Arboviral Diseases

Question 1

Arbovirus definition + most common viral families

Answer 1

• Viruses maintained in nature in cycles involving hematophagous arthropod vectors and susceptible vertebrate hosts
• Bunyaviridae
• Flaviviridae (Flaviviruses)
  
  • Dengue
  • West Nile
  • Yellow fever
• Togaviridae (Alphaviruses)

Question 2

General patterns of disease caused by arboviruses

Answer 2

• Encephalitis
• arthralgias
• sometimes hemorrhagic fevers (fever, bleeding, hypotension, edema, shock, death)

Question 3

West Nile Virus transmission cycle

Answer 3

• Generally: mosquito => bird => mosquito, etc.
  
  • Humans are “dead-ends” (mosquitoes can’t get infected from biting humans).
• Mosquito ingests blood from an infected (viremic) vertebrate. This infects the mosquito. The virus matures in the mosquito gut and spreads to the blood and saliva. There are no adverse effects on the mosquito.
• The infected mosquito bites another vertebrate and infects it.

Question 4

Sx of WNV

Answer 4

Generally asymptomatic; about 20% of infected patients get mild symptoms; older patients can get meningitis, encephalitis, or poliomyelitis.

Question 5

Transmission cycle of Yellow Fever and Dengue

Answer 5

primary hosts are monkeys and mosquitoes.

· Note the humans are not dead-end hosts for yellow fever and dengue (get high enough titers of viremia to infect new mosquitoes).

Question 6

Presentation/sx of Yellow fever and Dengue

Answer 6

· Yellow fever infects the liver (thus jaundice, thus yellow).

· Only one serotype of yellow fever; there’s a safe and efficacious vaccine.

· Four serotypes of dengue but no vaccine (see below).

· Generally the progression from infection to disease is rapid (about 7-10 days)– whether or not the bugs cause organ symptoms (eg. encephalitis) depends on whether or not it can ‘outrun’ the host’s immune response.

Question 7

Major approach to preventing arboviral disease

Answer 7

• mosquito control
• • Insecticides, reduction of container habitats, improved water supply & waste management
• • Prevention and education programs: use of repellents, proper clothing, avoid dawn/dusk, H2O mgmt.
• • Research: methods to reduce productive mosquito mating and mosquito lifespan

Question 8

What are the serotypes of dengue virus?

Answer 8

4 serotypes.

· Transmitted by

· Dengue can cause a variety of disorders depending on serotype:

· Dengue fever

· Dengue hemorrhagic fever

· Dengue shock syndrome

Question 9

Importance of serotype variety in Dengue

Answer 9

Generally with the first infection, you get dengue fever. With repeat infections, you have a much higher incidence of hemorrhagic fever or shock syndrome.

· Why this happens: evidently the antibody response to the first serotype cross-binds (non-neutralizing) to the other serotypes of dengue. This causes the bound, but not inactivated, dengue serotypes to get into phagocytic cells (with Fc receptors) and spread more systemically, causing high levels of cytokine release.

· There are no vaccines against dengue (don’t want to cause increased sensitivity).

Question 10

Vaccines for arboviral diseases

Answer 10

• There are vaccines against yellow fever and Japanese encephalitis. Generally you should vaccinate people going to yellow-fever-endemic areas (like lower Bolivia) or planning to stay in rural Asia for more than a month, respectively.
• · No vaccines against dengue.
• · No vaccines against West Nile.

Question 11

Non-mosquito transmission of WNV

Answer 11

• Solid organ transplantation
• Blood transfusion

Question 12

Tx of arboviruses

Answer 12

• no specific anti-virals
• supportive tx