A serological test based on mutated recombinant Fasciola hepatica cathepsin L protease for the diagnosis of equine fasciolosis.

Overview

• This research developed and optimized a blood test to detect antibodies against the liver fluke parasite, Fasciola hepatica, in horses.
• The test uses a modified form of a parasite protein (cathepsin L protease) to improve accuracy and was validated with horse blood samples from Ireland and Switzerland.

Background and Importance

• Fasciola hepatica is a parasite commonly infecting livestock like sheep and cattle, causing liver damage, health problems, and economic losses.
• Horses can also be infected but usually do not develop full patent infections (where parasites reproduce), so infections may be underdiagnosed.
• Accurate detection in horses is important to address potential underreported infections and to improve animal welfare, especially in regions where horses graze alongside ruminants.

Development of the Serological Test

• The test is based on detecting antibodies in horse serum that react to a key liver fluke protein, cathepsin L1 protease (FhCL1), using an ELISA technique.
• Researchers bioengineered mutated versions of this protein to modify diagnostic epitopes (parts recognized by antibodies) to enhance test specificity and reduce false positives.
• Different homologues (related variants) of FhCL proteases with canonical (original) and mutated epitopes were produced recombinantly.
• After screening, the best-performing mutated antigen was selected to maximize diagnostic accuracy.

Testing and Validation

• The optimized ELISA test was applied to 175 serum samples from Irish horses, some suspected of liver fluke infection.
• Seven suspected horses were monitored longitudinally for a year after receiving liver fluke treatment (triclabendazole).
• A large cohort of 368 Swiss horse serum samples was tested to estimate prevalence in another region.

Results

• The test sensitivity (ability to correctly identify infected horses) was 65%, while specificity (ability to correctly identify uninfected horses) was high at 97.4%.
• In treated horses, antibody levels decreased below detection thresholds within 6 to 9 months, correlating with improved liver enzyme levels, indicating recovery.
• This follow-up helped define test cutoff values to better distinguish between borderline and clearly positive results.
• In Swiss horses, prevalence of infection was estimated between 3.5% and 5.7%, suggesting the infection might be more common than previously recognized.

Conclusions and Implications

• The newly developed ELISA using a mutated FhCL antigen provides a reliable tool for diagnosing liver fluke infection in horses.
• Equine fasciolosis may be an underreported or neglected infection, particularly in regions where horses share pastures with infected ruminants.
• Reliable diagnostics are essential for identifying cases, especially in horses with unexplained liver disease symptoms or in endemic areas.
• Early detection combined with effective treatment could improve animal health and reduce economic losses associated with liver fluke infections in horses.