Early-life exposure to vector-borne pathogens in moose calves from Finland: molecular and phylogenetic evidence

Vector-borne pathogens are expanding in northern Europe as climate and host-vector communities change, shifting vector distributions, yet baseline data from boreal systems and early-life wildlife hosts remain scarce. Moose (Alces alces) represent a useful sentinel species for monitoring pathogen circulation at the wildlife-vector interface because they occupy diverse habitats and are widely distributed across boreal ecosystems. In this study, we investigated the occurrence and phylogenetic location of Trypanosoma spp., Anaplasma phagocytophilum and Bartonella spp. in moose calves during their first season of life, providing insight into early exposure patterns relevant to integrated surveillance. Whole-blood samples from 23 calves (twenty-two hunted animals and one found dead) were screened by PCR and sequenced for 18S rRNA (Trypanosoma), 16S rRNA (A. phagocytophilum) and rpoB (Bartonella).

At least one pathogen was detected in 44% (10/23) of calves. Trypanosoma DNA was found in 35% (8/23) and all isolates clustered within the TthII lineage of the Trypanosoma theileri complex, including three novel 18S rRNA haplotypes deposited in GenBank. Anaplasma phagocytophilum was detected in 17% (4/23), with sequences identical to reference haplotypes reported from Eurasia. Bartonella spp. were detected in 9% (2/23), with the rpoB haplotype identical to a lineage previously reported from North America and closely related to ruminant-associated Bartonella species.

The detection of multiple vector-borne hemoparasites in moose calves indicates that exposure to diverse pathogens can occur early in life in boreal cervid communities. Phylogenetic relationships suggest that the detected lineages are part of widely distributed pathogen populations rather than locally confined variants. Although this study was not designed to quantify zoonotic risk, documenting pathogen circulation in free-ranging moose may support One Health-oriented surveillance integrating wildlife hosts, vectors, and environmental factors, particularly in regions where hunters and rural communities may be exposed to vector-borne pathogens. These findings establish the grounds for future monitoring efforts aimed at understanding pathogen dynamics, host condition, and emerging vector-borne risks in boreal ecosystems of northern Europe.