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Lecture 2: Foodborne Virus (Introduction (Methods of transmission (Subject…
Lecture 2: Foodborne Virus
Introduction
Characteristics
Strict intracellular parasites with cellular specificity (cell tropism)
Replication - strongly dependent on host organism; cannot multiply outside the host
Small acellular microorganisms with diameters of 15-400 nm, each containing only one type of nucleic acid
Replicate process of viruses: Attachment, penetration, transfection, replication and synthesis, assembly, release
Methods of transmission
Subject soiled with human or animal
feces or vomit
Contact with
blood
of infected persons
Aerosol
Contact with
diseased
animals
Sexual intercourse
Vectors
(gnats or ticks) that can transmit arboviruses
Examples
Foodborne outbreaks: group B and C rotaviruses
Waterborne outbreaks: hepatitis E virus
Foodborne pathogens:
Norovirus
, hepatitis A virus
Symptoms and differences from bacterial infections
High numbers of viral particles are further
transmitted via feces
of infected people
Specific living cells
are necessary for virus replication; accordingly they cannot multiply in foods or water
Only a
few viral particles
are necessary for the disease to develop
Foodborne viruses are
relatively stable
and
acid-resistant
outside host cells
1. Foodborne viruses: Norwalk viruses
Characteristics
Small, non-enveloped RNA viruses
Family
Caliciviridae
Host: humans
Clinical attributes
Acute viral gastroenteritis
Symptoms: abdominal pain, nausea, vomiting (non-bloody), headache, malaise, myalgia
Transmission
Fecal-oral route
; eating contaminated food, drinking contaminated water
Person-to-person contact
; secondary transmission, direct contact
Pathogenesis
After ingestion, the virus will cause infection of the
mucosa of the proximal small intestine, damage of microvilli, malabsorption of D-xylose, lactose and fat
No invasion of the colon - no fecal leukocytes in the stool
Process: Entry, Infection (small intestine), disease (diarrhea), exit
2. Enteroviruses
Characteristics
Ubiquitous, enterically transmitted viruses - infect infants and children
Designation of enteroviruses - capability to multiply in the
intestine
Member of the broad
Picornaviridae
family of the RNA viruses; five major groups - polioviruses, group A coxsackieviruses, group B coxsackieviruses, echoviruses, newer identified enteroviruses
Resistant
to the impact of the environment; stable in
acid conditions
(pH 3-5), and also in gastric juices
Transmission
Fecal-oral route
; spread of certain species via
aerosol
Process: Viral particles are shed with with feces. Viruses enter the host with contaminated water or food and multiply in the digestive tract
Symptoms
Asymptomatic
Viruses may spread into other organs and cause diseases that are serious or fatal such as
aseptic meningitis
, and occasionally
paralysis
3.
Hepatovirus
Characteristics
Hepatitis A virus (HAV) - the only member of the genus
Hepatovirus
of the family Picornaviridae
Differs from enterviruses by certain biological characteristics
marked tropism for
liver cells
exceptional
thermostability
(survives heating for 30 min to 56 C)
acid-resistance
(tolerates pH 1)
slow replication
without cytopathic effect on the host cell
Transmission
Fecal-oral route
;
direct contact
with an HAV-infected person or by
ingestion
of HAV-contaminated food or water
viral infection of the liver spread when faecal matter enters the mouth
Symptoms: nausea, vomiting
4. Hepatitis E virus (HEV)
Characteristics
small non-enveloped virus
common in tropical and subtropical countries
Transmission:
Fecal-oral route
(fecal contaminated drinking water as usual vehicle)
Target
Young adults (15-30 years)
Pregnant women - may suffer high fatality rate from fulminant hepatic failure
Sources: (zoonotic virus) pigs/swine, rodents
5.
Rotavirus
Characteristics
segmented double-stranded RNA viruses - explains genetic variability and the presence of mixed infections; allows genomic re-assortment which results in development of new antigenic types
Serological groups - A (two to three subgroups and 11 serotypes) to E; Rotavirus F and Rotavirus G groups are provisional for the present. Group A, B and C - human rotaviruses
belong to family Reoviridae
non-enveloped virus - have a degree of robustness in the environment outside the host; can survive for weeks in potable and recreational waters, at least four hours on human hands
relatively resistant to commonly used hard-surface disinfectants and hygienic hand-wash agents
Sources: waste water; concentrated by shellfish
Transmission
Fecal-oral contact
(facilitated by deficient sanitary conditions) and possibly by
contaminated surfaces
and
hands and respiratory spread
May develop
directly
after consumption of meat from an infected animal, or
indirectly
by consumption of contaminated food usually eaten raw
Food
contaminated after being cooked
may also be the source of viral infection