Health Ministry-Sri Lanka

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There are about 140 species of mosquitoes in Sri Lanka. Out of them Aedes Aegypti and Aedes Albopictus mosquitoes are transmitting dengue virus to humans. Two types of mosquitoes can be differentiated by markings on their body.

Aedes Albopictus  Aedes Aegypti

Life Cycle

There is an aquatic phase (eggs, larvae, pupae) and a terrestrial phase (adults) in the life-cycle of Ae. aegypti and Ae. albopictus. Female mosquitoes of Aedes aegypti and Ae. albopictus lay their eggs on the inner walls of containers with water. The eggs hatch to larvae (picture 1, inset) when water inundates the eggs by any means such as rains or filling water by people. The mosquitoe larvae (picture 2) feed on microorganisms and particulate organic matter. The larvae shed their skins three times and develop first to fourth instars. The 4th instar larva develops (has acquired enough energy and size and is in the fourth instar, it will change into – can be deleted) to pupa (picture 3). Pupae do not feed and develop to (; they just change in form until the body of the – can be deleted) adult mosquito. (Then, the newly formed adult emerges from the water after breaking the pupal skin – can be deleted) (picture 4, inset). The entire life cycle lasts 8-10 days at (room temperature ?), depending on the level of feeding.

The eggs of Ae. aegypti and Ae. albopictus can withstand desiccation for several months. And also, the dengue virus can go to the next generation via the eggs (transovarian transmission). These are major threats for dengue control in the country.

Breeding Places

Dengue is an important vector-borne disease in Sri Lanka. First serologically confirmed case was reported in 1962 and the first documented dengue outbreak occurred in 1965- 1966, with few sporadic cases of haemorrhagic disease. According to the studies conducted at Medical Research Institute, there had being continued dengue transmission in 1970s and 1980s with periodic epidemics, without significant numbers of dengue haemorrhagic fever and dengue shock syndrome.  
These studies showed that during 1980 and 1985, 14% to 24% of viral syndrome cases being caused by dengue infection and all four dengue serotypes were circulated with the predominance of DEN- 2 and DEN- 3.
Sri Lanka experienced first epidemic of Dengue Haemorrhagic fever / Dengue Shock Syndrome caused by DEN- 3 sero type in 1989 – 1990. It has been suggested that a genetic change occurred in the DEN -3 virus increasing its epidemic potential/virulence may have contributed to emergence of DHF/DSS after many years of its circulation. Since then progressively larger epidemics with more severe and fatal DHF/DSS have occurred at regular intervals.

DF/DHF became a notifiable disease since 1996 in Sri Lanka.

Following are the number of cases reported since 2002.

Year Cases
2002   8 931
2003   4 672
2004 15 463
2005   5 994
2006 11 980
2007   7 332
2008   6 607
2009 35 095
2010 34 105
2011 28 140
2012 44 456

Trend and Case fatality ratio Upto 2012

Temporal Spread   


Seasonality upto 2012










In the last 25 years of the 20th century, a dramatic global geographic expansion of epidemic DF/DHF occurred, facilitated by unplanned urbanization in tropical developing countries, modern transportation, lack of effective mosquito control and globalization.

The global prevalence of dengue has increased dramatically in recent decades. Dengue fever and DHF/dengue shock syndrome (DSS) occur in over 100 countries and threaten the health of more than 2.5 billion people in urban and peri-urban areas especially in south and south East Asia including Sri Lanka.

Dengue is a viral infection transmitted by the bite of an infected mosquito. There are four closely related but antigenically different serotypes of the virus that can cause dengue (DEN1, DEN 2, DEN 3, DEN 4).Dengue has a wide spectrum of infection outcome (asymptomatic to symptomatic). Symptomatic illness can vary from undifferentiated fever (viral syndrome), dengue fever (DF), dengue haemorrhagic fever (DHF) and dengue with unusual manifestations. DF and DHF comprise the bulk of symptomatic illness while unusual dengue is a rare entity (usually <1%).

  • Dengue Fever (DF) – marked by an onset of sudden high fever, severe headache, pain behind the eyes, and pain in muscles and joints. Some may also have a rash and varying degree of bleeding from various parts of the body (including nose, mouth and gums or skin bruising).
  • Dengue Haemorrhagic Fever (DHF) – is a more severe form, seen only in a small proportion of those infected. DHF is a stereotypic illness characterized by 3 phases; febrile phase with high continuous fever usually lasting for less than 7 days; critical phase (plasma leaking) lasting 1-2 days usually apparent when fever comes down, leading to shock if not detected and treated early; convalescence phase lasting 2-5 days with improvement of appetite, bradycardia (slow heart rate), convalescent rash (white patches in red background), often accompanied by generalized itching (more intense in palms and soles), and diuresis (increase urine output).

Patients should seek medical advice in the presence of following features particularly when fever settles:

  • Severe vomiting
  • Abdominal pain  
  • Increase thrust
  • Drowsiness and excessive sleepiness
  • Refusing to eat or drink
  • Abnormal bleeding manifestations – eg: heavy menstrual bleeding or menstruation starting earlier than usual

If the following features are present seek medical attention immediately:

  • Cold clammy skin and extremities
  • Restless and irritability
  • Skin mottling
  • Decreased/no urine output
  • Behaviour changes – confusion or using foul language

Early detection of Dengue illness
Early identification and management of Dengue illness can minimize morbidity and mortality. In the present hyper-endemic setting in Sri Lanka, Dengue illness (Dengue Fever - DF /Dengue Haemorrhagic Fever - DHF) is considered in the differential diagnosis of patients presenting   with acute onset of fever with headache, retro-orbital pain, myalgia, arthralgia, rash (diffuse, erythematous, macular), haemorrhagic manifestation (petechiae, positive tourniquet test), Leukopenia (<5000/mm3), Platelet count ≤150,000/mm3 and rising Haematocrit of 5-10%.

Sometimes Dengue patients may present with atypical manifestations like respiratory symptoms such as cough, rhinitis or Injected pharynx and gastro-intestinal symptoms such as constipation, colicky abdominal pain, diarrhoea or vomiting without the classical clinical presentation described above.

If a patient with high fever is seen with flushed face/extremities (diffuse blanching erythema in adults) and a positive tourniquet test (even with a normal platelet count) with leukopenia (WBC <5000 /mm3) without any focus of infection, it is very likely that the patient is having Dengue illness.

In any patient who presents with shock (particularly afebrile at presentation with cold extremities and tachycardia with low volume pulse and hypotension) consider Dengue Shock as a likely diagnosis.

Detection of NS1 antigen from blood is novel laboratory diagnostic test for dengue during early febrile phase. However, NS1 only implies that the person is having dengue illness and it does not help in differentiating DF from DHF. Therefore, NS1 test may be useful in situations where early clinical diagnosis is doubtful.  

Value of Full Blood Count (FBC/CBC)
OPD level:

  • FBC is mandatory on all fever patients – from day 3 onwards
  • Special patient categories – FBC on day 1 or first day of visit/contact (Pregnancy, Infancy, elderly, those with co-morbidities, etc.)
  • FBC daily from day 3 if platelet (plt) count ≥150,000/ mm3
  • FBC twice daily when plt count  ≤150,000/ mm3  (admission to hospital based on clinical judgment, warning signs and social reasons)
  • Admit all patients with platelet count ≤100,000/ mm3  

Inward level

  • For any patient admitted to hospital on or before day 3 of illness same criteria of performing FBC as in OPD level is applicable unless and otherwise more frequent counts are requested by the clinician.   

Important Advice for Ambulatory Care Patients (OPD level):

  • First contact doctors should ensure adequate oral fluid intake.
  • In adults around 2500 ml for 24 hours (if the body weight is less than 50kg fluids given as 50ml/kg for 24hours or 2ml/kg/hr) is recommended during Febrile Phase (before admission to hospital).
  • In children calculation of maintenance fluid is as follows:

                     M (Maintenance)=100ml/kg for first 10 kg
                     +50ml/kg for next 10 kg
                     +20ml/kg for balance weight

Patients/parents should be asked to return immediately for review if any of the following occur on/beyond day three:

  • Clinical deterioration with settling of fever
  • Inability to tolerate oral fluid
  • Severe abdominal pain
  • Cold and clammy extremities
  • Lethargy or irritability/restlessness
  • Bleeding tendency including inter-menstrual bleeding or menorrhagia
  • Not passing urine for more than 6 hours

Differentiation of DHF from DF:
It is important to differentiate DHF from DF early because it is the patients with DHF who develop plasma leakage and resultant complications usually after the third day of fever. DHF may become evident as the fever settles. Tachycardia (increase heart rate) without fever (or disproportionate tachycardia with fever) and narrowing of pulse pressure (eg: difference between systolic and diastolic narrows from 40mmHg to 30 mmHg) is an early indication of leaking which warrants referral to the hospital. A progressively rising Haematocrit suggests that the patient may have entered the leaking phase. However, an ultra sound scan focused on chest and abdomen to detect selective and progressive fluid accumulation is a more objective evidence of plasma leakage in DHF.

Admission to a hospital:
The first contact doctor will decide to admit a patient to a hospital based on the clinical judgment. It is essential to admit the following patients:
-Platelet count below<100,000/mm3
-With the following warning signs on or beyond day 3 of fever/illness:

  • Abdominal pain or tenderness
  • Persistent vomiting
  • Mucosal bleeding (eg: bleeding from mouth, nose etc.)
  • Lethargy, restlessness
  • Liver enlargement >2cm
  • Rising HCT with rapid decrease in platelet count in FBC
  • Clinical signs of plasma leakage: pleural effusion, ascites (late sign)

Other patients who may need admission even without above criteria are:

  • Pregnant mothers - admission on second day of fever and close follow up with daily FBC is very important.
  • Elderly patients/infants
  • Obese patients
  • Patients with co-morbid conditions like diabetes, chronic renal failure, ischemic heart disease, haemoglobinopathies such as thalassaemia and other major medical problems
  • Patients with adverse social circumstances -e.g. living alone, living far from health facility without reliable means of transport.

Clinical and haemo-dynamical stability with no fever for 48 hours indicates recovery from Dengue illness.

Enhance community participation for sustainable DF/DHF control and prevention programme

  • Declaration of Mosquito Prevention Weeks and media seminars
  • Production of IEC materials
  • Advertising campaigns through electronic and  print media to create awareness of public on control / prevention strategies & to promote health seeking behavior

Communication for Behavioural Impact   

The strategies for the prevention and control of dengue include prompt diagnosis of fever cases, management or elimination of larval habitats in and around homes, work settings, schools, etc. and reducing human vector contacts.

A major obstacle to effective implementation of selective/ integrated mosquito control has been the inability to achieve and sustain expected desired behaviour. Despite growing levels of knowledge and awareness about dengue and mosquitoes, adopting and maintaining effective and feasible new behavior which remains a challenge.

Communication for behavioural impact (COMBI), espoused by WHO, is an innovative approach to fill this gap to mobilize individual and family action, utilizing social mobilization and communication to bring measurable change in behavior. It helps to plan, implement and monitor a variety of communication actions intended to engage individuals for adoption of healthy behaviours.

COMBI objectives include the clear identification of the target audience, a detailed description of the behaviour being promoted and the frequency of the behavior, the measurable impact that is desired over a specific time period: In other words the objectives should be ‘SMART’ (specific, measurable, appropriate, realistic,time-bound).

•    Specific: who or what is the focus; what change(s) are intended.
•    Measurable: specified quantum (e.g. % change intended).
•    Appropriate: based on target needs and aimed at specific health-related benefits.
•    Realistic: can be reasonably achieved.
•    Time-bound: specific time period to realize the objectives.
COMBI thus entails purposive and tailor-made strategic communication solutions intended to engage a specific target audience into responsive action.  

In developing the preliminary objectives, suitable recommendations for action by different segments should be considered.

•    Whose behaviour should be changed to bring about the desired outcomes? Who is the target audience?
•     What is required to be done? Is it feasible? Is it effective?
•     Why are they not doing it now? What are the barriers and motivators?
•     What activities can address the factors most influential to change behaviour?
•     Are materials/products/services needed to support those activities? If yes, are those easily available? If not, what should be done?

The behavioural objectives, target groups and key messages currently used are stated below:

Behavioural objectives and target groups:
1.To prompt housewives in 80-90% of homes in MOH areas to remove dengue breeding sites in their houses and surroundings at least once a week

2.To prompt principals and teachers in 80-90% of  schools to keep their school premises   free of dengue breeding sites through regular inspectionsevery Monday and Thursday

3.To establish “ Dengue Prevention Committees” in all government institutions to inspectand  remove dengue breeding sites in their premises and surroundings at least once a week

4.To motivate patients with fever for more than 02 days to seek treatment from a qualified doctor                                                                                                                                                                         

Key messages:
1. Every Sunday for 30 minutes, inspect your house and surrounding for dengue breeding sites. Remove or destroy them

2. Every Friday  for 30 minutes, inspect your school premises for dengue breeding sites. Remove or destroy them

3. Seek treatment from a qualified doctor,   if you have fever for more than 02 days

4. Do not take pain killers/ anti-inflammatory drugs, if you have fever

Enforcement of law against offenders 

Enforcement of law against the offenders who are keeping dengue mosquito breeding places in his/her premises which will endanger the lives of others

Mosquito Control in Schools

To be engaged on a weekly basis

Check for and eliminate mosquito breeding in the following places:

  • Discarded receptacles in open areas and under bushes in school premises
  • Open and closed drains
  • Manholes 
  • Cement lined ground ponds
  • Tree holes, bamboo stumps and leaf axil
  • Refuse bins and bin covers, especially when unused
  • Scupper drains in common corridors
  • Flower pots, plant pots and saucers and other ornamental structures
  • Air-conditioner trays
  • Unused equipments and other items for e.g. canvas sheet, dustpan, tyres, broken plastic chairs etc at storage areas
  • Cement rooftops and roof gutters
  • water storage tanks
  • Unused/ broken cisterns and bowls of toilets
  • Any other water-bearing receptacles

School Vacation

Maintain mosquito breeding free environment even in the school vacations, since several activities including examinations are held in the schools

School Hostel or Boarding House

Carry out the above mosquito control measures at the school hostel or boarding house too.

Vacant School buildings and constructions in schools

  • In vacant schools or schools undergoing constructions/demolition, eliminate mosquito breeding sites in discarded items left behind.
  • Seal/ cover up all toilet bowls/ cisterns/ gully traps with suitable mosquito proof material.
  • Check weekly water storage containers and other water collecting/ stagnated containers and receptacles.

Removal/ elimination of mosquito breeding in school premises

Following measures can be taken to eliminate mosquito breeding in the school premises during the inspection

  • Ensure the water storage tanks are properly covered and all drainage outlets are sealed
  • Collect and Burn, bury or dispose the discarded containers properly
  • Use larvivorous fish in ground level water storage tanks
  • Discourage planting water holding plants in its axils
  • Take immediate action to remove unwanted stored (inventory) items
  • Clean blocked roof gutters

Report to the school management committee all the breeding detected and the potential breeding habitats observed so that appropriate interim or permanent measures can be taken to eliminate the potential breeding grounds.

Mosquito Control in Construction Sites

Check for mosquito breeding in the following places:-

  • Discarded receptacles and building wastes in the worksite and site offices.
  • Building materials, canvas sheets, equipment and machinery.
  • Puddles on the concrete floors of all upper levels and basement
  • Water storage drums, tanks and containers.
  • Bulk waste containers
  • Lift wells
  • Safety barriers
  • Rooftops and water tanks
  • Treatment plants
  • Any other water-bearing receptacles

Destruction of mosquito breeding

Destroy/ eliminate all mosquito breeding sites found during the inspection

Report to the construction site supervisor and the head of the institution of the relevant authority all the breeding detected and the potential breeding habitats observed so that appropriate interim or permanent measures can be taken to eliminate the potential breeding grounds.


It is not mandatory to conduct fogging at construction sites. Fogging treatment should only be done when there is an impending disease outbreak or epidemic situations in the area.

Frequently Asked Questions

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