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Diagnosis of Equine Piroplasmosis

Equine Piroplasmosis (EP) can be diagnosed by

  •  serologic tests that detects sera antibodies against equine piroplasms and/or
  • by molecular tests that detects equine piroplasms in the circulating blood.

Each of these tests has advantages and disadvantages depending on Equine Piroplasmosis phase and diagnostics purpose. That said, to determine  Equine Piroplasmosis (EP)  freedom of infection is advisable to perform at least two different tests. 

 

See Table 1 extracted from the OIE Terrestrial Manual 2018. 

 

 

Figure 4 extracted from the VS guidance 13407.1/2018.

 

  

Equine Piroplasmosis tests explained

The serological tests  have high specificity and sensitivity  to detect chronic and/or inapparent infections. 

Several serologic tests have been developed to increase diagnostic sensitivity, such as competitive enzyme-linked immunosorbent assay (c-ELISA), the complement fixation test (CFT), and the indirect fluorescent antibody test (IFAT).

 c-ELISA

Since 2004, the c-ELISA is considered the gold standard method for the detection of chronic or innaparent phases. 

This test is reported as the most sensitive test for chronic or inapparent infection, detecting seroconversion 21 days after infection. 

  • The world organisation for animal health (OIE) and the United States Department of Agriculture (USDA) approved the c-ELISA (VMRD® Inc., Pullman, WA, USA ) as one of the regulatory test for the screening of horses for both Babesia caballi and Theileria equi before international transport to non-endemic nations.
  • c-ELISA for Babesia caballi and Theileria equi has a sensitivity of 95.0 % and 100% and a specificity of 99.5% and 100% , respectively.
  • c-ELISA has more sensitivity than CFT and IFAT.
  • c-ELISA can only detect Piroplasmosis after 21 days post infection.

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 CFT

The complement fixation test (CFT) has been used in the past by some countries and is still widely used in some regions, namely in the USA, to qualify horses for importation. 

  • CFT is accurate for detection of early (acute)  infections for which purpose it shows good sensitivity and specificity.
  • CFT detects piroplasmosis 8 to 11 days after infection. 
  • CFT is a highly specific test but lacks sensitivity in chronic and inapparent phases of infection;
  • Therefore, CFT should only be used in cases of acute infection.

 

IFAT

The indirect fluorescent antibody test (IFAT) it is the supplementary test when results obtained by c-ELISA and CFT are inconclusive.  This test demonstrate high specificity but lacks sensitivity. 

  • IFAT can detect seroconversion 3 to 20 days after infection.
  • Experimental infection studies have shown that a wider interval for detection of early infections. 
  • One challenge with the IFAT is the need to dilute sera to reduce non-specific  binding and subsequent background, which may preclude identification of intra-erythrocytic parasites and decrease the sensitivity of this test.

 

Identification of the agent 

     qPCR 

    Quantitative PCR (qPCR)  is a molecular or DNA based diagnostic techniques used to detect the parasite DNA in circulating blood.

    • qPCR techniques are the more sensitive techniques than any other methods and are best for diagnosis of animal in early (acute) infections and in chronic infections.
    • However, it has been demonstrated that after treatment the animal can be qPCR negative but c-ELISA positive for 24 months after clearance of the parasite. 

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