Spatial distribution of malaria in Peninsular Malaysia from 2000 to 2009

Background Malaria is still an endemic disease of public health importance in Malaysia. Populations at risk of contracting malaria includes indigenous people, traditional villagers, mobile ethnic groups and land scheme settlers, immigrants from malaria endemic countries as well as jungle workers and loggers. The predominant species are Plasmodium falciparum and P. vivax. An increasing number of P. knowlesi infections have also been encountered. The principal vectors in Peninsular Malaysia are Anopheles maculatus and An. cracens. This study aims to determine the changes in spatial distribution of malaria in Peninsular Malaysia from year 2000–2009. Methods Data for the study was collected from Ministry of Health, Malaysia and was analysed using Geographic Information System (GIS). Results Changes for a period of 10 years of malaria spatial distribution in 12 states of Peninsular Malaysia were documented and discussed. This is illustrated by digital mapping according to five variables; incidence rate (IR), fatality rate (FR), annual blood examination rate (ABER), annual parasite index (API) and slide positivity rate (SPR). Conclusion There is a profound change in the spatial distribution of malaria within a 10-year period. This is evident from the digital mapping of the infection in Peninsular Malaysia.


Background
Worldwide, there are 109 malaria endemic countries with an estimated 3.3 billion people at risk of malaria in 2010, out of which 1.2 billion are at high risk (>1 case/ 1000 population). Of the 1.2 billion, 37% reside in Southeast Asia [1]. Malaysia was highly endemic with malaria, and in 1892, nearly one third of all deaths in Penang (an island state on the north-west of Malaysia) were attributed to malaria. Introduction of a new drainage system scheme by one of the pioneer antimalaria workers, i.e. Malcolm Watson in Peninsular Malaysia in the early twentieth century, was recognised as an early control measure in the world, leading to great reduction of malaria cases [2].
Being one of the major parasitic diseases in Malaysia, malaria affects indigenous people, traditional villagers, mobile ethnic groups and land scheme settlers, immigrants from malaria endemic countries as well as jungle workers and loggers [3,4] The highest number of malaria deaths in Peninsular Malaysia was reported to be 29 in 2001 and this figure decreased to 5 in 2009. The highest malaria incidence was recorded in the 20-39 years old age group ( [3], Unpublished data from Disease Control Division Ministry of Health records). The younger age group who are actively working and highly mobile has increased the risk of being exposed to malaria infection, subsequently affecting the economic productivity due to work absenteeism. There were more males infected with malaria compared to females probably due to the former being involved in outdoor activities ( [3,6], Unpublished data from Disease Control Division Ministry of Health records).
Five Plasmodia species are known to infect humans, namely Plasmodium falciparum, P. vivax, P. ovale, P. malariae and P. knowlesi (simian malaria parasite). In Peninsular Malaysia, in year 2009, P. vivax is the predominant species detected with (49.5%), P. falciparum (36.1%), P. malariae (7.2%) and mixed infection (2.6%) ( Figure 2). P. knowlesi had shown an increasing trend with 41 cases in 2008 to 55 cases in 2009 (Unpublished data from Disease Control Division, Ministry of Health records). Chloroquine and Fansidar resistance to P. falciparum has been reported in Peninsular Malaysia [7]. Important vectors involved in malaria transmission in Peninsular Malaysia are Anopheles maculatus and An.  cracens. An. maculatus is the vector for human malaria whereas An. cracens is the vector for simian malaria caused by P. knowlesi [8]. With deforestation and environmental changes, new vectors have displaced the established vectors.

Study site
Peninsular Malaysia stretches between l°20′N to 6°40′N and from longitude 99°35′E to 104°20′E. It covers 131,598 km 2 of geographical area. Peninsular Malaysia comprised 23.5 million people as per provisional data of 2012 census. Mean daily temperatures range from about 25°C to 28°C. The climate is equatorial, with rain from both the northeast (November to March) and southwest (May to August) monsoons. The rainfall ranges from a maximum of 5000 mm and a minimum of 1750 mm. The average maximum relative humidity of the air varies between 94% and 100%, typical of the humid tropics. Peninsular Malaysia consists of 12 states; Perlis, Kedah, Pulau Pinang, Perak, Melaka, Negeri Sembilan, Selangor, Johor, Pahang, Terengganu, Kelantan and Federal Territory (Kuala Lumpur and Putrajaya) ( Figure 3) [9].

Study design
The study was conducted using retrospective secondary data of malaria for the period of 2000 to 2009. We obtained all annual reports of malaria for the mentioned period from the Ministry of Health (MOH) Malaysia. Besides that, the data was also obtained from public health centers and local journals. For the updated population numbers, the data was taken from Department of Statistics (DOS) Malaysia which is available online. The approval from Malaysia National Health Institute (NIH) was successfully obtained in order to conduct the research in MOH. A second approval was given by MOH to allow the data collection process. Collected data was then entered in Microsoft Excel computer program. After proper data cleaning, the data was analyzed using Geographic Information System (GIS) to produce digital maps of incidence rate (IR), fatality rate (FR), annual blood examination rate (ABER), annual parasite index (API) and slide positivity rate (SPR).

Results and discussion
Changes for a period of ten years of malaria spatial distribution in 12 states of Peninsular Malaysia are illustrated by digital mapping according to five parameters; IR, FR, ABER, API and SPR.
The changes of malaria IR for 12 states in Peninsular Malaysia from 2000 to 2009 is graphically shown in  [10]. Distribution of insecticide treated nets (ITNs) and indoor residual spraying (IRS) to vulnerable areas successfully decreased the malaria cases in Peninsular Malaysia [3]. Figure 5 shows the changes in FR for 12 states in Peninsular Malaysia from 2000 to 2009. There was no malaria fatality cases reported in Perlis. In Melaka, out of 15 confirmed malaria cases in 2001, two deaths were reported (13.33%). Kuala Lumpur only reported one fatality case (6.67%) from its total of 15 confirmed malaria cases in 2004. While in 2005, Negeri Sembilan reported one fatality case (9.09%) from its total of 11 confirmed malaria cases. In Kedah, Pulau Pinang, Perak, Pahang, Selangor, Kelantan, Johor and Terengganu the FR was <5% population within a 10 year period except for 2006 when Perak reported FR of 5.88% ( [3], Unpublished data from Disease Control Division Ministry of Health records). Most of the deaths were caused by cerebral and complicated malaria. Factors that contributed to malaria deaths included delay in detecting malaria due to lack of suspicion of malaria when patient was first seen, failure in detecting severe and complicated malaria which led to improper treatment, delay in treating patient with IV Quinine because of no storage in District Hospital and cases were sometimes misdiagnosed as dengue, septicemia, typhoid and hepatitis [3]. Figure 6 shows the changes of ABER in 12 states of Peninsular Malaysia from 2000 to 2009. ABER reflects the efficiency and adequacy of case detection mechanisms. There are three mechanisms of malaria case detection in Peninsular Malaysia; passive case detection (PCD), active case detection (ACD) and mass blood survey (MBS) [3].      population ( [3], Unpublished data from Disease Control Division, Ministry of Health records). Under NMEP, API value was fixed at <0.1/1000 population. To achieve the target, the area with high API values must be given priority and attention in terms of malaria control activities [11]. Figure 8 shows the changes in SPR in 12 states in Peninsular Malaysia from 2000 to 2009. Whenever ABER is adequate, SPR is a dependable parameter for determining the progress of measures and gives information of parasitic load in the community. SPR measures the prevalence of malaria parasites among those who seek care and are examined in health facilities [11].  [4]. WHO guidelines consider a country is ready to undergo transition from control to pre-elimination when the SPR value < 5% [11]. Malaysia is entering a pre-elimination stage and Peninsular Malaysia is targeted for malaria elimination by 2015 [4]. To achieve elimination, several strategies were implemented such as early case detection and prompt treatment, close monitoring of imported cases, residual spraying, usage of bed nets, environmental and anti larval management, monitoring of drug resistance and collaborating with the neighbouring countries [10].

Conclusion
There is a profound change in the spatial distribution of malaria within a 10-year period. This is evident from the digital mapping of the infection in Peninsular Malaysia. The reduction in the number of malaria indigenous cases has been attributed to a successful Malaria Control Program (1980), which includes the increase in laboratory diagnostic capability, prompt treatment, nationwide implementation of insecticide treated bed nets and regular insecticide spraying.