Sindbis virus neutralising antibodies detected in Swedish horses

Abstract

A number of viruses transmitted by mosquitoes are well known to cause disease in both humans and horses, ranging from mild fevers to mortal neurological disease. A recently discovered connection between the alphavirus Sindbis virus (SINV) and neurological disease in horses in South Africa initiated this serological study in northern Europe, where the same genotype of SINV (SINV-I) is also highly endemic. We tested 171 serum samples, originally obtained from horses for other reasons from April to October 2019, for presence of SINV neutralising antibodies using a plaque reduction neutralisation test (PRNT). The serum from six horses reduced the plaque count more than 80%, and two out of these reduced the plaque count more than 90%. These horses were sampled in six different regions of Sweden, and included individuals sampled from April to August. This study shows that horses in Sweden have become infected with SINV and developed neutralising antibodies. Potential connections between infection and development of disease are important questions for future studies.

Keywords: Alphavirus; Arbovirus; Equine encephalitis; Equine fever; Neutralisation test; Serology.

Fig. 1

Sampling regions of horses analysed for neutralising antibodies against SINV. Circles show number of horses sampled in that region. Regions where horses had a titer of neutralising antibodies of 80% or more (≥PRNT₈₀) are written out for comparison with Table 2.

Fig. 2

Wells of Vero cells showing plaques of dead cells, i.e. not stained by the red colour, caused by SINV. The two wells on the top row are duplicates of a sample reducing the number of plaques ≥80%. while the two wells on the bottom row are duplicates of a sample with <50% plaque reduction. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)