WOLBACHIA-INFECTED MOSQUITO FOR DENGUE VIRUS INFECTION CONTROL: FACTS AND CONTROVERSIES

By: Rifa’ah Rosyidah, Adhella Menur

Dengue virus infection in Indonesia

Dengue is a mosquito-borne (Aedes aegypti and Aedes albopictus), acute febrile illness caused by dengue virus (DENV serotype 1-4) infection, a spherical, single-stranded RNA virus belonging to the genus Flavivirus in the family Flaviviridae. DENV infection has become a significant public health concern, and the global incidence has increased over the past two decades. From 2000 to 2019, the World Health Organization (WHO) documented a ten-fold surge in reported cases worldwide, increasing from 500,000 to 5.2 million. Indonesia is among the world’s 30 most highly DENV-endemic countries, with all four serotypes circulating and experiencing outbreaks yearly. Since the first dengue report in Indonesia in 1968, disease epidemiology has undergone dynamic changes affecting all provinces. East Java, West Java, and Central Java are provinces with the highest dengue cases incidence (1). In 2022, the incidence rate (IR) was 52.1 per 100,000 population with the case fatality rate (CFR) was 0.86%.

The dengue economic burden is a major problem in Indonesia. In 2015, the estimated dengue treatment cost was 5.3 trillion rupiah, equivalent to 3% of the state budget and almost close to the cost of eliminating malaria in the Asia Pacific, around 6.3 trillion rupiah. In 2017, the estimated cost burden was twice as large. The National Health Insurance reported that the costs for dengue treatment at primary health care range from 883 million rupiah to 3.7 billion rupiah per month in 2020 (2). Since there have been significant steps forward in preventing dengue, like the Wolbachia method we will discuss here, there is hope that a mosquito bite will result in nothing more serious and burdening than an itching feeling that relieved with a scratch.

Figure 1. DENV infection cycle in the human body (3). Modified with Biorender.com.

Clinical manifestations of DENV infection in humans

A general overview of the DENV infection in humans is presented in Figure 1.

DENV infection has a broad spectrum of clinical presentations, often with unpredictable clinical evolution and outcome. While most patients recover following a self-limiting, non-severe clinical course, some progress to severe to fatal disease, characterized mainly by plasma leakage with or without hemorrhage (4). The clinical classification of symptomatic DENV infection has undergone revisions (1997, 2009, and 2011). The 2011 version was proposed by the WHO South-East Asia Regional Office, which included the concept of expanded dengue syndrome (patients with severe organ involvement but without evidence of plasma leakage). Despite the classification, the principal management for dengue is supportive, managing fever, bleeding, plasma leakage, and shock.

Figure 2. Classifica-tion of DENV infec-tion (the WHO Re-gional office for South-East Asia, 2011).

The Wolbachia method: How does it work?

Since effective antivirals and vaccines are still being developed, prevention has become the cornerstone of DENV infection control. Current strategies are limited to vector controls: efforts to suppress immature and adult mosquito numbers through insecticides that are not environmentally friendly and community campaigns to reduce breeding sites. Even with considerable resources invested in these activities, sustained suppression of mosquito densities has been elusive, mosquitoes become resistant to insecticide, and seasonal outbreaks continue. There is a run in searching for effective vector control innovation, and the most promising is the Wolbachia method.

The method utilizes a gram-negative bacteria named Wolbachia pipientis. It was first discovered in the reproductive tissues of mosquitoes Culex pipens by Hertig and Wolbach in 1924. Wolbachia is present in more than 60% of insects, including dragonflies, fruitflies, butterflies, and moths. Some mosquitoes are also carrying the bacteria, but Ae. aegypti don’t usually carry it. Wolbachia lives inside host cells, maintains an endosymbiotic relationship with hosts, and is passed from one generation to the next through an insect’s eggs. It manipulates the host characteristics and reproduction in many ways, all favoring Wolbachia-infected females in nature (5,6). Wolbachia-induced reproductive manipulations include parthenogenesis, the feminization of genetic males, male killing, and the most remarkable: cytoplasmic incompatibility (CI). CI is a phenomenon where mating between Wolbachia-infected males and uninfected females causes severe developmental defects in the early stages of embryogenesis, resulting in unhatched eggs. After more than a decade, researchers found a way to transfer strains of Wolbachia from another insect into Ae. aegypti through embryo microinjection. The Wolbachia strains named wMel (from Drosophila melanogaster) and wAlbB (from Ae. albopictus) can achieve stable transfection of Ae. aegypti. Surprisingly, not only does it reduce DENV transmission by shortening adult mosquitoes lifespan and CI phenomenon, but also the bacteria’s presence can block the DENV replication.

Figure 3. Mechanisms of the Wolbachia method (7). The release of Wolbachia-infected mosquitoes is expected to replace wild-type mosquitoes and reduce DENV infection. Modified with Biorender.com.

Releasing Wolbachia-infected mosquitoes: Facts

Studies conducted by the World Mosquito Program (WMP), a non-profit organization owned by Monash University, Australia, showed that when introduced into Ae. aegypti, Wolbachia can help to reduce the ability to transmit DENV to humans. It is proving highly effective in 14 countries across three continents, protecting almost 11 million people so far (December 2022) (5). Brazil, ranked first in dengue cases globally, began releasing Wolbachia-infected mosquitoes in September 2014 in Rio de Janeiro. Large-scale deployments in the country followed three years later, and a 2021 study in Niterói, Brazil, demonstrated a 69% reduction in DENV infection (6). A study in Northern Queensland also showed a 96% reduction in the incidence of DENV infection after adopting the Wolbachia method (8). A study in Singapore has thus far demonstrated reductions of Ae. aegypti populations and dengue incidence by 98% and 88%, respectively (9).

In 2017, the WMP collaborated with the Tahija Foundation and Gadjah Mada University, conducted a cluster randomized trial within a 26km2 area of Yogyakarta, Indonesia, named “The Applying Wolbachia to Eliminate Dengue” (AWED). Over a two-year trial period, the intervention clusters had a lower incidence of symptomatic dengue compared to the control clusters (67/2905 (2.3%) vs. 318/3401 (9.4%)). The efficacy of Wolbachia in protecting against DENV infection was 77.1% (95% CI 65.3-84.9) and was similar across all four DENV serotypes. Furthermore, the efficacy in preventing hospitalization due to dengue was 86.2% (95% CI 66.2-94.3) (10). Following the promising result, the Indonesia MoH included the method in the national strategy to manage dengue and has issued a decree (No 1341/2022) to conduct a pilot project for dengue control using Wolbachia-infected mosquitoes in five cities with high IR (above the global average of 10 per 100,000 population): West Jakarta, Bandung, Semarang, Bontang, and Kupang.

Method Implementation in Indonesia

Even though the Wolbachia method trial in Yogyakarta was proven successful, it is still challenging to implement broadly due to some community’s rejection. When the WMP and Save the Children organization were about to implement the program in Denpasar and Buleleng, Bali, in November 2023, there was resistance from the local government and community. More than 1000 people signed a petition against the release of the Wolbachia-infected mosquito because they feared that the method would ignite a new pandemic (11). Other rumors are also circulating in the community, some issues and facts are below:

The Importance of Community Engagement

Imagine a guest coming to our house to release a bucket of mosquito eggs. It is a normal reaction for people to fear, confuse, and reject. Therefore, it is important to strategize and involve experts in community engagement and mass communication. Also, convincing government officials from the provincial level down to the village level is not easy. The success of the Wolbachia method trial in Yogyakarta and Australia relied on an approach to build community engagement by applying the Public Acceptance Model (PAM) (12). The PAM consisted of four key components:

  1. Raising awareness by providing information to residents and key stakeholders about the program. These activities included face-to-face meetings, a public billboard and news-paper advertising, media events, a school outreach program, stalls at community markets, community associations, traditional and electronic mailouts of information letters and deployment coverage updates, information kiosks in public spaces, and social media incentive program.
  2. Quantitative surveys that measured community awareness and acceptance conducted by an external market research company.
  3. An issues management system that allowed community members to easily contact the program with questions or concerns and have them addressed by program staff typically within 24 hours of receipt. This also allowed residents to opt out of direct participation if they had concerns.
  4. A community reference group that consisted of respected community members from key stakeholder groups and included representation from the government, local community, local business, community development and environmental groups, tourism, and education sector. The reference group was tasked to evaluate activities and make a recommendation to the program management that community engagement had been sufficient for releases of mosquitoes to commence. The secondary functions were to test and comment on the suitability of engagement materials and approaches, to provide the program with feedback on community sentiment towards the program and identify potential issues that might require a proactive response (13).

Program implementers must provide the targeted community with the best possible explanation and assistance. Strong community engagement and multidisciplinary participation can ensure the effectiveness of the program. Prof. dr. Adi Utarini, M.Sc, MPH, Ph.D, the study lead of the successful Wolbachia method trial in Yogyakarta, in one interview with the media (Kick Andy, MetroTV, September 4th, 2023), shared that the team needed two years to approach and gain trust from the community to implement the method. She noted that researchers should learn to communicate with people to bring research benefits from the laboratory and desk to society. Parallel with the community engagement, Indonesia government is also preparing Wolbachia-infected mosquito production facilities. Setting up the facilities isn’t cheap or easy; it needs strict biosafety measures and produces many Wolbachia eggs and mosquitoes. Currently, Indonesia has two laboratories with facilities, i.e., the Universitas Gadjah Mada laboratory in Yogyakarta and the MoH public health laboratory in Salatiga, Central Java, which can produce about 7-8 million Wolbachia eggs every week. Indonesia MoH collaborates with the WMP and state-owned pharmaceutical holding PT Bio Farma (Persero) to increase the facility numbers. Hopefully, over time, people’s doubts will decrease with the increase in knowledge, and the Wolbachia method may be expanded and shape the way to limiting DENV infection worldwide.

References

  1. Haryanto, B. 2018. Indonesia dengue fever: status, vulnerability, and challenges. Current Topics in Tropical Emerging Diseases and Travel Medicine. 5,
    81- 92.
  2. Indonesia MoH. The national strategy to manage dengue 2021-2025.
  3. Dhiman M., et al. 2022. Traditional knowledge to contemporary medication in the treatment of infectious disease dengue: a review. Front Pharmacol. 13: 750494.
  4. World Health Organization. Dengue.
  5. https://www.worldmosquitoprogram.org/(accessed on 14 December 2023).
  6. Pinto S.B., et al. 2021. – Effectiveness of Wolbachia-infected mosquito deployments in reducing the incidence of dengue and other Aedes-borne diseases in Niterói, Brazil: A quasi-experimental study. PLoS Negl. Trop. Dis. 15 (7).
  7. Al Noman A., et al. 2023. Importance of Wolbachia-mediated biocontrol to reduce dengue in Bangla-desh and other dengue-endemic developing countries. Biosaf Health. 5(2):69–77.
  8. P.A. Ryan, et al. 2020. Establishment of wMel Wolbachia in Aedes aegypti mosquitoes and re-duction of local dengue transmission in Cairns and surrounding locations in northern Queensland, Australia, Gates Open Res.
  9. TNg LC. 2021. Wolbachia-mediated sterility sup-presses Aedes aegypti populations in the urban tropics. Preprint. medRxiv.
  10. Utarini A., et al. 2021. Efficacy of Wolbachia-Infected Mosquito Deployments for the Control of Dengue. N Engl J Med. 384(23):2177–86.
  11. Wolbachia mosquito egg spread program in Bali postponed due to community restlessness Available online: https://voi.id/en/news/332874.(accessed on 21 December 2023).
  12. Hugo L.E., et al. 2022. Wolbachia wAlbB inhibit dengue and Zika infection in the mosquito Aedes aegypti with an Australian background. PLoS Negl Trop Dis. 16:e0010786.
  13. O’ Neill S.L., et al. 2018. Scaled deployment of Wolbachia to protect the community from dengue and other aedes transmitted arboviruses. Gates Open Res. 2:36.
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