Bartonellosis is an infection caused by Bartonella bacteria, typically spread from animals carrying the disease. There are different types of Bartonellosis, including cat scratch disease, trench fever and carrion's disease, each caused by different species of Bartonella. Symptoms widely vary depending on the type of Bartonella infection and range in severity. 

Understanding the clinical symptoms associated with Bartonella is crucial for early diagnosis, allowing the administration of quick and effective treatments to prevent serious complications.

What is Bartonellosis?

Bartonellosis refers to the wider bacterial infections caused by several Bartonella species. Each species transmits infections through different vectors and has varying effects on the body. However, most of the species enter the human body to affect endothelial and erythrocyte cells. The invading of the red blood cells allows the bacteria increased transport around the body and evasion from the body’s immune responses.¹

Sources of Disease 

The disease is transmitted through animals that are already infected with the disease. This primarily involves insects such as fleas, flies and lice, but any animals that come into contact with these insects can become infected too such as cats, dogs and rats. Therefore, infection in humans can be transmitted by;

• Direct insect bites
• Infected-animal bites 
• Infected-animal scratches 
• Needle stick injuries² 

There have been studies proving transmission of Bartonella by ticks into mouse models, but so far no evidence of infection that can spread to humans.³ There is no evidence of Bartonella being transmissible from human to human.

There are over 20 different species of Bartonella discovered, although only a few have been seen to cause significant disease in humans. The most common infections and their pathogenic species include;

• Cat scratch disease - caused by B.henselae
• Trench fever - caused by B.quintana 
• Carrion’s disease - caused by B.bacilliformis 

Cat Scratch Disease 

Cat scratch disease is an infectious disease caused by Bartonella Henselae, a bacterium carried by fleas which can be transmitted to cats. The most common mode of transmission to humans is through scratches from infected cats, as their claws and fur can carry flea faeces. However, if transferred by flea bites, it can be directly spread to humans through cat's saliva, by biting or licking open wounds. 

Although the condition occurs worldwide, it is rare, with one study highlighting a prevalence of 4.5 per 100,000.⁴ 

Main symptoms 

• Swelling around bitten or scratched area
• Rash or bumps over the skin
• Swollen and/or painful lymph nodes

Within 10 days of infection, near the site of scratch/bite/lick, a red painless bump develops. Within a few weeks, the next symptom occurs - the swelling of the lymph nodes. It affects the lymph nodes closest to the bacterial entry point, most commonly on the neck or armpits. It will become swollen, painful and tender.

Other possible symptoms 

• Fever
• Fatigue 
• Body-aches or joint pains  
• Headaches 

The illness is self-limiting, meaning it takes its natural course, and usually resolves itself without treatment over time. After between 2-4 months, the swelling of lymph nodes subsides, along with the other symptoms.

Complications

• Abdominal pain, vomiting, and loss of appetite - indicative of liver and spleen lesions⁵
• Conjunctivitis⁶ - Parinaud oculoglandular syndrome
• Seizures⁷ - indicative of swelling of the brain - encephalitis 

Severe complications are extremely rare in healthy individuals. Atypical effects of cat scratch disease are reported to occur in 5-20% of those with the disease.⁸ 

There are higher risk groups, including immunocompromised individuals, which can be either from illness, medications or treatment they are currently on, causing their immune system to be more vulnerable to infection. The oldest and youngest of the population also have an increased risk.

Prevention

To prevent disease, you can;

• Regularly give pets flea treatments
• Avoid petting or touching stray animals 
• Wash hands after playing/petting 
• Wash clothes, blankets, and toys and bathe pets if fleas are found

Trench Fever 

Trench fever is a bacterial infection, caused by Bartonella Quintana, transmitted to humans through body lice. It was first discovered during WW1 when an epidemic occurred amongst soldiers given the name trench fever. The illness results in fever, weakness and dizziness, with more than 1 million soldiers affected during the war.⁹ 

Symptoms 

• Fever
• Weakness
• Dizziness
• Headache
• Severe shin pain and/or numbness 

Fever is the characteristic symptom of the disease, and it occurs in 3 different distinct patterns

• Abortive - high fever over several days, after which recovers and disappears
• Recurrent - various episodes of rising fever, which falls and returns to normal before rising again, commonly in 5-day intervals 
• Continuous - fever that remains high throughout the disease 

Due to the transmitting vector being body lice, basic hygiene practices have allowed cases of disease to be very rare. However, cases in certain populations will be higher such as in refugee, homeless or impoverished communities, as access to proper hygiene services is challenging. Prevalence is thought to be as high as 30% in homeless populations, although cases are hard to track, with many people being undiagnosed.¹⁰

Prevention

To prevent disease, you can;

• Regularly wash hands, body, face and clothes
• Seek lice treatment if lice are found 
• Seek information and help if access to hygiene or healthcare is a problem for you

Carrion’s Disease 

Carrion’s disease is a biphasic bacterial infection caused by an insect vector - female sand flies. The lutzomyia and phlebotomus sand flies primarily transmit Carrion’s disease within the regions of the Andean valleys in Peru, and other regions of South America, thriving at higher altitudes.^{1 1}The sand flies carry bacteria, Bartonella bacilliformis, transferred to humans through bites. The disease results in two phases of illness; oroya fever and Peruvian warts. 

Oroya fever

Symptoms of Oroya fever can be varied and non-specific, presenting similarly to other types of infectious disease.

These include;

• Fever
• Fatigue
• Anemia 
• Headache
• Confusion 
• Muscle pain
• Abdominal pain 
• Enlarged lymph nodes 

Without the quick response of antibiotics during this active phase, the fatality rate can be as high as 88%.¹¹ These symptoms usually continue for 1-4 weeks before the next stage of disease occurs.

Peruvian warts

After the Oroya fever has occurred, the appearance of small red papules on the skin appears. The warts can either be;

• Military - small (<3mm), close to the surface, numerous and painless
• Mular - larger (>5mm), deeper in the layers of skin, painful 
• Modular - larger and more prominent than the other two types

The lesions typically affect the legs and arms and can be present in large numbers which can eventually crust and bleed.¹²

Prevention

To prevent disease you can;

• Wear long sleeves, use bed nets, limit activities outdoors at peak times (dawn and dusk)
• Use of insect repellent 
• Research areas in South America before travelling and come prepared 

Of all the other species of Bartonella bacteria, Bartonella bacilliformis, the causative agent of Carrion's disease, is the most deadly. It requires medical intervention to prevent fatalities whereas the other species are self-limiting in most healthy populations. With the clinical presentation of bartonellosis being similar amongst the different bacterial species, accurate diagnosis is essential to provide the best outcomes for patients. 

Diagnostic Tests

Summary

Bartonellosis symptoms and clinical presentation depend on the type of infection caused by different bacterial species. Although a rare disease in the majority of the population, higher-risk groups such as immunocompromised individuals or impoverished communities can have higher incidences. Careful outlining of symptoms and thorough diagnostic tests are relevant to these higher-risk groups and others that do come in contact with the disease. Understanding the differences in Bartonella diseases allows the correct course of treatment to be considered for appropriate management of the disease and to reduce fatalities.