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Bartonella henselae (Cat-scratch disease and Bacillary angiomatosis)


Bartonella henselae (Cat-scratch disease and Bacillary angiomatosis)


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High Yield Notes
17 pages

Bartonella henselae (Cat-scratch disease and Bacillary angiomatosis)

6 flashcards

USMLE® Step 1 style questions USMLE

2 questions

A 25-year-old woman presents to an urgent care facility due to fever and discomfort in the right axilla for the past two days. The patient works as an accountant and lives alone with two cats and a parrot. Past medical history is unremarkable. Temperature is 38.0 ºC (100.4 ºF), pulse is 114/min, blood pressure is 115/70, and respirations are 18/minute. Physical examination shows several enlarged lymph nodes in the right axilla, which are tender to palpation. Additionally, scratch marks are noted on the patient’s right forearm. A biopsy is performed on one of the enlarged axillary lymph nodes. Which of the following is most likely to be seen on the biopsy?  

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Content Reviewers:

Bartonella henselae is a zoonotic bacteria which may cause Cat-scratch disease, or CSD, in humans.

Zoonotic bacteria refers to any bacteria which can be transmitted between animals and people.

Now, Bartonella henselae spreads between cats with the help of a cat flea, called Ctenocephalides felis, which feeds on the blood of an infected cat. Then, it drops its feces, which contain Bartonella henselae, on the cat’s body.

Finally, when the cat grooms or scratches, Bartonella henselae gets on its teeth and claws, and the cat may infect a human by scratching or biting - hence the name, “cat scratch disease”, or “cat scratch fever”.

There’s also bacillary angiomatosis, which is a severe form of cat scratch disease, that develops primarily in immunocompromised individuals.

Now, Bartonella henselae is a gram-negative bacillus, in other words, it's a rod-shaped bacteria that stains red or pink with Gram staining.

This is largely due to the fact that Bartonella henselae has a thin peptidoglycan wall that doesn’t retain crystal violet dye during Gram staining.

Sometimes, though, it doesn’t readily gram stain, so the silver nitrate-based Warthin-Starry stain is used for direct visualization.

Bartonella henselae is a facultative intracellular bacteria, which means that it's adapted to live inside cells to avoid the immune system.

Specifically, it hides inside endothelial cells lining up the interior surface of the blood vessels and lymph vessels.

Once inside the endothelial cell, Bartonella henselae can trigger an increased production of interleukin-10, which suppresses the action of immune cells; and interleukin-8, which promotes endothelial cell proliferation.

In humans, the response to infection depends on the immune system.

Immunocompetent individuals develop a simple form of the cat-scratch disease.

The most characteristic symptom is the swelling of a single lymph node or a cluster of lymph nodes, usually in the armpits, which are extremely painful to the touch.

This is known as regional lymphadenopathy, and it’s a consequence of Bartonella henselae triggering a never ending T-cell response, which creates an area of inflammation known as granulomas in the lymphoid tissue.

Other symptoms include fever, fatigue, abdominal aches and loss of appetite.

Additional symptoms may appear when the bacteria spread to the bloodstream, and from there, to different organs, causing complications.

For example, if it reaches the heart, it may cause endocarditis, and signs include prolonged fever, and new heart murmurs on physical examination.

Alternatively, if bacteria infect the central nervous system, there may be confusion, disorientation, and seizures.

Immunocompromised individuals, on the other hand, like those that are HIV-positive, tend to develop the severe form of cat scratch disease, called bacillary angiomatosis.

Bartonella henselae is a proteobacterium that can cause bacteremia, endocarditis, bacillary angiomatosis, and peliosis hepatis. It is also the causative agent of cat-scratch disease (bartonellosis) which, as the name suggests, occurs after a cat bite or scratch. The disease is characterized by lymphadenopathy and fever.