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

Overview

• This study investigated the diversity of parasites causing equine piroplasmosis in Guadeloupe, identifying different genetic types of Theileria and Babesia species.
• It reported the first detection of Theileria haneyi in the Caribbean, assessed diagnostic methods, and examined how horse movement influences parasite distribution.

Background on Equine Piroplasmosis

• Equine piroplasmosis is a significant tick-borne disease affecting horses, caused mainly by two parasites: Theileria equi sensu lato and Babesia caballi.
• The disease leads to health problems and economic losses in the horse industry due to its effects on horse health and movement restrictions.
• Diagnosis and control depend on understanding genetic diversity of these parasites and their transmission dynamics.

Study Design and Methodology

• In 2024, researchers collected 203 blood samples from asymptomatic horses in Guadeloupe, part of the Caribbean.
• They applied nested PCR (nPCR) targeting the 18S rRNA gene specific for each parasite genus to detect infections.
• Further molecular analyses employed nPCR assays targeting specific genes (ema-1 for T. equi and a specific nPCR for T. haneyi).
• Sequencing was used to identify the genetic genotypes present in infected horses.

Key Findings on Parasite Prevalence and Genotypes

• Prevalence: 79 horses (38.9%) were positive for Theileria equi and 9 horses (4.4%) for Babesia caballi. Three horses had co-infections.
• Only genotype A of B. caballi was identified in this population.
• For T. equi, genotypes A and C were detected as single infections in approximately 20% of infected horses each.
• Notably, a third genotype, genotype E, was found only in horses imported from Europe, especially France, where genotype E is common.

Identification of Theileria haneyi and Diagnostic Insights

• Most genotype C samples correlated with Theileria haneyi, confirmed using a specific nPCR assay—a significant finding since T. haneyi had not been previously reported in the Caribbean or South/Central America.
• The genotype E of T. equi could not be detected using nPCR assays targeting ema-1 or the T. haneyi-specific gene, highlighting diagnostic limitations.
• Combining different PCR methods, co-infections with genotypes A and C (now identified as T. haneyi) were most common (40.5%). Other co-infections involving genotype E were rare.
• One horse showed a triple infection with genotypes A, C, and E.
• Distribution of genotypes among isolates was 45.0% genotype A, 38.3% genotype C (T. haneyi), and 16.7% genotype E.

Impact of Horse Movement and Parasite Transmission

• Genotype E was exclusively found in imported horses, and was absent in locally born horses, suggesting that local tick vectors in Guadeloupe may not transmit this genotype.
• This implies that the introduction of genotype E into the Caribbean via horse importation does not currently lead to local parasite establishment or spread.

Conclusions and Significance

• This research provides the first molecular evidence of Theileria haneyi in the Caribbean and the Americas, expanding knowledge of equine piroplasm diversity in this region.
• The findings reveal complex infection patterns including multiple genotypes and co-infections, which have implications for diagnosis and disease management.
• There is a diagnostic challenge with detecting genotype E using standard ema-1 gene PCR, indicating a need to refine molecular tools for accurate detection of all genotypes.
• Understanding the effect of horse movement on parasite introduction without local transmission helps in developing better control strategies to prevent spread of exotic genotypes.