''Measles morbillivirus'' (MeV), also called measles virus (MV), is a
single-stranded, negative-sense,
enveloped, non-segmented
RNA virus
An RNA virus is a virusother than a retrovirusthat has ribonucleic acid ( RNA) as its genetic material. The nucleic acid is usually single-stranded RNA (ssRNA) but it may be double-stranded (dsRNA). Notable human diseases caused by RNA virus ...
of the genus ''
Morbillivirus'' within the family ''
Paramyxoviridae''. It is the cause of
measles
Measles is a highly contagious infectious disease caused by measles virus. Symptoms usually develop 10–12 days after exposure to an infected person and last 7–10 days. Initial symptoms typically include fever, often greater than , cough, ...
. Humans are the natural hosts of the virus; no animal reservoirs are known to exist.
Disease
The virus causes
measles
Measles is a highly contagious infectious disease caused by measles virus. Symptoms usually develop 10–12 days after exposure to an infected person and last 7–10 days. Initial symptoms typically include fever, often greater than , cough, ...
, a highly contagious disease transmitted by respiratory aerosols that triggers a temporary but severe
immunosuppression. Symptoms include
fever
Fever, also referred to as pyrexia, is defined as having a temperature above the normal range due to an increase in the body's temperature set point. There is not a single agreed-upon upper limit for normal temperature with sources using val ...
,
cough,
runny nose
Rhinorrhea, rhinorrhoea, or informally runny nose is the free discharge of a thin mucus fluid from the nose; it is a common condition. It is a common symptom of allergies ( hay fever) or certain viral infections, such as the common cold or COV ...
,
inflamed eyes and a generalized,
maculopapular,
erythematous
Erythema (from the Greek , meaning red) is redness of the skin or mucous membranes, caused by hyperemia (increased blood flow) in superficial capillaries. It occurs with any skin injury, infection, or inflammation. Examples of erythema not asso ...
rash and a pathognomic Koplik spot seen on buccal mucosa opposite to lower 1 st and 2 nd molars . The virus is spread by coughing and sneezing via close personal contact or direct contact with secretions.
Replication cycle
Entry
The measles virus has two envelope
glycoprotein
Glycoproteins are proteins which contain oligosaccharide chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glyco ...
s on the viral surface –
hemagglutinin (H) and
membrane fusion protein (F). These proteins are responsible for host cell binding and invasion. The H protein mediates receptor attachment and the F protein causes fusion of viral envelope and cellular membrane. Additionally, the F protein can cause infected cells to directly fuse with neighboring uninfected cells forming syncytia. Three receptors for the H protein have been identified to date: complement regulatory molecule
CD46, the
signaling lymphocyte activation molecule (
SLAMF1) and the cell adhesion molecule
Nectin-4.
For wild type and vaccine strains, extracellular domains of
CD150 (SLAM or SLAMF1) and/or of
nectin-4 (also called Poliovirus-Receptor-Like 4 (PVRL4)) mainly work as cell entry receptors. Minor fraction of wild type virus strains and all modern vaccine strains derived from the Edmonston strain also use
CD46.
Genome replication and viral assembly
Once the virus has entered a host cell, its strand of
negative sense ssRNA
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 carbohyd ...
(single stranded RNA) is used as a template to create a positive sense copy, using the
RNA-dependent RNA polymerase
RNA-dependent RNA polymerase (RdRp) or RNA replicase is an enzyme that catalyzes the replication of RNA from an RNA template. Specifically, it catalyzes synthesis of the RNA strand complementary to a given RNA template. This is in contrast to ...
that's included in the
virion. Then this copy is used to create a new negative copy, and so on, to create many copies of the ssRNA. The positive sense ssRNA is then mass
translated
Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transla ...
by host
ribosome
Ribosomes ( ) are macromolecular machines, found within all cells, that perform biological protein synthesis (mRNA translation). Ribosomes link amino acids together in the order specified by the codons of messenger RNA (mRNA) molecules to fo ...
s, producing all viral proteins. The viruses are then assembled from their proteins and negative sense ssRNA, and the cell will
lyse, discharging the new viral particles and restarting the cycle.
Genome and virion structure
The RNA genome of the virus codes 6 main proteins Nucleoprotein (N), Phosphoprotein (P), Matrix protein (M), Fusion protein (F), Hemagglutinin (H), and Large Protein (L),
which represents RNA dependent RNA polymerase (RdRp). The viral genome also codes two non-structural proteins C and V. These non-structural proteins are innate immunity antagonists; they help the virus to escape host immune response. Inside the virion genomic RNA is forming complex with N, L and P proteins. N, P and M proteins regulate RNA synthesis by RdRp. The virus is enveloped by a lipid membrane and glycoproteins H and F are virion surface proteins that are associated with this lipid membrane.
Evolution
The measles virus evolved from the now eradicated but formerly widespread
rinderpest virus, which infected cattle.
Sequence analysis has suggested that the two viruses most probably diverged in the 11th and 12th centuries, though the periods as early as the 5th century fall within the 95%
confidence interval
In frequentist statistics, a confidence interval (CI) is a range of estimates for an unknown parameter. A confidence interval is computed at a designated ''confidence level''; the 95% confidence level is most common, but other levels, such as 9 ...
of these calculations.
Other analysis has suggested that the divergence may be even older because of the technique's tendency to underestimate ages when strong
purifying selection is in action. There is some linguistic evidence for an earlier origin within the seventh century.
The current epidemic strain evolved at the beginning of the 20th century—most probably between 1908 and 1943.
Genotypes
The measles virus genome is typically 15,894 nucleotides long and encodes eight proteins. The WHO currently recognises 8
clades
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English te ...
of measles (A–H). Subtypes are designed with numerals—A1, D2 etc. Currently, 23 subtypes are recognised. The 450 nucleotides that code for the C‐terminal 150 amino acids of N are the minimum amount of sequence data required for genotyping a measles virus isolate. The genotyping scheme was introduced in 1998 and extended in 2002 and 2003.
Despite the variety of measles genotypes, there is only one measles serotype. Antibodies to measles bind to the hemagglutinin protein. Thus, antibodies against one genotype (such as the
vaccine strain) protect against all other genotypes.
The major genotypes differ between countries and the status of measles circulation within that country or region. Endemic transmission of measles virus was interrupted in the United States and Australia by 2000 and the Americas by 2002.
Infection
In the early stages of infection, the measles virus via
CD150 (SLAMF1) receptor infects immune cells located in the host respiratory tract such as
macrophage
Macrophages (abbreviated as M φ, MΦ or MP) ( el, large eaters, from Greek ''μακρός'' (') = large, ''φαγεῖν'' (') = to eat) are a type of white blood cell of the immune system that engulfs and digests pathogens, such as cancer ce ...
s and
dendritic cell
Dendritic cells (DCs) are antigen-presenting cells (also known as ''accessory cells'') of the mammalian immune system. Their main function is to process antigen material and present it on the cell surface to the T cells of the immune system. Th ...
s. They transmit the virus to the
lymphoid organs, from which it spreads systemically. In the later stages of infection, the virus infects other immune cell types, including
B cell
B cells, also known as B lymphocytes, are a type of white blood cell of the lymphocyte subtype. They function in the humoral immunity component of the adaptive immune system. B cells produce antibody molecules which may be either secreted o ...
s and
T lymphocytes also via
SLAMF1 receptor. In addition, it infects
epithelial cells
Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellu ...
located in the airways. These cells become infected via
nectin-4 receptor and by cell to cell contacts with infected immune cells. The infection of
epithelial cells
Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellu ...
allows the virus to be released via the airstream.
References
External links
*
{{Use dmy dates, date=April 2017
Measles
Morbilliviruses