A. Parvoviridae

Parvoviruses (from Latin parvus meaning small) are very small viruses with a particle size of about 18–26 nm. The particles have cubic symmetry, with 32 capsomeres, but they have no envelope. The genome is linear, single-stranded DNA, aver aging 5 kb in size. Replication occurs only in actively dividing cells; capsid assembly takes place in the nucleus of the infected cell. Human parvovirus B19 replicates in immature erythroid cells and causes several adverse consequences, including aplastic crisis, fifth disease, and fetal death.

B. Anelloviridae

 Anelloviruses (from Latin anello meaning ring) are small (~30 nm in diameter), icosahedral virions that lack an envelope. The viral genome is negative sense, circular, single-stranded DNA, 2–4 kb in size. Anelloviruses include the torque teno viruses, and are globally distributed in the human population and many animal species. No specific disease associations have been proven.

C. Polyomaviridae

Polyomaviruses are small (45 nm), nonenveloped, heat-stable, solubilization-resistant viruses exhibiting cubic symmetry, with 72 capsomeres. The name derives from Greek poly- (many) and –oma (tumor) and refers to the ability of some of these viruses to produce tumors in infected hosts. The genome is circular, double-stranded DNA, about 5 kb in size. These agents have a slow growth cycle, stimulate cell DNA synthesis, and replicate within the nucleus. The most well known human polyomaviruses are JC virus, the causative agent of progressive multifocal leukoencephalopathy; BK virus, associated with nephropathy in transplant recipients; and Merkel cell virus, found associated with the majority of Merkel cell skin carcinomas. SV40, a primate virus, can also infect humans. Most animal species harbor chronic infections with one or more polyomaviruses.

D. Papillomaviridae

Papillomaviruses are similar to polyomaviruses in some respects but with a larger genome (8 kb) and particle size (55–60 nm). The name refers to Latin papilla (nipple) and Greek –oma (tumor) and describes wart-like lesions produced by these viral infections. There are many types of human papillomaviruses, and certain high-risk types are causative agents of genital cancers in humans.

E. Adenoviridae

 Adenoviruses (from Latin adenos meaning gland) are medium-sized (70–90 nm), nonenveloped viruses exhibiting cubic symmetry, with fiber spikes protruding from capsomers that aid in host attachment. The genome is linear, double-stranded DNA, 26–48 kb in size. Replication occurs in the nucleus. Complex splicing patterns produce mRNAs. At least 67 types infect humans, especially in mucous mem branes, and some types can persist in lymphoid tissue. Adenoviruses can cause acute respiratory diseases, conjunctivitis, and gastroenteritis. Some human adenoviruses can induce tumors in newborn hamsters. Many serotypes infect animals.

F. Hepadnaviridae

Hepadnaviruses (from Latin hepa meaning liver) are small (40–48 nm), enveloped viruses containing circular, partially double-stranded DNA molecules that are about 3.2 kbp in size. Replication involves repair of the single-stranded gap in the DNA, transcription of RNA, and reverse transcription of the RNA to make genomic DNA. The virus consists of a 27-nm icosahedral nucleocapsid core within a closely adherent envelope that contains lipid and the viral surface antigen. The surface protein is characteristically overproduced during replication of the virus, which takes place in the liver, and is shed into the bloodstream. Hepadnaviruses such as Hepatitis B virus can cause acute and chronic hepatitis; persistent infections are associated with a high risk of developing liver cancer. Viral types are known that infect mammals and ducks.

G. Herpesviridae

Herpesviruses are family of large viruses 150–200 nm in diameter. The name refers to Latin herpes (creep), describing the spreading nature of skin lesions caused by these viruses. The nucleocapsid is 100 nm in diameter, with cubic symmetry and 162 capsomeres, surrounded by a lipid containing envelope. The genome is linear, double-stranded DNA, 120–240 kb in size. Latent infections may last for the life span of the host, usually in ganglial or lymphoblastoid cells. Human herpesviruses include herpes simplex types 1 and 2 (oral and genital lesions), varicella-zoster virus (chickenpox and shingles), cytomegalovirus, Epstein-Barr virus (infectious mononucleosis and association with human neoplasms), human herpesviruses 6 and 7 (T cell lymphotropic), and human herpesvirus 8 (associated with Kaposi sarcoma). Other herpesviruses occur in many animals.

H. Poxviridae

 Poxviruses are large brick-shaped or ovoid viruses 220–450 nm long × 140–260 nm wide × 140–260 nm thick. The particle structure is complex, with a lipid-containing envelope. The name derives from Anglo-Saxon pokkes meaning pouch, referring to their characteristic vesicular skin lesions. The genome is linear, covalently closed, double stranded DNA, 130–375 kb in size. Poxvirus particles contain about 100 proteins, including many with enzymatic activities, such as a DNA-dependent RNA polymerase. Replication occurs entirely within the cell cytoplasm. Some are pathogenic for humans (smallpox, vaccinia, molluscum contagiosum); others that are pathogenic for animals can infect humans (cowpox, monkeypox).

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اخبار العتبة العباسية المقدسة

الحزام الأخضر الجنوبي الأول يستضيف وفدًا شبابيًّا من محافظة المثنى

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المزيد

مواضيع ذات صلة

Chemical Composition of Viruses

Survey of RNA-Containing Viruses

Universal System of Virus Taxonomy

Human parainfluenza viruses (HPIV)

Complications of Influenza virus

Influenza virus

Chikungunya virus

West Nile virus

Transmission Cycle of Japanese encephalitis virus

Lab Diagnosis of Dengue virus

Pathogenesis of Dengue virus

Rotavirus