Human endogenous retroviruses HERV

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Endogenous retroviruses can be detected in the human genome by a variety of procedures such as hybridization or gene sequencing. They have a general structure similar to other retroviruses including long terminal repeat (LTR) regions and sequences homologous to the gag, pol and env genes of infectious retro-viruses. They can be classified on the identity of the tRNA homologous to the putative minus-strand primer binding site (18bp) located immediately downstream of the 5' LTR. On this basis, HERV-E (glutamic acid), HERV-R (argi-nine), HERV-I (isoleucine), HERV-H (histidine), HERV-P (proline), HERV-K (lysine) and HERV-W (tryptophan) were distinguished. A further six new HERV were detected using the human genome project mapping database and partially characterized (all were defective, with partial deletions of the genome): HERV-f and HERV-f (type B), primed by pheny-lalanine; HERV-R (type B), primed by arginine but different from the previously known HERV-R; HERV-S, primed by serine; and HERV-Z69907 and HERV-H49C23, where the 5' LTR sequence could not be detected. Others probably exist but have not yet been detected. Most HERVs contain numerous mutations creating stop-codons and other

Human foamy virus (HFV)

interruptions and so cannot be expressed. However, HERV-K contains very few mutations and is expressed in some tumor cell-derived lines including GH cells (human teratocarcinoma cells). Particles of this endogenous human retrovirus (termed HTDV for human terato-carcinoma derived virus) have been seen by thin-section electron microscopy of these cells. On average, 50 copies of HERV-K are present in the hap-loid human genome.

Blond JL et al (1999) J Virol 73, 1175 Tristem M (2000) J Virol 74, 3715 Wilkinson DA et al (1994) In The Retroviridae, vol. 3, edited by JA Levy. New York: Plenum Press, p. 465

human enterovirus A-D (HEV-A to D) Four species in the genus Enterovirus, containing 59 serotypes.

human enterovirus 68 (HEV68) A serotype of Human enterovirus D in the genus Enterovirus. Isolated from patients with pneumonia and bronchiolitis in California, USA.

Schieble JH et al (1967) Am J Epidemiol 85, 297

human enterovirus 69 (HEV69) A serotype of Human enterovirus B in the genus Enterovirus. Isolated in 1959 from a rectal swab of a healthy 4-year-old child in Toluca, Mexico. Few strains have since been detected. Not reported to cause disease in humans. Prototype strain Toluca-1.

Melnick JL et al (1974) Intervirology 4, 369

human enterovirus 70 (HEV70) A serotype of Human enterovirus D in the genus Enterovirus. Isolated in 1971 from epidemics of acute hemorrhagic conjunctivitis in Japan, Singapore and Morocco. These outbreaks were part of a pandemic involving millions of humans in Africa, South-East Asia, Japan, India and England during 1969-71. The virus can adsorb in vitro to cells from a wider range of species than most enteroviruses. In some it produces no CPE but in others, such as RK 13 (rabbit cells) and BK 1 (bovine cells), it produces virus and CPE. Prototype strain is AHC(J670/71).

Melnick JL et al (1974) Intervirology 4, 369 Yoshii T et al (1977) J Gen Virol 36, 377

human enterovirus 71 (HEV71) A serotype of Human enterovirus D in the genus Enterovirus. Isolated in 1970 from the brain of a fatal case of encephalitis in California, USA. Related strains have been isolated from stools of sporadic cases of meningitis and encephalitis in California and from outbreaks in Australia and Sweden. Associated with an epidemic of meningitis among children in Bulgaria in 1975, in which 21% of cases had paralysis. Has been isolated from cases of hand-foot-and-mouth disease in Japan, Malaysia and Taiwan. Prototype strain Br Cr. Shares an antigen with coxsackie A 16, but there is no cross-neutralization, although the sequences share considerable homol-ogy.

Hagiwara A et al (1978) Microbiol Immun 22, 81 Hsiung GD and Wang JR (2000) J Microbiol Immunol Infect 33, 1

Melnick JL et al (1979) Intervirology 12, 297

human enterovirus 73 (HEV73) Name proposed for a group of enteroviruses from California and Oman which could not be typed with standard enteroviral typing antisera, but were similar by sequence analysis and form a distinct cluster within the genus Enterovirus.

Oberste MS et al (2001) J Gen Virol 82, 409

Human foamy virus (HFV) Not a human virus. A species in the genus Spumavirus, now called Chimpanzee foamy virus. Isolated from a human nasopharyngeal carcinoma explant culture. Can be propagated in a variety of human and animal cell cultures but not in chick embryo cell culture. Antigenically closely similar to Simian foamy virus type C but unlike other foamy viruses. PCR tests failed to detect any viral sequences in samples of 223 patients, or foamy virus-specific antibodies in 2688 sera from suspected high-risk persons. Previous reports may have resulted from contamination with simian foamy virus. Persistent zoonotic infection of a human with simian foamy virus has been reported.

Synonyms: human spumavirus; human syncytial virus.

Callahan ME et al (1999) J Virol 73, 9619 Schweizer M et al (1995) AIDS Res Human Retro 11, 161

human hepatitis A virus (HHAV)

human hepatitis A virus (HHAV) See

Hepatitis A virus.

Human herpesvirus 1 (HHV-1) Type species of the genus Simplexvirus in the subfamily Alphaherpesvirinae. The genome DNA has been completely sequenced for the 17syn+ strain, and consists of about 150kb with a G+C of 67%. The DNA is infectious and has two components, L and S, each of which is bracketed by internal repeats. Primary infection is common in young children, often sub-clinical, but occasionally with acute stomatitis. The virus can pass along nerves and become latent in ganglia from whence it can be reactivated by non-specific stimuli (fever, sunlight, menstruation) to cause lesions, often around the mouth. Rarely, the virus may cause acute hepatitis, kerato-conjunctivitis or meningo-encephalitis. Vaccination has not been successful but treatment of kerato-conjunctivitis and skin lesions with locally applied acyclovir ointment is beneficial. In cases of encephalitis, neonatal herpes or disseminated infection, intravenous acyclovir is used. See Human herpesvirus 2. Synonyms: herpes febrilis; herpes simplex virus 1; herpesvirus hominis; Human her-pesvirus 1.

Feldman LT (1994) Semin Virol 5, 207 McGeoch DJ et al (2000) J Virol 74,10401

Human herpesvirus 2 (HHV-2) A species in the genus Simplexvirus. Genome DNA is related to HSV1 with about 85% homol-ogy in the open reading frames. Differs from Human herpesvirus 1 in that it is usually, though not always, transmitted venereally. Infection is therefore uncommon before the age of puberty. The virus usually causes genital lesions but can also be responsible for any of the lesions characteristic of Human herpesvirus 1. There is a high level of antigenic similarity between viruses 1 and 2 although each has antigens specific to itself. Glyco-protein G-specific assays provide the best differentiation. Acyclovir is an effective treatment.

Synonyms: herpes febrilis; herpes simplex type 2; herpesvirus hominis; Human her-pesvirus 2.

Stanberry LR (1993) Rev Med Virol 3, 37

Human herpesvirus 3 (HHV-3) Type species of the genus Varicellovirus, in the subfamily Alphaherpesvirinae. The genome DNA has been completely sequenced for the Dumas strain, and is 125kb in length, with a G+C of 46%. It consists of an L and an S component bounded by repeats. The S component can be inverted to form two isomers, and both are present in packaged genome DNA. The cause of common human infection. Causes chick-enpox on primary infection, usually in childhood. Incubation period 1-16 days, rarely up to 21 days. Causes herpes zoster, a painful local condition with skin lesions, usually in adults. The eyes may be involved. May follow exposure to infection but most commonly appears as a reactivation of latent infection. Encephalitis is a rare complication of chickenpox. Fetal malformations have been reported to follow maternal infection. All strains are antigenically similar. Convalescent serum has no therapeutic use but an attenuated vaccine developed in Japan (the Oka strain) is now licensed in many countries for use in children. Animals appear to be resistant to infection. The virus can be cultivated in HeLa and various monkey tissue cells, with CPE in 2-7 days. It remains cell-bound and difficult to separate, and is usually passaged with cellular material. Synonyms: chickenpox virus; herpesvirus varicellae; varicella-zoster virus.

Arvin AM (1996) Clin Microbiol Revs 9, 361 Chee MS et al (1990) Curr Top Microbiol Immun 154, 125

Hay J and Ruyechan WT (1994) Semin Virol 5, 241

Human herpesvirus 4 (HHV-4) Type species of the genus Lymphocryptovirus, subfamily Gammaherpesvirinae. The genome DNA has been completely sequenced for the B95-8 strain, and is 172kb in length with a G+C of 60%. First isolated from Burkitt tumors of African children. A very widespread human infection, mainly of children, in whom it rarely causes disease but produces a high level of immunity. However, primary infection of young adults may result in infectious mononucleosis, a febrile condition with enlargement of the lymph nodes and often a sore throat. The Paul-Bunnell test is positive. The virus is the probable cause of Burkitt tumors and carcinoma of the post-nasal space, but as the infection is universal and these tumors only occur in local areas, some accessory factors must be involved. After infection, the virus remains in the body as a latent infection of B lymphocytes. It can be propagated in human cell cultures, but is cell-associated and is difficult to purify. A number of virus-coded antigens have been identified in infected tissues, and antibodies to these are found in humans. They include the capsid antigen (VCA), antibodies to which are a good indication of primary infection, and a nuclear antigen (EBNA) which appears 4-6 weeks after disease onset.

Synonyms: Burkitt's lymphoma virus; Ebb virus; Epstein-Barr virus; glandular fever virus; infectious mononucleosis virus; human (gamma) herpesvirus 4.

Lee SP (1994) Semin Virol 5, 281 Middleton T et al (1991) Adv Virus Res 40, 19 Sugden B (1994) Semin Virol 5, 197

Human herpesvirus 5 (HHV-5) Type species of the genus Cytomegalovirus, subfamily Betaherpesvirinae. The genome DNA has been completely sequenced for the AD169 strain, and is 230kb in length with a G+C of 57%. A worldwide infection, common in humans. Usually a chronic silent infection of peripheral blood mono-cytes and cells of the salivary glands, but primary infection during pregnancy may lead to infection of the fetus with varying degrees of brain damage. Infection in utero or neonatal infection may cause severe and often fatal hepatitis, splenomegaly and anemia. Patients with AIDS or on immunosuppressive therapy and, occasionally, healthy people may develop fatal pneumonia, hepatitis or a form of glandular fever. Virus can often be isolated from the urine of patients, and sometimes from that of healthy children. An active vaccine (Towne 125 strain) has been made, is safe and will probably come into use. The virus is much less susceptible than other human herpesviruses to antiviral drugs such as acyclovir, but the derivative ganciclovir, administered parenterally, is effective and is licensed to treat retinitis in the immunosuppressed, especially patients with AIDS. There is replication in primary human fibroblast cultures with a slowly developing CPE

and formation of inclusion bodies. Hamster and human cells are transformed in vitro. The virus is cell-associated. No hemagglutinins. Sensitive to freezing and thawing and to prolonged storage at -70°C. Synonyms: giant cell pneumonia virus; human cytomegalovirus; inclusion body disease virus; visceral disease virus.

Chee MS et al (1990) Curr Top Microbiol Immun 154, 125

Sinclair J and Sissons JGR (1994) Semin Virol 5, 249

Human herpesvirus 6 (HHV-6) Type species of the genus Roseolovirus. Genome is 160kb in length, with a base composition of 43% G+C, and contains 119 open reading frames. HHV-6 is one of the most widespread of the herpesviruses, and seroprevalence rates exceed 90% by 2 years of age. Etiologically associated with exanthem subitum (roseola infantum), a common, usually benign, childhood disease, rarely associated with encephalo-pathy. There is abrupt onset of fever lasting 3 days then ceasing as a rash appears. HHV-6 has also been implicated in some cases of heterophile-negative mononucleosis, lymphadenopathy and extended low-grade fever and malaise. The virus commonly infects neuronal cells in the brain and has been suggested as a possible causative agent in multiple sclerosis. There are two closely related subspecies, HHV-6A and HHV-6B, that differ in growth properties, antigenicity, nucleotide sequence and epidemiological characteristics. HHV-6A is the virus associated with multiple sclerosis. HHV-6B is strongly associated with roseola infan-tum and is the virus that has been found in the CNS.

Akhyani N et al (2000) J Inf Dis 182,1321 Gompels UA et al (1995) Virology 209, 29 Pellett PE et al (1992) Adv Virus Res 41, 1

Human herpesvirus 7 (HHV-7) A species in the genus Roseolovirus. First described in 1990 as an infection in activated human T cells. A ubiquitous virus which is shed in the saliva of 75% of adults. Sero-prevalence appears to be at least 90% in the normal population with infection beginning by 6 months of age and widely prevalent by age 3 years. More closely related antigenically to HHV-6A and

HHV-6B than to other human her-pesviruses. Significance and possible role in human disease is presently unknown.

Black JB and Pellett PE (1993) Rev Med Virol 3, 217

Mega WAG et al (1998) Virology 244,119 Wyatt LS et al (1991) J Virol 65, 6260

Human herpesvirus 8 (HHV-8) A species in the genus Rhadinovirus. Identified by sequence representational difference analysis in tissues of patients with Kaposi's sarcoma. DNA and monoclonal antibody studies indicate that the virus latently infects cells of Kaposi's sarcoma (KS), multicentric Castleman's disease, and the rare primary effusion lymphoma, and is causally associated with these tumors.

Synonym: Kaposi's sarcoma herpesvirus.

Dupin N et al (1999) Proc Natl Acad Sci 96,4546

Ganem DC (1997) Cell 91, 157

McGeoch DJ and Davison AJ (1999) Semin

Cancer Biol 9, 201

Sharp TV and Boshoff C (2000) IUBMB Life 49,

Human immunodeficiency virus type 1

(HIV-1) A species in the genus Lentivirus, which is the primary etiologic agent of AIDS, a fatal disease first recognized in 1981 that results from gradual destruction of the helper T-cell population in infected individuals. The prototype strain is LAV LA1. Mature virions are spherical, 100-120nm in diameter, with a dense cone-shaped core, comprised of p24 capsid proteins, surrounded by an envelope with spike projections. The genome is diploid, consisting of two molecules per virion of positive single-stranded RNA 9800 nucleotides in length, linked near their 5' ends by non-covalent bonds. A host-cell-derived lysine t-RNA is the primer for reverse transcription of the genome RNA by the action of the virion reverse transcriptase (p51/66) into linear double-stranded DNA, which migrates into the nucleus and becomes integrated into the host cell genome through the action of a viral genome-encoded integrase (p34). The integrated DNA provirus contains long terminal repeat (LTR) elements at each end, as well as three structural genes (gag, pol and env) needed for replication. Additional genes involved in regulation of synthesis and processing of the virus include vif, vpr, vpu, tat, rev and nef. Transcription of the integrated DNA provirus requires cellular transcriptional activators such as TNFa and NFkB. Several virus-specified proteins are involved in transcription, including Tat, which binds to an element within the LTR region of the genome known as TAR. Expression of different genes is determined by differential splicing of the full length genome mRNA transcript. Splicing is in turn regulated by the Rev protein, which binds to a region of the mRNA termed the Rev responsive element (RRE), and inhibits splicing of the RNA. Early transcripts of the genome are multiply spliced, but as the amount of Rev accumulates, single spliced and unspliced transcripts accumulate, and this results in capsid protein synthesis. The major groups of proteins that are synthesized in HIV-infected cells are the gag, pol and env gene products. Gag proteins include the matrix (p18), capsid (p24) and nucleocapsid (p15) proteins of the virion; pol proteins include the protease (p10), reverse transcriptase (p51/66) and integrase (p34) proteins; and env proteins include the surface envelope glycoprotein (gp120) which binds to host cell receptors, and a transmembrane protein (gp41). In addition, a number of minor proteins are synthesized from spliced mRNA, including a myristylated membrane-associated non-structural protein termed Nef that is not required for replication in cell cultures but plays a role in HIV pathogenesis in vivo.

HIV-1 infects only humans or chimpanzees, although chimpanzees do not develop disease or evidence of immunodeficiency. In humans, the virus spreads by sexual transmission, blood transfusion, perinatal transmission and intravenous drug injection using unsteril-ized needles. Infected individuals develop a humoral immune response to the gp120 Env and p24 Gag proteins, and the latter is frequently used as a diagnostic indicator of infection. The USA Center for Disease Control and Prevention has classified HIV infection into four stages. In stage 1, acute infection, there is usually a febrile mononucleosis or influenza-like syndrome 3-4 weeks after exposure, which lasts 2-3 weeks before clinical recovery occurs. Stage 2, asymptomatic infection, usually lasts 7-9 years, but can be shorter. During this period, the health of the affected individual can be monitored by determining the numbers of CD4+ cells in peripheral blood. Many patients progress to stage 3 (persistent generalized lymphadenopathy) during otherwise asymptomatic infection. Finally, stage 4 disease (symptomatic HIV infection) usually develops after several years. Symptoms may include weight loss, diarrhea, encephalopathy and vision impairment, as well as a profound decrease in numbers of CD4+ helper T cells to less than 200 cells per microliter of blood. Other manifestations are thrombo-cytopenic purpura, anemia, dermatitis and peripheral neuropathies. A number of opportunistic infections and conditions, including Pneumocystis carinii pneumonia, Kaposi's sarcoma, mucosal candidiasis, cytomegalovirus infection and herpes simplex ulcers, may develop at this stage. Once the diagnosis of AIDS is confirmed, survival is usually less than 1 year. Progression to AIDS and disease severity can be correlated with the titer of HIV in the peripheral blood (viral load), but the factors which influence this are not yet clearly understood. Drugs which inhibit viral replication and so decrease viral load (such as zidovudine, AZT and the protease inhibitors, Indinavir, Nelfinavir, Ritonavir and Saquinavir) prolong survival of HIV-infected individuals (see HAART). Several genomic clades of HIV-1 are recognized (Table H2).

Barker E et al (1995) In The Retroviridae, vol. 4, edited by JA Levy. New York: Plenum Press, p. 1 Doms RW (2000) Virology 276, 229 Hahn BH et al (2000) Science 287, 607 Kolson DL et al (1998) Adv Virus Res 50, 1 Korber B et al (2000) Science 288,1789 Popik W and Pitha PM (2000) Virology 276,1 Simon F et al (1998) Nature Medicine 4, 1032

Human immunodeficiency virus type 2

(HIV-2) A species in the genus Lentivirus, related to HIV-1 about 40% by RNA sequence homology; the genome structure is similar except that the vpu gene is replaced by a vpx gene. The virus was identified serologically in West Africa and subsequently isolated and found to be more closely related to Simian immunodeficiency virus (SIV) than to HIV-1. The descriptive pathogenesis of HIV-2 infection is similar to HIV-1, involving immunodeficiency and neurological diseases, although HIV-2 appears to be less virulent than HIV-1. Several genomic clades of HIV-2 virus are recognized (see Table H2).

human leukocyte antigens (HLA) Major histocompatibility antigens of the human

Table H2. Examples of genomic clades of HIV

HIV virus type

Clade

human immunodeficiency virus type 1 90CR056 (HIV-1.90CR056)

Clade H

human immunodeficiency virus type 1 93BR020 (HIV-1.93BR020)

Clade F

human immunodeficiency virus type 1 ANT70 (HIV-1.ANT70)

Clade O

human immunodeficiency virus type 1 ARV-2/SF-2 (HIV-1.ARV-2/SF-2)

Clade B

human immunodeficiency virus type 1 BRU (LAI) (HIV-1.BRU(LAI))

Clade B

human immunodeficiency virus type 1 ELI (HIV-1.ELI)

Clade D

human immunodeficiency virus type 1 ETH2220 (HIV-1.ETH2220)

Clade C

human immunodeficiency virus type 1 HXB2 (HIV-1.HXB2)

Clade B

human immunodeficiency virus type 1 MN (HIV-1.MN)

Clade B

human immunodeficiency virus type 1 NDK (HIV-1.NDK)

Clade D

human immunodeficiency virus type 1 RF (HIV-1.RF)

Clade B

human immunodeficiency virus type 1 U455 (HIV-1.U455)

Clade A

human immunodeficiency virus type 2 BEN (HIV-2.BEN)

Clade A

human immunodeficiency virus type 2 D205 (HIV-2.D205)

Clade B

human immunodeficiency virus type 2 EHOA (HIV-2.EHOA)

Clade B

human immunodeficiency virus type 2 ISY (HIV-2.ISY)

Clade A

human immunodeficiency virus type 2 ROD (HIV-2.ROD)

Clade A

human immunodeficiency virus type 2 ST (HIV-2.ST)

Clade A

human immunodeficiency virus type 2 UC1 (HIV-2.UC1)

Clade B

species. Occur as alloantigens on the cell surface in two classes. Humans inherit and express different combinations of class I and class II alleles, and the combination of class I and class II allotypes expressed by a person is called the HLA type. The genes that encode HLA class I and class I alloantigens are closely linked on the short arm of human chromosome 6 in a region called the HLA complex, encompassing about 4 million bp of DNA. See major histocompatibility complex.

Marsh SS et al (2000) The HLA Facts Book. London: Academic Press human microvascular endothelial cell line (HMEC-1) A cell line that has proved useful for propagation of filoviruses, such as Marburg and Ebola virus.

Schnittler HJ et al (1993) J Clin Invest 91,1301

human monkeypox See Monkeypox virus.

Human papillomavirus (HPV-1 to 82) A

species in the genus Papillomavirus. There are 82 genotypes currently recognized, each differing by more than 10% in genome sequence from other types (see below). Cause papillomas of the epidermis in humans: skin warts (verrucae of various types), genital warts (condylo-mata acuminata) and laryngeal papillomas. Malignant change is reported in genital and laryngeal papillomas. The exact role of the virus in carcinoma of the cervix and other tumors remains to be elucidated. Virus is readily extracted from skin warts but less easily demonstrated in genital and laryngeal lesions. Accidental or experimental inoculation of virus into the skin of humans results in the development of warts. Does not replicate or produce papillomas on injection into animals. Virus replication in cell culture is extremely difficult to achieve and has only been possible in 'raft' cultures of human epithelial cells. When DNA from virus extracted from individual warts is cloned and sequenced, more than 80 different HPV types are revealed. Classification as a new genotype requires more than 10% dissimilarity in the combined nucleotide sequences of the E6, E7 and L1 genes when compared with those of any previously known type. Viruses with greater than 90% but less than 100% sequence homology are classified as subtypes. Using this classification, association of specific types with diseases can be observed as shown in Table H3. Synonym: human wart virus.

Delius H and Hofmann B (1994) Curr Top

Microbiol Immun 186, 13

zur Hausen H (1991) Science 254, 1167

human papovavirus This term includes Human papillomavirus and human poly-omaviruses.

Human parainfluenza virus type 1 (HPIV-

1) A species in the genus Paramyxovirus. Antibodies are common in humans, and in monkeys who have been in contact with humans. Causes acute laryngo-tracheitis (croup) in young children and occasionally mild upper respiratory tract infections in older children and adults. There may be more than one type of the virus. It is best isolated in primary human or monkey kidney cell cultures or diploid human cell lines, such as NC1-H292 cells. Replication is poor in eggs. CPE may be slight at first but becomes more marked on passage. Syncytia are formed which float off leaving holes in

Table H3. Specific types of human papillomaviruses and associated diseases

HPV types HPV-associated diseases

1, 2, 3, 4, 7, 10, 26-29, 41, 48, 60, 63, 65, 75-78

5, 8, 9, 12, 14, 15, 17, 19-25, 36-38, 46, 47, 49, 50

6, 11, 42-44, 54-61, 64, 66-68, 70, 74, 79, 84 30, 31, 33, 35, 45, 52, 56, 58, 69, 83

16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58 6, 11 16, 33 13, 32

Common warts (benign)

Epidermodysplasia verucciformis (EV), malignant

Anogenital condylomata (rarely malignant)

Anogenital condylomata (intermediately malignant)

Anogenital condylomata (highly malignant)

Laryngeal papilloma

Tonsillar carcinoma

Oral focal epithelial hyperplasia the cell sheet. Hemadsorption is better with chick or guinea pig red cells rather than human cells, but may not be demonstrable until day 10 on primary isolation. Hamsters and guinea pigs can be infected with the virus but no pathological changes are produced. Synonyms: acute laryngo-tracheo-bron-chitis virus; croup-associated virus; hemadsorption virus 2; influenza virus D; newborn pneumonitis virus.

Human parainfluenza virus type 2 (HPIV-

2) A species in the genus Rubulavirus. Causes croup in children under 5 years of age. Induces syncytia formation in cell cultures. Epidemics occur in the fall, usually every other year, in susceptible infants. Synonyms: acute laryngo-tracheo-bron-chitis virus; croup-associated virus.

Human parainfluenza virus type 3 (HPIV-

3) A species in the genus Paramyxovirus. Isolation is most efficient in primary human or monkey kidney cell cultures but the virus will replicate in cell lines such as HeLa, Hep-2 and NC1-H292. CPE on isolation may be minimal and hemadsorption is used. On passage the cell sheet is disrupted, the cells becoming long and narrow. Causes pharyngitis, bronchiolitis and pneumonia in young children, especially in nursery schools. Uncommon cause of 'colds' in adults. Inoculation into young hamsters causes inapparent infection or small lung lesions.

Synonym: hemadsorption virus 1.

Human parainfluenza virus type 4 (HPIV-4a and HPIV-4b) Species in the genus Rubulavirus. More difficult to isolate than HPIV-1 to -3. Isolation best in primary monkey kidney cell cultures but hemad-sorption may not be demonstrable for 3-4 weeks. Agglutinates guinea pig and rhesus monkey cells better than human cells. CPE poor in early passages. Common infection of young children causing mild upper respiratory disease but the virus is not easily isolated. No evidence of virus replication in eggs. Two antigenic types, a and b, recognized by hemagglutination inhibition tests. Not pathogenic for laboratory animals but produce high antibody levels in guinea pigs.

Human parechovirus 1 (HPeV-1) Type species of the genus Parechovirus, family Picornaviridae. Formerly called echovirus 22, parechoviruses multiply in the gastrointestinal tract causing diarrhea, frequently with respiratory complications. Ljungan virus, found in rodents in Scandinavia, shares many molecular features of the parechoviruses.

Niklasson B et al (1999) Virology 255, 86 Stanway G et al (2000) Rev Med Virol 10, 57

Human parechovirus 2 (HpeV-2) A species in the genus Parechovirus, formerly known as echovirus 23.

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