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Adenoviruses are unenveloped, icosahedral, double-stranded
DNA viruses that possess species-specific, group-specific and typespecific
antigens. There are more than 50 serotypes of human
adenoviruses, which are divided into six groups (A-F) on the basis
of their genomic homology.
Epidemiology and Clinical features
- Transmitted by direct contact and faecal-oral route.
- Pharyngoconjunctival fever is caused by serotypes 3 and 7.
- Acute febrile pharyngitis is caused by serotypes 1-7.
- Serotypes 40 and 41 cause enteric infection.
- Serotypes 8, 19 and 37 cause conjunctivitis.
- Serotypes 4, 17 and 14 cause respiratory infection.
- Haemorrhagic cystitis is caused by serotypes 11 and 21.
- Immunocompromised patients may suffer severe pneumonia
(serotypes 1-7), urethritis (serotype 37) and hepatitis in liver
- The clinical spectrum may vary depending on the site of
Genetically modified adenoviruses and adeno-associated viruses
are increasingly being explored as vectors for gene therapy.
Diagnosis is usually made by nucleic acid amplification test
(NAAT) but culture, serology and electron microscopy (EM) Diagnosis
Prevention and control
Outbreaks must be managed according to infection control practices
(both respiratory and contact). Outbreaks of ocular infection
at swimming pools are prevented by adequate chlorination. Transmission
between patients undergoing ophthalmic examination can
be prevented by single-use equipment, adequate decontamination
of equipment and appropriate hygiene by healthcare staff.
Parvoviruses are small, unenveloped, icosahedral, single-stranded
DNA viruses with one serotype, B19, known to cause human
disease and given the genus name Erythrovirus.
Infection is found worldwide and throughout the year. Transmission
is by the respiratory route. It may cause outbreaks of erythema
infectiosum in schools. Seroprevalence increases with age
with more than 60% of adults possessing antibody.
Pathogenesis and Clinical features
- Parvovirus B19 invades red blood cells through globoside P
replicating in immature erythrocytes.
- It produces erythema infectiosum, a mild febrile disease that
typically occurs in young children who may exhibit a 'slapped
- A symmetrical, small-joint arthritis may also develop, especially
- Red cell production is arrested by infection, which may cause
severe anaemia in patients with a high red blood cell turnover (e.g.
aplastic crises in patients with sickle cell disease).
- The risk of infection in pregnancy is low, but it may lead to
hydrops fetalis and fetal death, although there is no evidence that
parvovirus causes congenital abnormalities.
- Infection during the first 20 weeks of pregnancy results in 10%
Prevention and control
- Diagnosis is usually made clinically, but NAAT is the test of
- Detection of IgM is also used.
- Blood, nasal or throat washings, cord blood and amniotic fluid
can be examined by EM.
No specific treatment or vaccine is available at present.
Respiratory precautions should prevent transmission in the hospital
These are small, enveloped, double-stranded DNA viruses with
more than 100 types. Some are responsible for common warts and
genital warts. Types 16 and 18 predominate in cervical neoplasia;
they are transmitted by close contact, including by the sexual
route. Diagnosis of a common wart is clinical; cervical neoplasm
is diagnosed by cytology and NAAT. A vaccine against types 6,
11, 16 and 18 is now in use.
Poxviruses are double-stranded DNA viruses with complex symmetry
and a shape that resembles a ball of wool.
Once a major cause of death worldwide this has now been eradicated
but there are concerns that smallpox may become a bioterrorism
weapon, which have prompted some countries to produce
stocks of vaccine.
A zoonotic infection in rainforest areas of Central and West Africa
that is similar to smallpox. The case fatality rate can reach 10% in
Africa, but was much lower in the USA where there was an outbreak
associated with infected prairie dogs. Diagnosis is by EM
A zoonotic, pustular dermatitis originating in sheep and goats that
is characterized by a single vesicular lesion, which is typically
found on the finger and resolves spontaneously after a few weeks.
Diagnosis is usually clinical on the basis of appearance and a
history of exposure.
- A common condition, especially in children, with crops of small,
regular, papular, 'pearl-like' skin lesions, usually occurring on the
face, arms, buttocks and back.
- It may be transmitted sexually, by direct contact or on fomites.
- Steroid therapy and/or infection with HIV increase the extent of
- The microscopic appearance is of epidermal hypertrophy that
extends into the dermis, and cells with inclusion bodies that are
seen in the prickle-cell layer.
- Diagnosis is usually clinical and can be confirmed by EM examination
of lesion scrapings.
- The rash may last 1 year in immunocompetent individuals and
may become a chronic problem for patients with HIV infection.
Traditional treatment - by prodding the lesions with a sharp
implement - promotes healing.
Tanapox is a febrile illness usually associated with a single nodular
skin lesion that may ulcerate and heal spontaneously. Infection
is acquired in central and east Africa; the diagnosis is usually
suggested by the travel history and can be confirmed by EM