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Infectious Disease and Microbiology – Adenovirus Infections
Adenovirus infections are caused by nonenveloped, double-stranded DNA viruses measuring approximately 70–80 nm in diameter. Human adenoviruses belong to the genus Mastadenovirus and include more than 50 serotypes. These viruses possess an icosahedral capsid composed of 20 triangular faces and 12 vertices. The genome consists of linear double-stranded DNA encoding structural and nonstructural proteins. Infection may result in either lytic replication or latent persistence, and certain serotypes have demonstrated oncogenic potential in animal models.
Adenoviruses contribute to a proportion of viral respiratory illnesses. Although rhinoviruses are the most common cause of acute respiratory infections, adenoviruses account for up to 5% of respiratory infections in children and fewer than 2% in adults. Infections occur most frequently from fall through spring. Transmission occurs via inhalation of aerosolized particles, direct inoculation of conjunctival mucosa, and possibly via the fecal–oral route. Outbreaks of acute respiratory disease due to specific serotypes are well documented among military recruits, particularly in winter and spring. Following infection, type-specific antibodies develop and provide protection against reinfection with the same serotype. Severe or disseminated disease may occur in immunocompromised individuals, including patients with AIDS, solid-organ or bone marrow transplant recipients, and children with congenital immunodeficiencies.
In children, adenovirus commonly causes acute upper respiratory tract infection characterized by prominent rhinitis. Lower respiratory involvement, including bronchiolitis and pneumonia, may occur. Pharyngoconjunctival fever is a distinctive syndrome seen in outbreaks, particularly in summer camps, presenting with low-grade fever for 3–5 days followed by rhinitis, sore throat, cervical lymphadenopathy, and conjunctivitis, typically resolving within 1–2 weeks. Adenovirus also causes pharyngitis and, in young children, acute diarrheal illness. Other manifestations include hemorrhagic cystitis and epidemic keratoconjunctivitis. In adults, acute respiratory disease presents with sore throat, gradual onset of fever that may reach 39°C, cough, coryza, and lymphadenopathy. In immunocompromised patients, adenovirus pneumonia may present abruptly with fever, rigors, malaise, nonproductive cough, gastrointestinal symptoms, headache, and arthralgia.
Physical examination may reveal pharyngeal edema, injection, and tonsillar enlargement with minimal exudate. Ocular involvement presents with conjunctival injection and discharge. In immunocompromised hosts, localizing findings may be minimal despite severe disease.
Definitive diagnosis is established by viral culture or detection of adenovirus from conjunctival, oropharyngeal, sputum, urine, or stool specimens. Viral cytopathic effects in tissue culture can be confirmed by immunofluorescence or other immunologic assays. Certain enteric adenovirus types require specialized cell lines or direct ELISA testing of stool. Serologic diagnosis may demonstrate rising antibody titers using complement fixation, neutralization assays, ELISA, or radioimmunoassay. In adenovirus pneumonia, chest radiography often shows bilateral diffuse interstitial infiltrates and occasionally pleural effusions. The clinical presentation is frequently indistinguishable from other viral respiratory infections or Mycoplasma pneumoniae.
Management is primarily supportive, as no specific antiviral therapy is routinely indicated for immunocompetent patients. Live oral vaccines targeting adenovirus types 4 and 7 are used in military settings to prevent outbreaks. In immunocompromised individuals with severe infection, treatment with cidofovir and intravenous immunoglobulin has shown benefit in some cases. Intravenous gamma globulin and type-specific antibodies may also be helpful. Ribavirin and ganciclovir have been used in selected cases, although evidence remains limited.
In transplant recipients and other immunocompromised patients, adenovirus pneumonia carries significant morbidity and mortality, which may exceed 60%, underscoring the importance of early recognition and supportive management.
Adenovirus infections are caused by nonenveloped, double-stranded DNA viruses measuring approximately 70–80 nm in diameter. Human adenoviruses belong to the genus Mastadenovirus and include more than 50 serotypes. These viruses possess an icosahedral capsid composed of 20 triangular faces and 12 vertices. The genome consists of linear double-stranded DNA encoding structural and nonstructural proteins. Infection may result in either lytic replication or latent persistence, and certain serotypes have demonstrated oncogenic potential in animal models.
Adenoviruses contribute to a proportion of viral respiratory illnesses. Although rhinoviruses are the most common cause of acute respiratory infections, adenoviruses account for up to 5% of respiratory infections in children and fewer than 2% in adults. Infections occur most frequently from fall through spring. Transmission occurs via inhalation of aerosolized particles, direct inoculation of conjunctival mucosa, and possibly via the fecal–oral route. Outbreaks of acute respiratory disease due to specific serotypes are well documented among military recruits, particularly in winter and spring. Following infection, type-specific antibodies develop and provide protection against reinfection with the same serotype. Severe or disseminated disease may occur in immunocompromised individuals, including patients with AIDS, solid-organ or bone marrow transplant recipients, and children with congenital immunodeficiencies.
In children, adenovirus commonly causes acute upper respiratory tract infection characterized by prominent rhinitis. Lower respiratory involvement, including bronchiolitis and pneumonia, may occur. Pharyngoconjunctival fever is a distinctive syndrome seen in outbreaks, particularly in summer camps, presenting with low-grade fever for 3–5 days followed by rhinitis, sore throat, cervical lymphadenopathy, and conjunctivitis, typically resolving within 1–2 weeks. Adenovirus also causes pharyngitis and, in young children, acute diarrheal illness. Other manifestations include hemorrhagic cystitis and epidemic keratoconjunctivitis. In adults, acute respiratory disease presents with sore throat, gradual onset of fever that may reach 39°C, cough, coryza, and lymphadenopathy. In immunocompromised patients, adenovirus pneumonia may present abruptly with fever, rigors, malaise, nonproductive cough, gastrointestinal symptoms, headache, and arthralgia.
Physical examination may reveal pharyngeal edema, injection, and tonsillar enlargement with minimal exudate. Ocular involvement presents with conjunctival injection and discharge. In immunocompromised hosts, localizing findings may be minimal despite severe disease.
Definitive diagnosis is established by viral culture or detection of adenovirus from conjunctival, oropharyngeal, sputum, urine, or stool specimens. Viral cytopathic effects in tissue culture can be confirmed by immunofluorescence or other immunologic assays. Certain enteric adenovirus types require specialized cell lines or direct ELISA testing of stool. Serologic diagnosis may demonstrate rising antibody titers using complement fixation, neutralization assays, ELISA, or radioimmunoassay. In adenovirus pneumonia, chest radiography often shows bilateral diffuse interstitial infiltrates and occasionally pleural effusions. The clinical presentation is frequently indistinguishable from other viral respiratory infections or Mycoplasma pneumoniae.
Management is primarily supportive, as no specific antiviral therapy is routinely indicated for immunocompetent patients. Live oral vaccines targeting adenovirus types 4 and 7 are used in military settings to prevent outbreaks. In immunocompromised individuals with severe infection, treatment with cidofovir and intravenous immunoglobulin has shown benefit in some cases. Intravenous gamma globulin and type-specific antibodies may also be helpful. Ribavirin and ganciclovir have been used in selected cases, although evidence remains limited.
In transplant recipients and other immunocompromised patients, adenovirus pneumonia carries significant morbidity and mortality, which may exceed 60%, underscoring the importance of early recognition and supportive management.
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