32: Dengue & Zika

Question 1

dengue virus as an emerging infectious disease

Answer 1

increased numbers of infections in the last 20-30 years

Question 2

dengue virus characteristics

Answer 2

Flavivirus family
- closely related to WNV, Zika and hep C

10kB RNA virus encoding for 10 proteins

transmitted by Aedes aegypti and Aedes albopictus mosquitos (domestic daytime mosquitos)

infects people in tropical/subtropical regions, and causes explosive urban epidemics

Question 3

transmission of dengue virus

Answer 3

at some point, sylvatic cycle in mammals

primarily human-mosquito-human
- not a zoonosis primarily

mosquito is a vector and not a reservoir

Question 4

dengue disease statistics

Answer 4

50M cases annually worldwide of classic dengue fever

250-450K severe dengue cases
- dengue hemorrhagic fever/dengue shock syndrome

Question 5

disease pyramid of dengue

Answer 5

50M dengue fever cases but only 10-20% of them are diagnosed
- many asymptomatic infections

a lot of severe cases at the top of the pyramid
- maybe 10-50K children that die annually

Question 6

pediatric dengue

Answer 6

burden of disease and deaths highest among children < 15

most serious disease in SE Asia, leading cause of serious illness/death in children in Asia and Latin America
- higher than malaria, influenza, norovirus

Question 7

clinical symptoms of dengue

Answer 7

classic dengue fever
- high fever
- headache
- myalgias
- nausea and vomiting
- skin rash
- non-specific syndromes

dengue hemorrhagic fever/dengue shock syndrome
- internal haemorrhaging
- low platelets used up for clotting
- hypotension
- clinical signs of shock

Question 8

dengue serotypes

Answer 8

4 species - DENV1, DENV2, DENV3, DENV4

very little cross-protection

increased spread of all 4 serotypes which is believed to link to increase in severe disease

Question 9

why was there an increased incidence of hemorrhagic fever/shock between the 1970s and after 2000?

Answer 9

DENV1 antibodies might cause more severe disease when infected with DENV2, DENV3 or DENV4

antibody-definitive enhancement

antibodies are not sufficient to neutralise/opsonise sufficiently but trigger uptake
- causes more infection since the virus escapes into cytoplasm

Question 10

preventing the spread of dengue

Answer 10

no vaccine/drugs

only ways to control mosquito populations

use of insecticides like larvicides and adulticides

controlling where water collects/stagnates

use of biological agents to infect/target mosquitos

Question 11

zika virus characteristics

Answer 11

transmission by Aedes aegypti and Aedes albopictus

Flavivirus (RNA virus) in the same family as dengue, WNV, hep C, etc.

Question 12

antibodies to zika and dengue

Answer 12

can bind to each other because they are similar

however, antibodies to dengue do not seem to provide protection to zika

Question 13

main difference between zika and dengue

Answer 13

zika can be sexually transmitted and vertically transmitted to fetus

zika can be found in semen, cervical secretions, breast milk, etc. even after virus is cleared from blood
- areas with immune privilege

Question 14

is zika a zoonosis?

Answer 14

in Africa, still a zoonosis where it is endemic in countries like Nigeria

in places like Senegal, mostly in animals and less in humans

in Brazil, not a zoonosis but causing many infections

Question 15

zika disease statistics

Answer 15

10-25% infected people are symptomatic
- symptoms last between 7-15 days

very high asymptomatic rate

Question 16

clinical symptoms of zika

Answer 16

acute infection
- fever
- rash
- conjunctivitis
- myalgia
- arthralgia

cannot be diagnosed from symptoms - have to look at antibodies

neurological manifestations
- guillain-barre syndrome in adults (neurological paralysis)
- congenital zika syndrome in infants

Question 17

zika infection during pregnancy

Answer 17

can infect placenta and reach fetal tissue

infection during first trimester leads to the most severe microcephaly
- incredibly rapid growth and organs are starting to form

infection during 2nd or 3rd trimester can contribute to fetal abnormalities

Question 18

congenital zika syndrome

Answer 18

intracranial calcifications

brain abnormalites

eye abnormalities

hearing loss

impaired growth

spontaneous abortion

seizures

swallowing impairment

developmental delay

piercing scream

Question 19

microcephaly as a major manifestation of congenital zika syndrome

Answer 19

results as the failure of the brain to grow at a normal rate

severe when the head is 30-50% smaller than normal