Bartonella henselae (Cat-scratch disease and Bacillary angiomatosis)

Definitions & Key takeaways

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.
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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.
With bacillary angiomatosis, endothelial cell proliferation leads to benign papular vascular lesions on the skin. - this is especially common in HIV-positive people whose CD4+ cell count is less than 100 per cubic millimeters of blood.
These skin lesions are very similar to those seen in Kaposi’s sarcoma - an endothelial malignancy that frequently develops in HIV positive individuals with a human herpesvirus type 8 infection.
The difference between these two lesions lies in what inflammatory cell is mostly present in the lesion. In bacillary angiomatosis, the inflammation is mostly made up of neutrophils, whereas in Kaposi's sarcoma, the inflammation is made up of lymphocytes instead.
Other symptoms of bacillary angiomatosis include fever, chills, fatigue and weight loss. Complications may arise from bacillary angiomatosis when the lesions cause disfigurement, or when the lymph nodes inside the body become enlarged - for example, enlarged lymph nodes around the portal vein can compress the common bile duct, causing biliary obstruction, and jaundice.
Finally, if an angiomatous nodule forms in one of the eyes, it could cause unilateral vision loss. Bartonella henselae infection is usually diagnosed by using indirect fluorescence assay testing or enzyme-linked immunoassay to look for serum antibodies against Bartonella henselae.
Alternatively, a biopsy of affected tissue - either a swollen lymph node in cat-scratch disease, or a skin lesion in bacillary angiomatosis - can be done, and the tissue can be stained using the Warthin-Starry method, to directly visualize the bacteria.
Treatment is aimed at reducing symptoms, since Cat-scratch disease usually resolves on its own over a few months. However, antibiotics like azithromycin are sometimes used to prevent life-threatening complications.
Other alternatives like doxycycline and rifampicin can also be used to treat the disease. Antibiotics like erythromycin, doxycycline and tetracycline are used to treat bacillary angiomatosis.
Finally, a means of preventing infection in humans is elimination of fleas in a domestic cat’s environment. Alright, as a quick recap, Bartonella henselae is a gram-negative bacteria found in kittens.
It can be visualized with the help of a Warthin-Starry stain. And it’s responsible for causing Cat-scratch disease or CSD, in immunocompetent individuals, and Bacillary angiomatosis in immunodeficient individuals.
Cat scratch disease presents with regional lymphadenopathy, fatigue, and fever, and antibiotics like azithromycin, doxycycline and rifampin can be used.
Bacillary angiomatosis presents with skin lesions, fever, chills, fatigue and weight loss, and requires treatment with erythromycin, doxycycline or tetracycline.