Group IV ((+)ssRNA)
Higher order categories
Virus; Togaviridae; Alphavirus (SFV Complex); O’nyong’nyong
Description and Significance
O’nyong’nyong (ONN) virus is an Alphavirus (family Togaviridae, genus Alphavirus) and is classified in the Semliki Forest Virus (SFV) antigenic complex. The name O’nyong’nyong is derived from the Nilotic language of Uganda and Sudan and means “weakening of the joints”. It is closely related to both the chikungunya (CHIK) and Igbo Ora viruses. O’nyong’nyong virus single stranded, spherical, and has enveloped virions 60 nm in diameter. O'nyong'nyong virus was first isolated in northern Uganda in 1959 and was part of an arbovirus epidemic that had more than 2 million reported cases. It wasn’t until 1996 that it was again reported and isolated, this time in southern Uganda. It was thought that the O'nyong'nyong virus was closely related to the alphavirus, Igbo Ora virus. It is now known that the Igbo Ora virus is in fact a strain of the O'nyong'nyong virus, which both possess a stop codon at the nsp3–nsp4 junction. The importance of the O’nyong’nyong virus is that it is a virus which only springs up every few decades, but when it does it causes a widespread epidemic. Studies of this virus can lead to a better understanding of how exactly it works and specific targets in the human body it has. This will help to understand the O’nyong’nyong virus as well as other alphaviruses that it is closely related to.
The complete nucleotide sequence of the genomic RNA of O’nyong’nyong virus is 11,835 nucleotides long with the same basic organization as all alphaviruses. It is small, spherical, and enveloped with a genome of a single, positive sense strand RNA. It has a 5’ cap and a 3’ poly-A tail. There are 4 non-structural protein genes encoded into the 5’ two thirds of the genome and 3 structural protein genes, which are translated from subgenomic mRNA, encoded into the other third of the genome, the 3’ end. O’nyong’nyong virus, and all alphaviruses, also contain two open reading frames (ORF’s) that are non-structural and structural. The non-structural is the first and encodes proteins nsP1-nsP4. These proteins are necessary for the transcription and replication of the viral RNA. The second ORF encodes 3 structural proteins (nucleocapsid protein C, protein P62, and protein E1).
ONN contains enveloped virions 60 nm in diameter. The nucleocapsid is approximately 40 nanometers in diameter and contains 240 copies of the capsid protein. It also has a T = 4 icosahedral symmetry. E1 and E2 are viral glycoproteins that are embedded in the lipid bilayer, and single E1 and E2 molecules associate with one another for the formation of heterodimers. These heterodimers form one-to-one contacts between th E2 protein and the nucleocapsid monomers .
Reproductive Cycle in a Host Cell
There is no evidence that the virus can be transmitted through human to human contact. People are infected by bites from mosquitoes carrying the virus. It is then able to replicate in the cytoplasm of cells, and symptoms begin to show after an incubation period of about eight days. Replication of the O’nyong’nyong virus occurs within the cytoplasm, where virions mature by budding through the plasma membrane and virus-encoded surface glycoproteins (E1 and E2) are assimilated . It’s cell cycle can involve a sylvatic cycle. A sylvatic cycle is the fraction of the pathogen population's lifespan spent cycling between wild animals and vectors.
Viral Ecology & Pathology
Entry into target cells is via membrane fusion. Membrane anchored surface glycoproteins are responsible for entry as well as receptor recognition. Unlike CHIK and all other alphaviruses, ONN virus is unique in its transmission patterns: the virus is not transmitted by culicine mosquitoes, but rather by anophelines, typically Anopheles funestus and An. gambiae. ONN is a self-limiting febrile (illness that suddenly occurs with an onset of fever) viral disease, meaning that it follows a temporary course and usually will resolve by itself without the need for medical intervention. It is characterized by arthralgia or arthritis typically in the knee, ankle and small joints of the extremities, followed by a maculopapular rash in 60-70% of cases. Buccal and palatal enanthema can occur, and unapparent infections are common.
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Page edited by student, Jacob Marceau of Dr. Lisa R. Moore, University of Southern Maine