Adenovirus is a family of viruses that infects various parts of the human body. Symptoms of infection range from mild common cold-like symptoms (sore throat, runny nose, coughing, chills) to bronchitis, pneumonia or pink eye. Young children and people with weakened immune systems are more likely to develop severe adenovirus infections. Adenovirus can spread by close contact (shaken hands, kissing, hugging), through respiratory droplets released in sneezes and coughs, and by touching surfaces or objects with the virus on them and then touching your eyes, mouth or nose before washing your hands. Occasionally, intestinal adenovirus can cause a serious medical emergency called intussusception, in which one part of the intestine slides over another section like a telescope and causes abdominal pain, vomiting and diarrhea.
A slender, rod-shaped virus with a diameter of 70 to 100 nm, adenovirus consists of 252 capssomeres forming the icosahedral structure, each bearing two major core proteins and a short fiber that extends from the center of the capsid. Adenoviruses replicate in cells by dividing their genomes twice and then inserting the new DNA into the cell nucleus. The resulting DNA fragments are then packaged into capssomeres for further replication and release. Adenoviruses have also been used as vector systems in approaches towards human somatic gene therapy. Manipulated adenoviral genomes usually have deletions in the early region E3 which are not essential for viral replication in human cells, thus yielding space for insertion of foreign genes constructed for therapeutic purposes. The first clinical applications of adenoviral vectors are in the treatment of the genetic disease cystic fibrosis.
The adenovirus genome contains multiple regions encoding proteins involved in the infection cycle and other cellular functions. The genes are transcribed and translated in the host cell by adenovirus-specific RNA polymerase and encode proteins that are necessary for viral gene expression and replication, as well as structural and support proteins. The genome also contains a segment encoding small RNAs (VAI and VAII) that regulate the translation of the late genes into protein products.
Both in abortive and productively infected cells, adenovirus DNA recombines with host cell DNA. The early genes, which are expressed in adenoviral-infected cells, become preferentially integrated into the host cell genome in a manner that is dependent on site of integration, sequence of the integrate DNA and genetics of the cell. The integrated adenovirus DNA is then methylated by the host cell methyltransferase. This methylation is believed to prevent transcription of the integrated viral DNA.
Infection with adenovirus can be life-threatening for people with weakened immune systems. These include patients with stem cell transplantation, organ transplant recipients, people with HIV/AIDS and cancer. In addition, the virus is known to cause a severe, often fatal disease in infants, called invasive enteric adenovirus syndrome. The most severe form of this disease is characterized by intestinal intussusception, which occurs when a portion of the intestine slides over and blocks the stomach. Other complications can include urinary tract infection and gastrointestinal hemorrhage.