Five evolutionary genetic studies of<unk>  virus have been published of which four focused on phylogeny, genetic variation, and recombination dynamics by sequencing the envelope protein gene and parts of other genes. A recent evolutionary study based on 23 new full open reading frame sequences (near-complete genomes) found that the North American strains belonged to a single clade. Strains were isolated at different points in time (from 1933 to 2001) which allowed for the estimation of divergence times of<unk>  virus clades and the overall evolutionary rate. Furthermore, this study found an increase in the effective population size of the<unk>  virus around the end of the 19th century that corresponds to the split of the latest North American clade, suggesting a northwards colonization of<unk>  virus in the Americas, and a split from the ancestral South American strains around 1892. Scans for natural selection showed that most codons of the<unk>  virus ORF were evolving neutrally or under negative selection. Positive selection was statistically detected only at one single codon coding for amino acids belonging to the hypothesized N-linked glycosylation site of the envelope protein. Nevertheless, the latter can be due to selection in vitro (laboratory) rather than in vivo (host). In an independent study 14 out of 106 examined envelope gene sequences were found not to contain a specific codon at position 156 coding for this glycosylation site (Ser→Phe/Tyr). Another study estimated the evolutionary rate to be (95% confidence ). The virus seems to have evolved in northern Mexico and then spread northwards with migrating birds.
Saint Louis encephalitis
La Crosse encephalitis
Powassan encephalitis
Japanese encephalitis
Eastern equine encephalitis
Rasmussen's encephalitis
Viliuisk encephalomyelitis
Tick-borne encephalitis