Probable scrub typhus-like infection in Colombia: seroconversion and serological reactivity to Orientia spp. among patients with acute undifferentiated febrile illness in Villeta municipality

Background Scrub typhus, caused by Orientia spp., is a mite-borne disease historically restricted to the Asia-Pacific region. Autochthonous cases have been confirmed in southern Chile, while serological evidence has been reported in Peru, Honduras and Colombia, suggesting wider distribution in Latin America. Identifying recent exposure among febrile patients is essential to evaluate its role in acute undifferentiated febrile illness (AUFI) etiology. Aim To assess the possible implication of Orientia infection as a cause of AUFI in Villeta, Colombia. Methods Between September and December 2021, patients with AUFI were recruited. Whole-blood samples were tested for Orientia DNA by real-time PCR targeting the 16S rRNA gene. Acute and convalescent serum samples were analyzed for IgG antibodies by IFA and ELISA, with paired samples titration to assess seroconversion. Reactive sera were further confirmed by Western blot. Results Forty-one acute whole-blood samples were tested by qPCR; no Orientia DNA was detected. Serology identified antibodies in 27 % (11/41) of patients: six positive by ELISA, two by IFA, and three by both methods. Based on paired sera, eight cases (20 %) were classified as recent infections, including cases of seroconversion, and three (7 %) as previous exposures. Western blot confirmed specific reactivity against Orientia antigens in all positive samples. Conclusions This study provides serological evidence of Orientia circulation among febrile patients in Villeta, Colombia, including clear cases of seroconversion. Western blot validated reactivity against immunodominant proteins. Findings suggest a local scrub typhus–like illness and highlight the need for pathogen isolation and genetic characterization to clarify its contribution to AUFI.