One Health

• Malthus theory suggests that: Population growth is limited by the availability of resources.
• A vector transmit diseases between man and animal
• The 2 key species of Aedes in Singapore is Aedes Aegypti and Aedes Albopictus.
• Another species of mosquito that transmits diseases like malaria, filariasis is the Anopheles species
• A species of mosquito that transmits JE, West Nile is Culex
• Mansonia species of mosquito transmit filariasis and other arboviruses.
• SG has 4 dengue serotypes, with 1 and 2 being most common
• Key Drivers for escalation of dengue cases includes:

  • Mutation of new virus
  • Low population immunity
  • Increase in vector population
  • Weather
• A.aegypti thrives in built environments

  • Primary vector of dengue and zika
  • Secondary vector of chikungunya
• A.albopictus thrives in greenery and forests

  • Primary vector for chikungunya
  • Secondary vector for dengue
• Dengue viruses are

  • Single stranded RNA flavivirus
  • Evolved from sylvatic virus
  • No cross-protective immunity across serotypes
• For an arboviral infection in mosquito

  • Mosquito must blood feed on viraemic host
  • Infectious dose of virus must enter midgut lumen
  • Virions must be able to replicate to produce infectious virions
  • Virions must be able to disseminate from midgut epithelial cells
  • Virions must infect salivary glands
  • Virions must be secreted in saliva
• Roles of MOH in dengue

  • Clinical management
  • Case surveillance

  Roles of NEA in dengue

  • Vector surveillance
  • Dengue control
• Overlapping roles of MOH and NEA for dengue include:

  • Surveillance
  • Characterization of virus
  • Integration of human, virus, vector understanding
• WHO framework Integrated Vector Management:

  • Intersectoral Collaboration
  • Integrated disease control approach
  • Evidence Based Decision making
  • Advocacy, social mobilisation and legislation
  • Capacity Building
• Singapore's dengue control strategy involves keeping dengue incidence low by keeping mosquito population low and breaking diseases transmission via

  • Surveillance
  • Sustainable prevention and control
  • Outbreak management
  • Public Communications and Advocacy
• We can use switch in DENV serotype reported by the GPs to predict a dengue outbreak
• Wolbachia is a naturally occuring bacterium that is found in more than 60% of insect species including A.albopictus and Culex
• Families of positive sense RNA viruses include

  • Togaviridae
  • Flaviviridae
  • Coronaviridae
• Amongst Flaviviridae are: Dengue, Zika, Yellow Fever, JE
• Amongst togaviridae is the Chikungunya virus
• Amongst the coronaviridae are SARS and MERS
• Families of negative sense RNA viruses include:

  • Paramyxoviridae
  • Filoviridae
• Paramyxoviridae family includes the Nipah Virus
• Filoviridae virus includes the Ebola virus
•  primary host : an organism in which the parasite reaches the adult stage and reproduces.
• Secondary host – an organism that harbors the sexually immature parasite and is required by the parasite to undergo development and complete its life cycle. 
• Dead-end host – an organism that generally does not allow transmission to the definitive host, thereby preventing the parasite from completing its development.
• Humans and horses are dead-end hosts for West Nile virus
• Japanese encephalitis: Primary host is birds, amplifying host is pigs where disease can become an epidemic
• Aedes Aegypti are day biters and are mostly indoors
• Unlike dengue and zika, yellow fever's only vector is Aedes aegypti
• Ross River virus's vectors can be both aedes and culex
• The sylvatic cycle is the fraction of the pathogen population's lifespan spent cycling between wild animals and vectors
• Dengue virus is single stranded RNA with 4 serotypes. It evolved from sylvatic viruses to an urban cycle
• Incidental or dead-hosts often are such as virus levels in their blood do not become high enough to pass on the infection
• Global warming, increased population density, increased urbanization, increased travel and migration are drivers of increase in dengue cases
• Increase in urbanisation is also one of the drivers of Aedes aegypti related dengue transmission
• In Nepal with global warming, we are seeing

  • Shift of species distribution towards higher elevation
  • Reduced high over-wintering mortality of vectors
  • Increased length of transmission season
  • Increasing trend of epidemic potential
• There are two Wolbachia approaches

  • Suppression involving cytoplasmic incompatibility involving males
  • Replacement approach involving females infected to eventually replace existing mosquito population with one that carries wolbachia