The effect of rainfall on the spread of malaria in Indonesia

INTRODUCTION

The spread of malaria cases in Indonesia is increasingly worrying, amid advances in technology and information as well as increasingly adequate health facilities. Based on data from the 2018 Podes data, it is known that 1,497 villages experienced malaria cases in 2018. From these malaria cases, it is known that 82 people died from the outbreak.¹ If classified based on the islands in Indonesia, the eastern region of Indonesia has the largest portion when compared to the western region.

Malaria is caused by the plasmodium parasite which is spread by the bite of a female Anopheles mosquito. After the mosquito bite, the parasites enter the body and occupy the liver, where the parasites can grow and reproduce. When these parasites grow and become adults, they leave the liver and destroy red blood cells. Damage to red blood cells will cause symptoms of anemia in sufferers. Apart from being bitten by mosquitoes, the spread of malaria parasites can also occur due to exposure to the blood of malaria sufferers. Some conditions that can cause a person to be exposed to malaria due to human-to-human exposure include an infected fetus from his mother, receiving blood transfusions, sharing needles, and receiving organ donations.^2-5

The severity of the malaria symptoms that arise varies from person to person. People who live in areas with a lot of malaria cases have better immunity, so their symptoms will be less severe. However, this immunity can be lost once a person moves to an area where malaria is not common.

People who do not have immunity can experience more severe symptoms of malaria. Symptoms of malaria can generally be severe and can cause complications if they occur in infants, the elderly, pregnant women and their fetuses.^6-8

There are many types of malaria which are differentiated according to the type of parasite plasmodium that infects. However, only five types of plasmodium infect humans, namely: (i) malaria falciparum, caused by the parasite Plasmodium falciparum. This type of malaria is the most dangerous because it causes severe malaria with complications. Most of the deaths due to malaria are associated with this type of malaria. (ii) malaria vivax, the plasmodium vivax parasite that causes vivax malaria, can survive in an inactive state in the liver for several months or years. Thus, this type of malaria can recur when the parasites become active again. (iii) malaria ovale, this type is caused by the parasite Plasmodium ovale and the symptoms are not severe, and sometimes get better without treatment. (iv) malaria malariae, this type of malaria only causes symptoms after being infected with the Plasmodium malariae parasite for a long time. Therefore, sufferers of this type of malaria will experience chronic infections and are also associated with impaired kidney function. (v) malaria knowlesi, the same as malaria falciparum, malaria due to Plasmodium knowlesi can also progress quickly to become severe, even though the initial symptoms are mild.^9,10

Based on data from the Annual Parasite Incidence, there were 250,644 malaria cases recorded in 2019 in Indonesia. The highest case, 86 percent, occurred in Papua Province with 216,380 cases. This was followed by East Nusa Tenggara Province with 12,909 cases and West Papua Province with 7,079 cases. One of the things that causes eastern Indonesia to remain prone to malaria is geographic and cultural factors. In some areas in the region, there are still many people who live close to gardens, swamps, and trees that can become mosquito breeding grounds. This can increase the risk of malaria through mosquito bites.^11,12

In addition, the hotter air at night can also affect this risk. In fact, residents in the area are reluctant to use a mosquito net that prevents mosquitoes from biting because it will block the wind to sleep better. In fact, mosquito nets contain insecticides that can kill mosquitoes when they get caught in the nets. In addition, education regarding the risks from the dangers of malaria is still limited due to a lack of information distribution. In addition, the lack of people who get immunized makes the risk of people being attacked continues to increase. That way, the health role of the government is very important so that these infectious diseases can be overcome immediately.

There are differences in position, causing various climate differences in Indonesia. From Figure 1, it is known that the rainfall on Kalimantan Island is the highest, while Java Island has the highest wind speed. In addition, Kalimantan Island is an island that has high humidity, and Java Island has a high temperature. Apart from different geographical positions, regional characteristics (such as population density, regional economy, and the main source of income for the community) can also influence climatic conditions that occur in an area.

The condition of the area which is still filled with forests causes the islands of Papua and Kalimantan to tend to have high humidity and rainfall. From the environmental side, this is very good, because people can experience life that is still natural. However, the region is experiencing a disease that is not experienced by other parts of Indonesia, which have a warmer climate. The characteristics of the disease that arise are caused by organisms using a moist / watery medium for reproduction.

Based on the previous background, it is known that climate factors have a role in the spread of malaria. Indirectly, the rainfall and humidity in the area cause the reproduction rate of anopheles which causes malaria to be higher. Based on previous research, it is known that climate affects the spread of malaria.^13-16 Previous research has used data at both the state and provincial levels. In this study, using data on the number of incidents and the number of victims who died from malaria at the village level, so that the role of rainfall in influencing malaria in Indonesia will be known.

METHODS

The data used in this study are raw data from the 2018 PODES data collection, which describes the conditions for the spread of malaria at the village level. The PODES data collection is carried out by BPS and is specifically designed to collect data that can describe conditions in rural areas and sub-districts, as well as prepare future censuses through the collected data and information.

This study uses rainfall data as a variable of interest. The instrument variables in this study were wind speed, humidity, solar radiation, temperature, and air pressure. This study also uses several control variables, namely the village bordering the sea, the number of primary schools, the number of midwife practices, the number of village health centers, the presence of village midwives, and the number of poor families. The first stage model is the number of malaria incidents and the number of malaria deaths caused by malaria:

Instrumental variable model number of malaria incidence:

Instrumental variable model of the number of deaths from malaria due to malaria:

Ordinary least square model for the number of malaria incidence:

Ordinary least square model for the number of victims who die from malaria:

This study used the instrumental variable method, because the model that was built had endogeneity problems. Wooldridge (2016) states that instrumental variable analysis is used to overcome the problem of endogeneity. The OLS estimator will be biased and inconsistent if an important variable is not included in the model.

RESULTS

In Table 1, through the first stage on the instrumental variable method, it is known that wind speed, humidity, and air pressure have a significant positive effect on rainfall.

Source: Results of processing with Stata 16 (processed). Note: Notation level of significance *** p <1%.

Besides, solar radiation and temperature have a significant negative effect on rainfall. According to phenomena, the two groups are opposite each other, for example temperature and humidity. The high temperature of an area causes the humidity to be lower.

From Table 2 it can be interpreted that rainfall has a significant positive effect on the number of malaria incidences. The variable in the regression model that is formed can explain 0.38 percent of the incidence of malaria in an area. The coefficient formed from the regression IV is 0.0000779. These results can be interpreted that every 1 mm increase in rainfall will increase the chance of malaria incidence of 0.0000779.

Source: Results of processing with Stata 16 (processed). Note: Notation level of significance *** p <1%.

Source: Results of processing with Stata 16 (processed). Note: Notation level of significance ** p <5%.

Based on Table 3 it can be interpreted that rainfall has a significant positive effect on the number of victims who died from malaria. The variable in the regression model that is formed can explain 0.07 percent of the number of victims who died from malaria in an area. The coefficient formed from the regression IV is 0.0000142. These results can be interpreted that every 1 mm increase in rainfall will increase the number of victims who died from malaria of 0.0000142.

DISCUSSION

From the regression results, it is generally known that climate plays an important role in the spread of malaria and its impact on the disease. This result is in line with several previous studies which stated that climate has a positive influence on malaria.^18-20 Conditions in areas that have moderate to high rainfall are usually humid. This humidity makes it easier for female Anopheles mosquitoes to breed. In addition, if the area is a wilderness area, the breeding process will be faster. In line with the phenomenon, many malaria cases occur in the Provinces of Papua and West Papua, because these areas have a relatively humid climate and the condition of the area is still a lot of forest. Malaria in Papua and West Papua Provinces has become something that is not surprising, because this disease has experienced quite a lot of local people. It is believed that the local community has immunity against malaria.

The overall result of the calculation using the instrumental variable method is greater than the calculation using the ordinary least square method. This is according to the theory presented, that the instrumental variable method will solve the endogeneity problem, and if traced the coefficient formed will be greater than the ordinary least square method.¹⁷.

From Table 2 it can be indicate that there are most of the other variables that can influence the occurrence of malaria. Other things that can affect the disaster include the behavior of the community in protecting the environment, geographical factors, and the level of public knowledge. This result is in line with previous research which states that increased rainfall will result in higher spread of malaria.²¹ From these results it can be concluded that the spread of disease, especially malaria, during the rainy season is very high. Anticipation is needed to control this chronic disease. Anticipation that can be done by spraying disinfectants so that the proliferation of anopeles can be controlled as low as possible. In addition, the public can be given education regarding the storage of used goods that can hold water, especially during the rainy season. Objects that can hold water will become breeding grounds for anopeles.

Malaria incidents that occur not only have a negative impact on community activities, but these events also have an impact on casualties. Casualties due to malaria are usually from the poor who still lack knowledge of malaria. Local people usually only rely on information on traditional medicines from their ancestors to treat these diseases. These drugs have not been tested clinically, so their usefulness and side effects are not guaranteed. Rural communities tend to be lazy to go to health facilities, because of the remote location and because they feel afraid when they have to be examined by medical personnel. From Table 3 it can be indicate that there are most of the other variables that can affect the number of victims who die from malaria. Other things that can affect the disaster include, among others, health facilities in an area, previous illnesses, and area access to the nearest health facilities. This result is in line with previous research which states that increased rainfall will result in higher spread of diseases.^22-24

In this study, the climate variable is still used at the measurement station level, which is limited in number at the provincial level. It is hoped that future studies can use climate indicators at the village level, so that the analysis can be more representative. In addition, the use of other variables as instrument variables and control variables is needed to strengthen the model formed.

CONCLUSION

The high mortality rate due to malaria in Indonesia requires the government to focus on the eastern part of Indonesia.

Geographical factors that belong to eastern Indonesia tend to be moist and filled with forests, making it easier for female Anopheles to breed. From the results of this study, it is known that the rainfall factor influences the number of malaria incidents and also has a positive impact on mortality caused by malaria. Education is needed for the community to minimize malaria, which often occurs, generally in the Papua region. Through health promotion, it is hoped that the community will be able to live cleanly and healthily, as well as change their behavior in life considering that their area is vulnerable to malaria.

Funding: No funding sources

Conflict of interest: None declared

Ethical approval: The study was approved by the Institutional Ethics Committee

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