Transcript Powerpoint Slides 3C

4. Blood-borne, urogenital, sexual
transmission
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Different routes
 Important factor in common:
secretions/tissues from infected individual
come into contact with mucus membranes
of uninfected individual
 Minimum environmental exposure for virus
 Many examples-behavior is primary
ecological factor
The unusual case of Hepatitis Viruses
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Viral hepatitis
2 types recognized
“infectious” aka Type A (HAV)
“serum” aka Type B (HBV)
Tests available for HBV in the 1970s, reveal NANB
hepatitis, agent identified in 1989 (HCV)
Hepatitis delta agent (HDV) 1983
Hepatitis E, 1983, GI virus, (HEV)
Hepatitis F, 1994, (HFV) ??????
Hepatitis G, 1995, (HGV or GBV)
All of these viruses are hepatotropic!!!
Hepatitis virus families
Virus
Family or
genus
HAV
HBV
HCV
HDV
HEV
HFV
HGV
Picornaviridae
Hepadnaviridae
Flaviviridae
Deltavirus
Caliciviridae
???
Flaviviridae
Transmission of Hepatitis Viruses
 HAV,
HEV:
contaminated food or water
 HBV, HCV, HDV, HFV, HGV:
blood and blood products
shared needles
sexual transmission
transplants (nosocomial, iatrogenic)
Replication properties of Hepatitis
viruses
Virus
Replication-competent
HAV
HBV
HCV
HDV
HEV
HFV
HGV
Yes
Yes
Yes
No, defective and dependent on HBV
Yes
???
Yes
Hepatitis viruses and liver
complications
Virus
Initial Disease
HAV
HBV
HCV
HDV (+HBV
coinfection)
HEV
HFV
HGV
Acute
Acute
Chronic
Acute
Long-term disease
and Liver Cancer
++
+
++++
Acute
????
Chronic
????
????
HBV vs. HDV
 HBV
is an RNA/DNA virus that is unique
among viruses. It is fully functional and
often found by itself in patients.
 HDV is an RNA-based sub-viral pathogen
that shares features with (but is not
identical to) plant satellite viruses and
viroids. It is never found by itself in
patients.
Followup on HDV Structure
HBV-prototype hepadnavirus
 Extracellular
form is DNA
 Replicates via reverse transcriptase step
Outcomes of HBV infection
HEPATITIS B VACCINE
Early vaccine from killed virus-safety?
No good experimental models
Recombinant DNA vaccine-1980s
eg- RECOMBIVAX
Produced by recombinant DNA technology in yeast
Seroconverts 99% healthy adults 20 to 29 years old
Subunit vaccine: HBsAg
Vaccine protects against active Hepatitis B,
asymptomatic HBV, the carrier state, & HDV
Vaccine is 90-95% effective in a wide range of
population ages
5. Vector transmission
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Intermediate species carries virus from host to host
“biological” transmission
Arthropod vectors for animal viruses
Insects, ticks, etc.
“Arboviruses” are arthropod-borne
“Viruses maintained in nature principally,
or to an important
extent, through biological transmission between susceptible vertebrate hosts by haematophagous
arthropods or through transovarian and possibly
venereal transmission in arthropods.”
Arbovirus classification
Family
Genera
Example Virus
Togaviridae (Type A)
Alphavirus
Eastern Equine
Encephalitis
Flaviviridae (Type B)
Flavivirus
Yellow Fever
Bunyaviridae (Type C)
Bunyavirus
Bunyamwera
Nairovirus
Crimean-Congo
Hemorrhagic Fever
Phlebovirus
Sicilian Sandfly Fever
“Arbovirus” is jargon but widely used
Simplest transmission cycle
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Urban Dengue fever (Aedes spp.)
 Urban yellow fever (Aedes aegypti)
Dengue transmission-a more complete picture
Complex cycles are more common
This example involves several vertebrate and vector
species
Terms
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Reservoir, primary and secondary
Primary host, amplifying host, natural host
Primary, secondary vectors
Propagative vs mechanical transmission
circulative
Venereal, transovarial transmission
Dead-end host
Zoonosis, zoonotic disease
Endemic, enzootic, etc.
Skunks, raccoons, bats etc. are reservoirs of rabies virus
(a rhabdovirus) but not vectors.
Flaviviridae-Three Important Genera
1) Flavivirus (mainly mosquito or tick vectors Central
European encephalitis (TBE-W), Japanese encephalitis
(JE), St. Louis encephalitis (SLE), West Nile virus (WN),
Dengue (DEN), Yellow fever (YF). Symptoms include
fever, encephalitis, hemorrhagic fever
2) Pestivirus (not arboviruses) Contact and Saliva
transmitted. Bovine viral diarrhea (BVDV), hog cholera or
classical swine fever (CSFV), very important animal
diseases.
3) Hepacivirus (not arboviruses) blood borne pathogensHepatitis C (HCV)-liver disease and liver cancer
worldwide.
Flavivirus
“tree”
Tick-borne
Mospquito
Vectors
No known
Vectors
For some
Viruses
In each
cluster
Yellow Fever Virus
“vomito negro”, “yellow jack”
Philadelphia,
1793
Haiti,
1802
New Orleans,
Memphis,
1878
Panama,
1880s
YFV transmission involves multiple cycles
Yellow Fever Virus Infection
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Yellow fever is a viral haemorrhagic fever.
Incubation period usually is 3 to 6 days.
Mortality rate in severe yellow fever is 50% with death
occurring 7 to 10 days after onset.
Infection varies from a mild illness followed by death 2 to 3
days later to a very mild or subclinical infection.
Estimated 200,000 cases
worldwide and 3000 deaths
annually
Travellers at risk
Vector transmission of yellow
fever by mosquitoes was
proposed by Carlos Finlay in
1881 and demonstrated Walter
Reed and others 1898
The “Heroes” of Yellow Fever Research
Jesse Lazear
Died in YF transmission
experiments
Walter Reed
transmission of YF
Max
Theiler
William Gorgas
Developed
YF vaccine
Theiler- YFV vaccine
U.S. Surgeon General
Broke YF transmission
cycle in Cuba and Panama
Derivation of a Yellow Fever Virus Vaccine
 The original virus isolate was obtained from an African
named Asibi.
 Passed 53 times in monkeys with intermittent periods in
Aedes agyptii.
 Passed 18 times in minced mouse embryo tissue culture.
 Passed 50 times in minced whole chicken embryo tissue
culture.
 Passed 152 times in minced chicken embryos.
A marked change in virulence occurred between in vitro
passage 89 and 114. Vaccine was called 17D.
The 17D vaccine has permitted health authorities to break
the cycle of yellow fever and get the disease under
control in South America and Africa.
But YFV is NOT a good candidate for eradication.
Bunyaviridae
3
ssRNA genome segments
 + or – or +/ Varies w virus
 Envelope
 No matrix
 >300
known worldwide
 Many diseases
Bunyavirus Diseases and Vectors
Genus
Disease & Vector Relations
Orthobunyavirus California Encephalitis Group, others.
mosquito vectors - bird, rodent, human cycle
Hantavirus
Hemorrhagic fever & renal syndrome
Hantavirus pulmonary syndrome-(rodents)
Nairovirus
Crimean-Congo Hemorrhagic Feverticks.
Phlebovirus
Rift Valley Fever, plus several rodent & bird
viruses-mosquito, sandfly & tick
Tospovirus
Broadest host range known (>360 plant host
species-thrips.
LaCrosse virus
Now grouped with California
serogroup
But mainly in Eastern US
Treehole (woodland)
mosquito Aedes triseriatus
Most common in males
under 16
Approx. 90 cases per year
reported
Neurological sequelae
Total US cases
through 2010
Most frequent
Arboviral
infection in US
Case frequency
LaCrosse Transmission
Humans
accidental
hosts-dead
end hosts
Transovarial transmission
Venereal transmission
Vector transmission through blood
Vertical vs. horizontal transmission
in animals
Vertical transmission is from parent to offspring
in some way that is related to reproduction.
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Trans-placental-fetal (Rubella)
 Maternal-parturition (Herpes simplex)
 Maternal-neonatal (HIV)
 Germ line (?)
Plant virus transmission
The cell wall is a formidable barrier to
viruses.
Receptors?
There is only one known portal of entry for
plant viruses.
How is it created?
Mechanical transmission of plant
viruses
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Abrasions of leaves
or stems
 Field transmission
 Laboratory
transmission
 May require abrasive
material such as
carborundum
Vector transmission
Arthropods-aphids, thrips, leafhoppers,
whiteflies
Helper component of potyviruses
Nematodes (Nepoviridae, Tobraviridae)
Transmission by parasites
 Dodder
(Cuscuta subinclusa, etc.)
 Fungi (e.g. Olpidium brassicae), TNV,
STNV, lettuce big vein virus