''Henipavirus'' is a
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
negative-strand RNA virus
Negative-strand RNA viruses (−ssRNA viruses) are a group of related viruses that have negative-sense, single-stranded genomes made of ribonucleic acid. They have genomes that act as complementary strands from which messenger RNA (mRNA) is sy ...
es in the family ''
Paramyxoviridae
''Paramyxoviridae'' (from Ancient Greek, Greek ''para-'' “by the side of” and ''myxa'' “mucus”) is a family of negative-strand RNA viruses in the order ''Mononegavirales''. Vertebrates serve as natural hosts. Diseases associated with this ...
'', order ''
Mononegavirales
''Mononegavirales'' is an order of negative-strand RNA viruses which have nonsegmented genomes. Some common members of the order are Ebola virus, human respiratory syncytial virus, measles virus, mumps virus, Nipah virus, and rabies virus. All of ...
'' containing six established species, and numerous others still under study.
Henipaviruses are naturally harboured by several species of small mammals, notably
pteropid fruit bat
Megabats constitute the family Pteropodidae of the order Chiroptera (bats). They are also called fruit bats, Old World fruit bats, or—especially the genera ''Acerodon'' and ''Pteropus''—flying foxes. They are the only member of the sup ...
s (flying foxes),
microbats
Microbats constitute the suborder Microchiroptera within the order Chiroptera (bats). Bats have long been differentiated into Megachiroptera (megabats) and Microchiroptera, based on their size, the use of echolocation by the Microchiroptera a ...
of several species, and
shrew
Shrews (family Soricidae) are small mole-like mammals classified in the order Eulipotyphla. True shrews are not to be confused with treeshrews, otter shrews, elephant shrews, West Indies shrews, or marsupial shrews, which belong to different fa ...
s.
Henipaviruses are characterised by long
genome
In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...
s and a wide host range. Their recent emergence as
zoonotic
A zoonosis (; plural zoonoses) or zoonotic disease is an infectious disease of humans caused by a pathogen (an infectious agent, such as a bacterium, virus, parasite or prion) that has jumped from a non-human (usually a vertebrate) to a human. ...
pathogens capable of causing illness and death in
domestic animal
This page gives a list of domesticated animals, also including a list of animals which are or may be currently undergoing the process of domestication and animals that have an extensive relationship with humans beyond simple predation. This includ ...
s and humans is a cause of concern.
In 2009, RNA sequences of three novel viruses in phylogenetic relationship to known henipaviruses were detected in African straw-colored fruit bats (''
Eidolon helvum
The straw-coloured fruit bat (''Eidolon helvum'') is a large fruit bat that is the most widely distributed of all the African megabats. It is quite common throughout its area ranging from the southwestern Arabian Peninsula, across forest and sava ...
'') in
Ghana
Ghana (; tw, Gaana, ee, Gana), officially the Republic of Ghana, is a country in West Africa. It abuts the Gulf of Guinea and the Atlantic Ocean to the south, sharing borders with Ivory Coast in the west, Burkina Faso in the north, and To ...
. The finding of these novel henipaviruses outside Australia and Asia indicates that the region of potential endemicity of henipaviruses may be worldwide. These African henipaviruses are slowly being characterised.
''
Nipah
NIPA, Nipa or nipah may refer to:
* Shamim Ara Nipa, Bangladeshi dancer and choreographer
* Nipa hut, a type of stilt house indigenous to the cultures of the Philippines
* Nipah virus, a Henipavirus
NIPA
* National Income and Product Accounts ...
'' and ''
Hendra henipaviruses'' are both considered category C (USDA-HHS overlap)
select agent
Under United States law, Biological select agents or toxins (BSATs) — or simply select agents for short — are bio-agents which (since 1997) have been declared by the U.S. Department of Health and Human Services (HHS) or by the U.S. Department ...
s.
Structure
![Henipavirus genome](https://upload.wikimedia.org/wikipedia/commons/3/31/Henipavirus_genome.png)
Henipavirions are
pleomorphic (variably shaped), ranging in size from 40 to 600 nm in diameter.
They possess a
lipid
Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...
membrane overlying a shell of viral
matrix protein
Viral matrix proteins are structural proteins linking the viral envelope with the virus core. They play a crucial role in virus assembly, and interact with the RNP complex as well as with the viral membrane. They are found in many enveloped viruses ...
. At the core is a single helical strand of genomic
RNA
Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...
tightly bound to N (
nucleocapsid
A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may ...
) protein and associated with the L (large) and P (phosphoprotein) proteins, which provide
RNA polymerase
In molecular biology, RNA polymerase (abbreviated RNAP or RNApol), or more specifically DNA-directed/dependent RNA polymerase (DdRP), is an enzyme that synthesizes RNA from a DNA template.
Using the enzyme helicase, RNAP locally opens the ...
activity during replication.
Embedded within the lipid membrane are spikes of F (fusion) protein trimers and G (attachment) protein tetramers. The function of the G protein (except in the case of MojV-G) is to attach the virus to the surface of a host cell via
Ephrin B1, B2, or B3, a family of highly
conserved mammalian proteins.
The structure of the attachment glycoprotein has been determined by X-ray crystallography. The F protein fuses the viral membrane with the host cell membrane, releasing the virion contents into the cell. It also causes infected cells to fuse with neighbouring cells to form large, multinucleated
syncytia
A syncytium (; plural syncytia; from Greek: σύν ''syn'' "together" and κύτος ''kytos'' "box, i.e. cell") or symplasm is a multinucleate cell which can result from multiple cell fusions of uninuclear cells (i.e., cells with a single nucleus) ...
.
Genome
![Journal](https://upload.wikimedia.org/wikipedia/commons/3/37/Journal.pone.0199534.g001.A.png)
As all mononegaviral genomes, Hendra virus and Nipah virus genomes are non-segmented, single-stranded
negative-sense
In molecular biology and genetics, the sense of a nucleic acid molecule, particularly of a strand of DNA or RNA, refers to the nature of the roles of the strand and its complement in specifying a sequence of amino acids. Depending on the context, ...
RNA. Both genomes are 18.2 kb in length and contain six
gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
s corresponding to six structural proteins.
In common with other members of the ''
Paramyxoviridae
''Paramyxoviridae'' (from Ancient Greek, Greek ''para-'' “by the side of” and ''myxa'' “mucus”) is a family of negative-strand RNA viruses in the order ''Mononegavirales''. Vertebrates serve as natural hosts. Diseases associated with this ...
'' family, the number of
nucleotide
Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecules wi ...
s in the henipavirus genome is a multiple of six, consistent with what is known as the '
rule of six'. Deviation from the rule of six, through mutation or incomplete genome synthesis, leads to inefficient viral replication, probably due to structural constraints imposed by the binding between the RNA and the N protein.
Henipaviruses employ an unusual process called
RNA editing
RNA editing (also RNA modification) is a molecular process through which some cells can make discrete changes to specific nucleotide sequences within an RNA molecule after it has been generated by RNA polymerase. It occurs in all living organisms ...
to generate multiple proteins from a single gene. The specific process in henipaviruses involves the insertion of extra
guanosine
Guanosine (symbol G or Guo) is a purine nucleoside comprising guanine attached to a ribose (ribofuranose) ring via a β-N9-glycosidic bond. Guanosine can be phosphorylated to become guanosine monophosphate (GMP), cyclic guanosine monophosphate (c ...
residues into the P gene
mRNA
In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of Protein biosynthesis, synthesizing a protein.
mRNA is ...
prior to
translation
Translation is the communication of the Meaning (linguistic), meaning of a #Source and target languages, source-language text by means of an Dynamic and formal equivalence, equivalent #Source and target languages, target-language text. The ...
. The number of residues added determines whether the P, V C, or W proteins are synthesised. The functions of the V and W proteins are unknown, but they may be involved in disrupting host antiviral mechanisms.
Life Cycle
Cell receptor ephrin-B2, which is located on epithelial cells around smaller arteries, neurons, and smooth muscle cells, is targeted by the viral protein G. Once the protein G binds to ephrin-B2, the viral protein F facilitates fusion with the host cell membrane and releases viral RNA into the host cell cytoplasm. Upon entry, transcription of viral mRNA takes place using the viral RNA as a template. This process is started and stopped by the polymerase complex. Viral proteins are gathering in the cell as transcription occurs until the polymerase complex stops transcription and starts genome replication. Transcription of the viral RNA makes positive sense strands of RNA, which are then used as templates to make more negative sense viral RNA . Genome replication is halted before the viral particles can assemble to make a virion. Once the cell membrane is ready, new virions exit the host cell through budding.
Vaccine
Henipaviruses have high mortality rates in mammalian hosts, both human and animal. Because of this, there is a need for immunization against HeV and NiV. Both diseases can be transmitted from animals to humans and can cause respiratory and neurological issues. HeV and NiV appear as encephalitis or severe respiratory illnesses in human hosts. Animal hosts also experience respiratory distress and occasionally fever and neurological disease. Other vaccines for viruses in the Paramyxoviridae family use neutralizing antibodies directed to bind to the surface glycoproteins. A vaccine for henipaviruses has still not been made, but would probably follow the same model as other vaccines for Paramyxoviridae family viruses.
Causes of emergence
The emergence of henipaviruses parallels the emergence of other
zoonotic
A zoonosis (; plural zoonoses) or zoonotic disease is an infectious disease of humans caused by a pathogen (an infectious agent, such as a bacterium, virus, parasite or prion) that has jumped from a non-human (usually a vertebrate) to a human. ...
viruses in recent decades.
SARS coronavirus
Severe acute respiratory syndrome coronavirus 1 (SARS-CoV-1; or Severe acute respiratory syndrome coronavirus, SARS-CoV) is a strain of coronavirus that causes severe acute respiratory syndrome (SARS), the respiratory illness responsible for th ...
,
Australian bat lyssavirus
''Australian bat lyssavirus'' (''ABLV''), originally named ''Pteropid lyssavirus'' (''PLV''), is a zoonotic virus closely related to the rabies virus. It was first identified in a 5-month-old juvenile black flying fox (''Pteropus alecto'') col ...
,
Menangle virus
''Menangle pararubulavirus'', also called Menangle virus, is a virus that infects pigs, humans and bats.
History
Menangle virus was first identified in 1997 after a piggery in Menangle near Sydney, NSW, Australia experienced a high number o ...
,
Marburg virus
Marburg virus (MARV) is a hemorrhagic fever virus of the ''Filoviridae'' family of viruses and a member of the species '' Marburg marburgvirus'', genus ''Marburgvirus''. It causes Marburg virus disease in primates, a form of viral hemorrhagic f ...
and possibly
Ebola
Ebola, also known as Ebola virus disease (EVD) and Ebola hemorrhagic fever (EHF), is a viral hemorrhagic fever in humans and other primates, caused by ebolaviruses. Symptoms typically start anywhere between two days and three weeks after becom ...
viruses are also harboured by bats, and are capable of infecting a variety of other species. The emergence of each of these viruses has been linked to an increase in contact between bats and humans, sometimes involving an intermediate domestic animal host. The increased contact is driven both by human encroachment into the bats' territory (in the case of Nipah, specifically pigpens in said territory) and by movement of bats towards human populations due to changes in food distribution and loss of habitat.
There is evidence that habitat loss for flying foxes, both in South Asia and Australia (particularly along the east coast) as well as encroachment of human dwellings and agriculture into the remaining habitats, is creating greater overlap of human and flying fox distributions.
Taxonomy
See also
*
Animal viruses
Veterinary virology is the study of viruses in non-human animals. It is an important branch of veterinary medicine.
Rhabdoviruses
Rhabdoviruses are a diverse family of single stranded, negative sense RNA viruses that infect a wide range of ho ...
*
Paramyxovirus
References
External links
ICTV Report: ''Paramyxoviridae''Disease cardHenipavirus– Henipavirus Ecology Research Group (HERG) INFO
Virus Pathogen Database and Analysis Resource (ViPR): Paramyxoviridae
{{Authority control
Animal virology
Paramyxoviridae
Virus genera
*