Development of sensitive indirect enzyme-linked immunosorbent assays for specific detection of antibodies against fowl adenovirus serotypes 1 and 4 in chickens.

Conventional serological methods for detection and differentiation of antibodies against fowl aviadenoviruses (FAdVs) are laborious and time-consuming, therefore ELISAs based upon recombinant proteins were developed in the present study to overcome this limitation for clinically relevant serotypes FAdV-1 and FAdV-4. In order to develop serotype-specific ELISAs, the two distinct fibers, fiber-1 (fib-1) and fiber-2 (fib-2), characteristically present only in FAdV-1 and FAdV-4, were applied separately as coating antigens. Sera raised against each recombinant fib-1 and fib-2 of FAdV-1 and FAdV-4 did not react with any of the heterologous fiber ELISAs, as anticipated by the low degree of amino acid identity between those FAdV fibers (23.1-41.2%), indicating that heterologous fibers do not share common epitopes. Testing of 172 monospecific sera, raised against all FAdV serotypes (1-8a and 8b-11), retrieved specificities between 99.3% and 100.0% for the ELISAs, further substantiating the serotype-specificity of fibers. Investigating sera from chickens experimentally inoculated with different FAdV-1 or FAdV-4 strains revealed that ELISAs were equally or more sensitive than the virus-neutralization (VN) test. Furthermore, strong correlations were demonstrated between fiber antibody titres and neutralization activity. Particularly, sera directed against live virus showed a pronounced fiber antibody response, which might be explained by an excessive production of fibers during infection. Application of the newly developed fiber ELISAs on field sera with heterogeneous serological status demonstrated high sensitivity and serotype-specificity of this test system, providing for the first time a diagnostic tool for mass screening of chicken flocks against FAdV serotypes, namely FAdV-1 and FAdV-4.