Satellite virus

A satellite is a subviral agent composed of nucleic acid that depends on the co-infection of a host cell with a helper virus for its replication. Satellite viruses, which are most commonly associated with plants, but are also found in mammals, arthropods, and bacteria, have the components to make their own protein shell to enclose their genetic material, but rely on a helper virus to replicate. Most viruses have the capability to use host enzymes or their own replication machinery to independently replicate their own viral RNA. Satellite viruses in contrast, are completely dependent on a helper virus for replication. The symbiotic relationship between a satellite and a helper virus to catalyze the replication of a satellite viral genome is also dependent on the host to provide components like replicases to carry out replication. A satellite virus of mamavirus that inhibits the replication of its host has been termed a virophage. However, the usage of this term remains controversial due to the lack of fundamental differences between virophages and classical satellite viruses. The genomes of satellite viruses range upward from 359 nucleotides in length for satellite tobacco ringspot virus RNA (STobRV). Satellite viral particles should not be confused with satellite DNA. The tobacco necrosis virus was the virus that lead to the discovery of the first satellite virus in 1962. Scientists discovered that the first satellite had the components to make its own protein shell. A few years later in 1969, scientists discovered another symbiotic relationship with the tobacco ringspot neopvirus (TobRV) and another satellite virus. The emergence of satellite RNA is said to have come from either the genome of the host or its co-infecting agents, and any vectors leading to transmission. A satellite virus important to human health that demonstrates the need for co-infection to replicate and infect within a host is the virus that causes hepatitis D. Hepatitis D (HDV) was discovered in 1977 by an Mario Rizzetto and is unique from hepatitis A, B, and C because it requires viral particles from hepatitis B to replicate and infect liver cells. Hepatitis B (HBV) provides a surface antigen HBsAg which in return is utilized by HDV to create a super infection resulting in liver failure. Hepatitis delta virus is found all over the globe but most prevalent in Africa, the Middle East and southern Italy.