Adenovirus infection

Symptoms are variable, ranging from mild symptoms to severe illness.[5] They depend on the type of adenovirus, where it enters into the body, and on the age and well-being of the person.[2] Recognised patterns of clinical features include respiratory, eye, gastrointestinal, genitourinary and central nervous system.[2] There is also a widespread type that occurs in immunocompromised people.[2] Typical symptoms are of a mild cold or resembling the flu; fever, nasal congestion, coryza, cough, and pinky-red eyes.[6] Infants may also have symptoms of an ear infection.[2] Onset is usually two to fourteen days after exposure to the virus.[11] There may be tiredness, chills, muscle aches, or headache.[2] However, some people have no symptoms.[4] Generally, a day or two after developing a sore throat with large tonsils, glands can be felt in the neck.[16] Illness is more likely to be severe in people with weakened immune systems, particularly children who have had a hematopoietic stem cell transplantation.[8] Sometimes there is a skin rash.[5]

Adenovirus infection in humans are generally caused by Adenoviruses types B, C, E and F.[12]

Although epidemiologic characteristics of the adenoviruses vary by type, all are transmitted by direct contact, fecal-oral transmission, and occasionally waterborne transmission. Some types are capable of establishing persistent asymptomatic infections in tonsils, adenoids, and intestines of infected hosts, and shedding can occur for months or years. Some adenoviruses (e.g., serotypes 1, 2, 5, and 6) have been shown to be endemic in parts of the world where they have been studied, and infection is usually acquired during childhood. Other types cause sporadic infection and occasional outbreaks; for example, epidemic keratoconjunctivitis is associated with adenovirus serotypes 8, 19, and 37. Epidemics of febrile disease with conjunctivitis are associated with waterborne transmission of some adenovirus types, often centering on inadequately chlorinated swimming pools and small lakes. ARD is most often associated with adenovirus types 4 and 7 in the United States. Enteric adenoviruses 40 and 41 cause gastroenteritis, usually in children. For some adenovirus serotypes, the clinical spectrum of disease associated with infection varies depending on the site of infection; for example, infection with adenovirus 7 acquired by inhalation is associated with severe lower respiratory tract disease, whereas oral transmission of the virus typically causes no or mild disease. Outbreaks of adenovirus-associated respiratory disease have been more common in the late winter, spring, and early summer; however, adenovirus infections can occur throughout the year.[18]

Several adenoviruses, including Ad5, Ad9, Ad31, Ad36, Ad37, and SMAM1, have at least some evidence of causation of obesity in animals, adipogenesis in cells, and/or association with human obesity.[19]

Diagnosis is by signs and symptoms, and a laboratory test is not usually required.[4] In some circumstances such as severe disease, when a diagnosis needs to be confirmed, a PCR test on blood or respiratory secretions may detect adenovirus DNA.[4][8] Adenovirus can be isolated by growing in cell cultures in a laboratory.[3] Other conditions that appear similar include whooping cough, influenza, parainfluenza, and respiratory syncytial virus.[2] Since adenovirus can be excreted for prolonged periods, the presence of virus does not necessarily mean it is associated with disease.[20]

Infection by adenovirus may be prevented by washing hands, avoiding touching own eyes, mouth and nose before washing hands and avoiding being near sick people.[9] Strict attention to good infection-control practices is effective for stopping transmission in hospitals of adenovirus-associated disease, such as epidemic keratoconjunctivitis.[18] Maintaining adequate levels of chlorination is necessary for preventing swimming pool-associated outbreaks of adenovirus conjunctivitis.[9] A live adenovirus vaccine to protect against types 4 and 7 adenoviruses has been used in some military personnel.[9] Rates of adenovirus disease fell among military recruits following the introduction a live oral vaccine against types 4 and 7.[2] Stocks of the vaccine ran out in 1999 and rates of disease increased until 2011 when the vaccine was re-introduced.[2]

Treatment is generally symptomatic and supportive.[9] Medicines to ease pain and reduce fever can be bought over the counter.[9] For adenoviral conjunctivitis, a cold compress and lubricants may provide some relief of discomfort.[16] Steroid eye drops may be required if the cornea is involved.[16] Most adenovirus infections get better without any treatment.[9]

After recovery from adenovirus infection, the virus can be carried for weeks or months.[11]

Adenovirus can cause severe necrotizing pneumonia in which all or part of a lung has increased translucency radiographically, which is called Swyer-James Syndrome.[21] Severe adenovirus pneumonia also may result in bronchiolitis obliterans, a subacute inflammatory process in which the small airways are replaced by scar tissue, resulting in a reduction in lung volume and lung compliance.[21]

Adenovirus infections occur sporadically throughout the year, and outbreaks can occur particularly in winter and spring.[11] Epidemics may spread more quickly in closed populations such as in hospitals, nurseries, long-term care facilities, boarding schools, orphanages and swimming pools.[11] Severe disease is rare in people who are usually healthy.[11] Around 10% of respiratory infections in children are caused by adenoviruses.[11] Most are mild and by the age of 10-years, most children have had at least one adenovirus infection.[5]

Adenoviruses are the most common viruses causing an inflamed throat.[16] 75% of conjunctivitis cases are due to adenovirus infection.[14] Under two-year olds are particularly susceptible to adenovirus gastroenteritis by types 40 and 41, with type 41 being more common than type 40.[13] Some large studies have revealed type 40/41 adenovirus as one of the second most common causes of diarrhoea in children in low and middle income countries; the most common being rotavirus.[13] In 2016, the Global Burden of Disease Study estimated that globally, around 75 million episodes of diarrhea among children under the age of five-years, were attributable to adenovirus infection, with a mortality of near 12%.[13]

Research in adenovirus infection has generally been limited relative to other respiratory disease viruses.[13] The impact of type-40/41 adenovirus diarrhoea is possibly underestimated.[13]

The first adenoviral strains were isolated from adenoids in 1953 by Rowe et al.[15] Later, during studies on rotavirus diarrhoea, the wider use of electron microscopy resulted in detecting previously unrecognized adenoviruses types 40 and 41, subsequently found to be important in causing gastrointestinal illness in children.[5]

The illness made headlines in Texas in September 2007, when a so-called "boot camp flu" sickened hundreds at Lackland Air Force Base in San Antonio.[22] In 2018, outbreaks occurred in an adult nursing home in New Jersey, and a college campus in Maryland.[3] In 2020, as a result of infection control measures during the COVID-19 pandemic, rates of adenovirus diarrhoea declined significantly in China.[23]

Dogs can be affected by adenovirus infection.[24] Severe liver damage is a classical infectious disease seen in unvaccinated dogs.[25]