The causative agent of Oroya fever is which organism?

• A. Burkholderia mallei
• B. Bartonella bacilliformis
• C. Haemophilus aegyptius
• D. Yersinia pestis

Answer: (B)

Oroya fever is Carrion’s disease seen in the Andes, transmitted by sandflies, with the acute phase causing fever and severe anemia due to infection of red blood cells. The organism responsible is Bartonella bacilliformis, a small Gram-negative bacillus that invades erythrocytes and vascular endothelium, leading to the characteristic hemolytic anemia of Oroya fever and the later skin lesions of verruga peruana. This classic association with Andean transmission and the biphasic illness distinguishes it from the other bacteria listed, which cause glanders, conjunctivitis/Brazilian purpuric fever, or plague. Keep in mind that Bartonella bacilliformis is fastidious and grows slowly, so diagnosis often depends on epidemiology and specialized testing in the right clinical context.