Exposure of Mexico’s horses to pathogens behind equine piroplasmosis is high – study

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Horses in some parts of Mexico have significant exposure to the blood-borne protozoans that cause equine piroplasmosis, the results of fresh research show.
Protozoa that cause piroplasmosis. Photo: Centers for Disease Control/Steven Glenn (public domain)

Horses in some parts of Mexico have significant exposure to the blood-borne protozoans that cause equine piroplasmosis, the results of fresh research show.

Equine piroplasmosis can affect horses, mules and donkeys. The protozoans responsible are Babesia caballi and Theileria equi, both of which are spread by ticks of tropical and subtropical regions.

The diagnosis of equine piroplasmosis can be difficult because the clinical signs are not specific.

Elizabeth Salinas-Estrella and her fellow researchers, writing in the open-access journal PLOS ONE, noted that environmental factors in Mexico are suited to the persistence of both pathogens.

There was, they noted, a lack of molecular-based studies to evaluate the occurrence of both parasites in horses.

In their study, researchers took matching serum and whole blood samples from 269 horses living in 24 locations with a tropical or subtropical climate where ticks are known to be present.

The samples were tested serologically by ELISA and molecularly by nPCR and duplex qPCR.

Serological analysis showed a high number of animals were co-exposed to both pathogens. Of the 269 samples, 21.6% were positive for only T. equi, 8.9% were positive for only B. caballi, 22.7% were negative for both parasites, and 46.8% revealed exposure to both.

Hence, the total number of positive samples with antibodies against T. equi was 184 (68.4%), whereas 150 (55.7%) showed antibodies against B. caballi.

Of the 269 samples tested for the parasites by nPCR, the majority were positive for T. equi. In all, 72.9% were positive for T. equi, 1.9% were positive for B. caballi, 19.3% were negative for both parasites, and 5.9% were co-infected. Overall, 212 (78.8%) of the DNA samples were positive for T. equi, while 21 (7.8%) were positive for B. caballi.

Finally, the duplex qPCR test was performed to compare with the nPCR results, revealing T. equi prevalence of 59.11% and B. caballi prevalence of 15.24%.

From these results, 27 samples were genetically sequenced for T. equi and 13 for B. caballi, confirming the presence of both parasites that cause equine piroplasmosis, and suggesting that they are widespread in Mexico.

“This is the first study confirming the presence of B. caballi and T. equi in Mexico using both serological and molecular diagnostic methods,” they said.

The findings indicate a high level of exposure of horses in the studied areas, and highlight the risk of B. caballi and T. equi infection in horses from Mexico.

They said it was important to learn more about the transmission mechanisms of equine piroplasmosis, because the disease can be undetected once equines pass the acute stage and, mostly in the case of T. equi infections, become symptom-free carriers.

Chronically infected animals represent a reservoir for the potential spread of the disease, they said.

This is a major problem because of the movement of these animals through the likes of sports competitions. The issue is further complicated by the sale or movement of horses between properties and the potential loss of clinical information along the way.

The lack of information about the presence of the disease is also a hindrance, as is limited testing, among other factors.

The study team called for an efficient and representative epidemiological study of the disease in Mexico to determine the regions where horses are at greatest risk. A study on its transmission by different ticks is also needed to help establish preventive and control measures.

The study team comprised Salinas-Estrella, Massaro Ueti, Vladislav Lobanov, Evelio Castillo-Payró, Amelia Lizcano-Mata, César Badilla, Francisco Martínez-Ibáñez and Juan Mosqueda, from a range of institutions.

Salinas-Estrella E, Ueti MW, Lobanov VA, Castillo-Payró E, Lizcano-Mata A, Badilla C, et al. (2022) Serological and molecular detection of Babesia caballi and Theileria equi in Mexico: A prospective study. PLoS ONE 17(3): e0264998. https://doi.org/10.1371/journal.pone.0264998

The study, published under a Creative Commons License, can be read here

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