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PICORNAVIRIDAE and
CALICIVIRIDAE
By: Rochelle V. Villa-Abrille BSN-2
PICORNAVIRIDAE The name picornavirus means little RNA virus
(pico means very small). are among the oldest viruses. are also
among the most diverse viruses, with over 200 serotypes causing
infections such as polio, hepatitis -A,& the common colds.
foot- and-mouth disease virus (genus: Apthovirus), which causes
infections in livestock, was one of the first viruses to be
recognized (discovered by Loeffler and Frosch in 1898).
GENERA: Enterovirus Rhinovirus Hepatovirus Apthovirus
Cardiovirus Parechovirus Erbovirus Kobuvirus Teschovirus
GENOME STRUCTURE: consists of a single molecule of linear,
positive-sense, single strand RNA. non-segmented. the complete
genome is 7000-8500 nucleotides long. Internal Ribosome Entry Site
(IRES),w/c is a secondary structure distinguishes picornaviruses
from other RNA viruses; this structure is important in translation
and replication.
Virion Structure of a Picornavirus consist of a non-enveloped,
icosahedrally symmetric capsid. consist of 12 capsomers. has a
diameter of 27-30nm, which makes it one of the smallest of all
viruses. tightly packed into the capsid. four unique proteins of
capsid:-VP1,2,3,and 4.
Reproductive Cycle of a Picornavirus In a Host Cell it attaches
to a host cell. virus replication occurs entirely in the cytoplasm.
release of the virus occurs when cell lysis occurs.
4 Picornavirus Genera that cause Human disease: Enteroviruses
Rhinoviruses Hepatovirus Parechoviruses
Enteroviruses transmitted through the fecal-oral route and are
highly communicable. cause wide variety of syndromes that range in
severity from mild and non-neurologic to neurologic, paralytic, and
fatal. poliomyelitis commonly known as polio. infectious disease
caused by polioviruses 1,2, and 3 in the enterovirus genus.
transmitted through the fecal-oral route, either directly from
person-to-person or indirectly through contaminated water sources.
characterized by permanent paralysis due to spinal nerve damage and
muscular wasting. commonly affected are young children.
Rhinoviruses transmitted through the respiratory route and
replicate in the nose ( rhino ). it causes common cold.
Hepatovirus is the lone virus in its own genus. transmitted
through the fecal-oral route, which is manifested most often by
ingestion of contaminated food and water. the resulting disease is
Hepatitis-A.
Parechoviruses these viruses are closely related to the
ECHOvirus group, a name that refers to Enteric Cytophatic Human
Orphan virus.
CALICIVIRIDAE ***
DEFINITION are a family of viruses, members of Class IV of the
Baltimore Scheme. positive-sense, single stranded RNA which is
non-segmented. have been found in a number of organisms such as
humans, cattle, pigs, cats, chickens, reptiles, dolphins, and
amphibians. simple construction and are not enveloped.
capsid appears hexagonal/spherical and has icosahedral symmetry
w/ a diameter of 35-39nm. are not very well studied because until
recently they could not be grown in culture, and there is no
suitable animal model. the name calicivirus is derived from the
Greek word calyx meaning cup or goblet.
TaxonomyInclude the following genera: Lagovirus; type species:
Rabbit hemorrhagic disease virus. Nebovirus Norovirus; type
species: Norwalk virus. Sapovirus; type species: Sapporo virus.
Vesivirus; type species: Vesicular exanthema of swine virus.
2 additional genera have been proposed: a.) Recovirus- was
detected in stool specimens from rhesus monkeys. b.) Valovirus-
novel group of swine caliciviruses known as the St.-Valerien-like
viruses. These genera have yet to be officially approved. There are
a number of other unclassified caliciviruses including the chicken
calicivirus.
Transmission transmitted generally through the fecal-oral route.
also transmitted via the respiratory route.
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Human Disease commonly cause acute gastroenteritis which is the
inflammation of the stomach and intestines (e.g. Norwalk virus and
Sapovirus). symptoms include vomiting and diarrhea; generally last
for 3 days.
Epidemiology/Geographic distribution have a worldwide
distribution and noroviruses are a major cause of epidemic
non-bacterial gastroenteritis.
Treatment normally infections do not require medical attention.
rehydration therapy may be used in these instances.
Prevention handwashing is an effective preventative measure.
sanitizing surfaces is also recommended in preventing the spread of
infection.
