Molecular detection of Ehrlichia chaffeensis in marsh deer (Blastocerus dichotomus) and their parasitic Amblyomma triste ticks in Argentina suggests a local transmission cycle

Abstract Background Since the first finding of Ehrlichia chaffeensis in the Argentinian marsh deer populations in 2018, we have conducted ongoing surveillance efforts to better understand the ecological and epidemiological dynamics of this zoonotic tick-borne pathogen in the region. Methods Over a period of 7 years (2018–2024) we analyzed blood and tissue samples from 40 marsh deer (Blastocerus dichotomus) and 13 parasitic Amblyomma triste ticks in the Paraná River Delta, Argentina. Results We identified E. chaffeensis DNA in two deer blood samples and in the salivary glands of three A. triste ticks parasitizing one of those deer. The approach used for E. chaffeensis detection in the tick sample ensured that the identified DNA came from an active tick infection, not residual host blood in the gut. After sequencing generic genes (16S ribosomal RNA [rRNA], 23S rRNA and groEl) and the specific E. chaffeensis variable-length polymerase chain reaction target (VLPT) molecular marker, we identified a genotype previously reported in Argentina. Conclusions This first-time contemporary detection of zoonotic E. chaffeensis in both a wild vertebrate host and its parasitic generalist ticks in a natural setting, provides direct evidence of a putative transmission cycle in Argentina, highlighting the need of implementing multidisciplinary surveillance systems. Graphical Abstract