Equine piroplasmosis can be difficult to diagnose due to the variable and non-specific clinical signs exhibited by infected horses. Further complicating testing, false positive and false negative results can occur on common tests.
Piroplasmosis, considered an exotic disease in the United States, was recently discovered in horses in 11 states as an investigation into an outbreak in Texas expands (read more). Animal health authorities are testing epidemiologically linked horses, but which test should they use?
Researchers from the Central Veterinary Research Laboratory in Dubai, UAE, recently noted in a study that tests for equine piroplasmosis need to be both specific and sensitive, yielding few false results.
Currently, the immunofluorescence antibody test (IFAT) and enzyme-linked immunosorbent assay (ELISA) tests are the blood tests of choice for diagnosing latent infections. The research group used these tests, as well as a newer DNA-based assay called TaqMan real-time polymerase chain reaction (PCR), to test 105 blood samples from athletic horses in Dubai.
The researchers found that in total, 30 horses (28.6%) tested positive using the two serological and one PCR test. In addition, they noted that:
- 33 of the 105 horses were positive by TaqMan real-time PCR;
- 38 of the 105 horses were positive using the IFAT or ELISA tests;
- Eight of the 105 horses were only positive by the serological tests (IFAT or ELISA), and
- Three of the 105 horses were only positive with PCR.
The results show that the widely-used serology tests can fail to detect infected horses, possibly in horses with new infections in which antibodies might have not yet developed. Further, PCR tests can also fail to detect infected horses. The researchers suggested this might occur in horses in which the antibodies persist after the piroplasms have been eliminated.
This researchers also found that horses were more commonly infected with Theileria equi than Babesia caballi; 13 (12.4%) of horses had antibodies to both parasites.
The study, "A comparative study of serological tests and PCR for the diagnosis of equine piroplasmosis," is scheduled to be published in an upcoming edition of the journal Parasitology Research. The abstract is available on PubMed.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.