Adenoviruses are a group of medium sized, non enveloped, ds DNA viruses that share a common complement fixing antigen. They infect humans, animals and birds, shows strict host specifity. At least 47 serotypes of adenoviruses have been isolated from human sources. Adenovirus infections are common worldwide mostly in children. Many infections are asymptomatic. The virus may persist in the host for many months.It cause infections of the respiratory tract and eyes. These viruses carry DNA up to 7kb and are being investigated as potential vectors in gene therapy.
Morphology : Adenoviruses are 70-75 nm in size. The icosahedral capsid is composed of 252 capsomeres. A base is anchored at the 12 vertices regions of the capsid, and a projection consisting of a rod-like portion with a knob attached at the distal end.
Resistance : They are relatively stable, viable for a week at 370C, inactivated at 500C. They resist ether and bile salts.
Host Range : They are host specific. Human adenoviruses grow only in tissue culture of human origin such as HeLa, human embryonic kidney. After several days cytopathic effects- consisting of cell rounding and aggregation into grape-like clusters. Intranuclear inclusions seen in stained preparations.
Pathogenicity : Adenoviruses causes infections such as,
- Pharyngitis- Non bacterial pharyngitis, tonsilitis, presenting as common cold.
- Pneumonia- seen in adults, fatal in infants and young children.
- Acute Respiratory Diseases(ARD)- is a ;ower respiratory tract viral disease that range from mild to severe. Respiratory symptoms such as sore throat, cough and other cold symptoms, fever, headache, malaise are frequuently seen. Cases of viral ARD have been seen in military training facilities. The epidemic nature is due to crowding from different areas under stressful conditions.
- Epidemic keratoconjunctivitis(EKC)- sometimes called “shipyard eye”, workers are frequently infected from dust particles in the environment. After 8-10 days’ incubation the conjunctiva becomes inflammed, eyelid edema, pain, tearing and sensitivity to light follows. Within 2 days the infection spreads to the corneal epithelium and sometimes to deeper corneal tissue. Clouding of cornea can last upto 2 years. EKC acquired from eye clinics.
- Acute Follicular Conjunctivitis(AFC)- Inflammation of the conjunctiva with enlargement of the submucous lymphoid follicles.
- Diarrhoea- often isolated from feaces.
Laboratory Diagnosis : can be established by isolation of the virus from the throat, eye, urine or faeces. The materials are inoculated in tissue cultures. Preliminary identification by noting the cytopathic effects, complement fixation tests with antiserum. For serological diagnosis, rise in antibody titre demonstrated in paired sera. Electron microscopy for faecal virus, immunofluorescence for viral antigen detection are useful.
Prophylaxis : Killed and live vaccines available for ARD.