Genetic diversity of equine piroplasmosis agents in Guadeloupe (Caribbeans): first report of Theileria haneyi, evaluation of diagnostic tools and impact of horse movement.

Abstract

Equine piroplasmosis is a major tick-borne horse disease, caused by the intracellular development of piroplasms (Theileria equi sensu lato and Babesia caballi), with significant economic and sanitary consequences. In 2024, 203 blood samples were collected in Guadeloupe (Caribbean) from asymptomatic horses. Using an 18S rRNA nested PCR (nPCR) specific for each equine genus parasite, 79 samples tested positive for Theileria equi and 9 for Babesia caballi, resulting in respective prevalence of 38.9% and 4.4%. Three horses were co-infected. For B. caballi, 18S rRNA sequence analysis revealed the presence of the genotype A only. For T. equi, the genotypes A and C were evidenced as mono-infections A (16/79, 20.3% of the infected horses) or mono-infections C (15/79, 19.0% of the infected horses). Interestingly, mono-infections with T. equi genotype E (17/79, 21.5% of the infected horses) were also detected, but only on horses imported from Europe and especially from metropolitan France, where this genotype is dominant. Further characterization using published T. equi ema-1 and T. haneyi specific nPCRs revealed two major points. First, most 18S rRNA genotype C isolates (13/15) were detected using the T. haneyi specific nPCR. Second, the genotype E of T. equi could not be detected by any of these two nPCRs. Co-infection occurrence and types were then evaluated using a combination of the three analyses: 18S rRNA sequencing, T. haneyi specific nPCR and T. equi ema-1 nPCR. Horses co-infected with the genotypes A and C (T. haneyi) represented the main population (32/79, 40.5% of the infected horses), while the co-infections AE (5/79, 6.3% of the horses) and CE (2/79, 2.5% of the horses) were rare. One horse was detected with a triple infection ACE. Taking into account all detected genotypes (120), 45.0% of the isolates belonged to the genotype A (54/120), 38.3% to the genotype C T. haneyi (46/120) and 16.7% to the Eurasian genotype E (20/120). The rarity of co-infections with the genotype E and the absence of this genotype on locally born horses suggest the absence of transmission of the genotype E by locally present vector ticks. This work represents the first molecular record of Theileria haneyi in South and Central America and in the Caribbeans. We also demonstrate the introduction of T. equi genotype E from Europe with infected horses but not its installation, as well as a diagnostic issue to detect this genotype using PCR targeting ema-1 gene.