Validation of French Antibody ELISA for Liver Fluke

Summary

Existing faecal egg tests for liver fluke (Fasciola hepatica) in cattle are inaccurate, while a blood test (ELISA) to detect antibody used in NSW Agriculture laboratories lacks sensitivity. This project validated the Institut Pourquier (France) antibody-ELISA kit under Australian conditions. Over 1 500 samples were tested from artificial and natural infections, including paramphistomes (conical flukes) and tropical liver fluke (F.gigantica). The test had high specificity (>95%) and sensitivity (99%). It was substantially more sensitive than the existing blood test. Paramphistomes did not interfere with its accuracy, nor did previous nematode (roundworm) infection affect responses to later fluke infection.

An established in-house test and the commercial kit detected antibodies in early immature liver fluke infection, but kit positives were earlier (2 weeks), and reached maximum levels sooner (8 weeks). Positive results continued for 18 months without reinfection. There was no spike in antibodies when flukes matured, and no relationship between amount of antibody and numbers of adults or eggs. Pourquier kit is easy to use and is suitable for veterinary laboratories with an ELISA microplate reader. There is good standardisation and quality control of reagents. Kit can also detect antibodies in milk (requires further validation for Australia). Fluke infective stages (metacercaria) are eaten by cattle mainly from October to May. So, when used in fluke control programs to test cattle herds (beef or dairy) or individual animals, newly infected stock will not react strongly until after late November. Limitations are typical of antibody-ELISAs: inability to distinguish between current and previous infections, and potential for cross-reactions. Until new generation tests (antigen-detection or molecular procedures) are widely available, it will be useful.