32: Dengue & Zika Flashcards
dengue virus as an emerging infectious disease
increased numbers of infections in the last 20-30 years
dengue virus characteristics
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
transmission of dengue virus
at some point, sylvatic cycle in mammals
primarily human-mosquito-human
- not a zoonosis primarily
mosquito is a vector and not a reservoir
dengue disease statistics
50M cases annually worldwide of classic dengue fever
250-450K severe dengue cases
- dengue hemorrhagic fever/dengue shock syndrome
disease pyramid of dengue
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
pediatric dengue
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
clinical symptoms of dengue
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
dengue serotypes
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
why was there an increased incidence of hemorrhagic fever/shock between the 1970s and after 2000?
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
preventing the spread of dengue
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
zika virus characteristics
transmission by Aedes aegypti and Aedes albopictus
Flavivirus (RNA virus) in the same family as dengue, WNV, hep C, etc.
antibodies to zika and dengue
can bind to each other because they are similar
however, antibodies to dengue do not seem to provide protection to zika
main difference between zika and dengue
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
is zika a zoonosis?
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
zika disease statistics
10-25% infected people are symptomatic
- symptoms last between 7-15 days
very high asymptomatic rate
clinical symptoms of zika
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
zika infection during pregnancy
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
congenital zika syndrome
intracranial calcifications
brain abnormalites
eye abnormalities
hearing loss
impaired growth
spontaneous abortion
seizures
swallowing impairment
developmental delay
piercing scream
microcephaly as a major manifestation of congenital zika syndrome
results as the failure of the brain to grow at a normal rate
severe when the head is 30-50% smaller than normal
