Comparison of five tests for the serologic diagnosis of myiasis by Gasterophilus spp. larvae (Diptera: Gasterophilidae) in horses and donkeys: a preliminary study.

This study compares five different tests used for the diagnosis of myiasis, a parasitic infection caused by Gasterophilus larvae, in horses and donkeys. These tests include double immunodiffusion, counterimmunoelectrophoresis, indirect haemagglutination, thin layer immunoassay, and diffusion-in-gel ELISA. A total of 200 animals from twelve states in Mexico were tested and the most reliable tests were found to be the thin layer immunoassay and the diffusion-in-gel ELISA.

Study Overview

• The research involved testing sera (part of the blood) from 41 horses and 159 donkeys, originating from twelve different regions in Mexico.
• The researchers aimed to identify anti-Gasterophilus antibodies in the sera. These antibodies are produced by the body’s immune system in response to infection by Gasterophilus spp. larvae.
• The five serological tests compared were Double Immunodiffusion (DD), Counterimmunoelectrophoresis (CIE), Indirect Haemagglutination (IH), Thin Layer Immunoassay (TIA), and Diffusion-in-gel ELISA (DIG-ELISA).

Findings at Necropsy

• After the animals died, a necropsy (similar to an autopsy in humans) was performed. It was found that 33 out of 41 horses and 24 out of 159 donkeys were infected with G. intestinalis and/or G. nasalis.
• G. intestinalis was the species most commonly found in both the horses and donkeys.

Analysis of Sera

• When the sera were tested using the DD method, 21.2% of horses and 8% of donkeys showed a positive result for infection.
• Testing with the CIE method revealed a sensitivity of 69.7% in horses and 32% in donkeys. In this context, ‘sensitivity’ refers to the ability of the test to correctly identify those infected.
• Application of the IH method showed positive results of 87.9% in horses and 48% in donkeys.
• When the sera were tested using the TIA method, sensitivities of 93.9% in horses and 96% in donkeys were achieved. This indicates that TIA was a highly reliable method for detecting the infection.
• Lastly, using the DIG-ELISA method to analyze the horses’ sera resulted in a high sensitivity of 93.9%.

Conclusion

• The study revealed that the two most reliable serological tests for diagnosing myiasis in horses and donkeys were TIA and DIG-ELISA. These tests showed the highest sensitivity, meaning they were best at correctly identifying animals with the infection. This is important information for improving the diagnosis and subsequent treatment of myiasis in horses and donkeys.