Eilat virus

Eilat virus is from the family Togaviridae, genus Alphavirus. Alphaviruses are miniature spherical shaped (around 70 nm in diameter) enveloped viruses that consist of a positive sense (5' to 3') RNA genome, which encompasses two ORF's (Open Reading Frame which is an incessant stretch of codons that do not contain a stop codon).^[2] Four nonstructural proteins are encoded on two-thirds of the genome (5' end), which include nsP1, nsP2, nsP3, nsP4. While five structural proteins ( sPs; Capsid, E1, E2, E3, and 6K) are encoded on the one third part of the genome ( 3' portion).

By receptor-mediated endocytosis, alphaviruses gain entry into a host cell. After acquiring access, the low endocytic pH allows for a conformational change that discloses an E1 fusion peptide. Thus, inducing the release of the nucleocapsid into the cytoplasm of the host cell. The nucleocapsids in turn aid in initiating virion budding from the host cell membrane.

Eilat virus was isolated during an arbovirus survey in the Negev desert between the years 1982 and 1984. However, it was initially obtained by Joseph Peleg from a pool of Anopheles coustani mosquitoes (from the isolates back in 1982). This specific isolation was performed in a study for over ninety-one identified viruses, and the EILV virus was found and isolated from the gut of the collected mosquitoes.

Eilat virus is located primarily in Africa and parts of the Middle East. It is found in regions where its natural vector (the Anopheles coustani) is situated. The place of its study however, plays an important role in the evolutionary significance of the EILV. The Negrev desert (being almost 13,000 km²) is considered the natural area of the virus. The area's average climate ranges from the lowest being -5 °C to the highest of around 46 °C (yearly). The EILV was named after the city of Eilat which is located in the south area of the Negev desert (close to the region where the pool of Anopheles coustani's are located).

Eilat virus shows an evolutionary change which may have occurred to alphaviruses. Normally, an alphavirus similar to that of the EILV would use mosquitoes as the vector of transmission to other (usually vertebrates) creatures. However, the Eilat virus can replicate consummately in an insect host and fails completely to even enter the cells of vertebrates. Based on experimental evidence when a relativity similar virus (SINV) was injected into vertebrate cell lines, the cells showed to have a great cytopathic effect. While when the same test was done on the EILV, the virus showed no cytopathic effect on the vertebrate cell lines.^[1] Therefore, evolutionary these results aid in suggesting that EILV lost its capability in infecting vertebrate cells. Thus, EILV appears to be mosquito-specific and represents a previously undescribed complex within the genus Alphavirus. Reverse genetic studies of EILV may help in the discovery of determinants of alphavirus host range which balances disease emergence.

When tested on four different mosquito species, Eilat virus had similar effects on certain organs of the mosquitos and did not infect other organs.^[3] This bar graph shows the percentage of the specified mosquito species infected by the EILV in several different organs of the host.

The virus's main hosts are mosquitoes, however it does have the ability to infect other insect cells. Eilat virus's incapability of entering vertebrate cells was proven by infection with the EILV-expressing red fluorescent protein which was obtained from a second genomic promoter. The red fluorescent protein was promptly observed in mosquito cells and unseen in vertebrate cells.^[2]

Eilat virus is unable to infect its host in low doses orally. When a few species of mosquito were fed (a blood meal) containing Eilat virus in high doses, all test species did in fact get infected; however, when the dose range was lowered, the species would fail to get infected.

This virus (EILV) is typically transmitted sexually from one organism to another. This allows or aids Eilat virus to naturally keep its complex in circulation. However, researchers are still contemplating the fact that the virus was found to be unable to infect the ovaries, which would normally be a subsequent event following sexual transmittance in other alphaviruses.

Though EILV is host specific (insect only), it is highly related to a series of viruses which have a more expansive host range. This relation assists in diagnostic testing with the vertebrate infecting viruses. Researchers discovered that the structural proteins of the EILV can be replaced by those of (pathogenic to mammals) related viruses (by super infection exclusion/ Homologous interference).^[4] This in turn will allow the virus to form a virus, (of broader host ranges), look alike to the immune system. Therefore, helping the immune system recognize these harmful viruses.^[5] Researchers at the University of Texas Medical Branch used this concept for the Chikungunya virus by creating the UTMB test. This test aids in clinical diagnoses and is an affordable alternative to the use of inactivated viruses in diagnostic testing.^[6]