Adenoviridae
Adenoviridae is a family of viruses known as adenoviruses, which can cause a range of diseases and asymptomatic infections in vertebrate animals, including humans. These viruses are globally distributed and vary in prevalence based on geographic location and time. Adenoviruses have a unique structure, characterized by a symmetrical, nonenveloped particle that includes a protein capsid and a double-stranded DNA genome that can be infectious on its own. They primarily infect epithelial cells in the respiratory and gastrointestinal tracts, as well as other tissues like lymphatic tissue and the eyes. Symptoms of adenovirus infections can range from mild to severe and may include respiratory illnesses, conjunctivitis, and gastrointestinal issues, particularly affecting young children and immunocompromised individuals. Although most cases are mild, there are no specific antiviral treatments available for the general public; supportive care is typically recommended. Preventative measures, such as mask use and chlorination of water, can reduce the risk of spread, and a vaccine is available specifically for U.S. military personnel.
Adenoviridae
- TRANSMISSION ROUTE: Direct contact
Definition: cause various diseases and asymptomatic infections in vertebrate animals, including humans
Adenoviridae is a family of adenoviruses that cause various diseases and asymptomatic infections in vertebrate animals, including humans.
Natural Habitat and Features
Adenoviruses are thought to be distributed worldwide. Different types of adenovirus have different prevalence rates and geographic distributions that vary with time. Adenoviruses infect all classes of vertebrate animals examined, are found in some amoebas, and remain infectious for weeks on common surfaces.
An adenovirus virion is a symmetrical, nonenveloped particle having a diameter of 80 to 110 nanometers (nm). It comprises an external capsid (protein shell), a core, and some of the enzymes needed for viral replication. The virion capsid has twenty sides made of hexon capsomeres and has twelve vertices made of penton capsomeres that join the sides and are joined to one or two fibers having a terminal knob. Particular fiber lengths of 9 to 77.5 nm are characteristic of the different types of adenovirus. The virion core contains one linear double-stranded molecule of genomic deoxyribonucleic acid (DNA), containing from 33,000 to 45,000 nucleotide base pairs associated with proteins. This DNA itself is infectious. The ends of the DNA molecule contain repeated sequences of nucleotide base pairs. The five-prime end of each DNA strand is attached to one molecule of terminal protein that primes DNA replication.
Different types of adenovirus within each species share an overall pattern of traits, such as calculated degree of evolutionary relatedness, DNA structure, kinds of animals they infect, kinds of diseases they cause, growth characteristics, ability to cause erythrocytes to clump, and ability of fiber and hexon to bind to particular antibodies. The ability of fiber and hexon to bind to particular antibodies also defines the different types of adenovirus within each species. Molecular diagnostic methods such as polymerase chain reaction (PCR), restriction analysis, and DNA sequencing can be used to rapidly identify the species or type of an adenovirus.
Pathogenicity and Clinical Significance
Different types of human adenovirus cause different diseases, in part because their type-specific fibers and penton capsomeres specify the infection of different cell types. Human adenoviruses most frequently infect epithelial cells, specifically those of the respiratory or gastrointestinal tracts, lymphatic tissue, kidney or bladder, or eye conjunctiva. Infection can be lytic, whereby disease symptoms result from the destruction of the host cell, caused by the production and release of newly formed viruses, or infection can be asymptomatic, whereby those symptoms and processes can be delayed or greatly diminished for years. People without symptoms may shed infectious virus for years after infection. More than one type of adenovirus can co-infect a cell, facilitating genetic recombination that creates new types of adenovirus.
Nearly all adults have been infected by adenoviruses at some time in their lives and have serum antibodies to several types of adenovirus. Immunocompromised personssuch as those receiving tissue or organ transplants or those with acquired immunodeficiency syndromebabies and young children, and military recruits are at greatest risk for severe, and sometimes fatal, disease. Crowded conditions, such as in daycare centers, hospitals, military housing, shipyards, and summer camps, increase the risk of infection.
Reported clinical illnesses caused by, or associated with, adenovirus infection include intussusception in babies; acute febrile pharyngitis, acute hemorrhagic cystitis, diarrhea, pertussis-like syndrome, and pneumonia in babies and young children; adenopharyngoconjunctival fever in school-age children; acute respiratory disease with pneumonia in military recruits; epidemic keratoconjunctivitis in adults; severe disseminated disease in immunocompromised people; cardiomyopathy; encephalitis; follicular conjunctivitis; gastroenteritis; meningitis; obesity; and skin rash. The most prevalent human adenoviruses causing clinical illness are species B types 3 and 7; species C types 1, 2, and 5; species E type 4; and species F types 40 and 41.
Drug Susceptibility
No drugs or therapies generally available to the public specifically prevent or treat human adenoviral infections. Because most adenovirus infections of previously healthy people are self-limited and mild, caregivers usually treat only the symptoms and provide supportive care.
The spread of adenovirus can be decreased through the use of masks and gloves by caregivers and by chlorinating water used for drinking and swimming.
An enteric live oral vaccine directed against human adenovirus types 4 and 7, available only to the US military, has been used to effectively prevent respiratory disease among recruits. Development of adenovirus-specific T cell vaccines for immunocompromised people is also underway.
Severe infections, which can result in death, have been treated with general virus inhibitors such as ribavirin, cidofovir, ganciclovir, leukocyte transfusions, or intravenous immunoglobulin. The safety and efficacy of such treatments remains to be established.
Bibliography
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