Viruses Blood and Insect borne Flashcards
give some examples of physical barriers to infection
- skin (physical barrier)
- stomach pH
- GI flora
- mucous in lungs
how do blood and insect borne viruses infect?
they get past skin as a barrier
what are the 2 shared features of blood and insect borne viruses?
1) direct introduction to bloodstream
2) require high levels of viraemia (presence of blood in bs)
what are the 4 unique features of blood and insect borne viruses?
1) different entry into the bs (insect bite, skin damage, medical)
2) cell/tissue tropism may be different (blood cells/liver cells)
3) clinical symptoms may vary by virus
4) epidemiology (person to person vs intermediate host transmission)
what is a tropism?
cells/tissues of a host that support growth of a particular tissue
how much of blood is plasma? what does it do?
- ~1/2 is plasma
- mostly water, ions to maintain isotonic
- proteins
what are the formed elements of blood?
- mostly RBC
- platelets
- leukocytes
- neutrophils etc
give 4 examples of blood borne viruses?
1) HIV
2) Hep B,C,D
3) HCMV (human cytomegalovirus)
4) HTLV1 (human T-cell lymphotropic virus)
what are the common ways of transmission for blood borne viruses?
- unprotected sex
- mother to baby
- sharing injecting equipment
- contaminated blood transfusions & organ transplants
where are viruses that cause blood borne disease found in the body?
- blood
- semen
- vaginal secretions
- other fluids that may contain blood (but aren’t supposed to) i.e urine, saliva
what is the family of HIV?
what is the genus?
Retroviridae
Lentivirus
what are 2 strains of HIV?
HIV-1 (global)
HIV-2 (West Africa)
how does HIV cause long term persistence?
integrates into the host genome
what is the tropism for HIV?
immune cells: CD4+ T cells, macrophages and dentritic cells
- infection results in DESTRUCTION OF CD4+ T cells
what does initial infection w/ HIV cause?
mild symptoms
what happens after long incubation periods in HIV?
causes AIDS (acquired immunodeficiency syndrome)
how do patients with AIDS die? how?
die from opportunistic infections
(HIV itself doesn’t kill)
- CD4+ T cells (normally 600 cells/mm3) are attacked but if AIDS, it drops below 200 cells/mm3
what can AIDS cause?
- HIV related Encephalopathy
- Cytomegalovirus Retinitis
- Atypical Pneumonia
- Chronic Intestinal Cryptosporidiosis
- Invasive Cervical Cancer
describe the progression of HIV to AIDS
week 0 (point of infection) - replication of virus begins
week 6
- peak in virus replication
- ACUTE phase
- seeding in all lymphoid organs
- non specific symptoms
- dip in CD4+Tcells
week 12
- virus paritially controlled by immune syst
- increase in CD4+ T cells
- but virus NOT CLEARED
- virus integrates into CD4+ T cell genome
week 12–> year 7
- clinical latency
- CD4+ T cellcount decreases
year 7 onwards - CD4+ T cells reach below 200 cells/mm3 AIDS -less able to fight infection - immune system less able to control HIV O massive increase in HIV replication
DEATH (v late, 9/10 years)
are there vaccines for HIV?
no
what is the treatment for HIV?
does it cure?
highly active antiretroviral therapy (HAART)
- combination drug therapy
- prevents progression to AIDS
- not curative
Hep B, C and D are all what?
chronic, without integration into the host genome
what is the family and genus of Hep C?
Flaviridae
Hepacivirus
what is the family and genus of Hep B?
Hepadnaviridae
Orthohepadnavirus
Hep D is what?
a VIROID (subviral satellite)
describe Hep D
- can only replicate in the presence of HBV
- transmitted with HBV, or to a chronic HBV patient
- inc SEVERITY of HBV disease
what is the tropism of Hepatitis blood borne?
- liver cells (hepatocytes)
- infection causes chronic liver inflammation
what are the symptoms of intial infection with Hep?
mild symptoms
what does a long incubation period cause in Hep?
liver failure and cancer
how does Hep progress?
- initial inf
- replication in liver
75-85% get chronic Hep: inflammation of liver causes FIBROSIS - 20-25 years later
CIRRHOSIS (extensive scarring, loss of blood flow, reduced liver function - 25-30 years later
HCC (hepatocellular carcinoma)
ESLD (end stage liver disease)
Death
Hepatocellular carcinoma
end stage liver disease
is there a vaccine for Hep C?
no
what is the treatment for Hep C? how long for?
does it cure?
- direct antiviral drugs
- 12 week treatment
- curative
- expensive
how is Hep C prevented?
good medical practice (screening of blood supply, no reuse of needles)
is there a vaccine for Hep B?
yes, also protects against HDV
what is the progression of HCV?
- initial inf
- 1-3 weeks viral particles in bs due to replication
- jaundice/flu like
MAY RECOVER FROM THIS if antibodies formed
IF NOT
continuous replication
20-30 years later, liver damage causes death
what can transmit arthropod borne viruses?
1) insects
- mosquitos
- sandflies
- midges
2) ticks
what are the major insect borne viruses that affect humans?
- Flaviviruses genus Flavivirus
- Alphavirus
- Bunyavirus
- Rhabdovirus
why are arboviruses limited to certain regions?
they are limited to the area in which the vector is found
what is the name of the human-vector-human cycle of mosquito virus transmission?
urban epidemic cycle
what is the enzootic cycle in mosquito borne transmission?
transmission in the wild, mosquitos—> non-human animals
this can spill over to humans (DEAD END HOST)
what is the epizootic cycle in mosquito borne transmission?
spillover of the enzootic cycle into domesticated animals, then possibly spill over to humans (DEAD END HOST)
what is a dead end host?
one that won’t transmit the disease on further
what is the species of mosquito that causes yellow fever?
Aedes aegypyti
Aedes albopictus is called what? what is it more tolerant to?
Asian tiger mosquito
more tolerant to cold
where are New World Alphaviruses found? give an example of one
Americas
Venezuelan Equine Ecephalitis
what do New World Alphaviruses cause generally?
encephalitis
where are Old World Alphaviruses found? give an example of one
Africa, Asia
Chikungunya
what do Old World Alphaviruses cause generally?
Arthiritis
what is the family of Chikungunya virus?
Togaviridae
what is the genus of Chikungunya virus?
Alphavirus
what is the tropism for Chikungunya virus?
broad
- immune cells (macrophages & dendritic cells)
- fibroblasts (connective tissue)
- endothelial (lining of blood vessels)
- myocytes
what are the symptoms of inital Chikungunya virus?
acute inital
some develop CHRONIC ARTHIRITIS (lasts ~2 years)
what transmits Chikungunya virus?
Ae. aegypti, Ae. albopictus
via urban transmission
where is Chikungunya found?
worldwide
is there vaccine/treatment for Chikungunya virus?
no, only prevention via mosquito control
what are the symptoms of Chikungunya?
- fever
- headache
- rash
- myalgia
- ARTHIRITIS
describe the infection life cycle of Chikungunya?
- infected mosquito bites human, virus introduced into skin and bloodstream
- virus replicates in fibroblasts of dermis and disseminates through bs to tissues
- viral REPLICATION in target tissues (muscle, liver, joints, spleen, meninges in neonates & immunocompromised)
- inflammation of joints
what family and genus is Venezuelan equine encephalitis (VEE)?
Togaviridae Alphavirus
what is the tropism of VEE?
- immune cells and CNS
- initial replication in DENDRITIC cells in blood
- inf of PNS (nose, mouth)
- spread along nerves to CNS
is there persistence of VEE?
no, acute inf only
what is the major symptom of VEE? what are other symptoms?
ENCEPHALITIS
- severe headache
- photophobia
- chills
- malaise
- fever etc
how did VEE emerge into humans?
the virus can infect multiple mosquito species (Culex)
what is the enzootic cycle of VEE?
what changes when there is an outbreak of VEE?
Culex breeds in permanent water sources
- flooding attracts new types of mosquitos that can transmit the virus to human (inc in population)
in VEE outbreaks tend to occur in what animal before humans?
horses (hence name V EQUINE E)
in VEE humans are wjat kind of host?
dead end host
- VIRAEMIA IS HIGH
- mosquitos involved in transmission do NOT bite humans often enough to sustain urban human transmission cycles
are there vaccines for VEE?
how else can VEE be prevented?
veterinary vaccine for horses
prevented by mosquito control
what is the family and genus of the virus that causes West Nile virus?
Flaviviridae Flavivrus
what is the tropism of West Nile virus?
immune cells, endothelial cells, and CNS
where is initial replication of West Nile virus?
where does it spread to?
endothelial cells, monocytes, macrophages and dendritic cells
spread to neurones
is West Nile virus persistent?
no
what isWest Nile virus transmitted by?
Culex spp mosquitos
where is West Nile virus found?
worldwide
what are the natural vertebrate hosts for West Nile virus? how does it infect humans?
birds (epizootic)
sporadic spillover to humans/horses (dead end hosts as VIRAEMIA IS NOT HIGH ENOUGH FOR TRANSMISSION BACK TO HOST).
what are the symptoms of West Nile virus?
in 20-30% - fever - headache - EYE PAIN - MACULOPAPULAR RASH (self lim) NEUROINVASIVE (1/150 cases) - encephalitis - meningitis - movement disorders - long term cognitive and neurological impairment - 10% mortality (high in older people)
how is West Nile virus treated?
no specific antiviral or vaccine
can be prevented by mosquito control
