Detection of seroconversion to West Nile virus, Usutu virus and Sindbis virus in UK sentinel chickens

Abstract

We previously reported evidence of West Nile virus (WNV) circulation in UK birds, probably introduced by migratory birds from overseas. We now demonstrate WNV-specific seroconversion in sentinel chickens raised on an English farm. Maternal neutralizing antibodies to WNV in hatchlings declined within three weeks. During the following months, healthy chickens developed WNV neutralizing antibodies that were confirmed by immunoblotting and indirect immunofluorescence tests using WNV antigens. The proportion of seropositive chickens was higher for WNV than for Usutu virus or Sindbis virus. Attempts to isolate infectious virus or to detect viral RNA in the sera, failed.

Figure 1

Neutralization results (PRNT₅₀) obtained for all sentinel chicken sera tested against each of the four viruses and grouped according to age at time of sampling. All chicken sera were coded and all tests were carried out on these coded sera. The codes were revealed only after the results had been presented. The percentages of positive sera recorded at each antibody dilution are shown using a colour scheme; White <1/10; Green 1/10; Yellow 1/20; Orange 1/40; Red 1/80.

Figure 2

Western blot using gradient-purified West Nile virus antigen and sera (diluted 1/100) from sentinel chickens. Tracks 1 and 2, hyperimmune mouse serum prepared against WNV (positive control) or SINV (negative control) respectively; tracks 3 to 10 pairs of chicken sera that produced neutralization titres of 1/10, 1/20, 1/40, and 1/80 respectively.

Figure 3

Indirect immunofluorescence microscopy performed on chicken sera with a neutralization titre of 1/80 (diluted 1:1000 in PBS) on West Nile virus infected Vero cells (Bar 50μm).