Genetic and antigenic diversity among eastern equine encephalitis viruses from North, Central, and South America.

This research study examines the genetic and antigenic diversity of the Eastern equine encephalitis virus (EEEV) across the Americas. The scientists discovered there is greater diversity within the South American EEEV variety, identified three main South/Central American lineages and noted the North American EEEV forms a highly conserved, single lineage.

Research Background and Approach

• The Eastern equine encephalitis virus (EEEV) is the sole species in the EEE antigenic complex. Antigenic varieties of the virus have previously been divided into North and South American categories based on hemaglutination inhibition tests. Hemaglutination inhibition tests are used to determine the concentration of virus in a sample.
• The research team performed serologic and phylogenetic analyses on a variety of these virus samples, which covered the entire geographic and temporal range available. A serologic analysis measures the amount of specific types of antibodies in the blood, while a phylogenetic analysis looks at the evolutionary relationships between different species.

Key Findings

• The phylogenetic analyses and nucleotide sequencing revealed a higher level of genetic diversity within the South American EEEV variety. Three distinct South/Central American lineages were identified.
• One of these lineages was represented by a solitary isolate from eastern Brazil, while the other two lineages had broader distributions across Central and South America.
• In contrast, all the North American EEEV isolates belonged to a single, highly conserved lineage. These strains were generally grouped by the time of their isolation and, to a lesser extent, their location.
• A strain of EEEV isolated from an equine outbreak in Tamaulipas State, Mexico in 1996 was found to be closely related to recent isolates from Texas, suggesting that the virus could travel southwards beyond its presumed endemic area.
• When plaque reduction neutralization tests were performed, it was found that each of the four principal lineages represented a distinct antigenic subtype. Plaque reduction neutralization tests are a method used to quantify a virus’s ability to infect cells, thus determining the virus’s potency.

Implications and Suggestions

• The study suggested a taxonomic revision of the EEE complex might be necessary given the discovery of additional genetic diversity and distinct antigenic subtypes within the EEEV species. Taxonomy refers to the scientific classification of organisms into different categories based on their characteristics.

In essence, the study adds important new information about the genetic diversity and geographical distribution of EEEV, which could potentially inform measures to control the spread of the virus and manage the disease it causes.