a large outbreak from 2007–2010 that was linked to infected goat farms. Lack of animal contact doesn’t mean Q fever should be overlooked, airborne transmission of C. burnetii can occur with no direct animal exposure history.
Sheep, cattle, and goats are the primary reservoirs for C. burnetii, however, infection has been found in other vertebrates including cats, dogs, marsupials, birds, and ticks. As far as marsupials are concerned, it’s known that Coxiella burnetii has been found in kangaroo faeces.
The incubation period is dose-dependent and is typically 2–3 weeks with a range of 3–30 days.
Transmission occurs through airborne movement of Coxiella burnetii in dust or aerosols contaminated by placental tissues, birth fluids, and waste from infected animals. Airborne particles containing organisms may be carried downwind for a distance of 1 kilometre or more.
Contamination also occurs through direct contact with contaminated materials, such as wool, straw, and laundry. Raw milk from infected cattle or goats contains viable organisms and may be responsible for human transmission. Direct transmission by blood or marrow transfusion has been rarely reported.
Sporadic cases of nosocomial transmission have been reported during postmortem and obstetrical procedures of infected women.
Risk groups include veterinarians, dairy farmers, veterinary researchers, and abattoir workers. Persons with valvular heart disease or vascular defects, pregnant women, and persons who are immunosuppressed are at risk for chronic Q fever after an acute infection.
Immunisation with vaccines prepared from formalin-inactivated C. burnetii is useful in protecting laboratory workers and is strongly recommended for those working with live C. burnetii. It should also be considered for abattoir workers and others in hazardous occupations. To avoid severe local reactions, vaccine administration should be preceded by a skin sensitivity test with a small dose of diluted vaccine. The vaccine should not be given to individuals with a positive skin or antibody test or a documented history of Q fever.
Treatment for acute and chronic disease involves antimicrobials. In chronic disease, the treatment may last up to two years. In some patients with heart disease, surgery may be necessary.
Another consideration is that Coxiella burnetii has been used in biological weapons programs.
Questions for readers and listeners
Have you ever heard of Q fever?
Can you think of any other diseases beginning with the letter Q?
Did you know that Coxiella burnetii has been found in kangaroo faeces?
Please leave your answers in the comments section of the show notes or on the Facebook page or on YouTube.
That’s episode 92 in the can.
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If you have any questions or comments please let me know. If I’ve said anything incorrect I welcome correction.
I’ll catch you next week for episode 93. Something beginning with the letter R. Send me suggestions.
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Thank you, and good night.