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======Serology======
======Serology======
The presence of viral Abs within 24hours of the initial viraemia typically precedes clinical signs. Ab titre increases sharply then deteriorates over 6 months. Samples taken when clinical signs appear are likely to miss the Ab peak and may thus demonstrate a decreasing titre. Serological confirmation of EEE or WEE virus infection requires a four-fold or greater increase or decrease in antibody titre in paired serum samples collected 10-14 days apart. A presumptive diagnosis can be made on a single sample if an unvaccinated horse with appropriate clinical signs has antibody against only EEE or WEE virus. Maternal-derived Ab may interfere with diagnosis in foals. The serum half-life of colostral Ab in foals is around 20days.
*Complement fixation: to avoid anti-complementary effects, sera should be separated from the blood as soon as possible.
*Complement fixation (CF): to avoid anti-complementary effects, sera should be separated from the blood as soon as possible.
*Haemagglutination inhibition: titres of 1/10 and 1/20 are suspect, titres of 1/40 and above are positive.
*Haemagglutination inhibition (HAI): titres of 1/10 and 1/20 are suspect, titres of 1/40 and above are positive.
*ELISA may be used to detect viral-specific IgM to the surface glycoprotein of Venezuelan EEV, from 3 days post-onset of clinical signs up to 21 days post-infection. This is useful in acute infections where convalescent serum samples are unobtainable.
*ELISA may be used to detect viral-specific IgM to the surface glycoprotein of Venezuelan EEV, from 3 days post-onset of clinical signs up to 21 days post-infection. This is useful in acute infections where convalescent serum samples are unobtainable.
*The PRN test is very specific and can be used to differentiate between EEE and WEE infections. It is performed in duck embryo fibroblast, Vero, or BHK-21 cell cultures. Serum used in the PRN assay is tested against 100 plaque-forming units of virus. Endpoints are based on a 90% reduction in the number of plaques compared with the virus control flasks.
*The PRN test is very specific and can be used to differentiate between EEE and WEE infections. It is performed in duck embryo fibroblast, Vero, or BHK-21 cell cultures. Serum used in the PRN assay is tested against 100 plaque-forming units of virus. Endpoints are based on a 90% reduction in the number of plaques compared with the virus control flasks.
The PRN test or, preferably, a combination of PRN and HAI tests is the procedure most commonly used for the detection of Ab against Eastern and Western EEV. There are cross-reactions between Ab against bith viruses in the CF and HAI tests.CF Ab against both viruses appears later and does not persist; thus, it is less useful for serological diagnosis.
======Clinical Pathology======
======Clinical Pathology======