Human adenoviruses are a group of DNA viruses discovered in 1953 by Wallace P. Rowe. The U.S. cancer researcher and virologist isolated the viruses from human pharyngeal tonsils, known as adenoids. From this, the name human adenoviruses is derived for the types of viruses that affect humans.
What are human adenoviruses?
To date, 19 species with more than fifty serotypes are known of the human adenoviruses. The viruses do not have an envelope but a so-called capsid with a diameter of seventy to ninety nanometers. The capsid consists of regularly arranged proteins in the shape of a dodecagon with antenna-like extensions at the corners. Because human adenoviruses do not have a delicate envelope, they can survive for long periods outside a host. The core of the viruses consists of a linear, double-stranded DNA. This special form of DNA makes them very resistant to physical and chemical influences. Thus, the viruses are quite robust against alcoholic disinfectants. They can also tolerate strongly acidic or basic pH values. However, they are quite sensitive to temperature. If human adenoviruses are exposed to temperatures of 56 degrees Celsius or higher for at least ten minutes, they are completely inactivated.
Importance and function
Of the known 19 species of human adenoviruses, six can cause disease in their host. However, by no means is every infection detected. About half of all infections proceed without the affected person developing visible symptoms. Infections in which symptoms do develop take a mild course in the majority of cases. In this case, treatment is either not carried out at all or only symptomatic. In more severe cases, only complications and symptoms can be treated, as there are no virus-inhibiting drugs. The severity of the course of infection may depend on the site of entry of the virus. Thus, an oral infection may be asymptomatic or mild, whereas infection by inhalation may lead to severe disease. Adenoviruses are transmitted by direct contact with a host, or in the case of poor hygiene, fecal-oral as a smear infection. Occasionally, infection can also occur via water. Once human adenoviruses have entered the body, they usually infect the epithelial cells of the nose, throat, lungs, and digestive tract. Less frequently, they also infect the eye. In addition to acute infectious diseases resulting from infection, there is also a suspected link between obesity and a particular serotype of adenoviruses. Apart from their harmful effect, adenoviruses can also be used to treat diseases. For example, they can be used to produce genetically modified vaccines against the highly dangerous Ebola virus. In cancer therapy, they help to inhibit tumor growth. Gene therapy also benefits from the viruses. For example, human adenoviruses are used in gene therapy for a certain form of muscle atrophy.
Diseases
The respiratory tract is most commonly affected by human adenoviruses. The manifestation of the infection here can range from a simple cold with a runny nose and sore throat to bronchitis and even pneumonia. They are therefore of particular importance in epidemic flu infections of varying severity. Immunocompromised people in particular run the risk of developing severe complications. They may, for example, suffer acute lung failure. If human adenoviruses settle in the digestive tract, they can cause gastrointestinal inflammation with diarrhea, nausea, vomiting, and abdominal pain. Further along the digestive tract, they can also infect the mucous membranes of the bladder and cause cystitis. For example, by rubbing with contaminated hands, it is possible for adenoviruses to be carried into the eye. There they lead to inflammation of the conjunctiva and cornea and to dry eyes. Often, diseases of the eye caused by these viruses stem from bathing in small lakes or inadequately chlorinated swimming pools. If infections with human adenoviruses are spread, serious diseases can be the result. For example, an infestation of the lungs can develop into an inflammation of the cartilaginous bronchial tissue, which is accompanied by asthma-like symptoms. If the viruses migrate in the body, they can also cause pain in joints or disturbances in heart muscle function.Hearing loss or the development of type 1 diabetes are also possible late effects of infection with human adenoviruses.
