Viral Hemorrhagic Fevers Flashcards
What is VHF used to describe?
A host of viruses that cause severe, multi-organ, life-threatening disease
What are 3 common clinical manifestations of VHF?
- Fever + other non specific symptoms
- Shock
- Hemorrhage
What other nonspecific symptoms usually accompany fever?
headache, malaise, myalgias, arthralgias, abdominal pain, nausea, and diarrhea
What is occurring during shock?
body is not getting enough blood
- life threatening
is hemorrhagic bleeding usually life threatening?
no not the bleeding itself
Do you always see hemorrhage with VHFs?
no not always - most are not hemorrhagic in fact
How many virus families are primarily the cause of VHFs? what are they?
- Arenaviruses (ex. Lassa)
- Filoviruses (ex. Ebola)
- Bunyaviruses (ex. Hanta viruses)
- Flaviviruses (ex. Dengue)
What is a common structural/genomic feature of all VHF virus families?
All are enveloped RNA viruses
What containment level(s) are required to work with VHF causing viruses?
Mainly BSL4 but some are BSL3
VHF viruses rely on what kind of transmission and hosts?
They are zoonotic and therefore require reservoir hosts to survive
- from small mammals like rodents to large ones like monkeys
How does transmission of VHFs usually occur?
usually through animal or arthropod vectors
What are 2 typical animal vectors?
rodents or bats
What are 2 typical arthropod vectors?
ticks and mosquitos
What is the geographical distribution of VHF viruses like?
geographically restricted to areas where the hosts/vectors live
Which 3 Arboviruses cause Hemorrhagic fever in humans?
- Dengue fever
- Rift Valley fever virus
- Yellow fever virus
What are the major vectors for arboviruses?
mosquitos and ticks
What is the geographical distribution of Flaviviruses? What is the vector for them?
central and south america, india, south east asia, central africa
- aedes aegypti mosquito
What is the distribution of crimean congo hemorrhagic fever (CCHF)? What transmits it?
Mostly in Africa
- similar distribution to its vector, the Hyalomma sp of tick
What is the distribution of rift valley fever virus? whats the vector?
Africa mainly - Aedes is is the vector
Where are Hanta virus reservoirs?
north and south america, Europe, and China
Where’s the general distribution of Arenaviruses?
south america and parts of africa
Fruit bats of the Pteropodidae family for example are vectors of what type of viruses?
Filoviruses like Marburg and zaire ebola viruses
How frequent are the outbreaks or cases of VHFs in humans ?
they occur sporadically
for primary VHF transmission, this usually occurs..
accidentally to humans - not the natural reservoir
When do primary infections in humans tend to occur? What kinds of contact
when the activities of infected reservoir hosts or vectors and humans overlap
- direct contact with rodent feces or urine for example
- indirect through bites of mosquito or tick
- direct contact during care or slaughter of animals
How common is secondary transmission?
not that common among VHFs, only a couple of viruses have person-to-person transmission
ex: Lassa, Marburg, Ebola, CCHF
How does secondary transmission typically occur?
direct close contact with infected people or their bodily fluids
- aerosol uncommon
What are the 2 modes of transmission for Hantavirus?
aerosol or direct contact with abraded skin
What is the vector of Hantavirus? How is the virus usually spread from them
Rodents
Spread indirectly through their feces or urine
RVF virus is spread through what kind(s) of transmission?
primary only
CCHF is spread through what kind(s) of transmission ?
primary and secondary
Marburg is spread through what kind(s) of transmission ?
primary and secondary
Ebola is spread through what kind(s) of transmission ?
primary and secondary
How does primary transmission typically occur for Ebola?
Bats have high viral titre in feces and are then used as food
How does secondary transmission occur for Ebola?
Direct contact with blood or secretions
- urine, feces, semen, breast milk
can occur through the mucosal or breaks in the skin
Appropriate PPE for ebola needs to protect against…
contact, droplet,
need an N95 for aerosol generating procedures
What is the incubation period for Ebola ?
up to 21 days but average is 11
When do patients with Ebola not transmit?
when they are asymptomatic
What are the 3 phases of Dengue Fever?
- Febrile phase
- Critical phase
- Recovery phase
What are some symptoms of the febrile phase of dengue?
sudden onset fever, headache, mouth and nose bleeding, joint pain, vomiting, rash, diarrhea
What are 4 features of the critical phase of dengue?
hypotension, pleural effusion, ascites, GI bleeding
What are 4 features of the recovery phase of Dengue.
Altered LOC, seizures, itching, slow heart rate
What is antibody dependent enhancement? (ADE)
When you get infected by one serotype of Dengue and then later infection by another serotype results in more severe disease because of antibodies that don’t completely neutralize the virus resulting in the virus being delivered into the wrong compartment in dendritic cells and therefore can replicate
What are the 2 causes of death from ebola?
hypovolemic shock and multiorgan failure
What is a “cytokine storm”
uncontrolled cytokine response
what causes bleeding in the liver in most cases of VHF?
infection and necrosis of the liver combined with decreased clotting factors
Fluid loss is usually a result of ..
increased vascular permeability
Infection of cortical cells in the adrenal glands results in..
decreased production of steroids –> hypotension and then hypovolemic shock
What is the mortality of Ebola vs Lassa vs Dengue ?
30-90% for ebola but most recent outbreak around 50%
Lassa: 15-25%
Dengue is 10%
Diagnosis of VHF is based initially on..?
clinical criteria and judgment
What are 4 lab based methods for confirming VHFs ? When are they used?
Serology - IgM and IgG, paired
acute/convalescent
Molecular: RT-PCR
Immunohistochemistry - tissues
Electron microscopy (EM) and viral culture -Extremely dangerous, only in BSL-4 labs if necessary
For most VHFs, what are the 3 modes of treatment?
- Supportive care to manage symptoms
- rehydration is key - Antivirals but are not usually very effective
- Convalescent phase plasma
Mostly there are no vaccines for VHFs except for?
Dengue, Argentine hemorrhagic fever, yellow fever
- Ebola is being developed
What 2 families of viruses are of concern for being used as biological weapons?
Filoviruses and Arenaviruses
Aerosolized VHF preparations are considered potentially suitable as biological weapons because..?
- Low infectious dose
- High morbidity and mortality
- Potential for person-to-person transmission
- Effective therapy and vaccines are not available
