Bartonellosis

Bartonellosis is a group of infectious diseases caused by bacteria that can spread to humans through cat scratches, flea bites, body lice, or sand fly bites. These infections range from mild illness that goes away on its own to severe complications affecting the heart, brain, and other organs.

Table of contents

• What Is Bartonellosis?
• Main Types of Bartonella Infections
• How Bartonella Spreads
• Signs and Symptoms
• How Doctors Diagnose Bartonellosis
• Treatment Approaches
• Prevention

What Is Bartonellosis?

Bartonellosis refers to any infectious disease caused by Bartonella bacteria, which are tiny organisms that can live inside the cells of humans and animals^[1]. These bacteria are gram-negative, meaning they have a specific type of cell wall that affects how they respond to treatments^[2].

Scientists have identified roughly 20 to 26 different species of Bartonella bacteria, and about 14 to 15 of these can cause illness in humans^[6][7]. These bacteria are intracellular parasites, which means they invade and live inside body cells, particularly red blood cells, certain immune cells called macrophages, and cells that line blood vessels (endothelial cells)^[3][13].

cat scratch disease, trench fever, Carrion’s disease, Oroya fever, verruga peruana, five-day fever

Main Types of Bartonella Infections

The three most important Bartonella species that cause human disease are Bartonella henselae, Bartonella quintana, and Bartonella bacilliformis^[1][5]. Each causes a different type of illness.

Cat Scratch Disease

Cat scratch disease is caused by Bartonella henselae and is the most common form of bartonellosis in the United States, affecting approximately 20,000 people each year^[3][13]. This infection happens when bacteria are transmitted through a cat scratch, bite, or lick of an open wound^[4].

About 40% of cats carry these bacteria at some point in their lives, with kittens being more likely to carry and spread the infection^[14]. Cats get infected when fleas bite them, and the bacteria can get under their claws or in their mouths from contaminated flea droppings^[7].

Cat scratch disease most commonly affects children aged 5 to 9 years^[2][5]. The disease is found worldwide and tends to occur more frequently in warmer, humid areas where fleas are more common^[7].

Trench Fever

Trench fever is caused by Bartonella quintana and spreads through body lice^[1][4]. This disease got its name because it was common among soldiers living in trenches during World War I and World War II^[2][6].

Trench fever occurs most often in crowded living conditions with poor hygiene and sanitation, particularly among people experiencing homelessness^[4][5]. While more common in warm climates, outbreaks have occurred in the United States as well^[5].

Carrión’s Disease

Carrión’s disease is caused by Bartonella bacilliformis and occurs only in certain mountainous regions of South America, particularly Peru, Colombia, and Ecuador^[2][5]. The disease was first identified in 1870 when thousands of railway workers died during an outbreak while building a line from Lima to Oroya in Peru^[2].

This infection spreads through the bite of infected sand flies that are active at night^[4]. The disease has two distinct phases: an acute phase called Oroya fever and a chronic phase called verruga peruana (Peruvian warts)^[4][5].

How Bartonella Spreads

Bartonella bacteria spread to humans through several routes. The specific bacteria species determines how it gets transmitted^[1]:

• Cat scratches or bites: Bartonella henselae spreads when a cat that has been exposed to infected fleas scratches or bites a person, or licks an open wound^[14]
• Flea bites: Fleas contaminated with bacteria can spread infection through their bites or droppings^[1][7]
• Body lice: Human body lice transmit Bartonella quintana^[1][5]
• Sand fly bites: Sand flies spread Bartonella bacilliformis in certain geographic areas^[1][5]

According to the Centers for Disease Control and Prevention (CDC), there is no evidence that ticks spread Bartonella infection to people^[1]. Studies showing ticks could carry the bacteria only used mice and artificial feeding systems, which do not prove that ticks can transmit the bacteria to humans or that the bacteria can survive in ticks for extended periods^[1].

People at higher risk for Bartonella infections include pet owners, veterinarians, veterinary staff, and anyone who regularly works with animals^[8]. Immunocompromised individuals, such as those with HIV/AIDS, undergoing cancer treatment, or who have received organ transplants, are at higher risk for severe complications^[4][5].

Signs and Symptoms

Symptoms of bartonellosis vary depending on which bacteria species causes the infection and the person’s immune system status^[5].

Cat Scratch Disease Symptoms

With cat scratch disease, symptoms typically appear days to weeks after exposure^[4][7]. The first sign is usually a small red bump or blister at the scratch or bite site. This bump appears about 3 to 10 days after infection and may fill with fluid before drying up and healing, sometimes leaving a scar^[4][7].

One to three weeks later, lymph nodes (small organs that are part of the immune system) near the infection site become swollen, tender, and warm^[4][7]. These enlarged lymph nodes, called lymphadenopathy, can occur in the armpit, neck, or groin area depending on where the scratch occurred^[9]. The swelling can last 2 to 12 months^[4].

Other symptoms may include:

• Fever (particularly in children)
• Fatigue
• Headache
• Body aches and general discomfort
• Poor appetite

In most healthy people, cat scratch disease is mild and resolves on its own within two to four months without treatment^[3][4]. However, some people can develop complications affecting the eyes, bones, liver, spleen, or nervous system^[3][13].

Trench Fever Symptoms

Trench fever causes sudden onset of flu-like symptoms^[6]. Common signs include:

• Fever that comes and goes, with episodes lasting 4 to 5 days and recurring 3 to 5 times
• Severe headaches
• Bone pain, especially in the shins, neck, and back
• Rash on the abdomen
• Chills
• Enlargement of the spleen or liver

Symptoms typically appear 15 to 25 days after infection^[6]. In people with healthy immune systems, the disease usually resolves on its own, though some cases involve relapsing symptoms or chronic infection in the bloodstream^[6].

Carrión’s Disease Symptoms

Carrión’s disease has two distinct phases. The acute phase, called Oroya fever, causes sudden onset of high fever and severe hemolytic anemia, a condition where red blood cells are destroyed^[4][9]. This phase typically lasts two to four weeks and without treatment can be fatal in up to 90% of cases^[9].

The chronic phase, called verruga peruana, causes reddish-purple bumps or nodules to appear on the skin^[4][5]. These skin growths can persist for months or years^[9].

Complications

Bartonella bacteria can spread to various organs in the body, causing serious complications^[5]. The most common complication is endocarditis, inflammation of the heart valves^[5][6]. This condition has an 11.9% mortality rate globally^[6].

Other complications include:

• Inflammation of the brain (encephalitis) or abnormal brain function (encephalopathy)
• Eye problems, including inflammation and vision issues
• Liver and spleen swelling
• Bone and joint infections
• Heart failure
• Anemia

People with weakened immune systems can develop particularly severe conditions. Bacillary angiomatosis causes abnormal growth of blood vessels, creating masses or cysts on organs and bones, along with large raised bumps on the skin^[5][9]. Bacillary peliosis causes blood-filled cysts to form on the liver^[5]. Without treatment, these conditions can be fatal^[6].

How Doctors Diagnose Bartonellosis

Diagnosing bartonellosis can be challenging because symptoms may be nonspecific and similar to other illnesses^[3][13]. Healthcare providers often diagnose cat scratch disease based on typical symptoms combined with a history of exposure to cats^[14].

Laboratory tests used to confirm Bartonella infection include^[3][5][13]:

• Blood tests: Doctors can test blood for antibodies (proteins the immune system makes to fight infection) using techniques like immunofluorescent antibody (IFA) assays
• PCR testing: Polymerase chain reaction (PCR) is a molecular technique that can detect Bartonella DNA in blood, spinal fluid, tissue samples, or heart valve tissue
• Culture: Growing the bacteria in a laboratory is possible but difficult because Bartonella grows very slowly and requires special conditions
• Biopsy: Taking a small tissue sample from lymph nodes or skin lesions for examination

However, these tests have limitations. Antibody tests can produce false negatives (showing negative results when infection is present) and may only detect infection in about 30% of confirmed cases^[3][13]. The tests also may not reliably distinguish between different Bartonella species, and positive antibody results can persist for years even after successful treatment^[14]. PCR testing may be more reliable but is less sensitive when testing blood samples compared to tissue samples^[14].

When visiting a healthcare provider, it is important to mention any contact with cats, recent travel, or exposure to fleas or lice^[5].

Treatment Approaches

Treatment for bartonellosis depends on which Bartonella species is causing the infection and how severe the symptoms are^[5].

Cat Scratch Disease Treatment

For uncomplicated cat scratch disease in healthy individuals, antibiotic treatment is often not necessary because the infection typically resolves on its own^[3][13][14]. There is insufficient evidence that antibiotics shorten the duration of illness^[3][13].

However, doctors may prescribe the antibiotic azithromycin when lymph nodes are very swollen or painful, as studies show it can reduce lymph node size more quickly than no treatment^[11][14]. The typical dose for adults and children over 45.5 kg is 500 mg on the first day, followed by 250 mg daily for four days^[14].

Other antibiotics that may be used include erythromycin, doxycycline, or co-trimoxazole^[11]. Treatment duration is typically 3 to 6 weeks^[10][11].

For complications affecting the eyes, brain, or other organs, treatment with antibiotics is recommended^[11]. Eye inflammation (retinitis) is typically treated with doxycycline and rifampin for 4 to 6 weeks, sometimes with corticosteroids added^[11].

Trench Fever Treatment

Trench fever is typically treated with doxycycline 100 mg taken by mouth twice daily for at least 4 weeks^[11]. People with weakened immune systems or those with organ involvement may require longer treatment courses^[11].

Carrión’s Disease Treatment

The acute phase (Oroya fever) requires immediate antibiotic treatment to prevent high mortality rates^[11]. Antibiotics used include chloramphenicol, ciprofloxacin, or doxycycline for at least one week, with longer courses sometimes needed^[11].

Severe Infections and Complications

People with heart valve infection (endocarditis) often require a combination of antibiotics, typically including rifampin or gentamicin for at least 14 days along with doxycycline for at least 6 weeks^[10][11]. Damaged heart valves may need surgical replacement^[10][11].

For bacillary angiomatosis in people with weakened immune systems, treatment typically involves erythromycin, doxycycline, or similar antibiotics for at least 3 months^[11]. Severe cases may require doxycycline combined with rifampin or gentamicin^[11].

Prevention

Several measures can help reduce the risk of Bartonella infection^[1][8]:

• Flea control: Use monthly parasite prevention products on cats to protect against fleas
• Avoid rough play: Be careful when playing with cats to avoid bites and scratches, especially from kittens
• Wash wounds promptly: Clean any cat scratches, bites, or licks on open wounds immediately with soap and water
• Hygiene practices: Maintain good personal hygiene to reduce risk of body lice infestation
• Protective measures: Veterinary professionals should take precautions to avoid contact with blood and bodily fluids from cats and dogs, and avoid accidental needle sticks
• Insect protection: In areas where sand flies are present, use insect repellent and protective clothing

People experiencing homelessness or living in crowded conditions should have access to facilities that allow for good hygiene practices to reduce the risk of body lice transmission^[5][6].