Epidemiology Clinical features Epidemiological Investigation DENGUE Epidemiology Clinical features Epidemiological Investigation

DENGUE Dengue Fever/DHF/DSS Mosquito Aedes aegypti Aedes albopictus Infectious agent Dengue virus 4 serotypes DEN-1,-2,-3,-4. Infection to one serotype confers lifelong immunity to the serotype but not to the other 3

Aedes albopictus indigenous to Singapore, feed in one meal Aedes aegypti imported after WWII, feed in multiple meals

Infectious Period Incubation Period 1 - 2 weeks Up to 5 days after onset of illness Infectious Period

Clinical Features Dengue fever

Signs & symptoms Sudden fever Headache Muscle & joint pain (“saddle-back” pattern) Headache Muscle & joint pain Nausea/vomiting Macular papular rash (D3-5 when fever subsides)

Petechial Rash

Dengue Serology IgG & IgM Haemagglutination WBC count Laboratory Diagnosis Dengue Serology IgG & IgM Haemagglutination WBC count

Dengue Haemorrhagic Fever/Dengue shock syndrome Associated with secondary infection of a different serotype Bleeding tendencies (platelet decreased) Fits/seizures or convulsions Mortality rate is 30% if not properly treated

4 necessary criteria: Fever or recent history of acute fever Hemorrhagic manifestations Low platelet count (1000,000/cu mm or least) Objective evidence of “leaky capillaries” -elevated hematocrit (20% or more over baseline). Packed cell volume (PCV) or erythrocyte volume fraction (EVF), is the volume percentage (%) of red blood cells in blood. It is normally about 45% for men and 40% for women.[ -low albumin -Pleural or other effusion (excess fluid that accumulates between the two pleural layers, the fluid-filled space that surrounds the lungs.

Haemorrhagic Manifestations

Vector control strategies in Singapore Launched in 1970 -Source reduction Environmental control -Elimination of larval habitats in residential premises -Public education -Law enforcement -Chemical control

Possible reasons for re-emergence of dengue Lowered hers immunity Alerted vector bionomics Delayed infection- from childhood to adulthood Changed in vector control -From prevention to case response “Swimming in the sea of dengue” Gubler DJ. Dengue Bulletin 2002, 26: 96-106

Lowered herd immunity

Seroprevalence in primary school children Singapore- 6% Ratchaburi Province, Thailand- 71% Dominican Republic- 56%

Altered vector bionomics

House indices (Tan 1997). -Residence. Landed residential properties 2 House indices (Tan 1997) -Residence .Landed residential properties 2.1% .Apartments 0.6% -Non-residences .Construction sites 8.3% .Factories 7.8% .Vacant premises 14.6% .School 27.0% House indices (Chan et al 1971) -Slum houses 27.2% -Shop houses 16.4% -Apartment 5.0%

Delayed infection

Infection in adulthood vs childhood Less likely to be subclinical with increased age of onset Endermic stability (Coleman et al. Lancet 2001, 357: 1384-6)

Changes in vector control strategy Return to entomological based approach rather than case reactive Involvement of the public (Ovitrap/gravitrap) Lower importation of virus-control dengue outside of Singapore? Lower susceptibility to dengue through antivirals as prophylaxis

Dengue vaccine approved for use in Singapore 5th October 2016 The Health Science Authority studied Dengvaxia vaccine since March, fast-tracked its approval process because of public health concerns. The decision was based on 24 studies conducted by vaccine manufacturer Sanofi Pasteur, which involved more than 41,000 people and showed the vaccine to be safe for use and effective against dengue. Given in three doses over a year, the vaccine is approved for use in those aged between 12 and 45. Those outside this age group can be vaccinated if they so wish, but should seek a doctor's advice first. For people aged two to 16, Dengvaxia was shown to reduce the number of dengue cases by 60 per cent as compared with those who had not been vaccinated. This figure went up to 84 per cent when it came to preventing severe dengue infections in the same age group. Additional studies showed that the vaccine was effective up to age 45, said the HSA. But, though formulated against all four strains of the virus, the vaccine is less effective against the Den-1 and Den-2 strains, which account for three-quarters of the dengue cases here. Its efficacy is 50 per cent and 40 per cent respectively, compared with 75 per cent and 77 per cent for the other two strains. Studies also showed that the vaccine provided better protection for those who had been exposed to the dengue virus than for those who had not, with efficacy at 81 per cent and 38 per cent respectively.