New equine piroplasmosis test shows potential for screening in the field

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Protozoa that cause piroplasmosis. Photo: Centers for Disease Control/ Steven Glenn (Public domain)

A new test developed to detect equine piroplasmosis shows real potential for on-site screening of horses, according to researchers.

The test is able to detect the presence of either of the two protozoa, Theileria equi and Babesia caballi, that cause the disease.

The test, developed by Rong Lei, Xinyi Wang and their colleagues, amplifies specific genes in each organism for identification.

Ticks transmit the protozoa responsible for the infection, which is widely distributed in Asia, Europe, Africa and South America. It causes economic loss and affects international horse movements.

There are differences between B. caballi and T. equi in both the tick vector and the horse host, which is reflected in disease severity and drug susceptibility.

Infected animals present with severe acute disease characterized by high fever, lethargy, poor appetite, swelling in the extremities, an enlarged spleen, destruction of red blood cells, a rapid heart rate, urine discoloration, and occasionally death.

Animals who recover from primary infection remain recessive carriers with fluctuating levels of the parasite.

Infectious carriers are not always symptomatic, raising the risk of spreading the disease to new areas if these horses are transported any distance.

Therefore, developing sensitive and specific diagnostic methods are essential for identifying carriers.

The researchers, writing in the journal Scientific Reports, note that several diagnostic methods are currently employed, with molecular diagnostics widely recognized for its accuracy and sensitivity.

However, there are shortcomings. For example, identification of the species involved can require a thermocycler, skilled personnel and a long detection time, which makes it inappropriate for field diagnostic applications.

The duplex tests the study team developed could allow fast identification of the equine-piroplasmosis-causing T. equi and B. caballi, showing great potential for on-site screening of horses, they say.

The developed strategy has a simpler operating process with a lower constant reaction temperature and was more suitable to test blood specimens in the field as a rapid diagnostic method compared with traditional testing using the same technology.

“Furthermore, a duplex analysis strategy based on the bc48 gene of B. caballi and the 18S rRNA gene of T. equi  … needed only 20 minutes to amplify the pathogens in horse blood specimens.”

Lei, R., Wang, X., Zhang, D. et al. Rapid isothermal duplex real-time recombinase polymerase amplification (RPA) assay for the diagnosis of equine piroplasmosis. Sci Rep 10, 4096 (2020). https://doi.org/10.1038/s41598-020-60997-1

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

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