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Introduction of Adenovirus                                 

Rowe and associates in 1953. The adenovirus is isolated from adenoids originally. Adenovirus shares a common complement-fixing antigen. The virus infects humans, birds, and animals, and infections are most common in children.  

Morphology of Adenovirus

It is a non-enveloped, icosahedral symmetry, linear Double-stranded DNA virus. The size of a virus is 70-90nm and contains 252 capsomers and 240 hexagons. The virus has 12 fibrillar pentons, and it was space vehicle shaped appearance. 

Resistance

It is a heat-stable virus and readily inactivated at 50◦C. They resist ether and bile salts. 

Epidemiology

It is an endemic disease and is transmitted through droplets, Direct contact, Feco-oral transmission. Its 1/3rd of human serotypes cause human illness. 

Virus effects on cells:

It saws in marked rounding, enlargement, and aggregation of affected cells which are grape-like clusters. Rounded intra-nuclear inclusion containing DNA present in the cells.

Pathogenesis

  • It generally causes infection of the respiratory tract, eye, GIT & UTI.
  • Infection occurs through conjunctiva or nasal mucosa.
  • Children- fecal-oral transmission.
  • Incubation period: 5-7 days
  • Multiply initially in the conjunctiva, pharynx, or small intestine and spread to draining L.nodes
  • Serotype 1- 8 most common
    • Subgenus(SPS) C – Acute febrile pharyngitis
    • Subgenus B- Acute respiratory disease
    • Serotype 40 and 41 – infantile gastroenteritis
    • Serotype- 8, 19, 37- eye infection
    • Serotype 19,37- genital infection
    • Serotype 3, 4, 11 – acute follicular conjunctivitis

Immunity

  • Induces long-lasting immunity
  • Maternal antibodies protect infant

Lab Diagnosis of Adenovirus

Specimen

  • Throat swab
  • Nasopharyngeal aspirates
  • Bronchial lavage
  • Conjunctival swab
  • Corneal scraping
  • Urine
  • An anal swab
  • Genital secretions
  • Feces, rectal swab, and biopsy

Microscopy

  • Virus particles in stool by EM
  • Virus isolation:
    • Primary human embryonic kidney cell line and A549 cell line. 
    • HEp-2, HeLa, and KB cell lines

Viral growth

  • Can be detected through the Cytopathic effect: Rounding and grape-like clustering of swollen cells.
  • Antigen detection by Direct-IF test.
  • Shell vial technique
  • Explant culture: It can grow on adenoid explants. However, it is no longer in use now.

Serotyping

  •  By Hemagglutination test and Neutralization test
  •  PCR for the gene coding for type-specific antigens, More sensitive and rapid.

Direct –IF test 

  • Detect the adenoviral antigens from clinical samples such as the throat or conjunctival secretions by using 
    • fluorescent-tagged anti-hexon antibody
    • Fastidious enteric serotypes such as 40 and 41 from stool: Can be detected by EM or by antigens detection by ELISA
    • Serum antibody detection: 
      • CFT
      • Neutralization test
      • ELISA
      • HAI (Hemagglutination inhibition test)-for few hemagglutinating serotypes.

Clinical Findings

  • Pharyngitis-acute febrile
  • Pneumonia
  • Conjunctivitis-Acute follicular conjunctivitis, Epidemic keratoconjunctivitis
  • Infantile Gatroenteritis
  • Acute hemorrhagic cystitis

Diarrhea

  • Enteric type adenovirus-serotypes 40, 41
  • Not grown in routine cell culture
  • Trypsinised MK cells or transformed HEK cells
  • Can be identified by stool ELISA

Transformation of cells

  • Heubner reported types 12 and 18 produced sarcoma in baby hamsters-1962
  • Types 12, 18, and 31 –induce tumors only in animals.
  • In culture, all types of cells transform

Gene Therapy

  • They have a spare capacity to carry DNA inserts
  • Potential vectors in gene therapy
  • Used in cancer therapy and gene therapy

Prevention and control

  • Hand washing
  • Chlorination of swimming pools
  • Environmental surfaces disinfected by sodium hypochlorite
  • A live vaccine to 4, 7 –applied to military recruits

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