Abstract
<title>Abstract</title> <p> A sandfly-borne pathogen, Chandipura Virus (CHPV), causes sporadic Acute Encephalitis Syndrome (AES) outbreaks with high mortality among children in India. In response to AES cases in July 2024 in Udaipur and Dungarpur districts of Rajasthan, we conducted an outbreak investigation to characterize the outbreak and assess potential animal and vector links. We defined a case as the presentation of acute fever with new-onset seizures or change in mental status during the period 01 June−14 August 2024, among residents aged <16 years in these districts. We conducted a stimulated passive case search in all hospitals, interviewed all suspect cases, and collected sandfly samples from cases’ homes and neighbourhoods for species identification. We collected blood samples from cases and cattle, as well as from neighbourhood houses, for CHPV testing. We identified 58 suspect cases (Dungarpur: 15; Udaipur: 43), including 13 (22%) deaths. We collected 247 sandflies; identified species were <italic>Phlebotomus papatasi and Sergentomiya punjabensis.</italic> We collected 10 human blood samples; one tested positive. Of 129 cattle blood samples, 12% (7/60) in Udaipur and 26% (18/69) in Dungarpur tested positive for CHPV. The detection of Chandipura virus in cattle, combined with sandfly presence near animals and human cases, is consistent with possible zoonotic and sandfly-mediated transmission, but the transmission chain was not fully established. </p>