Adeno Viruses: Composition, Classification and Pathogenesis

In this article we will discuss about Adeno Viruses, these viruses were first detected by Rowe et al (1953) in human adenoid tissue (adeno, from adenoid) and are non-enveloped DNA viruses of medium size.

Contents:

1. Composition of Adeno Viruses
2. Classification of Adeno Viruses
3. Pathogenesis of Adeno Viruses
4. Immunity of Adeno Viruses
5. Laboratory Diagnosis of Adeno Viruses
6. Epidemiology of Adeno Viruses

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1. Composition of Adeno Viruses:

Adeno viruses are 70-90 nm in diameter with an icosahedral capsid which encloses a double stranded DNA in association with polypeptides. The capsid is made of 252 capsomeres arranged as an icosahedron with 20 triangular facets and 12 vertices. The capsid consists of 240 hexons and 12 pentons and a thread-like structure projects from each of the 12 vertices for red cell.

Each of the 12 capsomers at the vertices is surrounded by 5 others and are called pentons, whereas the hexons are surrounded by 6 neighbours (capsomer).

2. Classification of Adeno Viruses:

Adeno viruses are grouped into two genera:

(1) Aviadeno viruses (adeno viruses of birds) and Mastadeno viruses (adeno viruses of mammals). Human adeno viruses are divided into 6 subgenera – A to F, on the basis of haemagglutination and oncogenic potential. There are about 47 known human adeno virus serotypes. They share a common complement fixing antigen.

3. Pathogenesis of Adeno Viruses:

Adeno viruses cause infection of the respiratory, gastrointestinal, urinary tract and eyes. After entry into the body, they multiply locally and spread to draining lymph nodes and remain there localised. Incubation period is 5-7 days.

Serotypes 1 to 7 are responsible for most illnesses associated with adeno viruses. Group C (Types 1, 2,5 and 6) viruses cause latent infections in adenoids and tonsils and the excretion of the virus in the faeces may continue for many months.

Group B viruses cause acute respiratory diseases and Group C viruses cause acute febrile pharyngitis Types 3 and 7 and acute follicular conjunctivitis whereas type 8 is responsible for acute epidemic keratoconjunctivitis (EKC) in industrial workers. Though many adeno viruses multiply in intestinal cells, Types 40 and 41 cause diarrhoea and are abundant in diarrhoeal stool.

4. Immunity of Adeno Viruses:

Because of the long lasting immunity induced by adeno viruses, attacks from the same serotype is rare. Infants can be protected by maternal antibodies.

5. Laboratory Diagnosis of Adeno Viruses:

(1) Isolation of Virus:

By tissue culture in human epithelial cell lines i.e. HeLa, Hep 2 or KB, adeno virus can be isolated from throat, conjunctiva or stool. The cytopathic effects (CPE) are rounding, and grape-like clusters of swollen cells after 10-28 days of incubadon. Fluorescence antibody CF and haemagglutination tests can identify the virus.

(2) Serological Tests:

Rising titre of CF antibodies can be seen in paired sera. Neutralisation (N+), Haemagglutination (HI) tests can be carried out for specific identification.

6. Epidemiology of Adeno Viruses:

Transmission of adeno virus infection from man to man is via respiratory and alimentary route, whereas eye infection is by hand to eye transfer. Adeno virus can be transmitted to the recipient from donor by bone marrow transplantation.