Epidemiology of Dengue

Seminar outline

Dengue is a threat to the health care system as it costs the government to treat the disease. More importantly the mortality rate among those with dengue can spike up especially during an outbreak.

The pathogenesis was discussed in the first few slides as the importance of knowing how the mosquito breeds and the disease is spread is vital in controlling and preventing the disease. Early notification was pointed out as an important activity to help control the disease from an outbreak. The mapping done normally is for high risk areas to help identify the areas for fogging and helps in the high level of suspicion from the doctors.

The number of cases in Malaysia are as follows:

Year	1997	1998	1999	2000	2001	2002	2003	2004	2005
Total	19429	27381	10146	7103	16386	32767	31545	33895	39654

As it can be observed the trend is cyclical, thus the next possible outbreak can be anticipated. Environmental factors like high index rain levels are prognostic factors.

Distribution of these cases are done by gender, state, ethnicity and locality. Information of such can always be obtained from the district health office as al the reporting is done there.

The vector: Aedes aegypti is known to be the main cause in Malaysia

The agent: ssRNA of dengue

The host: Humans where it can circulate in the variation from 3-10 days during incubation and in the system from 2-7 days when infected. The pathogenesis is not clearly understood but the mode of spread- breeding of the mosquito in clear clean water and household areas that can cause water stagnating were identified.

Clinical symptoms of Dengue Fever and Dengue Hemorrhagic Fever was touched upon. The clinical detection through Hess test and lab investigations were discussed and thrombocytopenia event in Dengue was stressed upon as that was the main cause of patients going into shock and death.

The strategies used in the prevention and control of dengue are contained in the Vector-borne Disease Control Programme Sixth Malaysia Plan include:

1) Anti-larval measures-larval surveys and source reduction of larval breeding habitats both indoors and outdoors

2) Anti-adult measures-destruction of infected adult Aedes mosquitoes through fogging activities as soon as a case is notified.

3) Health education-Anti-dengue campaigns are scheduled at a 3-monthly basis (i.e. January, April, July and October) and whenever there is an outbreak.

* No vaccine is available for Dengue fever yet.

ACTIVITIES AND ACHIEVEMENTS:

(i) Anti-larval activities:

-House inspection; to reduce breeding sites in all

dwelling facilities.

-The use of larvicide (temephos)

-Enforcement of Destruction of Disease-Bearing

Insects Act. 1975; by issuing notices &

compounds so that legal actions will be

taken to those who does not follow the rules.

(ii) Anti-adult activities:

-Fogging-done whenever a case is reported and in

'high-risk' areas.

(iii) Health education activities:

-continuously strengthened in order to gain

public support and cooperation.

(iv) Community participation:

- Agencies involved are from government, non

Government and voluntary organisations.

They also facilitate health workers in prevention

and control activities.

Surveillance

Done by regular larval surveys of Aedes mosquitoes and computing of Aedes Index (AI) and Breateau Index (BI) according to specific localities.

PROBLEMS AND CONSTRAINTS

• Delay and non-compliance in the notification of cases.

• Delay in fogging activities in certain local authority areas.

Neglected and unusual potential breeding sites

• Inadequate public compliance towards prevention and control of Aedes breeding.

Additional learning objectives:

1) How do the authorities predict the epidemic?

2) How and what do they prepare?

3) How is the case reporting done?

4) How fast does the authority react to an outbreak?

5) What is the allocation for dengue prevention?

6) Fogging: - what are the area

-how the areas are selected

-how extensive the fogging is done

-what chemical compound is used

-what's the mechanism of the chemical action

7) how an area is said to be a hyper endemic area? How these areas are