Molecular detection of Ehrlichia ruminantium in ticks from ruminants during the 2021 Rift Valley fever outbreak in Mananjary, Madagascar.

Abstract

Ehrlichia ruminantium, the causative agent of heartwater, is a tick-borne pathogen affecting livestock in Africa and the Caribbean. This disease is transmitted primarily by Amblyomma variegatum ticks and poses a significant threat to animal health. In Madagascar, the prevalence of E. ruminantium remains poorly documented. During a Rift Valley fever (RVF) outbreak in Mananjary, Madagascar (April-May 2021), we conducted a field study to assess the circulation of vector-borne pathogens in ticks collected from ruminants. Ticks were morphologically identified, and DNA was extracted for quantitative PCR targeting the pCS20 gene of E. ruminantium. Statistical analyses were performed to explore associations between tick infection status, ruminant health, and infestation levels. A total of 332 ticks were collected from 25 ruminants. The tick species identified included Rhipicephalus microplus (51.5%) and Amblyomma variegatum (48.2%). E. ruminantium DNA was detected in 5.1% (17/332) of ticks, consisting of 16 A. variegatum and one R. microplus, with the majority being male. No association was observed between ruminant clinical signs and the presence of infected ticks. This study provides the first molecular evidence of E. ruminantium circulation in ticks from Madagascar during an RVF outbreak. Our findings emphasize the need for improved disease surveillance and integrated tick control strategies to mitigate the impact of heartwater on livestock.