Dengue

ASIAN MEDICAL STUDENTS’ ASSOCIATION MALAYSIA

DENGUE CONTROL AND PREVENTION IN MALAYSIA

20^th EAST-ASIAN MEDICAL STUDENTS’ CONFERENCE, 2007, TAIWAN 

ACKNOWLEDGEMENT

The authors would like to express their gratitude to Professor Dr. Syed Aljunid, Consultant and Head of Community Health Department and Associate Professor Dr. Khalib bin Abdul Latiff, Head of Health Promotion Unit, Department of Community Health, for expanding our context of the research topic.

The authors would also like to thank Aland Shum Koin Lon, Queck Kian Kheng and the Academic Department of AMSA Malaysia for their contributions in aiding with this paper. Special mention also goes out to all the lecturers, staff of the Ministry of Health and delegates who were directly or indirectly involved in producing this paper.

Finally, we would also like to extend our appreciation to the various sponsors, whom have made this paper research possible.

OBJECTIVES

1. To investigate why emerging dengue epidemics make such tremendous effects on Malaysian community.

2. To share how various authorities, generally and the medical field, in particular deal with dengue in Malaysia.

3. To discuss the attitude we should attain when facing dengue epidemic (especially from the medical aspects).

METHODOLOGY

Several methods of data collection were employed in this research. Through books, journals, websites and press articles, various information were gathered. Personal phone conversations and interviews with local public health experts such as Associate Prof. Dr. Syed Aljunid and Prof. Dr. Khalib bin Abdul Latiff were equally enlightening. The data were utilized to review the prevalence of dengue cases in Malaysia, its consequences towards the community and to highlight the several activities that were carried out in Malaysia in dealing with dengue.

DENGUE CONTROL AND PREVENTION IN MALAYSIA

YC Lim, SY Wu, GL Teo, WJ Lee, HT Leow, SY Chin

ABSTRACT:

Dengue Fever and Dengue Hemorrhagic Fever is the most important emerging viral disease affecting nearly half of the world’s population. It is estimated that each year, there are between 50 to 100 million cases of Dengue Fever and about 500,000 cases of Dengue Hemorrhagic Fever which require hospitalization.

Over the past 3 decades, dengue cases in Malaysia had increased exponentially from 830 cases in 1975 to a total of 39,654 cases in 2005. This number is still rising. Dengue hemorrhagic fever, a nightmare among Malaysians, has increased to 2042 cases in 2005 and claimed 107 lives that year. During an epidemic, dengue patients have been seen filling in nearly half of the acute cubicles in medical wards.

Rapid urbanization and population growth, change of lifestyle, throwing non-biodegradable containers, rapid transportation, poor living condition in squatter areas, abandoned construction sites, have all contributed in the rising incidence of Dengue Fever. At times of an epidemic, with the media highlighting the issue, the local authorities carry out knee jerk actions to pacify the public. On the other hand, the ignorant publics were practically ‘breeding’ Aedes mosquitoes in the comfort of their own homes.

In absence of a vaccine for prevention of Dengue Fever, eliminating the breeding places of Aedes mosquitoes is still the only effective strategy to control the disease. Why are the people still maintaining practices that promote mosquito breeding? What are the major problems and challenges for disease control? How can we fight this catastrophe? We would like to answer them in this paper research.

INTRODUCTION

Ever since the very first of its existence over 300 years ago, dengue fever has subsisted and grows with mankind. The first cases were recorded in 1779 in Batavia, Indonesia, and Cairo.¹ Urbanization and globalization come with a price and one of them is none other than the emergence of dengue hemorrhagic fever and dengue shock syndrome.

Dengue is a mosquito-borne infection, which in recent years has become a major international public health concern in Malaysia. Dengue is found in tropical and sub-tropical regions around the world, predominantly in urban and semi-urban areas.

In 1944, taxonomist Albert Sabin successfully isolated dengue virus. He found that it is an Arbovirus that belongs to the family Flaviviridae and categorized together, under the Linnaeus’s Binomial classification, with other viruses of similar properties including Yellow Fever and Japanese Encephalitis Viruses. There are four serotypes of dengue virus (DEN-1, DEN-2, DEN-3 and DEN-4). They are antigenically very similar to each other but different enough to elicit only transient partial cross-protection after infection by each other of them. Antibodies to one type cross react in tests with other antigens. Therefore serological antibody tests, in general, do not differentiate between the dengue serotypes.²

Modes of Transmission

Dengue viruses are transmitted to humans through the bites of infective female Aedes mosquitoes. Mosquitoes generally acquire the virus while feeding on the blood of an infected person. After virus incubation of eight to ten days, an infected mosquito is capable, during probing and blood feeding, of transmitting the virus, to susceptible individuals for the rest of its life. Infected female mosquitoes may also transmit the virus to their offspring by transovarial (via the eggs) transmission, but the role of this in sustaining transmission of virus to humans has not yet been delineated.³

Humans are the main amplifying host of the virus, although studies have shown that in some parts of the world monkeys may become infected and perhaps serve as a source of virus for uninfected mosquitoes.³ The virus circulates in the blood of infected humans for two to seven days, at approximately the same time when they have fever; Aedes mosquitoes may acquire the virus when they feed on an individual during this period.

Pathophysiology of Dengue Fever

Once inoculated into a human host, dengue has an incubation period of 3-14 days which averages about 4-7 days. Following incubation, 5 to 7 days of acute febrile illness ensues. Recovery is usually complete by 7-10 days. Dengue haemorrhagic fever (DHF) or dengue shock syndrome (DSS) usually develops around the third to seventh day of illness, approximately at the time of defeverescence. The major pathophysiological abnormalities that occur in DHF and DSS are plasma leakage and bleeding. Plasma leakage is caused by increased capillary permeability and may be manifested by hemoconcentration, as well as pleural effusion and ascites. Bleeding is caused by capillary fragility and thrombocytopenia and may present in various ways, ranging from petechial skin hemorrhages to life-threatening gastrointestinal bleeding.

Most patients who develop DHF or DSS have had prior infection with one or more dengue serotypes.² In individuals who were previously exposed to a dengue serotype, non-neutralizing antibodies that is produced, when bound by macrophage and monocyte F_c receptors, has been proposed to result in increased viral entry and replication, and increased cytokine production and complement activation. This phenomenon is called antibody-dependent enhancement. In addition, certain dengue strains, particularly those of DEN-2, have been proposed to be more virulent, in part because more epidemics of DHF have been associated with DEN-2 than with the other serotypes.

Most of the cases are reported among the urban population with the highest incidence in the working and school age group, which correlates with the relatively high Aedes density in construction sites, factories and schools.⁴

 

EARLY SUSPICION AND DETECTION

Dengue is the most common and widespread arthropod-borne arboviral infection in the world nowadays. The geographical spread, incidence and severity of dengue fever (DF) and dengue hemorrhagic fever (DHF) are increasing in America, South-East Asia, the Eastern Mediterranean and the Western Pacific.²

In Malaysia, dengue fever was first reported in 1902 in Penang and had since became a major public health problem, especially after the first major outbreak of DHF which occurred in 1962.²

Early detection of disease outbreaks enables public health officials to implement disease control and prevention measures at the earliest possible time. Early suspicion and detection of an epidemic depends on a case definition of dengue fever that must be highly sensitive; timely and frequent reporting in high-risk area; high availability and application of its confirmatory investigations in medical centres. Because the onset of a disease outbreak is hardly predictable, early detection methods rely on continuous evaluation of different incoming data streams (e.g., ambulance dispatches, emergency department [ED] visits, pharmacy sales, or health insurance claims). Furthermore, due to the fact that early evidence of an outbreak may be localized, systems need to monitor multiple locations simultaneously before the extent or geographical pattern of the outbreak is apparent.

It is important to establish a sensitive case definition of dengue fever, i.e. a standard set of criteria, for deciding whether a person should be classified as having the disease or health condition under study. A case definition usually includes four components:

• Clinical information about the disease
• Characteristics about the people who are affected
• Information about the location or place
• A specification of time during which the outbreak occurred

Under this case definition, clear distinctions are made between DF and DHF, in order that their number of cases is disjointedly attainable.

Dengue fever is classified into probable and confirmed case. A probable case is defined as an acute febrile illness on which a confirming test has not been carried out and with 2 or more of the following manifestations:²

· Headache

· Retro-orbital pain

· Myalgia

· Arthralgia

· Rash

· Hemorrhagic manifestations

· Leukopenia

On the other hand, a confirmed case of dengue fever is a case that has been confirmed by one of the following laboratory criteria:

· Isolation of the dengue virus from serum or autopsy samples; or

· Demonstration of a fourfold or greater change in reciprocal IgG or IgM antibody titres to one or more dengue virus antigens in paired serum samples; or

· Demonstration of dengue virus antigen in autopsy tissue, serum or cerebrospinal fluid samples by immunohistochemistry, immunofluorescence or ELISA; or

· Detection of dengue virus genomic sequences in autopsy tissue, serum or cerebrospinal fluid samples by polymerase chain reaction.

As for DHF, all the following clinical manifestations and laboratory evidences must be present:

· Fever or history of acute fever, lasting for 2-7 days, occasionally biphasic

· Hemorrhagic tendencies, evidenced by at least one of the following:

1. a positive tourniquet test

2. petechiae, ecchymoses or purpura

3. bleeding from the mucosa, gastrointestinal tract, injection sites or other locations

· thrombocytopenia (100,000/mm³ or less)

· evidence of plasma leakage due to increased vascular permeability, manifested by at least one of the following:

1. hemoconcentration (equal to or greater than 20% above average for age, sex and population)

2. a drop in haematocrit following volume replacement equal to or greater than 20% of haematocrit at presentation

3. signs of plasma leakage evidenced by pleural effusion, ascites and hypoproteinemia

Other clinical manifestations that are suggestive of DHF are hepatomegaly, which may be tender on palpation, and circulatory disturbance.

DHF has a critical stage that accompanies the febrile phase of the illness or takes place shortly after the febrile phase where a rapid drop in temperature occurs. Varying degree of circulatory disturbances may arise at this stage, which rarely lasts longer than 48 hours.

In order to detect an epidemic, the health officials must first ensure that the problem has been properly diagnosed. Secondly, they must be certain that the increase in diagnosed cases is not the result of a mistake in the laboratory. Verifying the diagnosis requires that they review the clinical findings (the symptoms and features of illness) and correlate them with the laboratory results.

Notification of dengue fever and DHF in Malaysia was implemented in 1971.² The attending physicians or Medical Officers must notify all the probable and confirmed cases to the nearest district health office within 24 hours of diagnosis. Early notification is essential for early detection of an outbreak and for the control measures to be instituted immediately to prevent outbreaks. The increased availability of electronic health-care services will enhance the possibility of earlier outbreak detection which in turn make possible an efficient and effective intervention.

Many outbreaks are first recognized and reported by concerned health care providers or citizens. However, the first cases to be recognized usually are only a small proportion of the total number. As disease detectives aiming to spot an early outbreak, the health officials must “cast the net wide” to determine the true size and geographic extent of the problem. When identifying cases, they should use as many sources as they can; furthermore the health personnel also need to be creative and aggressive in identifying these sources. They can direct their case finding at facilities which include physicians’ offices, clinics, hospitals, and laboratories.

It is important to verify that a suspected outbreak is indeed a real outbreak. This is usually done by comparing the current number of cases with the number from the previous few weeks or months, or from a comparable period during the previous few years.⁵

 

DIAGNOSIS

Both clinical manifestations and laboratory investigations are equally as important in early detection of dengue fever.²

Pointers to the clinical diagnosis of dengue infection, which do not have to be entirely present at the same time, are:

· High continuous fever of 3 days or more

· Headache, backache and retro-orbital pain

· Abdominal pain, vomiting, loose stool

· Petechial hemorrhage and/or spontaneous bleeding

· Generalized flushing or maculopapular rash

· Hepatomegaly

· Shock

· Fall in platelet count that precedes or occurs simultaneously with a rise in the haematocrit

· Normal white cell count or leucopenia with relative lymphocytosis

Laboratory diagnosis consists of serology, virus isolation and molecular technique.

Serology

Serology is the most practical method available for the laboratory diagnosis of dengue infection in Malaysia. The serological test of choice is by far the enzyme linked immunosorbent assay (ELISA), which is simple, fast and cost effective.

ELISA can be used to detect dengue specific IgM which appears in both primary and secondary infection. With ELISA, 100% of dengue infection may be diagnosed with paired sera, taken 7 to 14 days apart but only about 60% with a single serum sample taken on day 5 to 6 of the illness.²

The interpretation of serological results must be carefully considered with respect to clinical features of the illness and not interpreted in distinct isolation. A positive dengue IgM result indicates acute or recent past infection of up to 90 days. However, ELISA IgM result may be negative in early acute blood specimen and a repeat specimen should be tested before confirming or excluding dengue infection.

The simple rapid tests such as the strip assays are available for the rapid detection of specific IgM and IgG but are relatively costlier.

Virus isolation

This is by far the most definitive method for the diagnosis of dengue infection. It is only performed in a few research laboratories because it is laborious, time consuming, costly and it is sensitive only if the blood is collected in the early acute phase of illness. Four isolation systems have routinely been used for dengue viruses; intracerebral inoculation of 1- to 3-day-old baby mice, the use of mammalian cell cultures (primarily LLC-MK₂ cells), intrathoracic inoculation of adult mosquitoes, and the use of mosquito cell cultures.

Molecular technique

This technique employs the amplification and detection of dengue ribonucleic acids by Reverse Transcriptase- Polymerase Chain Reaction (RT-PCR). The method is rapid, sensitive, simple, and reproducible if properly controlled and can be used to detect viral RNA in human clinical samples, autopsy tissues, or mosquitoes. Since RT-PCR is highly sensitive to amplicon contamination, without proper controls false-positive results may occur. Improvements in this technology, however, should make it even more useful in the future.

Autopsy specimens

Post mortem specimens include biopsy from lymph nodes, spleen, liver and brain. Specimen is collected in a sterile bottle with no preservatives and transported in dry ice. It is crucial to communicate with the relevant virology laboratory prior to dispatch of specimen. If delay in transport is anticipated, it necessitates the storage in -70ºC or in dry ice to conserve the sample.

PREVALENCE AND INCIDENCE OF DENGUE IN MALAYSIA

Prevalence Rate of Dengue Cases (Clinical) In Malaysia from 1975 till 2005⁷

YEAR	DF		DHF
	Case	Death	Case	Death	C.F.R (%)
1975	400	0	430	41	9.53
1976	349	0	441	35	7.94
1977	391	0	389	38	9.77
1978	475	0	454	33	7.27
1979	465	0	397	26	6.55
1980	369	0	300	25	8.33
1981	254	0	270	17	6.30
1982	2,146	0	860	35	4.07
1983	575	0	215	5	2.32
1984	551	0	151	5	3.31
1985	252	0	115	12	10.43
1986	1,115	0	293	8	2.73
1987	1,719	0	306	8	2.61
1988	1,195	0	233	3	1.29
1989	2,047	0	517	16	3.09
1990	4,235	0	645	21	3.25
1991	5,888	0	740	39	5.27
1992	4,828	0	645	24	3.72
1993	5,060	0	555	23	4.14
1994	2,877	0	256	13	5.08
1995	6,156	0	387	28	7.23
1996	13,723	2	532	30	5.64
1997	18,642	3	787	49	6.23
1998	26,240	18	1,141	64	5.61
1999	9,602	6	544	31	5.69
2000	6,692	4	411	41	9.97
2001	15,446	3	922	47	5.09
2002	30,807	2	1,960	72	3.67
2003	30,220	4	1,325	68	5.13
2004	32,422	7	1,473	95	6.45
2005	37,612	0	2,042	107	5.23

 

Prevalence Rate of Dengue Cases (Clinical) in Malaysia from 1975 to 2005

The prevalence rate of both dengue and dengue haemorrhagic fevers are generally rising from 1975 to 2005. From 1975 to 1985, the prevalence rate was decreasing. There was increase in prevalence rate from 1985 to 2005. In fact, dengue fever showed a very steep increase in prevalence rate from 6692 cases in 2000 to 37612 cases in 2005. The ratio of DF to DHF cases is 27.3:1 in adults and 6.7:1 in children.

This increase in prevalence rate is due to the rapid development that Malaysia is undergoing which is not matched by an equal increase in infrastructure such as solid waste disposal. The increase in 1985 happened at the same time that urbanization was on the rise.

The peak in 1998 tallies with the water and the economic crisis, contributing to the problem as many residents resorted to water storage in their homes. Another major problem was abandoned projects, which created potential breeding areas for Aedes mosquitoes.

In 1999, there was a drop of dengue fever from 26,240 to 9,602. One of the reasons for this drop was the success of the ‘National Cleanliness and Anti-mosquitoes Campaign’ launched in April 1999 aimed to increase awareness among all citizens on the cleanliness at home, workplace and surroundings and its relationship to mosquito-borne disease. Another reason for the reduction of cases was the predominance of Dengue-2 virus for the last few years contributing to the herd immunity to this strain of virus.¹¹

The steep increase from 2001 onwards is in line with the Eighth Malaysia Plan (from 2001 to 2005) to improve the national economic growth, national export and productivity (GDP) and at the same time reduce unemployment. There has been a proliferation of construction sites that fill with water and become an ideal breeding ground for Aedes mosquitoes. Building of more factories and schools are also attributed. The increase in population has also been implicated, with a resulting increase in garbage which allows for mosquito breeding. This incidence is predicted to continue increasing in the future, as a result of both the rapid infrastructural development and increase in population.

In the Malaysian context, health reforms in the late nineties that integrated the vertical organization structure of the Vector Borne Disease Control Programme with the general health services resulted in loss of technical expertise as well as constraints in funding, as limited health resources were moved to other competing programmes under the Ministry of Health. In 2000, the control of vector borne diseases in the bigger towns and cities were made the responsibility of their respective local governments. Unfortunately, many of these local authorities neither have the expertise nor the political will to implement sustainable and effective vector control measures. At times of an epidemic, with the media highlighting the issue, the local authorities carry out knee jerk actions to satisfy the public. However, many of these actions are designed for short-term political visibility rather than being based on good epidemiology.

 

Incidence of Total Dengue Cases (Clinical) In Malaysia from 1975 till 2005⁷

YEAR	TOTAL
	Case	Death	C.F.R (%)
1975	830	41	4.94
1976	790	35	4.43
1977	780	38	4.87
1978	929	33	3.55
1979	862	26	3.02
1980	669	25	3.74
1981	524	17	3.24
1982	3,006	35	1.16
1983	790	5	0.63
1984	702	5	0.71
1985	367	12	3.27
1986	1,408	8	0.57
1987	2,025	8	0.40
1988	1,428	3	0.21
1989	2,564	16	0.62
1990	4,880	21	0.43
1991	6,628	39	0.59
1992	5,473	24	0.44
1993	5,615	23	0.41
1994	3,133	13	0.41
1995	6,543	28	0.43
1996	14,255	32	0.22
1997	19,429	52	0.27
1998	27,381	82	0.30
1999	10,146	37	0.36
2000	7,103	45	0.63
2001	16,368	50	0.30
2002	15,493	54	0.34
2003	31,545	72	0.22
2004	33,895	102	0.30
2005	39,654	107	0.26

Note: CFR = Case Fatality Rate

 

Total Dengue Cases (Clinical) in Malaysia from 1975 to 2005

The total dengue cases have also been on the rising trend, with an average of 1294.1 new cases per year.

From 1975 to 1985, there was in fact a drop in the total cases with a decrease of 46.3 cases per year. From 1985 to 2000, the increase averaged 449.1 cases per year. From 2000 to 2005, the increase was greater, at 6398.2 cases per year.

The total dengue cases were predicted to rise by double the amount in 2010 if the trend persists.

 

Total Death from Dengue Cases from 1975 to 2005

This shows the same graph pattern as the total dengue cases in Malaysia. There was a decrease of 2.9 deaths per year from 1975 to 1985. Since then, there was an increase of 2.2 deaths per year from 1985 to 2000. There was a greater increase of 12.4 deaths per year from 2000 to 2005. The death rates are expected to rise by double the amount in 2010 considering that the incidence rate of dengue is on a rising trend.

BACKGROUND OF VECTOR BORNE DISEASES CONTROL IN MALAYSIA

The Vector Borne Diseases Control Programme (VBDCP) started off as three separated Malaria Eradication Programme (MEP) in Peninsular Malaysia, Sabah and Sarawak which were as follows⁷

 

PENINSULAR MALAYSIA

The Malaria Eradication Programme (MEP) in Peninsular Malaysia was launched in 1967. A Malaria Pilot Project (1960 - 1964) demonstrated that there was a practical and feasible method of controlling the malaria situation in Peninsular Malaysia. A nation-wide malaria survey in 1965-1966 showed that there were about 300,000 malaria cases annually in Peninsular Malaysia. At that time of launching in 1967, the original objective was to completely eradicate malaria from Peninsular Malaysia by 1982. This objective was no longer attainable due to various administrative, technical and operational problems. The Malaria Eradication Programme was changed to a Malaria Control Programme in 1980.

SARAWAK

The first malaria survey in Sarawak was carried out in 1952 by De Zulueta. With the assistance of WHO, this was followed by a Malaria Control Pilot Project which was carried out in 1953 - 1954 in the Baram Valley in Fourth Division of the state covering an area of about 5,100 square kilometers and a population of about 6,400 people. In 1961 it was decided to undertake a Malaria Eradication Programme based on the same attack measures that were used in the Malaria Control Pilot Project.

Due to various problems being encountered by the Eradication Programme, such as the influx of malaria carriers from the neighbouring Provinces/States, the nomadic groups of the population in some areas, difficult terrain and communication, it was not possible to achieve the complete interruption of malaria transmission. The Malaria Eradication Programme was then changed to Malaria Control Programme in 1972.

 

SABAH

A Malaria Pilot Project (1956 - 1960) demonstrated that there was a practical and feasible method of controlling malaria in Sabah. The Malaria Eradication Programme (MEP) was launched in 1961 and continued for ten years. The Malaria Eradication Programme was changed to Malaria Control Programme in 1971 due to administrative, technical and operational difficulties.

In 1980, the Ministry of Health of Malaysia made an important policy decision of converting the existing Malaria Eradication Programme (MEP) in all its states into Vector Borne Diseases Control Programme (VBDCP). Basic strategies and activities of the MEP are also applicable to the control of other diseases transmitted by the mosquito vectors.

Such diseases are:

• Malaria with Anopheline mosquitoes as vectors
• Filariasis with Anopheline and Mansonia mosquitoes as vectors
• Dengue Fever/Dengue Hamemorrhagic Fever with Aedes mosquitoes as vectors
• Japanese B.Encephalitis with Culicine mosquitoes as vectors
• Plague with fleas (Xenopsylla cheopis) as vectors
• Yellow Fever with Aedes mosquitoes as vectors
• Murine Typhus with fleas as vector and Scrub Typhus with mites as vector.

The development of the Vector Borne Diseases Control Programme (VBDCP) was implemented in three phases:

Phase I - Formation of the Anti Malaria Programme (1981 - 1982). Malaria control services both inside and outside the Local Authority areas were taken over and integrated with the Malaria Eradication Programme to form the Anti Malaria Programme.

Phase II - Formation of the Vector Borne Diseases Control Programme (VBDCP) 1983-1984. During this period, the programme’s activities and scope were expanded to include other common mosquito-borne diseases in Malaysia, e.g Filariasis, Dengue/Dengue Haemorrhagic Fever and Japanese B Encephalitis. This resulted in the formation of the Vector Borne Diseases Control Programme (VBDCP).

Phase III - Further Expansion of the Scope of the VBDCP (1985 Onwards). The VBDCP will take over control of other vector borne diseases such as Scrub Typhus which is transmitted by mites and Murine Typhus by fleas. Although there has not been a case of plague in this country for a long time, a check will be kept on the presence of the flea (Xenopsylla cheopis) whose natural habitat are rodents. There is no Yellow Fever at present although the Aedes mosquitoes are present in the country. In line with Article 20 of the International Health Regulation (IHR), all airports are to be kept free of Aedes mosquitoes.

 

CONTROL OF DENGUE IN MALAYSIA

In Malaysia, the control of dengue by the government is under the authority of Section of Vector Borne Diseases, Department of Public Health, Ministry of Health Malaysia.

The aim of control include:

1) To reduce the density of Aedes mosquitoes to the level that dengue epidemics would not occur.

2) To encourage the co-operation and involvement of the society in the prevention and control of dengue.

3) To eradicate or to reduce the number of Aedes breeding sites.

4) To get as much help as possible from the local authorities in dengue prevention and control activities.

Methods of Control

Generally, the methods of control are divided into five different modalities which include: -

i) environmental control

ii) biological control

iii) chemical control

iv) information, education and communication

v) law and enforcement.

I) Environmental Control

This is by far the most effective modality which involves the reduction of the breeding sites of Aedes mosquitoes (source reduction). It is a long-term measure to reduce the number of mosquitoes’ population. Therefore, it requires a lot of commitment and involvement from the community.

The communities are encouraged to eradicate the source of larvae in the environment especially at their premises. They are pleaded to collaborate with the health authorities during house inspection, fogging, campaigns and health education. Self inspection of twice weekly and removal of all water-containing vessels is encouraged. In cases where water container cannot be removed, the use of chemical control such as Abate or biological control such as fish is employed.

Proper solid waste disposal and improved water storage practices, including covering containers to prevent access by egg-laying female mosquitoes are among the methods that are encouraged through community-based programmes.⁸

II) Biological Control

The control is achieved by breeding of certain bacteria such as Bacillus thuringiensis israeliensis, Bacillus sphaericus, larvae-eating fish such as Gambusia affinis, Poecilla retiiculata, insect predator such as Toxorhynchites sp. or water fleas such as Mesocyclops sp. in water container that cannot be removed.

One variety of the larvae of jungle mosquito, the Toxorhynchites splendens, consume larvae of other mosquito species, particularly the Aedes aegypti. These cannibalistic mosquitoes are bigger in size. However, the adults are not bloodsuckers but subsist on nectar and other natural carbohydrates. By introducing them into the urban environment it is hoped that they will help check the breeding of Aedes.⁸

Such measures may be needed in the war against the Aedes mosquito as it is evolving into a super resistant breed.⁹ It is very important to reduce mosquito-breeding sites, as fogging only kills the adult mosquitoes. Draining water containers without cleaning them is not enough as the eggs can stick to the sides of the containers even when the water is drained, and survive for up to six months without water. On coming into contact with water, the eggs will hatch and the larvae will find their way into waterlogged areas. The government has also started to use larvicidal biological control BTI (bacillus thuringiensis israeliensis) in the fogging of dengue-prone areas. But unlike any insecticide, this agent will not have the side effect of causing mosquitoes to be more resistant or kill any other insect or animal that fed on
mosquitoes.⁸

 

III) Chemical Control

Chemical control of dengue is generally divided into larvicide, adulticide and repellents. Larvicide is used to kill larvae which include Temphos (Abate). Adulticide is used to kill adult mosquitoes which include fogging and aerosol. Examples of repellents are mosquitoes coils and mosquitoes mats.

The application of appropriate insecticides such as Abate to larval habitats, particularly those which are considered useful by the householders, e.g. water storage vessels, prevent mosquito breeding for several weeks but must be re-applied periodically. During outbreaks, emergency control measures include the application of insecticides through fogging to kill adult mosquitoes using portable or truck-mounted machines or even aircraft. However, the killing effect is only transient, variable in its effectiveness because the aerosol droplets may not penetrate indoors to microhabitats, where adult mosquitoes are sequestered, and the procedure is costly and operationally very demanding. Regular monitoring of the vectors' susceptibility to the most widely used insecticides is necessary to ensure the appropriate choice of chemicals. Active monitoring and surveillance of the natural mosquito population should accompany control efforts in order to determine the impact of the programme.⁸

 

IV) Information, Education and Communication

This includes organizing cleanliness campaign and ‘gotong-royong’ in community. Besides, talks and lectures are also given to instill the awareness of the importance of keeping the environment clean and free of mosquitoes. In school setting, health quizzes and health related VCD or DVD could be used to enhance the knowledge of the diseases among the students. The information regarding the diseases can be channeled to the public through posters, brochures or flyers.

V) Law and Enforcement

Several acts have been amended by Malaysian government to control dengue in Malaysia which include Destruction of Disease-bearing Insects Act, 1975, Prevention and Control of Infectious Diseases Act 1988 and Local Government Act 1976.

The Destruction of Disease-bearing Insects Act, 1975 provides the authority for the implementation of the various control measures, including the prosecution of offenders.¹⁰

Under Prevention and Control of Infectious Diseases Act 1988, all the probable, suspected and confirmed dengue cases are made compulsory to be notified to the local health authorities.¹⁰

 

PREVENTION OF A SECOND OUTBREAK

At present, the only method of controlling or preventing outbreaks of DF and DHF is to combat the vector mosquitoes.

In Malaysia, Aedes aegypti breeds primarily in man-made containers like earthenware jars, metal drums and concrete cisterns used for domestic water storage, as well as discarded plastic food containers, used automobile tyres and other items that collect rainwater. It also breeds extensively in natural habitats such as tree holes and leaf axils.

Vector control is implemented using environmental management and chemical methods as mentioned above.

MAJOR PROBLEMS AND CHALLENGES FOR DISEASE CONTROL

The reasons for the persistence or global emergence of DF/DHF as a major public health problem are complex and not fully understood. Globally, effective mosquito control is the exception rather than the rule in dengue-endemic countries. Major global demographic changes have occurred, especially uncontrolled population growth, mobility and unplanned urbanization. Among many other man-made items, good larval habitats are provided by household water storage containers, discarded solid waste items, such as plastics, glass containers and used automobile tyres. Increased travel by humans serves to spread dengue viruses between population centres of the tropics. And finally, decentralized and often weak public health infrastructures now place emphasis on implementing emergency control methods in response to epidemics as opposed to developing programmes to prevent epidemic transmission. In the face of poor surveillance, epidemics often reach or pass peak transmission before they are detected. Epidemics can be averted by timely and intensive vector control by a concerted effort of all related authorities and the community at large. A strong political will is also necessary to ensure the continuity and success of anti-dengue programmes as to control, prevent and ultimately eradicate the disease.

 

REFERENCES

1. Seminar in Biology; Cell and Molecular Biology: Emerging Diseases (http://justice.loyola.edu/%7Eklc/BL472/Dengue/Dengue.home.html)

2. Clinical Practice Guideline, Dengue Infection in Adults, Dengue Consensus 2003, Academy of Medicine Malaysia, Ministry of Health

3. World Health Organization (www.who.int/topics/dengue/en/)

4. E-medicine (www.emedicine.com/emerg/topic124.htm)

5. Valnis Barbara, Epidemiology in Health Care, 3^rd edition, Appleton & Lange United States

6. Ministry of Health Malaysia (www.moh.gov.my)

7. Department of Public Health Malaysia (www.dph.my)

8. Malaysian Medical Association (www.mma.org.my)

9. The Star Online Newspaper (www.thestar.com.my/news/story)

10. Sarawak Health Department (http://www.sarawak.health.gov.my/cdc.htm)

11. Zahari Che Don, 2001: Vector-borne Disease Control Unit.