Viral Hemorrhagic Fever

Question 1

Arenaviridae

Answer 1

Viral Hemorrhagic Fever
• Segmented, single-stranded, negative-stranded, ambisense linear RNA genome
– Ambisense: proteins are translated off both orientations of RNA – positive sense and negative sense
• Helical
• Enveloped, spherical
• Medium to large (60-300 nm)
• Replicates in the cytoplasm
**LASSA FEVER
• Reservoir: “multimammate rat”
• Transmission:
– Commonly due ingestion or inhalation (or through cuts or sores) of virus-containing rat urine or droppings
– Direct person-to-person contact;
– Nosocomial infections
• Symptoms:
– Low case fatality rate (~1%) but fairly common
– May cause spontaneous abortions in pregnant women; maternal death
– May cause deafness in 1/3 of survivors
• Treatment
– ribavirin (only one effective)

Question 2

Bunyaviridae

Answer 2

Viral Hemorrhagic Fever
• Segmented, single-stranded, negative-stranded, ambisense linear RNA genome
• Helical
• Enveloped, spherical
• Medium (80-120 nm)
• Replicates in the cytoplasm
**Crimean-Congo hemorrhagic fever virus (CCHF)
• Natural reservoir: Hyalomma ticks (a type of Ixodes tick).
– bc the virus can be transmitted transovarially the tick is both the reservoir and the vector
• Amplifying host: cattle, goats, sheep & hares
• Transmission: contact with infected ticks or animal blood; direct person-to-person contact with infectious blood or body fluids; nosocomial infections
• Symptoms:
– Severe bruising, nosebleeds & bleeding at injection sites
– Case fatality up to 50%
**Rift Valley Fever
• Reservoir: Aedes mosquitoes
– The virus can be transmitted transovarially
• Severe disease of livestock (cattle, buffalo, sheep, goats, camels); >90% abortion rate
• Transmission:
– primarily by exposure to infected animal blood or tissues (during slaughtering or vet procedures-these are called “bridging vectors”), or mosquito bites
– Aerosols in laboratory environment;
– No human-to-human transmission
• Symptoms:
– Most human cases are symptomatic or mild disease with fever & liver abnormalities
– Severe disease in humans (8-10%)
• Ocular (leading to blindness)
• Encephalitis
• Hemorrhagic fever (case fatality 50%)

Question 3

Filoviridae

Answer 3

Viral Hemorrhagic Fever
• Single-stranded, negative-stranded linear RNA genome
• Helical
• Enveloped, filamentous
• Large (790-970 nm long)
• Replicates in the cytoplasm
**Marburg Hemorrhagic Fever
• Reservoir: African fruit bat (Rousettus aegyptiacus)
• Infects & causes disease in non-human primates
• Transmission:
– contact with bat feces or aerosols?;
– direct person-to-person contact (so caregivers and hospital personnel are at risk)
– handling or coming into direct contact with infected non-human primates (fluids or even cell cultures)
– nosocomial infections
**Ebola virus
• Reservoir: fruit bat?
• Infects & causes disease in non-human primates
• Transmission:
– handling bushmeat;
– contact with infected bats?;
– person-to-person contact including semen; burial ceremonies;
– Can be transmitted on objects like needles and syringes
– nosocomial infections
• Long-term complications: joint and vision problems
• There are actually five different species of Ebola, of which four can cause disease in humans. It is not really known yet if a person who survives Ebola virus disease, is immune to the other three Ebola types or not

Question 4

Flaviviridae

Answer 4

Viral Hemorrhagic Fever
• Single-stranded, positive-sense linear RNA genome
• Icosahedral
• Enveloped, spherical
• Small (50 nm)
• Replicates in the cytoplasm
• The Flaviviridae family also includes Hepatitis C virus, yellow fever virus & West Nile virus
• Four different serotypes (DENV1-4);
• immunity to one serotype may enhance disease manifestations with subsequent serotypes = “antibody-dependent enhancement” hypothesis
**Dengue Fever
• Reservoir: Humans (& sometimes other primates)
• Vector: Aedes mosquitoes
• Transmission:
– mosquito bites;
– no human-to-human transmission;
– rarely, blood transfusion, organ donation & perinatal
• Symptoms
– ~3/4 of infections are asymptomatic;
– 1/1000 infections may develop “severe dengue” (~2.5% case fatality)
• Symptomatic infections are usually painful – like “your bones are breaking”, hence dengue fever is sometimes referred to as “breakbone fever”.
• Severe Dengue dengue is also called” dengue hemorrhagic fever and dengue shock syndrome”
• For severe dengue with proper treatment, the case fatality rate is relatively low at less then 3 percent.