BIOTECH Outline
Ms Steffens, Period 2+6
TOPIC:
Retro Viruses and others - Taxonomy
1. Animal virus structural generalizations:
a) Among DNA viruses which infect animals, all are double-stranded except those known as
parvoviruses (which have single-stranded DNA genomes).
b) Among RNA viruses which infect animals, all are single stranded except those known as
reoviruses (which have double-stranded RNA genomes).
c) # Illustration, variation in virus genomes
d) # Virus taxonomy
2. Classification:
A. Morphological classification:
a) Host range aside, viruses traditionally are distinguished by their morphologies (at least, of
course, in the present electron microscopy era).
b) Much of virus classification has consequently been done mostly via the study of
morphologies and is called virus taxonomy.
B. Genomic classification:
a) Viruses are also differentiated by similarities and differences in their genomes . See virus
species.
b) The morphologies of various families of human-infecting viruses are shown in tables 11.1
and 11.2 (p. 276, Black, 1996) along with a listing of representative virus genera and
common names.
3. Virus types
A. Standard nomenclature:
a) Viruses are first classified as having animal, plant, bacterial, etc. hosts. Within each large
host-based phylogenetic grouping there exist numerous schemes of virus classification.
b) "A widely used scheme for classifying animal viruses first assigns them to one of two
superfamilies, either those containing DNA or those containing RNA. DNA viruses can be
further subdivided into six families, and RNA viruses into 17 families, for a total of 19
families.” (p. 169, Talaro and Talaro, 1996; see also pp. 170-171 )
c) Virus families are given a name comprised of a Latin root followed by -viridae.
Characteristics used for placement in a particular family include type of capsid, nucleic
acid strand number, presence and type of envelope, overall viral size, and area of the
host cell in which the virus multiplies. . . Each different type of virus is also assigned
genus status according to its host, target tissue, and the type of disease it causes. Viral
genera are denoted by a special Latinized root followed by the suffix -virus (for example,
Enterovirus and Herpesvirus).
“Because the use of standardized species names has not been widely accepted, the
genus or common English vernacular names (for example, poliovirus and rabies virus)
predominate in discussions of specific viruses." (Talaro and Talaro, 1996)
4. These are the viruses found in animals:
A) Double-stranded, enveloped, DNA viruses of animals:
1. Hepadnaviridae (hepa-DNA-virus) infect the liver and includes hepatitis B virus (HBV). All
health workers should be vaccinated against HBV.
2. Herpesviridae include:
a. herpes simplex 1 (oral herpes)
b. herpes simplex 2 (genital herpes)
c. herpes zoster (varicella-zoster, a.k.a., chickenpox)
d. cytomegalovirus (CMV)
e. Epstein-Barr virus (EBV)
f. etc.
3. Herpesviruses have a tendency toward latent and recurrent infections, and have an
associated tendency to incorporate their genome into that of their host.
4. Latent herpes infections lead to complications particularly in the immunosuppressed.
5. Poxviridae are the largest and most complex of viruses. The Poxviruses incluce the
smallpox virus (Variola major and minor), vaccinia virus, etc.
B) Double-stranded, non-enveloped, DNA viruses of animals:
a. Adenoviridae are one of the etiologies of the common cold. About 30 adenovirus
strains are known. They can also cause conjunctivitis as well as chronic
respiratory infections.
b. Papovaviridae include those which cause warts (papillomaviruses).
C) Single-stranded, nonenveloped, DNA viruses of animals:
1. Parvoviridae cause some human disease, though in most cases symptoms are mild.
D) Segmented, single-stranded, enveloped, negative sense, RNA viruses of animals:
a. Arenaviridae
b. Bunyaviridae includes California encephalitis virus, Hanta virus (hemorrhagic
fever).
3. Orthomyxoviridae includes influenza virus.
E) Non-segmented, single-stranded, enveloped, negative sense RNA viruses of animals:
1. Filoviridae includes Ebola fever virus, Marburg virus.
2. Paramyxoviridae includes:
a. measles virus
b. mumps virus
c. respiratory syncytial virus
3. Rhabdoviridae includes the rabies virus.
F). Non-segmented, single-stranded, enveloped, positive sense RNA viruses of animals:
1. Coronaviridae includes common cold viruses.
2. Togaviridae includes:
a. dengue fever virus
b. equine encephalitis viruses
c. rubella virus
d. yellow fever virus
G) Non-segmented, single-stranded, nonenveloped, positive sense RNA viruses of animals:
1. Caliciviridae includes Norwalk virus.
2. Picornaviridae includes hepatitis A virus, polio virus, rhinoviruses.
H). Retroviridae are animal viruses with the following characteristics:
a) 1. nonsegmented
2. single-stranded
3. enveloped
4. positive sense
5. diploid
6. reverse transcriptase using
7. RNA genomes
b) . Examples include:
1. human immunodeficiency virus (HIV, a.k.a., HTLV-III)
2. human T-cell leukemia virus (HTLV-I)
3. hairy cell leukemia virus (HTLV-II)
4. etc.
I) . Reoviridae:
a) Reoviridae are segmented, double-stranded, nonenveloped (double capsid) positive
sense, RNA viruses of animals.
b). Examples include tick fever virus and rotavirus gastroenteritis.