Dengue Fever to Send

7/27/2019 Dengue Fever to Send

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Dengue Fever – the basicfacts

Major international public health concernFound primarily in tropical & sub-tropicalregions

Mosquito-borne viral infectionIn 2012, ranks as the most importantmosquito-borne viral disease in the worldOutbreaks exert HUGE burden onpopulations, health systems & economies inmost tropical countriesNo longer confined to tropics

Serious public health problem



Causative AgentVirus (DENV) - flavivirus4 related serotypes: DEN-1 throughto DEN-4

Recovery from infection from oneprovides lifelong immunity againstTHAT serotype but not againstothers

Subsequent infections by other serotypes increases risk of developing severe dengue: denguehaemorraghic fever (DHF) and

dengue shock syndrome (DSS).



DENV – up close and personal



TRANSMISSIONDengue is transmitted between people by themosquitoes A edes aegyp t i and Aedes a lbopic tus , which are found throughout theworld.

Aedes aegypti , the principal mosquito vector of dengue viruses, is closely associated withhumans and their dwellings.Virus transmitted to humans through the bites of infected female mosquitoes



People & Mosquitoes UnitePeople provide the mosquitoes with blood meals

AND water-holding containers in and around thehome needed to complete their development.The mosquito lays her eggs on the sides of containers with water and eggs hatch into larvaeafter a rain or flooding.

A larva changes into a pupa in about a week andinto a mosquito in two days.People also furnish shelter as Ae.aegypti preferentially rests in darker cool areas,such as closets, leading to their ability to bite

indoors.



InfectionSymptoms of infection usually begin 4 - 7 daysafter the mosquito bite and typically last 3 - 10days.For transmission to occur the mosquito must feedon a person during a 5- day period when largeamounts of virus are in the blood.Female mosquitoes use blood for protein for eggs

After entering the mosquito in the blood meal, thevirus will require an additional 8-12 daysincubation before it can then be transmitted toanother human.

Virus enters gut cells of mosquito, replicates then



The mosquito remains infected for the remainder of its life, which might be days or a few weeks.When infected female mosquitoes bite, they injectsaliva (with anti-clotting agent) which may containvirus

Virus can then enter many different cell typesincluding WBCsProteins in viral outer coat bind to proteins in cellmembranes, permitting viral core entry by

endocytosisCytokines produced in immune response stimulateantibody productionSome antibodies bind to viral proteins – complexthen engulfed by phagocytic cells that may merely



Thus viruses continue to replicate

Infected cells accumulate in lymph nodes Activated T cells proliferate in response but theyare not particularly effectiveSo, infected humans are the main carriers andmultipliers of the virus, serving as a source of thevirus for uninfected mosquitoes



Replication of DENV in humancells



GLOBAL BURDENIncidence grown dramatically recently>40% of world’s population AT RISK

Approx. 50 – 100 million infections

globally/year Whereas incidence of severe epidemics wasrestricted to 9 countries <1970, NOW dengueis ENDEMIC in >100 countries in Africa, theAmericas (including the Caribbean) , theEastern Mediterranean, South-east Asia andthe Western Pacific



Global impactThe World Health Organization (WHO) estimates500,000 DHF cases and 22,000 deaths, mostlyamong children.In Puerto Rico, and most of the Caribbean Basin,the principle dengue vector Ae. aegypti isabundant year-round.Reported cases continue to increase as denguespreads to NEW areasExplosive outbreaks are occurringOften under-reported and misclassifiedStaggering human and economic costs of this

neglected tropical disease



DENGUE INCIDENCE – Reasons

Several factors combined produce conditions indeveloping countries in tropics and subtropicsthat favour viral transmission by main mosquitovector, Aedes aegypti

rapid population growthrural-urban migrationinadequate basic urban infrastructure (eg.unreliable water supply leading householders to

store water in containers close to homes)increase in volume of solid waste, such asdiscarded plastic containers and other abandoned items which provide larval habitatsin urban areas.



Dengue SeasonsIn many parts of the tropics and subtropics,dengue is endemic , that is, it occurs every year,usually during a season when Aedes mosquitopopulations are high, often when rainfall is

optimal for breeding.These areas are additionally at periodic risk for epidemic dengue, when large numbers of peoplebecome infected during a short period.

Dengue epidemics require a coincidence of largenumbers of vector mosquitoes, large numbers of people with no immunity to one of the four virustypes (DENV 1, DENV 2, DENV 3, DENV 4), andthe opportunity for contact between the two.



Plus!Geographical expansion of the mosquito hasbeen aided by international commercial tradeparticularly in used tyres which easily accumulaterainwater.Increased air travelBreakdown of vector control measures have alsocontributed greatly to the global burden of dengueand DHF.Global warming?



Signs & Symptoms



Characteristics of Dengue Fever Severe, flu-like illnessSeldom causes deathHigh fever, accompanied by two of followingsymptoms: severe headache, pain behind eyes,muscle & join pains, nausea, vomiting, swollenglands and rash.Symptoms last 2 – 7 days after incubation period

of 4 – 10 days after bite from infected mosquito.No specific treatment – no drugs can kill virusCan only ensure hydrated & take analgesics



Severe: dengue haemorrhagicfever

Potentially deadly complication due to plasmaleaking, fluid accumulation, respiratory distress,severe bleeding, organ impairmentDue to damage to endothelium of blood vessels &

disruption of blood clotting processTemperature drops, abdominal pain, persistentvomiting, rapid breathing, bleeding gums, fatigue,restlessness, blood in vomit

Can be lethal (in 5% of cases)Proper medical care required to reduce mortalityrates from >20% to <1%Must maintain body fluid volume



Issues with controlNo vaccine to protect against dengueSome progress (under trial) but challengingTHUSOnly method to control or prevent transmission isto combat mosquito vector & avoid being bitten



Prevention & ControlPrevent mosquitoes from accessing egg-layinghabitats by environmental management &modificationDisposing of solid waste properly & removingartificial man-made habitatsCovering, emptying & cleaning domestic water storage containers on weekly basis

Applying appropriate insecticides to water storageoutdoor containersUsing personal household protection e.g. windowscreens, long-sleeved clothes, coils, vaporisers



Prevention & ControlImproving community participation & mobilisation

Applying insecticides as space spraying duringoutbreaksIntroduce fish or tiny crustaceans that feed onmosquito larva

Active monitoring and surveillance of vectors soas to determine effectiveness of control

interventionsNOTE that spraying effect is transient and variesin effectiveness as aerosol droplets often do notpenetrate indoors to microhabitats.

Procedure is costly.



Mosquito hangout spots Aquatic habitats are containers in which eggsdevelop into adult mosquitoes. Mosquitoes layeggs on the walls of water-filled containers in thehouse and patio. The eggs hatch whensubmerged in water and can survivefor months. Mosquitoes can lay dozens of eggsup to 5 times during their lifetime.There is a great variety of man-made containersthat collect rain water or that are filled with water by people where dengue vectors thrive.



Vector (Mosquito) ControlVery difficult to control or eliminate Ae.aegypti mosquitoes because they have adaptations tothe environment that make them highly resilientThey can rapidly bounce back to initial numbers after disturbances resulting from natural phenomena (e.g.droughts) or human interventions (e.g. controlmeasures).Eggs can withstand desiccation (drying) & survivewithout water for several months on the inner walls of

containers. If we eliminated all larvae, pupae, andadult Ae. aegypti at once from a site, its populationcould recover two weeks later as a result of egghatching following rainfall or the addition of water tocontainers harbouring eggs.



Know your vector!Unlike other mosquitoes, Ae. Aegypti is a daytimefeeder Peak biting periods are early in the morning & inthe evening before dusk

Female mosquitoes bite multiple people duringeach feeding period

Ae. albopictus , secondary vector in Asia, hasspread to North America & Europe largely due to

international used tyre etc. trade. This species ishighly adaptive and can survive in cooler temperate regions of Europe.Its spread is due to its tolerance of lowtemperatures, hibernation & ability to shelter inmicrohabitats.



Recent reseach

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