Human herpesvirus 7
Encyclopedia
Human herpesvirus 7 is one of eight known members of the Herpesviridae
family, also known as human herpes virus. HHV-7 is a member of Betaherpesviridae, a subfamily of the Herpesviridae
that also includes HHV-6 and Cytomegalovirus
(HHV-5 or HCMV). HHV-7 often acts together with HHV-6, and the viruses together are sometimes referred to by their genus
, Roseolovirus
. HHV-7 was first isolated in 1990 from CD4+ T cells taken from peripheral blood lymphocytes
by Niza Frekel, et al.
, although HHV-7 causes the disease less frequently than HHV-6B. HHV-7 infection also leads to or is associated with a number of other symptoms, including acute febrile respiratory disease
, fever, rash, vomiting, diarrhea, low lymphocyte counts, and febrile seizures, though most often no symptoms present at all.
There are indications that HHV-7 can contribute to the development of drug-induced hypersensitivity syndrome, encephalopathy
, hemiconvulsion-hemiplegia-epilepsy syndrome, hepatitis
infection, postinfectious myeloradiculoneuropathy, pityriasis rosea
, and the reactivation of HHV-4
, leading to "mononucleosis
-like illness".
Complications with HHV-7 infection has been shown to be a factor in a great variety of transplant types.
The genome
of HHV-7 is very similar to that of HHV-6, although it is about 10% smaller, with a DNA genome of about 145,000 base pair
s. There are a number of key differences between the genome of HHV-7 and that of HHV-6, but the importance of them for viral DNA replication
is not yet known.
, albeit only in certain strains of them. To enter CD4+ T cells, HHV-7, unlike HHV-6, uses CD4 and possibly some cell-surface glyoproteins
to enter CD4+ T cells. About a week after HHV-7 has infected a cell, it begins to downregulate
CD4 transcription, which interferes with HIV
-1 infection but may reactivate HHV-6 infection. It is however unclear exactly what effect HHV-7 has on HIV infection.
HHV-7 also has a number of other effects on cells. Among these include membrane leaking, the presence of lityic syncytia, occasional apoptosis
, the supporting of latent infection
, and increases and decreases in levels of certain cytokine
s.
test has been developed yet for HHV-7 alone, but multiple are in the process of being developed. The use of PCR assays to test for HHV-7 is also being explored.
No treatment for HHV-7 infection exists, but no clinical situation where such treatment would be useful has yet been discovered.
Herpesviridae
The Herpesviridae are a large family of DNA viruses that cause diseases in animals, including humans. The members of this family are also known as herpesviruses. The family name is derived from the Greek word herpein , referring to the latent, recurring infections typical of this group of viruses...
family, also known as human herpes virus. HHV-7 is a member of Betaherpesviridae, a subfamily of the Herpesviridae
Herpesviridae
The Herpesviridae are a large family of DNA viruses that cause diseases in animals, including humans. The members of this family are also known as herpesviruses. The family name is derived from the Greek word herpein , referring to the latent, recurring infections typical of this group of viruses...
that also includes HHV-6 and Cytomegalovirus
Cytomegalovirus
Cytomegalovirus is a viral genus of the viral group known as Herpesviridae or herpesviruses. It is typically abbreviated as CMV: The species that infects humans is commonly known as human CMV or human herpesvirus-5 , and is the most studied of all cytomegaloviruses...
(HHV-5 or HCMV). HHV-7 often acts together with HHV-6, and the viruses together are sometimes referred to by their genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
, Roseolovirus
Roseolovirus
Roseolovirus refers to both Human herpesvirus 6 and Human herpesvirus 7, both members of the Betaherpesviridae subfamily of herpesvirus. They can both cause the childhood disease of roseola.-External links:* , New York Times* *...
. HHV-7 was first isolated in 1990 from CD4+ T cells taken from peripheral blood lymphocytes
Peripheral Blood Lymphocytes
Peripheral blood lymphocytes are mature lymphocytes that circulate in the blood, rather than localising to organs . They comprise T cells, NK cells and B cells....
by Niza Frekel, et al.
Signs and symptoms
Both HHV-6B and HHV-7, as well as other viruses, can cause a skin condition in infants known as exanthema subitumExanthema subitum
Exanthema subitum , also referred to as roseola infantum , sixth disease and baby measles, or three-day fever, is a disease of children, generally under two years old, although it has been known to occur in eighteen year olds, whose manifestations...
, although HHV-7 causes the disease less frequently than HHV-6B. HHV-7 infection also leads to or is associated with a number of other symptoms, including acute febrile respiratory disease
Influenza-like illness
Influenza-like illness , also known as acute respiratory infection and flu-like syndrome, is a medical diagnosis of possible influenza or other illness causing a set of common symptoms, with SARI referring to Severe Acute Respiratory Infection.Symptoms commonly include fever, shivering, chills,...
, fever, rash, vomiting, diarrhea, low lymphocyte counts, and febrile seizures, though most often no symptoms present at all.
There are indications that HHV-7 can contribute to the development of drug-induced hypersensitivity syndrome, encephalopathy
Encephalopathy
Encephalopathy means disorder or disease of the brain. In modern usage, encephalopathy does not refer to a single disease, but rather to a syndrome of global brain dysfunction; this syndrome can be caused by many different illnesses.-Terminology:...
, hemiconvulsion-hemiplegia-epilepsy syndrome, hepatitis
Hepatitis
Hepatitis is a medical condition defined by the inflammation of the liver and characterized by the presence of inflammatory cells in the tissue of the organ. The name is from the Greek hepar , the root being hepat- , meaning liver, and suffix -itis, meaning "inflammation"...
infection, postinfectious myeloradiculoneuropathy, pityriasis rosea
Pityriasis rosea
Pityriasis rosea is a skin rash. It is non-dangerous but may inflict substantial discomfort on some people...
, and the reactivation of HHV-4
Epstein-Barr virus
The Epstein–Barr virus , also called human herpesvirus 4 , is a virus of the herpes family and is one of the most common viruses in humans. It is best known as the cause of infectious mononucleosis...
, leading to "mononucleosis
Mononucleosis
Mononucleosis , is a disease most commonly caused by the Epstein-Barr virus . The EBV virus affects the lymphocytes- white blood cells that battle infections by attacking antibodies. Mononucleosis can also be caused by Cytomegalovirus , a herpes virus most commonly found in body fluids...
-like illness".
Complications with HHV-7 infection has been shown to be a factor in a great variety of transplant types.
Structure
A mature virus particle measures about 170 nanometres (1,700 Å) in diameter.The 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....
of HHV-7 is very similar to that of HHV-6, although it is about 10% smaller, with a DNA genome of about 145,000 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. There are a number of key differences between the genome of HHV-7 and that of HHV-6, but the importance of them for viral DNA replication
DNA replication
DNA replication is a biological process that occurs in all living organisms and copies their DNA; it is the basis for biological inheritance. The process starts with one double-stranded DNA molecule and produces two identical copies of the molecule...
is not yet known.
Cellular effects
HHV-7 resides mostly in CD4+ T cellsT helper cell
T helper cells are a sub-group of lymphocytes, a type of white blood cell, that play an important role in the immune system, particularly in the adaptive immune system. These cells have no cytotoxic or phagocytic activity; they cannot kill infected host cells or pathogens. Rather, they help other...
, albeit only in certain strains of them. To enter CD4+ T cells, HHV-7, unlike HHV-6, uses CD4 and possibly some cell-surface glyoproteins
Proteoglycan
Proteoglycans are proteins that are heavily glycosylated. The basic proteoglycan unit consists of a "core protein" with one or more covalently attached glycosaminoglycan chain. The point of attachment is a Ser residue to which the glycosaminoglycan is joined through a tetrasaccharide bridge...
to enter CD4+ T cells. About a week after HHV-7 has infected a cell, it begins to downregulate
Downregulation and upregulation
Downregulation is the process by which a cell decreases the quantity of a cellular component, such as RNA or protein, in response to an external variable...
CD4 transcription, which interferes with HIV
HIV
Human immunodeficiency virus is a lentivirus that causes acquired immunodeficiency syndrome , a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive...
-1 infection but may reactivate HHV-6 infection. It is however unclear exactly what effect HHV-7 has on HIV infection.
HHV-7 also has a number of other effects on cells. Among these include membrane leaking, the presence of lityic syncytia, occasional apoptosis
Apoptosis
Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...
, the supporting of latent infection
Virus latency
Virus latency is the ability of a pathogenic virus to lie dormant within a cell, denoted as the lysogenic part of the viral life cycle. A latent viral infection is a type of persistent viral infection which is distinguished from a chronic viral infection...
, and increases and decreases in levels of certain cytokine
Cytokine
Cytokines are small cell-signaling protein molecules that are secreted by the glial cells of the nervous system and by numerous cells of the immune system and are a category of signaling molecules used extensively in intercellular communication...
s.
Detection and treatment
In adults, the effects of HHV-7 separate from HHV-6 have not been well-researched. One reason for this is because the detection of HHV-7 was at first difficult to do quickly, as the process for doing so involves a procedure that is difficult to do in commercial laboratories and because viral isolation and serological testing are long processes that do not lend themselves to finishing quickly. A process known as loop-mediated isothermal amplification (LAMP) has recently been developed to speed up detection of HHV-7, although a larger sample size of patients must be tested first to see if the test will still work across a broad range of subjects. No reliable serologicalSerology
Serology is the scientific study of blood serum and other bodily fluids. In practice, the term usually refers to the diagnostic identification of antibodies in the serum...
test has been developed yet for HHV-7 alone, but multiple are in the process of being developed. The use of PCR assays to test for HHV-7 is also being explored.
No treatment for HHV-7 infection exists, but no clinical situation where such treatment would be useful has yet been discovered.