Coxiella burnetii (Q fever)

Definitions & Key takeaways

Coxiella burnetii is a gram-negative short rod-looking bacterium that causes the disease Q fever. Q fever is a zoonotic infection transmitted through aerosolized spores from animal fluids such as livestock or raw milk. Symptoms of Q fever include fever, fatigue, headache, muscle aches, and chest pain. Persons at high risk for developing severe illness if infected with Coxiella burnetii include pregnant women, the elderly, and those with weakened immune systems.

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Coxiella burnetii is a gram negative rod that causes a condition called Q fever. This bacterium is highly resistant to environmental stressors including high temperatures and ultraviolet light and spreads to human from animals like cows, sheep and goats.
So Q fever is considered a zoonotic infection. Now, Coxiella burnettii is considered a gram negative obligate intracellular organism.
So it can only replicate inside other cells like our macrophages. See, burnettii is also non modal and has a biphasic life cycle that consists of an environmentally stable nonreplicating form called small cell variant or SCV for short and a metabolically active replicating large cell variant or LCV when it feels threatened by the environment, like when the temperature becomes too high or too low in case of extreme dryness or when there is harmful radiation around.
See, burnettii transforms into the SCV by shrinking and condensing its DNA and periplasmic space in this form. It's able to resist heat, harsh chemicals, digestive enzymes and even antibiotics.
Remarkably, the SCV can survive for years, waiting for favorable conditions to come and then convert into the LCV that can then grow and divide inside host cells.
Now, the primary disease that Coxiella burnetii causes is called Q fever. This disease is most commonly acquired by inhalation of aerosolized sea burnettii from an infected animal infection can happen during parturition when large amounts of bacteria are released in birth fluids or from dust contaminated by animal excrement such as when cleaning a barn.
It can also be picked up through ingestion of raw milk or other unpasteurized dairy products or by contact with contaminated animal materials.
So people at highest risk for infection include those in close contact with farm animals such as farmers and veterinarians and also slaughterhouse workers.
In terms of pathogenesis. The exact mechanism of disease is poorly understood.
What is known is that the small cell variant is highly infectious and once it enters the body, it attaches to receptors on phagocytes like macrophages in the lung.
Now, normally phagocytes destroy invading bacteria via endocytosis, which is when bacteria are engulfed by the phagocyte and wrapped in a vesicle called a phagosome.
The phagosome normally merges with an acidic intracellular organelle called a lysosome forming a phagolysosome. Lysosomes release hydrolytic enzymes inside the phagolysosome which normally destroy the invading bacteria.
But here's the thing. See burnettii is unusual because instead of being destroyed, it can modulate the process, allowing it to survive and even replicate in the acidic phagolysosome.
The acidic environment triggers transformation of the SCV to the replicating LCV. And within 24 to 48 hours, the phagolysosome can be filled with replicating LCV forms how see, burnettii, both avoids destruction by the hosts immune system and replicates so efficiently are still not fully understood.
This ability to survive and replicate inside macrophages allows it to travel through the bloodstream to infect multiple organs such as the heart, especially the valves, liver, central nervous system, lymph nodes and others.
Now, clinical manifestations of c burnettii infection can be divided into acute and chronic Q fever. Acute Q fever takes 2 to 3 weeks to develop after exposure and can present with nonspecific flu like symptoms such as high fevers, chills, fatigue and muscle aches.
Infection can also show up as an atypical pneumonia characterized by nonproductive cough and pleuritic chest pain as well as nausea, vomiting or diarrhea.
Other presentations include hepatitis and less commonly meningoencephalitis. It's important to keep in mind though that acute Q fever can often be asymptomatic leaving a person with no symptoms at all.
On the other hand, chronic Q fever takes months to years to develop and is most classically associated with S burnettii endocarditis.
An infection of the inner lining of the heart that often involves the heart valves. People with prosthetic or damaged valves are at especially high risk.
The diagnosis of Q fever is tricky because the disease presents with nonspecific signs and symptoms. So it may not be obvious to test for s burnettii.
General laboratory studies usually demonstrate an elevated white blood cell count, elevated inflammatory markers like ESR or CRP and elevated liver enzymes if the bacteria invade the liver.
Q fever should be suspected in patients with a history of frequent contact with animals like cattle, sheep or goats and subsequent development of compatible symptoms.
Serologic testing is the preferred method for diagnosis. Coxiella burnettii expresses two types of antigens called phase one and phase two antigens which lead to antibody production in the body detection of these specific antibodies using indirect immunofluorescence assay or ifa or enzyme immunoassay.
Also known as EI A or Eliza can be used to confirm infection with sea burnettii polymerase chain reaction. Or PCR is another test that can be done which will directly identify bacterial DNA.
Treatment of acute Q fever is with doxycycline for 14 days. For most patients on the flip side, chronic Q fever requires a longer term management with a combination of drugs such as doxycycline and hydroxychloroquine for at least 18 months as well as serologic testing to monitor treatment response.
All right, it's a quick recap. Coxiella burnettii is a small pleomorphic gram negative rod.
That is an obligate intracellular bacterium. It causes a zoonotic infection that is transmitted primarily via aerosols and people at highest risk are individuals in contact with farm animals.
The primary condition that Coxiella burnettii causes is Q fever which can be further divided into acute and chronic Q fever.
Acute Q fever can be asymptomatic or associated with nonspecific flu like symptoms such as fever, fatigue and muscle aches.
Serologic testing is the primary method of diagnosis with PCR also used in some cases. Treatment of acute Q fever involves a course of doxycycline.
On the other hand, chronic Q fever is most classically associated with infective endocarditis. The treatment here includes a combination of doxycycline and hydroxychloroquine for at least 18 months.