DNA Viruses and Adenoviridae Overview

DNA Viruses

• All DNA viruses replicate in the nucleus except for Poxviridae
• Poxviridae replicate in the cytoplasm
• All DNA viruses are double stranded except for Parvoviridae
• Poxviridae is a complex virus, all other viruses are icosahedral

Adenoviridae

• First isolated in 1953
• Many infections are subclinical
• Virus can persist in the host for months
• Early genes control host and viral transcription and DNA replication, late genes are for virion structure
• Viral infectious cycle takes about 24 hours
• Produces about 100,000 virus particles per cell
• Assembly process is inefficient
• Adenoviruses are cytopathic for human cells
• They do not induce syncytia or multinucleated giant cells

Adenovirus Infections

• Marked rounding, enlargement and aggregation of affected cells into grape-like clusters
• Can morphologically transform cells in culture but are not thought to be important in human cancer
• Cells infected with oncogenic adenoviruses contain rounded intranuclear inclusions containing DNA

Adenovirus Eye Infections

• Transmitted in several ways but hand to eye transfer is most common
• Types 3, 7, and 21 are associated with pharyngoconjunctival fever
• Symptoms are similar to acute febrile pharyngitis but conjunctivitis is also present
• Occurs in outbreaks
• Duration of the illness is 1 to 2 weeks
• Most people recover completely without lasting sequelae

Adenovirus Eye Infections Cont.

• Types 8, 19, and 37 are associated with epidemic keratoconjunctivitis
• Occurs mainly in adults and is highly contagious
• Resolves in 2 weeks but may leave sub epithelial opacities for up to 2 years

Adenovirus Gastrointestinal Disease

• Many adenoviruses replicate in intestinal cells and are present in the stool without being associated with GIT disease
• Types 40 and 41 are associated with 5-15% of viral gastroenteritis cases in young children

Adenovirus Other Infections

• Transplant patients may suffer adenovirus infections, especially in the gastrointestinal tract
• Liver transplant patients may develop adenovirus hepatitis in the allograft
• Heart transplant patients who develop myocardial adenovirus infections are at increased risk of graft loss
• Immunocompromised patients suffer adenovirus infections, especially in the gastrointestinal tract
• Types 11 and 21 may cause acute hemorrhagic cystitis in children, especially boys
• Adenoviruses are commonly found in the urine of immunocompromised patients

Adenovirus Canine Infections

• A form of adenovirus that is highly infectious in dogs causing an acute liver infection
• CAdV-1 causes infectious canine hepatitis, respiratory and eye infections
• CAdV-2 is a potential cause of kennel cough
• Core vaccines for dogs include attenuated live CAdV-2, which produces immunity to CAdV-1 and CAdV-2

Adenovirus Other Animal Infections

• Adenoviruses are known to cause respiratory infections in horses, cattle, pigs, sheep, and goats

Adenovirus Immunity

• Most healthy adults have antibodies to several adenovirus types
• Maternal antibodies protect infants from severe adenovirus respiratory infections
• Resistance to clinical disease is directly related to the presence of circulating neutralizing antibodies, which probably persist for life

Parvoviridae Replication

• The viral mRNA is synthesized by cellular RNA polymerase from the double-stranded DNA intermediate
• Newly synthesized single-stranded DNA is converted to double-stranded DNA and serves as a template for transcription or replication
• Progeny virions are assembled in the nucleus.
• They are released by cell lysis
• There are two capsid proteins
• Viral replication results in cell death

Parvoviridae Transmission

• The respiratory route
• Parenterally by blood transfusions
• Vertically from mother to fetus

Parvoviridae Transmission Cont.

• There is no evidence of virus excretion in feces or urine
• Transmission of B19 from patient with aplastic crisis to members of the hospital staff has been documented
• Patients with aplastic crisis are likely to be infectious during the course of their illness
• Patients with fifth disease are probably no longer infectious by the time of onset of the rash

Parvoviridae Pathogenesis

• Erythema infectiosum (fifth disease), a common childhood exanthem
• Aplastic crisis (anemia) in patients with hemolytic disorders
• Fetal death
• Chronic anemia in immunocompromised individuals
• Polyarthralgia-arthritis syndrome in adults

Parvoviridae Erythema Infectiosum

• Most common in children of early school age
• Illness is biphasic: First and Second
• Both sporadic cases and epidemics have been described
• Symptoms mimic rheumatoid arthritis and the arthropathy may persist for weeks, months, or years