First cluster of relapsing fever compatible with louse-borne transmission in southern Saudi Arabia: An eight-case series from Najran.

Louse-borne relapsing fever (LBRF), caused by Borrelia recurrentis, is a neglected vector-borne infection associated with overcrowding, migration, and poor hygiene conditions. We describe eight spatiotemporally linked cases of Borrelia spp. relapsing fever compatible with louse-borne transmission identified in Najran, southern Saudi Arabia. This retrospective case series included eight patients diagnosed between March 2013 and August 2013, identified during routine malaria smear examination. Seven patients were undocumented East African migrants who had recently entered through the Yemeni border. One patient was an Indian agricultural worker residing with a newly arrived Somali national. All patients presented with high-grade fever. Thrombocytopenia and hyperbilirubinemia were observed in the majority of cases. Diagnosis was established by visualization of spirochetes on thick and thin blood films obtained during febrile episodes. Louse-borne transmission was presumed based on epidemiological and clinical context; tick-borne relapsing fever cannot be definitively excluded in the absence of molecular confirmation and vector identification. All patients received appropriate antimicrobial therapy, with favorable clinical outcomes and no mortality. Infection control and empirical delousing measures were implemented, and no additional cases were identified following intervention. To our knowledge, this represents the first documented cluster of relapsing fever compatible with louse-borne transmission in Saudi Arabia.