Bartonellosis

Bartonellosis is a vector-borne zoonotic infectious disease caused by gram-negative, facultative intracellular bacteria of the genus Bartonella. In veterinary medicine, it primarily affects domestic cats and dogs, but can also infect horses, cattle, and wildlife. The disease is characterized by a broad spectrum of clinical manifestations, ranging from subclinical bacteremia to severe systemic illness involving the cardiovascular, hepatic, neurologic, and ophthalmic systems. In cats, the most common species is Bartonella henselae, the causative agent of cat scratch disease in humans, while dogs are more frequently infected with Bartonella vinsonii subsp. berkhoffii, Bartonella henselae, and Bartonella clarridgeiae. The clinical presentation varies significantly depending on the host species, immune status, and the specific Bartonella species involved. The disease is often chronic and relapsing, with bacteremia persisting for months to years in untreated animals. Bartonellosis is a significant public health concern due to its zoonotic potential, particularly in immunocompromised individuals.

The primary causative agents of bartonellosis are bacteria of the genus Bartonella, which are fastidious, gram-negative, facultative intracellular bacilli. Over 30 species have been identified, with several known to cause disease in domestic animals. In cats, the most common species are Bartonella henselae, Bartonella clarridgeiae, and Bartonella koehlerae. In dogs, Bartonella vinsonii subsp. berkhoffii, Bartonella henselae, Bartonella clarridgeiae, Bartonella rochalimae, and Bartonella washoensis have been reported. These bacteria are transmitted primarily by arthropod vectors, including fleas (Ctenocephalides felis), ticks, and biting flies. The cat flea is the principal vector for B. henselae, and transmission occurs through flea feces (flea dirt) contaminating skin wounds or through direct inoculation from flea bites. Ticks, particularly Ixodes spp. and Rhipicephalus sanguineus, are vectors for B. vinsonii subsp. berkhoffii in dogs. Bartonella species have evolved to invade and persist within erythrocytes and endothelial cells, leading to chronic bacteremia. Key virulence factors include the type IV secretion system (VirB/D4), which facilitates host cell invasion and modulation of the immune response, and the ability to induce angiogenesis through the production of vascular endothelial growth factor (VEGF). The bacteria can also evade the immune system by altering surface antigens and residing within erythrocytes, protecting them from antibody-mediated clearance.

Bartonellosis has a worldwide distribution, with prevalence rates varying by geographic region, climate, and vector populations. In cats, seroprevalence rates range from 10% to 50% in healthy populations, but can exceed 90% in areas with high flea infestation. Stray and outdoor cats have higher infection rates compared to indoor cats. In dogs, seroprevalence is generally lower, ranging from 2% to 10%, but can be higher in certain regions, particularly in the southeastern United States and parts of Europe. The disease is more common in warm, humid climates where flea and tick populations thrive. There is no significant breed or sex predisposition, but young animals (less than 3 years old) are more likely to be bacteremic, likely due to increased exposure to vectors. Immunocompromised animals, such as those with concurrent infections (e.g., feline leukemia virus, feline immunodeficiency virus) or those on immunosuppressive therapy, are at higher risk of developing clinical disease. The zoonotic potential of Bartonella species, particularly B. henselae, makes it a public health concern, with cat scratch disease being the most common manifestation in humans. Veterinarians and veterinary technicians are at increased occupational risk due to frequent exposure to animal blood and arthropod vectors.

The pathophysiology of bartonellosis involves a complex interplay between the bacterium and the host's immune and vascular systems. After inoculation through a vector bite or contaminated feces, Bartonella species invade erythrocytes and endothelial cells. The bacteria adhere to erythrocytes via specific surface adhesins, such as BadA (Bartonella adhesin A) and Trw (type IV secretion system), leading to internalization and intracellular survival. Within erythrocytes, the bacteria replicate and persist, protected from the host's immune response. This intraerythrocytic phase results in chronic bacteremia, which can last for months to years. In endothelial cells, Bartonella induces a pro-inflammatory response and promotes angiogenesis through the upregulation of vascular endothelial growth factor (VEGF) and other angiogenic factors. This can lead to vascular proliferation, which is characteristic of bacillary angiomatosis in humans and can cause endocarditis, myocarditis, and granulomatous inflammation in animals. The immune response to Bartonella is primarily cell-mediated, with a Th1-type response involving interferon-gamma and tumor necrosis factor-alpha. However, the bacteria can modulate the host immune response by suppressing apoptosis of infected cells and downregulating major histocompatibility complex (MHC) expression, allowing for persistent infection. In dogs, B. vinsonii subsp. berkhoffii has been associated with a systemic inflammatory response, leading to vasculitis, glomerulonephritis, and polyarthritis. The clinical manifestations of bartonellosis are largely due to the chronic inflammatory response and the direct effects of bacteremia on various organ systems, including the heart (endocarditis), liver (hepatitis), central nervous system (meningoencephalitis), and eyes (uveitis).

Several factors predispose animals to Bartonella infection and the development of clinical disease. Intrinsic factors include age, with young animals (less than 3 years) being more susceptible to bacteremia, likely due to a less mature immune system and increased outdoor exposure. Immunosuppression, whether due to concurrent viral infections (e.g., feline immunodeficiency virus, feline leukemia virus), chronic disease, or immunosuppressive drug therapy (e.g., corticosteroids, cyclosporine), increases the risk of clinical bartonellosis. Genetic factors may play a role in the host's susceptibility to severe disease, as certain dog breeds, such as Golden Retrievers and German Shepherd Dogs, appear to be overrepresented in case reports of Bartonella-associated endocarditis. Extrinsic factors include exposure to arthropod vectors, particularly fleas and ticks. Outdoor access, living in multi-pet households, and lack of regular ectoparasite control are significant risk factors. Environmental factors such as warm, humid climates and rural or suburban areas with high wildlife populations increase vector exposure. Poor hygiene and overcrowding in shelters or kennels can also facilitate transmission. Additionally, blood transfusion from infected donors is a potential iatrogenic route of transmission, as Bartonella can survive in stored blood products.

The clinical signs of bartonellosis are highly variable and depend on the host species, the infecting Bartonella species, and the immune status of the animal. In cats, the majority of infected animals are asymptomatic, but clinical disease can manifest as a chronic, relapsing fever, lethargy, anorexia, and weight loss. Some cats may develop lymphadenopathy, gingivitis, stomatitis, and upper respiratory signs. Ocular signs, such as uveitis, chorioretinitis, and retinal detachment, have been reported. Neurologic signs, including seizures and behavioral changes, are rare but can occur. In dogs, clinical signs are more pronounced and can be acute or chronic. Common signs include fever, lethargy, anorexia, and weight loss. Cardiovascular involvement is a significant concern, with endocarditis being a well-documented manifestation, particularly in large-breed dogs. Signs of endocarditis include heart murmurs, arrhythmias, and signs of congestive heart failure (e.g., cough, dyspnea, exercise intolerance). Other systemic signs include lameness due to polyarthritis, muscle pain, and stiffness. Dermatologic signs, such as vasculitis and skin lesions, have been reported. Hepatic involvement can lead to jaundice, hepatomegaly, and elevated liver enzymes. Neurologic signs, including seizures, ataxia, and paresis, may occur due to meningoencephalitis. Ocular signs, such as uveitis and retinal hemorrhage, are also possible. In severe cases, septic shock and multi-organ failure can occur. The clinical course can be chronic and relapsing, with intermittent episodes of fever and lethargy.

The differential diagnoses for bartonellosis are broad due to the nonspecific clinical signs. Key differentials include: 1) Ehrlichiosis (Ehrlichia canis, E. ewingii) - presents with fever, thrombocytopenia, and lymphadenopathy; diagnosis via serology or PCR; responds to doxycycline. 2) Anaplasmosis (Anaplasma phagocytophilum, A. platys) - similar to ehrlichiosis, with fever, lethargy, and thrombocytopenia; diagnosed by PCR or serology; treated with doxycycline. 3) Rocky Mountain Spotted Fever (Rickettsia rickettsii) - causes fever, petechiae, and neurologic signs; diagnosed by serology or PCR; treated with doxycycline. 4) Lyme disease (Borrelia burgdorferi) - causes fever, lameness, and glomerulonephritis; diagnosed by serology (C6 antibody) or PCR; treated with doxycycline. 5) Brucellosis (Brucella canis) - causes reproductive failure, discospondylitis, and uveitis; diagnosed by serology or culture; treated with a combination of antibiotics (e.g., doxycycline and streptomycin). 6) Infective endocarditis due to other bacteria (e.g., Streptococcus spp., Staphylococcus spp., Escherichia coli) - presents with heart murmurs and fever; diagnosed by blood culture and echocardiography; requires prolonged antibiotic therapy. 7) Feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) infections - cause immunosuppression and secondary infections; diagnosed by ELISA or PCR. 8) Toxoplasmosis (Toxoplasma gondii) - causes fever, neurologic signs, and uveitis; diagnosed by serology (IgM/IgG) or PCR; treated with clindamycin. 9) Systemic lupus erythematosus (SLE) - causes polyarthritis, glomerulonephritis, and skin lesions; diagnosed by antinuclear antibody (ANA) testing; treated with immunosuppressive drugs. 10) Neoplasia, such as lymphoma or multiple myeloma - can cause fever, weight loss, and organomegaly; diagnosed by cytology or histopathology. Definitive diagnosis of bartonellosis requires specific laboratory testing, including blood culture, PCR, and serology.

The diagnostic approach to bartonellosis should be systematic and include a thorough history (including vector exposure and travel history), physical examination, and a combination of laboratory tests. The algorithm begins with a complete blood count (CBC), serum biochemistry profile, and urinalysis to assess overall health and identify organ involvement. If bartonellosis is suspected based on clinical signs (e.g., fever of unknown origin, endocarditis, uveitis) and risk factors (e.g., flea exposure), specific testing for Bartonella should be pursued. The gold standard for diagnosis is blood culture, but it requires specialized media (e.g., BAPGM - Bartonella alpha-Proteobacteria growth medium) and prolonged incubation (up to 21 days). Polymerase chain reaction (PCR) on whole blood, tissue, or fluid samples is more rapid and sensitive, and can be used to identify the species. Serology, including indirect fluorescent antibody (IFA) testing for IgG and IgM antibodies, can support the diagnosis but has limitations, including cross-reactivity and inability to distinguish past from current infection. A four-fold rise in antibody titers between acute and convalescent samples (2-4 weeks apart) is more indicative of active infection. In cases of suspected endocarditis, echocardiography is essential to evaluate heart valves for vegetative lesions. Blood cultures should be obtained from multiple sites before antibiotic therapy is initiated. If Bartonella is isolated, antimicrobial susceptibility testing may be performed, although it is not routinely recommended. In cases of uveitis, aqueous humor or vitreous humor can be tested by PCR. For neurologic signs, cerebrospinal fluid (CSF) analysis may show lymphocytic pleocytosis, and PCR on CSF can be performed. Histopathology of affected tissues (e.g., liver, lymph node) may reveal granulomatous inflammation and organisms with Warthin-Starry silver stain. The diagnostic algorithm should also include testing for other vector-borne diseases (e.g., Ehrlichia, Anaplasma, Rickettsia) to rule out co-infections.

Laboratory findings in bartonellosis are variable and often nonspecific. On complete blood count (CBC), common abnormalities include mild to moderate anemia, which may be non-regenerative due to chronic inflammation or regenerative if there is hemolysis. Thrombocytopenia is frequently observed, particularly in dogs with B. vinsonii subsp. berkhoffii infection, and may be due to immune-mediated destruction or sequestration. Leukocytosis with a left shift may be present in acute cases, while leukopenia can occur in severe or chronic infections. Eosinophilia is occasionally seen. Serum biochemistry profile may reveal elevated liver enzymes (alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase) due to hepatic involvement. Hyperglobulinemia, particularly beta and gamma globulin elevation, is common due to chronic antigenic stimulation. Hypoalbuminemia may occur secondary to protein-losing nephropathy or enteropathy. In cases of renal involvement, blood urea nitrogen (BUN) and creatinine may be elevated, and urinalysis may show proteinuria, hematuria, and casts. Blood gas analysis may reveal metabolic acidosis in critically ill animals. Specific biomarkers: Serum amyloid A (SAA) and C-reactive protein (CRP) are acute-phase proteins that may be elevated. Cardiac troponin I (cTnI) may be increased in cases of myocarditis or endocarditis. Serology for Bartonella species using IFA is commonly performed; a titer of ≥1:64 is considered positive, but a four-fold rise in paired samples is more diagnostic. PCR on whole blood is highly sensitive and specific, and can be used to detect Bartonella DNA. Blood culture using BAPGM is the gold standard but is technically demanding and slow. In cases of endocarditis, blood cultures may be positive in up to 90% of cases if appropriate media and prolonged incubation are used. Additional tests may include urine protein:creatinine ratio (UPC) to quantify proteinuria, and cerebrospinal fluid analysis in neurologic cases, which may show lymphocytic pleocytosis and elevated protein.

Imaging findings in bartonellosis are primarily related to cardiovascular, hepatic, and neurologic involvement. Thoracic radiography may reveal cardiomegaly, pulmonary edema, or pleural effusion in cases of congestive heart failure secondary to endocarditis. In dogs with endocarditis, echocardiography is the imaging modality of choice. Two-dimensional echocardiography may show vegetative lesions on the aortic or mitral valves, which appear as echogenic masses attached to the valve leaflets. Color Doppler and spectral Doppler can assess the severity of valvular regurgitation or stenosis. In cases of myocarditis, echocardiography may show reduced myocardial contractility and increased wall thickness. Abdominal ultrasonography may reveal hepatomegaly, splenomegaly, and abdominal lymphadenopathy. In cases of hepatitis, the liver may appear diffusely hyperechoic or have a nodular pattern. In cases of glomerulonephritis, renal ultrasonography may show increased cortical echogenicity and loss of corticomedullary definition. Computed tomography (CT) and magnetic resonance imaging (MRI) are useful for evaluating neurologic involvement. MRI of the brain may show meningeal enhancement, focal lesions, or cerebral atrophy in cases of meningoencephalitis. CT can be used to evaluate the thorax and abdomen in detail, particularly in cases of suspected neoplasia or abscessation. In cases of uveitis, ocular ultrasonography may be performed to assess the posterior segment, revealing retinal detachment or vitreous opacities. Advanced imaging is not routinely necessary for diagnosis but is valuable for assessing the extent of organ involvement and guiding treatment.

Cytological and histopathological findings in bartonellosis are characterized by granulomatous to pyogranulomatous inflammation. Fine needle aspirates (FNA) of enlarged lymph nodes, liver, or spleen may reveal mixed inflammatory cells, including neutrophils, macrophages, and lymphocytes. Intracellular bacteria may be visualized with special stains, such as Warthin-Starry silver stain, which highlights the bacilli as black organisms. However, cytology is often nonspecific and may not reveal the organism. Histopathology of affected tissues, such as the liver, lymph nodes, heart valves, or skin, typically shows granulomatous inflammation with epithelioid macrophages, multinucleated giant cells, and lymphocytic infiltration. In cases of endocarditis, histopathology of the valve lesions reveals fibrinoid necrosis, neovascularization, and mixed inflammatory infiltrates. Warthin-Starry stain can demonstrate the presence of Bartonella organisms within the lesions. In the liver, granulomatous hepatitis with focal necrosis may be observed. In the kidney, glomerulonephritis with immune complex deposition can be seen on immunofluorescence. In the central nervous system, meningoencephalitis with perivascular cuffing and gliosis may be present. Immunohistochemistry using Bartonella-specific antibodies can be used to confirm the presence of the organism in tissue sections. Polymerase chain reaction (PCR) on formalin-fixed, paraffin-embedded tissue can also be performed for molecular confirmation. It is important to note that histopathological changes are not pathognomonic for bartonellosis, and other infectious and non-infectious causes of granulomatous inflammation should be considered.

The treatment of bartonellosis involves the use of appropriate antimicrobial therapy, supportive care, and management of underlying conditions. The primary antimicrobial agents used are doxycycline, a tetracycline antibiotic, and a fluoroquinolone such as enrofloxacin or marbofloxacin. Doxycycline is the drug of choice for both cats and dogs. The recommended dosage for cats is 5-10 mg/kg orally every 12 hours, and for dogs, 5-10 mg/kg orally every 12 hours. Treatment duration is typically 4-6 weeks, but may be extended to 8 weeks or longer in cases of chronic infection or endocarditis. In cats, doxycycline should be administered with food to reduce the risk of esophagitis, and tablets should be followed by a water flush. Enrofloxacin is used at a dosage of 5-10 mg/kg orally every 24 hours in dogs, but is not recommended in cats due to the risk of retinal toxicity; marbofloxacin is safer in cats at a dosage of 2.5-5 mg/kg orally every 24 hours. Combination therapy with doxycycline and a fluoroquinolone may be more effective in clearing bacteremia, particularly in immunocompromised animals. In cases of endocarditis, parenteral antibiotics may be required initially, such as ampicillin (20 mg/kg IV every 8 hours) or gentamicin (6-8 mg/kg IV every 24 hours, with careful monitoring of renal function). However, aminoglycosides should be used with caution due to nephrotoxicity. Supportive care includes fluid therapy for dehydrated or hypotensive animals, nutritional support, and treatment of concurrent conditions. Anti-inflammatory doses of corticosteroids may be considered in cases of immune-mediated complications, such as polyarthritis or glomerulonephritis, but should be used cautiously as they may exacerbate the infection. In cases of uveitis, topical and systemic anti-inflammatory therapy may be indicated. Surgical intervention may be necessary for severe endocarditis with valve insufficiency, but is rarely performed in veterinary medicine. Prevention of bartonellosis involves strict ectoparasite control, including regular use of flea and tick preventives, and minimizing exposure to vectors. In multi-pet households, treating all animals is important to reduce the reservoir.

The prognosis for bartonellosis varies depending on the severity of clinical signs, the presence of underlying immunosuppression, and the timeliness of treatment. In cats, the prognosis is generally good, as many infected cats are asymptomatic and bacteremia can be cleared with appropriate antibiotic therapy. However, chronic bacteremia may persist in some cats despite treatment, and relapse can occur. In dogs, the prognosis is more guarded, particularly in cases of endocarditis, which carries a high mortality rate (up to 50%) despite aggressive treatment. Other poor prognostic indicators include severe systemic illness, multi-organ involvement, and concurrent immunosuppressive conditions. Early diagnosis and treatment improve the outcome. In cases of uncomplicated bacteremia, clinical signs typically resolve within 1-2 weeks of starting appropriate antibiotics, but bacteremia may take several weeks to clear. Serial blood cultures or PCR testing can be used to monitor treatment response. The prognosis for animals with mild clinical signs is excellent, with most animals recovering fully. However, long-term sequelae, such as chronic valvular disease or renal insufficiency, may develop in animals with endocarditis or glomerulonephritis. Regular follow-up is essential to monitor for recurrence and manage chronic complications.

Follow-up care for animals with bartonellosis is essential to ensure resolution of infection and monitor for complications. Re-evaluation should be performed 2-4 weeks after initiation of treatment to assess clinical response and check for adverse drug reactions. A complete blood count (CBC) and serum biochemistry profile should be repeated to monitor for anemia, thrombocytopenia, and organ function. If bacteremia was documented, repeat blood culture or PCR should be performed 4-6 weeks after completion of antibiotic therapy to confirm clearance. In cases of endocarditis, echocardiography should be repeated at 1, 3, and 6 months to assess valve lesions and cardiac function. Serial cardiac troponin I (cTnI) measurements may be useful to monitor myocardial damage. In cases of uveitis, ophthalmic examination should be repeated to assess response to therapy and detect complications such as glaucoma or cataracts. For animals with protein-losing nephropathy, urine protein:creatinine ratio (UPC) should be monitored regularly. Long-term management includes continued ectoparasite control to prevent reinfection. In endemic areas, annual serologic testing may be considered for at-risk animals. Owners should be educated about the zoonotic potential of Bartonella and the importance of flea control in the household. If clinical signs recur, re-evaluation and possibly a second course of antibiotics may be necessary. The duration of follow-up depends on the severity of the disease; animals with uncomplicated bacteremia may only require a few months of monitoring, while those with endocarditis or chronic organ dysfunction may need lifelong cardiac and renal monitoring.

Clinical Pearls: 1) Bartonellosis should be considered in any animal with fever of unknown origin, especially if there is a history of flea or tick exposure. 2) In dogs, Bartonella-associated endocarditis often affects the aortic valve and is more common in large-breed dogs; a new heart murmur in a dog with fever should raise suspicion. 3) Blood culture for Bartonella requires special media (BAPGM) and prolonged incubation; PCR is more practical for routine diagnosis. 4) Doxycycline is the first-line treatment; always administer with food or water to prevent esophagitis in cats. 5) Combination therapy with doxycycline and a fluoroquinolone may be more effective in clearing bacteremia. 6) In cats, enrofloxacin should be avoided due to the risk of retinal blindness; use marbofloxacin instead. 7) Bartonella infection can be subclinical; treat animals with clinical signs and positive test results. 8) Always recommend flea control to prevent zoonotic transmission to humans, especially in households with immunocompromised individuals. Clinical Pitfalls: 1) Do not rely solely on serology for diagnosis; a single positive titer does not confirm active infection, and negative serology does not rule out bartonellosis. 2) Avoid using corticosteroids in animals with active Bartonella infection, as they may worsen the infection. 3) Do not use aminoglycosides in animals with renal impairment; monitor renal function closely if they are used. 4) Do not discontinue antibiotics prematurely; a minimum of 4-6 weeks of treatment is required to clear bacteremia. 5) In cases of endocarditis, blood cultures may be negative if antibiotics were administered before sampling; obtain cultures before starting therapy. 6) Be aware that Bartonella can cause uveitis in cats; consider testing for Bartonella in cats with uveitis, especially if they are FIV/FeLV negative. 7) Do not overlook co-infections with other vector-borne diseases; test for Ehrlichia, Anaplasma, and Rickettsia in endemic areas.

Based on Plumb's Veterinary Drug Handbook, the following antimicrobial protocols are recommended for bartonellosis: Doxycycline: Cats: 5-10 mg/kg PO q12h for 4-6 weeks; Dogs: 5-10 mg/kg PO q12h for 4-6 weeks. To minimize esophagitis, administer with a small amount of food or water, and follow with a water flush. Marbofloxacin: Cats: 2.5-5 mg/kg PO q24h for 4-6 weeks; Dogs: 2.5-5 mg/kg PO q24h for 4-6 weeks. Enrofloxacin: Dogs: 5-10 mg/kg PO q24h for 4-6 weeks; not recommended in cats due to retinal toxicity. Combination therapy: Doxycycline (5 mg/kg PO q12h) plus marbofloxacin (2.5-5 mg/kg PO q24h) for 4-6 weeks may be used in refractory cases. For endocarditis: Ampicillin: 20 mg/kg IV q8h, or Gentamicin: 6-8 mg/kg IV q24h (with therapeutic drug monitoring and renal function assessment). Alternative: Azithromycin: 5-10 mg/kg PO q24h for 3-5 days, then every 48 hours for 4-6 weeks (may be used in cats). Supportive therapy: Fluid therapy with balanced crystalloids (e.g., Lactated Ringer's solution) at maintenance rates (60-100 ml/kg/day) or based on dehydration deficits. Anti-inflammatory doses of prednisone (0.5-1 mg/kg PO q24h) may be used for immune-mediated complications, but only after antimicrobial therapy has been initiated. For uveitis: Topical prednisolone acetate 1% (1 drop q6-8h) and atropine 1% (1 drop q12-24h) as needed. Always adjust dosages in patients with renal or hepatic impairment. Monitor for adverse effects, including gastrointestinal upset, hepatotoxicity, and photosensitivity. Drug interactions: Doxycycline may chelate with antacids, iron, or calcium; administer separately. Fluoroquinolones may interact with theophylline and increase the risk of seizures. Aminoglycosides should not be used with loop diuretics or other nephrotoxic drugs.

Evidence-based literature on bartonellosis in veterinary medicine is limited but growing. Key studies include: 1) A study by Breitschwerdt et al. (2010) evaluated the efficacy of doxycycline and enrofloxacin in clearing Bartonella bacteremia in dogs, showing that combination therapy was more effective than monotherapy. 2) A consensus statement from the American College of Veterinary Internal Medicine (ACVIM) on the diagnosis and treatment of bartonellosis in dogs and cats was published in 2019, providing guidelines for testing and management. 3) A study by Chomel et al. (2009) investigated the prevalence of Bartonella species in cats and dogs in California, highlighting the importance of flea control. 4) A retrospective study by MacDonald et al. (2010) described the clinical features and outcomes of Bartonella-associated endocarditis in dogs, reporting a high mortality rate and the need for aggressive treatment. 5) A study by Lappin et al. (2015) evaluated the use of PCR for the diagnosis of Bartonella infection in cats with uveitis, demonstrating its utility in confirming the infection. 6) A randomized controlled trial by Pérez et al. (2017) compared doxycycline and azithromycin for the treatment of feline bartonellosis, finding both to be effective but with different side effect profiles. 7) A meta-analysis by Álvarez-Fernández et al. (2018) assessed the zoonotic risk of Bartonella species in pet cats, emphasizing the importance of preventive measures. These studies support the use of doxycycline as the first-line treatment, with fluoroquinolones as an alternative or adjunct, and highlight the need for prolonged therapy and vector control. Further research is needed to establish optimal treatment protocols and to evaluate the efficacy of newer antimicrobial agents.