Semliki Forest Virus
Encyclopedia
The Semliki Forest virus was first isolated from mosquito
es in the Semliki Forest, Uganda
by the Uganda Virus Research Institute
in 1942. It is known to cause disease in both animals and man. It is an Alphavirus
found in central, eastern, and southern Africa
.
The Semliki Forest virus is a positive-stranded RNA virus with icosahedral capsid
which is enveloped by a lipid
bilayer, derived from the host cell. The outermost surface of the virus is almost entirely covered by heterodimers of glycoproteins E1 and E2, arranged in interconnective trimers, which form an outer shell. Trimers are anchored in the membrane by an E2 cytoplasmic domain that associates with the nucleocapsid.
The size of the virus genome
is approximately 13,000 base pair
s. The 5’ two thirds of the genome encode non-structural proteins and the structural proteins are encoded in the 3’ third. Replication occurs via a negative strand intermediate giving rise to a full length genomic RNA for export in new virions and a subgenomic message that is translated into the structural proteins.
Semliki Forest virus is spread mainly by mosquito bites. It is not able to infect mammal
s through inhalation
or gastrointestinal
exposure although rodent
s in the laboratory can be infected by intranasal instillation. The virus is able to cause a lethal encephalitis
in rodents, but only one lethal human infection has been reported. Even in this one case, the patient was immunodeficient
and had been exposed to large amounts of virus in the laboratory.
Semliki Forest virus has been used extensively in biological research as a model of the viral life cycle and of viral neuropathy. Due to its broad host range and efficient replication, it has also been developed as a vector
for gene
s encoding vaccine
s and anti-cancer
agents, and as a tool in gene therapy
.
Mosquito
Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...
es in the Semliki Forest, Uganda
Uganda
Uganda , officially the Republic of Uganda, is a landlocked country in East Africa. Uganda is also known as the "Pearl of Africa". It is bordered on the east by Kenya, on the north by South Sudan, on the west by the Democratic Republic of the Congo, on the southwest by Rwanda, and on the south by...
by the Uganda Virus Research Institute
Uganda Virus Research Institute
The Uganda Virus Research Institute , located in Entebbe, Uganda, was established in 1936 as the Yellow Fever Research Institute by the Rockefeller Foundation. In 1950, after gaining regional recognition it was renamed the East African Virus Research institute...
in 1942. It is known to cause disease in both animals and man. It is an Alphavirus
Alphavirus
In biology and immunology, an alphavirus belongs to the group IV Togaviridae family of viruses, according to the system of classification based on viral genome composition introduced by David Baltimore in 1971. Alphaviruses, like all other group IV viruses have a positive sense single stranded RNA...
found in central, eastern, and southern Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
.
The Semliki Forest virus is a positive-stranded RNA virus with icosahedral capsid
Capsid
A capsid is the protein shell of a virus. It consists of several oligomeric structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may not correspond to individual proteins, are called capsomeres. The capsid encloses the genetic...
which is enveloped by a lipid
Lipid
Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...
bilayer, derived from the host cell. The outermost surface of the virus is almost entirely covered by heterodimers of glycoproteins E1 and E2, arranged in interconnective trimers, which form an outer shell. Trimers are anchored in the membrane by an E2 cytoplasmic domain that associates with the nucleocapsid.
The size of the virus genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
is approximately 13,000 base pair
Base pair
In molecular biology and genetics, the linking between two nitrogenous bases on opposite complementary DNA or certain types of RNA strands that are connected via hydrogen bonds is called a base pair...
s. The 5’ two thirds of the genome encode non-structural proteins and the structural proteins are encoded in the 3’ third. Replication occurs via a negative strand intermediate giving rise to a full length genomic RNA for export in new virions and a subgenomic message that is translated into the structural proteins.
Semliki Forest virus is spread mainly by mosquito bites. It is not able to infect mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s through inhalation
Inhalation
Inhalation is the movement of air from the external environment, through the air ways, and into the alveoli....
or gastrointestinal
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....
exposure although rodent
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
s in the laboratory can be infected by intranasal instillation. The virus is able to cause a lethal encephalitis
Encephalitis
Encephalitis is an acute inflammation of the brain. Encephalitis with meningitis is known as meningoencephalitis. Symptoms include headache, fever, confusion, drowsiness, and fatigue...
in rodents, but only one lethal human infection has been reported. Even in this one case, the patient was immunodeficient
Immunodeficiency
Immunodeficiency is a state in which the immune system's ability to fight infectious disease is compromised or entirely absent. Immunodeficiency may also decrease cancer immunosurveillance. Most cases of immunodeficiency are acquired but some people are born with defects in their immune system,...
and had been exposed to large amounts of virus in the laboratory.
Semliki Forest virus has been used extensively in biological research as a model of the viral life cycle and of viral neuropathy. Due to its broad host range and efficient replication, it has also been developed as a vector
Vector (molecular biology)
In molecular biology, a vector is a DNA molecule used as a vehicle to transfer foreign genetic material into another cell. The four major types of vectors are plasmids, viruses, cosmids, and artificial chromosomes...
for gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s encoding vaccine
Vaccine
A vaccine is a biological preparation that improves immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism, and is often made from weakened or killed forms of the microbe or its toxins...
s and anti-cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
agents, and as a tool in gene therapy
Gene therapy
Gene therapy is the insertion, alteration, or removal of genes within an individual's cells and biological tissues to treat disease. It is a technique for correcting defective genes that are responsible for disease development...
.