The number of horses in France infected with the blood parasite Theileria equi seem to have increased over the years, researchers report.
Clémence Nadal and her fellow researchers carried out a major investigation in France into the circulation of Babesia caballi and Theileria equi, which cause equine piroplasmosis.
The parasites, which are normally spread by ticks, pose major health and economic issues for the equine industry.
The researchers, writing in the journal Pathogens, tested for the seroprevalence of each parasite in 16,127 equine serum samples obtained between 1997 and 2003 from all over France.
The seven-year collection of samples was analysed using complement fixation tests, which can detect the presence of specific antibodies or specific antigens in samples.
The study team found that 18.5% of the samples were positive for at least one of the piroplasms, with 13.2% being positive for T. equi and 9.5% being positive for B. caballi. In all, 4.1% of the samples were positive for both parasites.
Among the positive samples, nearly one in four were positive for both.
Seroprevalence varied widely by region, ranging from 5 to 27% for T. equi and 3 to 25% for B. caballi.
Horses from the southern regions of France had the highest proportion of seroprevalence among the samples, while the proportion of horses having antibodies against T. equi increased over the seven years monitored in the study.
The results, they said, highlight the diverse character of the circulation of both piroplasms, which may be linked with ecological diversity and tick distribution.
The results point to an overall increase compared with previous studies conducted in the same laboratory. In samples from 1973 and 1976, 4.3% were positive; while from 1974 to 1988, 9% of samples were positive.
The authors said the results confirm the presence of the parasites across the entire French territory, with five regions in southern France being particularly affected.
“By shedding light on the most strongly impacted regions, studies focusing on the dynamics of piroplasm circulation can now target specific areas in the study of risk factors, which are still lacking to date.”
The recent establishment of equine piroplasmosis vectors previously absent from the country, such as the tick Hyalomma marginatum in the south of France, makes it particularly important to conduct further studies, they said.
“Confirming the trend observed in the years preceding our study, T. equi infections generally seem to have increased over the years.
“Given the impact of equine piroplasmosis on the French equine industry, it would be interesting to determine if this pattern still prevails today.”
The authors said that, unfortunately, because of a lack of information on individual horses whose samples were analysed, the clinical status of each horse was not known, making it impossible to relate seropositivity to any signs of disease.
They said although their serological findings amount to a good proxy for piroplasm circulation, the lack of knowledge on the clinical status of the horses and a lack of reliable estimations of the horse population by region or by year in France makes it unlikely to be a reliable estimation of national seroprevalence.
Their study, they said, fills a gap in our knowledge of the circulation of both T. equi and B. caballi in France and should serve as a basis for comparison of studies to be carried out today to monitor the evolution of equine piroplasmosis in the country.
The baseline information established through the study makes it possible to select regions for future studies on risk factors. That could lead to the design and implementation of effective targeted measures against equine piroplasms.
The study team comprised Nadal, Maud Marsot, Gaël Le Metayer, Pascal Boireau, Jacques Guillot and Sarah Bonnet, variously affiliated with a range of French institutions.
Nadal, C.; Marsot, M.; Le Metayer, G.; Boireau, P.; Guillot, J.; Bonnet, S.I. Spatial and Temporal Circulation of Babesia caballi and Theileria equi in France Based on Seven Years of Serological Data. Pathogens 2022, 11, 227. https://doi.org/10.3390/pathogens11020227