Post infection serosurveillance study of foot and mouth disease using NSP 3AB3 as antigen by DIVA ELISA

Abstract

Foot and mouth disease (FMD) remains a tremendous problem in developing countries like Bangladesh where proper vaccination strategy was maintained haphazardly to protect the disease stature. Sometimes animals become infected but do not show any clinical symptoms and constantly shed virus and become the most important source of disease spread. Affected animals, through their mouth secretions, milk and semen secretions as well as from their infected hooves shed virus into the environment which can spread 300km in water course and 60km by air. FMD vaccine is produced from structural protein of the FMD virus and but in case of live viral infection, antibodies produced in the cattle body are against structural and non-structural protein. DIVA ELISA test is a serological test, which has been devised to determine the immune status of animals form the basis of understanding that it could differentiate infected from vaccinated animals. Tests have been devised to use non-structural proteins (NSP) of FMDV since it is only on infection that antibodies are produced against such proteins. This study through DIVA ELISA testing was conducted to show the clinical status of different crossbreed cattle and native/indigenous cattle to determine carrier status and to observe the effect of vaccination against FMD in different organized and unorganized dairy farms in different districts of Bangladesh after a severe outbreak recorded at the end of 2011. For this purpose, 218 cattle sera were collected from various regions, where cattle are reared. Serum sample were divided into three groups depending on the vaccination history. Blood samples were collected from the infected animals, susceptible animals and disease free animals during or/after infection. The study was conducted to find out if any, relevance between breed and vaccination status, to reveal antibody response against 3AB3 non-structural protein between native and crossbreed cattle and to explore any relevant significant relationship between breed and non-structural protein 3AB3. There was significant relevance found between vaccination and breed preference than other criteria set to conduct the test. People were more curious to vaccinate cross breed cattle than native cattle. Presently, such tests are at the heart of confirming whether an organized farm is free from FMD virus (replication) even where there is no observed clinical disease which is vital to trade issues, milk and meat production in live animals and animal products. What is apparent from this work and other data is that the criteria for selecting cutoffs as to whether animals are positive or negative have to be re-assessed. Another finding is that the tests are very useful at the herd level, but due to the measured diagnostic uncertainly, are not so useful at the single animal level in tune with most serological testing. Single ELISA systems using NSP for screening are powerful tools for assessing infection in a herd since they only require a single test, but are best backed up by confirmatory tests.