Vector Transmitted Viruses Flashcards
Western Equine virus
Vector: Mosquito
Pathogenesis:
- Virus enters blood stream
- Local replication in endothelium
- Secondary viremia = seeds CNS
- Replicates in CNS
- Causes direct and inflammatory damage
Major Syndromes:
Encephalitis
Prevention:
- Vector control
- Vaccines from horses, lab workers
Eastern Equine virus
Vector: Mosquito
Pathogenesis:
- Virus enters blood stream
- Local replication in endothelium
- Secondary viremia = seeds CNS
- Replicates in CNS
- Causes direct and inflammatory damage
Major Syndromes:
Encephalitis
Prevention:
- Vector control
- Vaccines from horses, lab workers
LaCrosse virus
Vector: Mosquito
Pathogenesis:
- Virus enters blood stream
- Local replication in endothelium
- Secondary viremia = seeds CNS
- Replicates in CNS
- Causes direct and inflammatory damage
Major Syndromes:
Encephalitis
Prevention:
- Vector control
- No vaccine
West Nile Virus
Vector: Mosquito
Pathogenesis:
- Virus enters blood stream
- Local replication in endothelium
- Secondary viremia = seeds CNS
- Replicates in CNS
- Causes direct and inflammatory damage
Major Syndromes:
Encephalitis
West Nile Fever
Aseptic Meningitis
Prevention:
- Vector control
- Behavior (repellent, etc.)
- No vaccine
- Screen organ donors and blood supply
Dengue Virus
Vector: Mosquito
Pathogenesis:
-Replicate in blood vessel endothelium = kills cells, induces cytokines → fever or hypovolemic shock (fluid loss) in severe cases
Major Syndromes:
Febrile illness, hemorrhagic fever
Prevention:
- Vector control
- No vaccine
Rabies Virus
Vector:
Bats, skunks, raccoons, foxes (dog transmission virtually eliminated due to vaccination)
Route of transmission:
Animal bites or spelunkers inhaling virus shed in dried bat urine
Pathogenesis:
- Local replication in muscle tissue
- Virus spreads to nerve cells → retrograde travel to CNS
- Replicates in gray matter
- Spreads via nerves to salivary glands and other tissues
Major Syndromes:
Encephalitis
Prevention:
- Vaccine: killed version; used in high risk individuals and those bitten by animals
- Rabies Ig’s used in exposed individuals
Sin Nombre Virus
Vector:
Rodents
Route of transmission:
Inhaled in dried rodent urine and feces
Pathogenesis:
Replicates in lungs → acute respiratory distress syndrome with edema and inflammatory infiltrate into lungs
Major Syndromes:
Hantavirus pulmonary syndrome (HPS): mortality rate 76%
Prevention:
- Vector control
- No vaccine
Explain “urban cycle” and “sylvan cycle” and be able to cite examples of each.
Urban transmission pattern
o Requires virus cause high titer and prolonged viremia in vertebrate host
o Maintained in urban setting = humans are reservoir species
o Ex: Yellow Fever, Dengue
Sylvan cycle
o Maintained in wild with transmission between some animal and insect vector
• Most common: birds (West Nile) and rodents (Lacroose)
• Usually asymptomatic infection in endemic host
• Sometimes = infection is lethal (Ex: West Nile virus kills crows)
NOTE on animal transmission:
o Requires that virus can replicate in animal host
o Ex: rabies virus replicates in salivary gland = transmitted by bites
o Ex: transmitted through urine or feces = Hantaviruses, Lassa Fever, Ebola, Marburg viruses
o Humans = incidental hosts (infected because at wrong place at wrong time)
Describe the role of the immune system in the pathogenesis of Dengue Hemorrhagic Fever. Describe why this does not happen with other viruses listed in this outline.
Dengue Hemorrhagic Fever
o Occurs during 2nd infection with Dengue virus
4 Dengue serotypes
o Able to cross-react
o BUT only serotype-specific Ab’s are protective → multiple infections possible
If have non-protective Ab → immune enhancement
o Host produces Ab’s against virus that bind but don’t neutralize
o Result: infection of cells with Fc receptors
o Increased formation of immune complexes that precipitate in tissues and organs
o Macrophage infection → releases lots TNFα
DHF = can cause disseminated intravascular coagulation and shock
o Also: arthritis, arthralgias
Describe how rabies virus is transmitted and spreads in the host.
Transmission:
Result of bite from infected animal
• Local replication in muscle tissue
Inhalation of aerosolized virus from bat secretions during spelunking
• Local replication in nasopharyngeal mucosa
• Spread to olfactory nerves →CNS
Spread to nerves cells via retrograde transport
o Replicates in CNS gray matter
Spreads via nerves to salivary glands and other tissues
Long incubation period = time to use vaccine and rabies immunoglobulin
Symptoms = from cytolysis of infected cells and inflammation
Pathology = Negri bodies
o Eosinophilic cytoplasmic inclusion body
