What is Adenovirus?
Adenoviruses are a family of very common viruses. On a molecular level, they are large, double-stranded DNA viruses, meaning that their genomic material consists of the same structure as the human genome.
Adenoviruses are very common and known for causing upper respiratory tract infections in children and adults alike. In addition, adenoviruses can cause a variety of diseases affecting multiple organ systems, including:
Adenoviruses are common across the animal kingdom as well, infecting hosts ranging from lizards and frogs through dolphins, birds and humans. Evolutionarily, this makes adenovirus one of the most successful pathogens, due to its ability to infect and replicate in a wide range of hosts [5].
This evolutionary success makes adenoviruses an effective tool in modern biomedical research and medicine. They are common vectors in gene therapy, where the virus is engineered to not cause disease, however insert a gene of interest for example into a cancerous tumour (this is called an oncolytic virus) [6, 7].
Adenoviruses are also used in vaccines as vectors, such as the Oxford-AstraZeneca COVID-19 vaccine, which uses an adenovirus vector to introduce the COVID-19 spike protein into the human body, allowing the immune system to mount a response.
Symptoms, Diagnosis and Treatment of Adenovirus
The most common clinical presentation of adenovirus is it's respiratory form. This presents with symptoms similar to those of a common cold, including:
- runny nose (rhinorrhea),
- cough,
- fever,
- sore throat [8].
In more severe forms, adenovirus can lead to bronchitis (inflammation of the bronchi) and pneumonia, which can be even fatal [8].
Other diseases with distinct presentations can be associated with an adenovirus infection, including:
- conjunctivitis (pink eye) - inflammation of the conjuctiva, which is a transparent membrane shielding the eye,
- gastroenteritis - inflammation in the gastrointestinal tract,
- cystitis - inflammation of the bladder,
- myocarditis and cardiomyopathy - inflammations in the heart,
- meningoencephalitis - inflammation in the meninges (protective layers around the brain) [8].
Diagnostic Process of Adenovirus
Diagnosis of adenovirus infection is often challenging due to the nonspecific nature of the symptoms, particularly in its most common respiratory form. However, the virus can be diagnosed through laboratory tests including:
- detection of adenovirus antigen in nasopharyngeal swabs or feces [9],
- PCR test on throat swabs or specimen from the bronchi [10, 11],
- immunosorbent assays for adenovirus-specific antibodies [11].
In difficult cases, the viral load in the blood is often monitored to provide insight into the success of the treatment [12].
Treatment for Adenovirus Infection
Currently, there are no specific drugs approved for adenovirus infection. In most cases, the disease is mild and usually resolves on its own. It is important to not administer antibiotics for a viral infection, as this leads to development of antimicrobial resistance.
For advanced and complicated cases, antiviral drugs such as cidofovir or brincidofovir have been found to be effective, however they are not currently approved specifically for adenovirus [12, 13].
Other treatment modalities for difficult cases include respiratory support and bronchoscopy, immunomodulatory therapies and blood purification [10, 14].
How Long is Adenovirus Contagious?
Adenovirus can be contagious for varying lengths of time. The time of clearance of the infection period depends on the type of infection, the exact virus that is infecting the patient, the organ systems involved, and, most importantly, the immune system of the patient. Patients with lower functionality of the immune system tend to clear infections slower, and have more complicated progression of the disease (any disease, including adenovirus infection).
As for numbers, most adenovirus infections clear within two weeks, with most infections being cleared within a week. Interestingly, adenovirus can survive up to 8 days on paper and up to 10 days on cloth, metal, and plastic 6.
In a study of nosocomial (hospital-borne) conjunctivitis caused by adenovirus type 4, infectious virus was regularly present in the affected eyes for one week but not usually for more than 10 days after the onset of symptoms [15].
In another study of adenoviral conjunctivitis in the US, there was no detectable virus by the day 14 visit in 6 out of 8 patients [16].
However, in immunocompromised patients, the clearance is much slower. In a case of gastroenteritis due to adenovirus type 41 in an immunocompromised patient, adenovirus particles were detected in stool specimens collected between 5 and 39 days after the onset of the diarrheal illness [17].
Summary
Adenovirus is a very common virus, most commonly causing mild respiratory illness that clears within a week. However, the exact duration can vary depend on factors such as the type of adenovirus, the type of infection, and the individual's immune status.