The causative agent of the septicemic, hemolytic disease known as Oroya fever is which organism?

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

Answer: (A)

Oroya fever is caused by Bartonella bacilliformis, a bacterium transmitted by sandflies in the high Andes. It targets red blood cells and vascular endothelium, leading to bacteremia and severe hemolytic anemia during the septicemic phase. Clinically, this illness can present with fever and marked anemia, and may progress to the cutaneous verruga lesions seen in later stages. The organism can be visualized inside erythrocytes on a blood smear stained with Giemsa, a classic diagnostic clue. This distinguishes it from the other organisms: Burkholderia mallei is associated with glanders, Haemophilus aegyptius causes conjunctivitis, and Yersinia pestis causes plague with a different clinical and epidemiological profile. Thus Bartonella bacilliformis best explains the septicemic, hemolytic disease known as Oroya fever.