The Semarang City has been dubbed as quite successful in its efforts to tackle dengue. However, experts say climate change presents new threats and will potentially trigger a rise in cases. 

Yuliati has just thoroughly cleaned the area around her house. Then she grabbed a small container right under the dispenser faucet in the living room. After discarding the water inside, Yuliati cleaned it with a cloth before finally putting it back in its place.  

For some people, water in a small container looks trivial. But, not to this 42-year-old woman. Yuliati is aware that the water collected from the droplets after taking drinking water may become a breeding ground for mosquitoes.  

“Trivial things like this get very little attention. It could be a larvae’s nest,” said Yuliati who lives in Kedungmundu Village, Semarang City, Central Java. “There were many dengue cases in the past, so don’t allow it to happen again, especially now that the rainy season has arrived,” continued Yuliati when this reporter met her  at the terrace of her house on Thursday, 27 October 2021.  

Yuliati is right to be wary. The city of Semarang was once one of the epicenters of dengue cases in Indonesia. In 2010, the number exceeded 5000 cases. However in recent years, following a few public health programs, the number of diseases caused by the Aedes aegypti mosquito has been successfully suppressed. 

“Every Friday morning, residents clean their neighborhood. Everything that has the potential to become a place for mosquitoes to lay eggs is cleaned, like gutters, and areas under trees are all cleaned up, including the dispenser because usually there is water under it that goes unnoticed,” said the woman. 

Abdul Hakam,  Head of the Semarang Health Office (Kadinkes), said larvae monitoring is one of the flagship programs of the Semarang City administration in suppressing dengue cases in the area. An application has also been developed to support a centralized reporting system at the city level.  

“We have the Tunggal Dara application to facilitate a centralized larva reporting system,” said Hakam on Thursday, 23 December 2021 The advantage of this system is that the public can report the findings of mosquito larvae quickly to be followed up in less than 24 hours.  

Hakam said that Tunggal Dara stands for Bersatu Menanggulangi Demam Berdarah or United to Tackle Dengue Fever. The system, which was initiated in 2015, is part of the Asian Cities Climate Change Resilience Network program and has received support from Mercy Corps Indonesia. Through this system, the community and cadres can directly and quickly report the results of their larval monitoring.  

According to Hakam, the existence of this system is quite effective. Of the 1,508 urban wards in Semarang City, 1,403 of them, or 93 percent, are actively reporting. “In terms of reporting, it is quite effective in accelerating information so that the health centers (Puskesmas) can immediately follow up,” said Hakam. In addition, in terms of incidence, cases of dengue have seen a downward trend compared to previous years.

However, the threat of dengue cases spreading like in the past decade looms. A public health expert from Diponegoro University (UNDIP) Semarang, Anies, said that climate change presents a new threat in the health sector.  

“It is crucial to build awareness that climate change is not only a matter of rain and weather. We need to be concerned about the impacts on the health sector, even if the impacts may not be direct. It [awareness] has to be built,” explained Anies. 

According to the Regional Regulation 5 of 2010 on Dengue Disease Control, Semarang City recorded its first dengue case in 1969. However, the findings of many cases that prompted the administration to declare Extraordinary Events (KLB) status in 1973 and 2010.When cases were spreading across Semarang City, the administration carried out fogging with insecticides, from airplanes, in hopes to control the mosquito population  

Since 2010, Semarang has been included as one of the dengue-endemic cities in Indonesia.  

Responding to surging cases in 2010, the Semarang administration ratified the Regional Regulation (Perda) 5 of 2010 concerning Control of Dengue Hemorrhagic Fever (DHF). This regulation is the legal framework for formulating policies, planning, and implementation for agencies related to dengue control. 

Environmental factors  

The Ministry of Health (Kemenkes) defines dengue as an infectious disease caused by the dengue virus and transmitted through mosquito vectors of the Aedes aegypti or Aedes albopictus species. Some of the symptoms of dengue fever include fever for 2-7 days, weakness, red spots on the skin, bleeding from the nose, and pain in the upper part of the liver caused by the bleeding in the stomach. 

Dengue Hemorrhagic Fever (DHF) is classified as a zoonoses, an infectious disease that is transmitted from animals to humans. These infections can be caused by disease-causing microorganisms (pathogens) such as bacteria, viruses or parasites. These pathogens can move and develop in the human body through a series of genetic mutations. 

Some zoonotic transmissions can take the form of animal bites (rabies) or result from eating infected animals (neurocysticercosis) or even direct contact with infected animal skin (anthrax). A government sanctioned health information provider, Hello Sehat,  changes in the environment due to human activities such as deforestation, intensive animal agriculture, and industry are increasing the risk of zoonoses. 

Sugiyono, a zoonotic expert from the National Research Agency (BRIN), said that humans, animals, and the environment are closely interrelated, which has a bearing upon disease emergence, including . Sugiono noted people’s behavior, such as allowing stagnant water where mosquitoes lay their eggs, contributed to the emergence of this disease.  

Climate change contributes to the intensity of rain and in turn increases the chance of standing water and puddles. “It means that dangerous mosquitoes have the potential to increase their population as well,” explained Sugiyono.  

The chart below shows dengue cases in Semarang City from 2010 to 2021:

Professor of Environmental Health at the University of Diponegoro, Semarang, Anies explained that climate change is not only affecting the behavior of Aedes aegypti, the vector that causes dengue, but also speeds its reproduction. 

The central government is also aware of the threat of an increase in dengue cases resulting from climate change. In particular, dengue is predicted to contribute to state losses of up to Rp31 trillion. Besides health, other sectors that are also affected are agriculture, clean water, and marine and coastal areas, with total loss of Rp115 trillion in 2024.

In response, the National Planning and Development Agency (Bappenas) published a climate resilient development (PBI) document published in a series of six books, on April 2021. 

Concerning dengue, the document highlights several regions in Indonesia that are predicted to see cases increasing due to climate change. Semarang City has been listed as a priority area. 

Anies said the high potential for losses in the health sector is triggered by the increasing threat of various diseases resulting from climate change. “The increase in temperature makes it easier for bacteria and microbes to breed. As a result, the threat of the disease increases, as well as the zoonoses.”  

Anies considers the study conducted by Bappenas as a mitigation effort, helping the public understand and quickly adapt their response to threats of climate change impacts on health. “Mosquitoes have a higher adaptability to environmental temperatures compared to other animals. Because of insects’ ability to breed faster, their population grows exponentially,” Anies explained. 

“It is crucial to build awareness that climate change is not only a matter of rain and weather. We need to be concerned about the impacts on the health sector, even if the impacts may not be direct. It [awareness] has to be built,” explained Anies. 

It is crucial to build awareness that climate change is not only a matter of rain, and weather. We need to be concerned about the impacts on the health sector. even if the impacts may not be direct. It [awareness] has to be built.

Anies, environmental health expert, University of Diponegoro, Semarang

Animal health specialist from the Center for Indonesian Veterinary Analytical Studies (CIVAS), Tri Satya Putri said that climate change has consequences on the environment—causing unstable temperatures, humidity, and rainfall. These instabilities ultimately affect the behavior of the pathogenic agent.  

He said that changes in temperature and humidity would impact the spread and ecology of infectious animal diseases (zoonoses). In addition, the frequency and transmission are predicted to increase along with the uptick in rainfall and flooding. 

“This means that climate change will have an impact on pathogenic agents and vectors which then affect population dynamics, growth cycles (breeding), and also the spread of diseases,” explained the author of the book Animal Health for Human Welfare. And, mosquitoes, he said, have the ability to adapt to uncertain weather conditions. 

Changes in mosquito behavior  

Environmental conditions play an essential role in determining public health quality. Researchesearch by Risqa Novita, a biomedical expert from the Research and Development Center for Biomedical and Basic Health Technology at the Ministry of Health, reveals that 45 percent of a person’s health is influenced by environmental conditions.  

“While other factors, such as behavior accounted for 30 percent, health services 20 percent, and genetic 5 percent,” Risqa wrote in the report published in late 2020.  

With increases in temperature and weather, such as humidity and rainfall, causing mosquitoes to breed more quickly, the trend of mosquito-borne diseases is increasing in several South and Southeast Asian countries.  

Risqa further explained that climate change  not only affects the life cycle of mosquitoes. But, also the intensity of the suction. Not only do they breed faster, mosquitoes are also more active in biting;no longer limited to certain hours. That happens because mosquitoes are ectothermic insects, which means their body temperature depends on the surrounding temperature (ambient temperature). 

Mosquitoes have a habit of biting inside and outside the house at night. After feeding, they rest inside or outside the house. “The most conducive air temperature is between 25-30 Celsius and 60-80 percent humidity,” said Risqa in her report. 

Sugiyono added that the warm rainy season could cause mosquitoes to survive throughout the year. Many species of mosquitoes are surprisingly able to adapt to different environments, not only in the tropics but also in the subtropics.  

He said, as they further expand their range, they would also adapt to new conditions.  

“With the growing population of mosquitoes, the potential for the spread of disease agents or viruses they carry is even greater,” he explained. And one way to anticipate the risk of transmission is to suppress the mosquito population. 

Uptick in dengue cases 

Data from the Data and Information Center (Pusdatin) of the Ministry of Health shows an uptick in dengue cases in Indonesia in the last seven years. In 2014, there were 100,347 cases, which increased to 126,674 cases in 2015.   

In 2016, the number of cases jumped sharply to 204,171. Although cases fell drastically to 68,407 and 65,602 cases in 2017 and 2018, this trend did not last. Dengue infections soared  to 137,000 in 2019.  

However in 2020, when the Covid-19 pandemic was in full swing, the number of dengue cases reached 98,000. Meanwhile, until August 2021 the number of dengue cases recorded was 30,000 cases. 

The chart shows dengue cases in Semarang and five other district/city in 2021:

The government has carried out mapping related to the impact of climate change in the health sector. Uncertain weather patterns certainly increase the risk of dengue transmission. Several regions in Indonesia are predicted to experience an increase in cases.  

One of them is Semarang City, which had become the epicenter of dengue with more than 1000 cases from 2010 to 2014 (see the graphic).  

The head of the Semarang Health Office, Abdul Hakam, admitted that Semarang contributed to the most dengue cases in Central Java. Several programs, however, have helped reduce the number of cases. 

“This includes the 2021-cases. The graph of Semarang City’s dengue cases up to July 2021 is still under control. When compared to 2020, the monthly cases are still lower,” Hakam explained.   

He said that there was a decline of up to 50 percent when compared to the same period last year. As an illustration, in January-July 2020, dengue cases reached 274 cases. In 2021, 137 cases were recorded. 

Unfortunately, the decline in dengue cases did not last long. Dengue cases started to rise in the second semester of this year. In November, the number of cases reached 36. Up until early December of 2021, the total number of dengue cases in Semarang City was 280 people with six deaths. 

Larva monitoring cadres and application 

In the Action Plan for Activities (RAK) 2020-2024 document prepared by the Directorate General of Disease Prevention and Control of the Ministry of Health, the government said that the morbidity and mortality rate due to zoonoses in Indonesia is still quite high. This condition is supported by the increasing mobility of humans and animals – as a source of zoonotic transmission – and the difficulty in controlling animal traffic between regions. 

The relationship between humans and the environment/wildlife is getting closer as a consequence of the increasing number of forest areas cleared, so that climate change carries the risk of increasing zoonoses. On the back of this condition, the government recognized the necessity to accelerate the prevention and control of zoonotic sources from the upstream. 

The Ministry of Health said that multi-sectoral involvement through the “One Health” approach is key to ensure zoonotic prevention efforts can run effectively as management of zoonoses requires a collaboration of various sectors from health, environment, to agriculture. 

The One Health approach is what the Semarang City Health Office is trying to implement in tackling DHF. The head of the Semarang Health Service, Abdul Hakam said that the Covid-19 pandemic that had occurred since March 2020 had raised concerns that efforts to control dengue fever would be neglected in Semarang. However, with cooperation and synergy between related agencies, this concern did not occur, the fear was unfounded. 

Hakam said he had worked with his staff to stay focused on health programs that were being implemented, including the control of dengue. Some of the control efforts include the appointment of larva monitoring cadres, not only in each neighborhood but also in the household level. Their role is optimized through the use of the Tunggal Dara application. 

The chart below shows dengue cases in Indonesia from 2014 to 2021:

Wolbachia technology, mosquito vs mosquito

Conventional methods through larval monitoring are not the only way to suppress the Aedes aegypti population. The application of Wolbachia bacteria technology, initiated by the World Mosquito Program (WMP) is now being developed in many countries. This intervention is also considered successful in preventing the transmission of this deadly disease. 

In Indonesia, the pilot study of populating Wolbachia-infected mosquitoes was centered in the Special Administrative Region, Yogyakarta. 

Riris Andono Ahmad, a co-researcher for WMP Yogyakarta and director of the center for tropical medicine at the Gadjah Mada University (UGM), said the development of the technology started in 2011. 

Warsito Tantowijoyo,  an epidemiologist who also serves as the team leader for WMP Yogyakarta explained, Wolbachia is a natural bacterium found in 60 percent of insects and only lives inside the insect’s body.  

He said, in the body of Aedes aegypti, Wolbachia works by supressing the development of the dengue virus   

“When a bite occurs, the virus that is in the mosquito does not enter humans because the bacteria have blocked it,” he explained. 

In practice, this genetic engineering is done by depositing buckets containing Wolbachia-infected mosquito eggs in people’s homes and/or public facilities. So, after the mosquito eggs develop into adult mosquitoes, they will produce offspring of Wolbachia mosquitoes. 

The process of replacing Wolbachia mosquito eggs is done every two weeks for six months. As a result, areas with the distribution of Wolbachia mosquitoes can protect themselves from attacks by dengue cases. 

After confirming the safety of Wolbachia, the research then continued with release in a limited area. “It’s been six years running. In Yogyakarta, the Wolbachia efficacy test was conducted utilizing the randomized trial method in 2017,”  Riris said in her written response to questions from Mongabay Indonesia. 

Technically, the implementation of this test is done by dividing the Yogyakarta area into 24 clusters – 12 clusters as the location for the distribution of Wolbachia and 12 others as control clusters. “The results of the Wolbachia efficacy test are quite encouraging; Wolbachia is effective in reducing 77 percent of dengue cases and reducing 86 percent of dengue cases treated in hospitals,” said Riris. 

The results of this study have been published in the New England Journal of Medicine (NEJM). In addition, this technology has also been reviewed at the 13th WHO Vector Control Advisory Group Meeting on 7-10 December 2020. 

WMP Yogyakarta is currently collaborating with the Sleman District administration through the health office to start implementing Wolbachia technology. And in 2022, the technology will be applied in Bantul District, Yogyakarta.  

“There needs to be an active role from all parties so that this technology can be implemented in other areas to accelerate national efforts to control dengue,” explained Eggi. 

The WMP Yogyakarta Stakeholder Engagement and Policy Specialist, Achmad An’am Tamrin said there haven’t been any significant challenges in the implementation of this Technology in Yogyakarta. However, intense education about technology has helped in ensuring a smooth implementation. 

Tamrin said, aside from Sleman and Bantul in Yogyakarta, several other districts and provinces in Indonesia have expressed interest in utilising the Wolbachia mosquitoes for dengue control including Boyolali in Central Java, Bontang in East Kalimantan, Batam, East Nusa Tenggara and Bali. 

“We are currently putting together an implementation strategy for other regions in Indonesia. At the very least, public education, as implementation, will require a lengthier process. We are also looking into regulations to see whether they are synched. Or we need new regulations,” said Tamrin. 

The WMP team is currently coordinating with the Disease Control and Eradication directorate general of the Health Ministry and the health research and development unit of the National Research and Innovation Agency (BRIN). 

The Ministry of Health welcomed the findings. On November 21 last year, eight representatives of districts/cities, including Semarang Cityin Indonesia, were also invited to explore further implementation of this method.  

Hakam said that it is possible to use Wolbachia as another instrument tackling dengue fever depending on the case development and the situation on the ground.  

“On 24 November, we participated in the ‘kick off’ program together from the Ministry of Health. There are eight cities/districts involved. The first four will be selected for the next implementation, so we are still waiting. ,” explained Hakam. 

He hopes that the existence of Wolbachia-aedes suppression technology will become a complementary policy in dealing with dengue fever in Indonesia.  

Climate change does not only have an impact on the environmental sector. But, also health because it triggers an increase in zoonotic diseases. And, what should be noted, dengue is only one of hundreds of zoonotic species that have the potential to see an increase in cases due to climate change. More serious efforts are needed to prevent this threat from actually happening.  

An earlier version of this story was published in Indonesian by Mongabay Indonesia on 2 February 2022. This story was produced with support from Internews’ Earth Journalism Network.