Introduction

Bartonellosis is a bacterial infection caused by a bacterial genus called Bartonella. There are multiple different species of which fourteen may cause infection in humans however most are quite rare. The most common species to cause Bartonellosis are Bartonella henselae (cat scratch fever), Bartonella quintana (trench fever), and Bartonella bacilliformis (Carrion’s disease). The infections Bartonella species cause vary from mild symptoms to serious infections affecting key body organs like, for example, the brain, heart, liver, and more.¹

Cat scratch fever

Transmission 

As indicated by the name, cat scratch fever caused by Bartonella henselae is transmitted to humans via contact with infected cats. The type of contact that may cause transmission includes being scratched or bitten by a cat, or by an open wound licked by a cat. Cats tend to become infected via flea bites, which induce the presence of the bacteria in the cat’s blood allowing them to transmit the disease further, especially considering that cats tend to be asymptomatic for months.²

Infection mechanisms

The bacteria cause disease by targeting a specialised white blood cell that acts as an endothelial cell precursor. Endothelial cells are a specific type of cell that line blood and lymphatic vessels. The bacteria invades these cells and forms a protective ‘pouch’ around itself called a vacuole to aid their survival. The bacteria also produce a toxin called lipid A, which contributes to symptoms such as fever. The bacteria begin with this invasion and later move on and infect other organs, leading to a range of different symptom exhibitions.³

Signs and symptoms

Bartonella henselae tends to have a three to ten-day incubation period, i.e. the time taken between exposure to the pathogen and development of symptoms. Symptoms in the acute phase usually include:

• Fever
• Body aches (muscles, bones, joints)
• Swollen lymph nodes
• Skin issues like bumps or cysts under the skin, or a rash
• Fatigue
• Appetite or weight loss

As aforementioned, after the acute phase, the bacteria may spread to multiple organs, causing more serious diseases such as:

• Endocarditis; which is an inflammation of the lining of the heart. This will present with body aches, chest pain, and night sweats
• Hepatosplenomegaly; which in simpler words means swelling of the liver and spleen, making them appear larger. This will be accompanied by symptoms like nausea, vomiting, and abdominal pain
• Encephalopathy; which is a disease of the brain that may show up with symptoms like confusion, headaches, altered brain function, and less commonly seizures
• Neuroretinitis, or in simple words, swelling of the eye and optic nerve, leading to issues with vision.
• Parinaud's oculoglandular syndrome; which involves inflammation and redness of the conjunctiva of the eye as well as lymph node swelling near the ears²

Trench fever

Transmission 

Bartonella quintana is transmitted by human body lice bites. The bacteria multiply in the louse’s intestinal lumen and are then transmitted to humans when the contaminated faeces of the louse inoculate the skin or conjunctiva. These lice may be transmitted from person to person by close contact and by sharing bedding, or clothing. It is most commonly spread in conditions of poor hygiene, most commonly due to lack of access to proper sanitation, and crowding. 

Signs and symptoms

The incubation period of trench fever tends to be around a week. The disease may then present either with mild, moderate, or debilitating influenza-like symptoms. These include:

• Fever
• Pain in the bones, most often in the neck, back, and shins
• Malaise
• Headache
• Nausea and vomiting
• Weight Loss
• Feeling dizzy
• Bacillary angiomatosis; which is a skin lesion that is usually purple or red and may resemble a berry in shape, surrounded by scaly skin

The bacteria may also spread further and cause other disease like:

• Endocarditis
• Bacteremia (infection of the blood); which will also present with rapid breathing and heart rate, chills, low blood pressure, diarrhoea, nausea and vomiting, and abdominal pain^4,5,6

Carrion’s disease

Transmission 

Bartonella bacilliformis is transmitted by the bite of an infected sandfly. This disease was previously known as the South American bartonellosis as it mostly occurs in the Andes mountains and so covers South American countries like Peru, Colombia, and Ecuador. Therefore, people living in or travelling to those areas are most at risk of contracting Carrion’s disease.⁷

Infection mechanisms

In Carrion’s disease, the bacteria usually invade erythrocytes (red blood cells), replicate within them and cause them to rupture. The flagella (a hair-like structure which allows bacteria to move around) of the bacteria is not recognised by the usual receptors of the body, which prevents the activation of the innate immune defence (first line, non-specific defence). The bacteria also have adhesins, which help them clump together to prevent phagocytosis (being engulfed and killed by a white blood cell).⁸

Signs and symptoms

Carrion’s disease has two main stages which present with different symptoms. One of them is called Oroya fever, which includes symptoms like:

• Fever
• Muscle aches
• Headache
• Abdominal pain
• Severe anaemia (lack of red blood cells or haemoglobin to carry oxygen around the body)

The other stage is verruga peruana which involves the development of nodules on the skin, which are red or purple in colour and may bleed. There are many possible complications of Carrion’s fever which include:

• Endocarditis
• Pericardial effusion; which is when excess fluid builds up in the pericardial sac surrounding the heart. This may present with multiple symptoms like chest pain, shortness of breath, lightheadedness, fatigue, fainting, rapid heartbeat, behavioural changes (due to insufficient oxygen delivery to the brain), cyanosis (lips and fingernails becoming a blue/grey colour), coughing, hiccups, and issues swallowing⁹
• Pulmonary oedema involves fluid buildup in the lungs and presents with symptoms like wheezing, shortness of breath, suffocating feeling, chest tightness, coughing up blood, gasping for air, fatigue, and swelling of the legs¹⁰
• Cardiogenic shock occurs when the heart is unable to pump enough blood around the body to meet demand. This may be recognised by symptoms such as pain in the upper body, left arm, throat, or jaw, sweating, rapid and irregular heartbeat, trouble breathing, lightheadedness, confusion, tiredness, low blood pressure, weak pulse, swelling in legs and abdomen, pale skin, weak pulse, less frequent urination, cold hands and feet, and loss of appetite¹¹
• Heart failure is when the heart becomes very weak. It is characterised by symptoms like constant breathlessness, extreme tiredness, lightheadedness, swelling of the legs and ankles, cough, rapid heart rate, and dizziness¹²

Diagnosis

Bartonellosis may be diagnosed using multiple methods such as culturing, serology, or histopathology (viewing cells or tissues under a microscope). A blood sample will be drawn from the patient and may be tested either by carrying out a polymerase chain reaction to detect bacterial DNA, checking for Bartonella antigens or by carrying out serological tests to check for antibodies specific to Bartonella. Culturing the bacteria is less common as it takes a long time to grow. Histopathology may also be used to check for Bartonella-infection-defining components from a sample of affected tissue. 

Treatment 

Treatment of Bartonellosis usually includes the administration of antibiotics as it is a bacterial infection. The type and amount of antibiotic used depends on the species of Bartonella causing infection as well as the complications of the infection. 

Long-Term Outcomes

The development of chronic bartonellosis is possible, which may affect many different parts of the body. It may lead to problems of the eyes, which may cause issues like blurred vision, photophobia (eyes very sensitive to light), and eye irritation. It may also affect the bones due to bone marrow infection. Some people may also experience foot pain when walking due to blood vessel damage. If the infection affects the brain, patients may experience memory issues, cognitive impairment, inability to sleep, restlessness, and balancing issues. Sometimes, bartonellosis may also induce anaemia due to the red blood cell damage.³

Prognosis

The prognosis of bartonellosis is usually a full recovery within a few months as the infection usually tends to be mild. However, in some cases, especially with immunocompromised individuals, more serious diseases may occur, which could end in death if not treated. 

Prevention 

Cat scratch fever

As it is a disease caused by cats the best way to prevent infection is to:

• Attempt to avoid being bitten or scratched by a cat
• Keep cats inside to decrease their chance of a flea bite. Wash your hands after coming into contact with cats
• Do not touch stray cats
• Do not allow cats to lick scratches or wounds²

Trench fever

The best preventative measures for trench fever include:

• Do not share bedding, towels, clothes, or beds with someone you suspect to have body lice
• Shower and do laundry regularly
• If you suspect the presence of lice on any laundry items, make sure to wash and dry them at temperatures of at least 55 degrees Celsius to kill the lice⁴

Carrion’s disease

To prevent Carrion’s disease you must do your best to avoid being bitten by a sand fly. This may be done by wearing long-sleeved tops and trousers, using an effective insect repellant and avoiding going outdoors when there is increased sand fly activity, for example at dusk and dawn⁷

Summary 

Bartonellosis is a bacterial infection caused by bacteria of the Bartonella genus. The most common species which cause infection are Bartonella henselae, Bartonella quintana, and Bartonella bacilliformis. The range of disease varies with the bacteria causing mild, self-limiting symptoms, or spreading to other organs and causing debilitating and life-threatening disease. The prognosis is usually recovery but may include death in more serious, untreated cases. The bacteria are also able to establish chronic infection affecting the eyes, bones, red blood cells, or brain.