Biomedical Engineering Reference
In-Depth Information
Buffalopox, cowpox, and monkeypox produce diseases in animal reser-
voirs and rarely infect humans. Human infections occur from close contact
with infected animals and manifest much like smallpox, but milder.
Members of Class Parapoxvirus infect vertebrates, particularly sheep,
goats, cattle, and red squirrels. Orf virus causes “sore mouth” or “scabby
mouth” disease of sheep and goats. Humans, though rarely infected, may
develop painful hand sores. A similar condition can occur in humans who
handle the udders of cows infected with Milker's nodule virus.
Class Molluscipoxvirus contains one species infectious in humans,
Molluscum contagiosum virus. Molluscum contagiosum is an eruption of
wart-like skin lesions that are easily diagnosed on histological examination
by their distinctive cellular inclusions (so-called molluscum bodies). There
are no known animal reservoirs. Infection is spread from human to human.
Treatment is not always necessary, as individual lesions will regress within
two months. However, auto-inoculation of the virus may produce new skin
lesions, thus prolonging the disease.
Members of Class Yatapoxvirus infect primates in equatorial Africa.
Infections can spread to humans by insect vectors. Tana poxvirus produces a
pock-forming skin infection, with fever and lymphadenopathy in infected
humans (like a mild form of smallpox). The Yaba monkey tumor virus pro-
duces histiocytomas in monkeys. Histiocytomas are proliferative lesions of
fibrous tissue that yield tumor-like nodules. These virally induced histiocyto-
mas in monkeys grow rapidly following infection, and then regress over the
ensuing month [127]. Yaba monkey tumor virus and Yaba-like disease virus,
like all members of Class Yatapoxvirus, are considered potential human
pathogens.
Group I, dsDNA
Unassigned
Nucleocytoplasmic large DNA viruses (NCLDV viruses)
Mimiviridae
Mimivirus
*Acanthamoeba polyphaga mimivirus (pneumonia)
Class Mimiviridae, discovered in 1992, occupies a niche that seems to span
the biological gulf separating living organisms from viruses. Members of
Class Mimiviridae are complex, larger than some bacteria, with enormous
genomes (by viral standards), exceeding a million base pairs and encoding
upwards of 1000 proteins. The large size and complexity of Class Mimiviridae
exemplifies the advantage of a double-stranded DNA genome. DNA is much
more chemically stable than RNA, and can be faithfully replicated, even when
its length exceeds a billion base pairs. A double-stranded DNA genome can be
protected by DNA repair enzymes, and by external modifications to the DNA
structure. Class Megaviridae is a newly reported (October, 2011) class of
viruses, related to Class Mimiviridae, but larger [128].
