Cat Scratch Disease: An Emerging Zoonosis

Cat Scratch Disease (CSD) is an emerging zoonotic infection caused by Bartonella henselae, a gram-negative, facultative intracellular bacterium. The prevalence of disease is more common in warm, humid and temperate climates such as in developing countries like India. Bartonella henselae is primarily transmitted via cat flea (Ctenocephalides felis). Infected fleas excrete the bacteria for up to 9 days and it can survive in faeces for 3 days. As a biological vector, the cat flea spreads the infection among cats and indirectly to humans via scratches, bites, broken skin or mucous membranes contact with flea feces. Pathogenesis involves bacterial adhesion via Bartonella adhesin A (Bad A), invasion of erythrocytes and endothelial cells, angiogenesis and immune evasion through apoptosis inhibition and cytokine modulation. Domestic cats, particularly kittens under one year age, serve as the primary reservoir. Most infected cats are asymptomatic, while in humans, CSD typically presents as self-limiting regional lymphadenopathy, especially in children and adolescents. However, the disease can manifest atypically with severe systemic complications, including osteomyelitis and encephalopathy particularly in immunocompromised individuals. Diagnosis of disease relies on a combination of clinical history, serological testing, PCR and microbial culture. In immunocompromised individuals, the diagnosis is often supported by histopathological examination of skin lesions and regional lymph nodes, which may reveal lymphoid hyperplasia and prominent arteriolar proliferation, findings suggestive of CSD. Treatment depends on disease severity, while many cases resolve spontaneously, antibiotics such as azithromycin or rifampin are used for complicated cases. Prevention focuses on flea control and public education. Increasing urbanization highlights the importance of a One Health approach, integrating human, animal and environmental health.