Established a vector research team for mosquito-borne diseases

  The NMDC’s “dengue fever epidemic seed instructors” are well trained in dengue epidemic prevention. In addition, all team members continue to receive advanced training, allowing continuous improvement in knowledge of entomology, prevention technology, and big data application analysis. The main tasks of team differ according to the epidemic situation.

In non-epidemic periods, the major tasks of the team mainly include:

  • monitoring of vector mosquito density in the planned pilot areas and report the results regularly to the central government and local governments;
  • establishing a mosquito species resources center by collecting mosquito species from various local administrative regions in Taiwan; testing resistance to and the efficacy of chemical control agents by using the local mosquito species, and providing local governments with suggestions of appropriate drugs and dosages;
  • developing novel vector mosquito monitoring models and monitoring tools;
  • assisting the training of epidemic-prevention personnel and the promotion of prevention education.

During an epidemic, the main actions of the team include:

  • providing emergency support and assisting local governments in planning epidemic prevention;
  • assisting in assessing the effectiveness of chemical controls;
  • helping with searches for hidden sputum sources to suppress the spread of the epidemic.
Figure 1. The research team for the mosquito-borne disease prevention project.

  Through the establishment of the epidemic prevention research team, the most innovative concepts and technologies can be brought to the forefront and provide the authorities with effective epidemic prevention and control strategies.

Development of a new vector mosquito monitoring index – Ovitrap Index (OI)

  The Breteau Index (BI) is currently the most commonly used indicator to monitor the density of vector mosquitoes in a region. When the mosquito density is extremely high, the BI can accurately reflect the density of local vector mosquitoes. However, when the density of the vector mosquito is low, the BI will underestimate the number of vector mosquitoes because of a lack of sensitivity and thus fail to provide an early warning. To improve the sensitivity of the vector mosquito density monitoring system, a new monitoring index to assist the BI is needed. The NMDC team monitors the density of the vector mosquitoes in Tainan, Kaohsiung, and Pingtung pilot areas by using ovitraps. The monitoring results were cross-matched with the BI to develop an ovitrap index (OI). When the positive rate of the ovitrap in the monitoring area is greater than 60% and the number of eggs collected is more than 500, the area is marked as “urgent” on the OI. The relevant epidemic prevention units must then take action to decrease the number of mosquitoes to avoid the occurrence of an outbreak. When the positive rate of the ovitrap is greater than 60% or the number of eggs collected is more than 500, the monitoring area is marked as one to “watch,” and the epidemic-prevention units must continue to pay attention to the number of mosquitoes in that environment. Monitoring with ovitraps can also be combined with the use of bait agents, thereby simultaneously working to reduce the number of mosquitoes. The Tainan, Kaohsiung, and Pingtung areas continue to conduct environmental monitoring using the OI. The results are promptly reported to the local government to help with epidemic prevention. In summary, the OI is an important indicator for vector mosquito monitoring, one that can directly assist epidemic-prevention work.

Figure 2. Development of a new vector mosquito-monitoring index – Ovitrap Index (OI)

Establishing a biological control technology for mosquito-borne diseases

  Mosquitoes are among the most dangerous insects in the world and are often vectors for carrying and transmitting diseases, including malaria, dengue, Zika, and chikungunya. Among these diseases, dengue fever is an emerging threat. To respond to this, in recent years countries around the world have not only applied traditional chemical control methods but also increasingly promoted biological control methods to help create a friendly living environment. The release of Aedes aegypti infected with Wolbachia is one of these new biological prevention and control technologies. Due to cytoplasmic incompatibility, male Aedes aegypti infected with Wolbachia cannot produce viable offspring when they mate with wild females; thus, releasing large numbers of such males reduces the population of vector mosquitoes in the community and helps prevent and control diseases. At present, Singapore, the United States, Australia, Brazil, Indonesia, Vietnam, India, and China have begun to try this new vector control approach. These studies have shown that the method can be deployed successfully at low cost across small cities. Other reports also revealed that this technology is a safe, effective, and environmentally friendly strategy for the prevention and control of mosquito-borne diseases.

  The NMDC has established a biological control laboratory, nicknamed the “Wolbachia mosquito factory,” at the Tainan Research Center through collaboration with Professor Zhiyong Xi’s research team at Michigan State University. The breeding technologies including egg hatching, larvae and adult breeding, and the separation of male and female pupas; related molecular testing methods were established. Taiwanese native Aedes aegypti strains infected with Wolbachia have already been established. The correctness of the strain and the frequency of Wolbachia in the mosquito population has remained stable after several generations. The standard production process of the mosquito factory has been completed; later, production will be upgraded and optimized. In addition, semi-field tests can help to characterize the biological features of the factory producing mosquitoes, especially comparisons of the competition and adaptability abilities of Wolbachia-infected mosquitoes and wild-type mosquitoes.

  Before any new vector-control approach can be deployed at scale, it should first go through laboratory-based experiments and then semi-field releases followed by open-field releases. To achieve this, the NMDC must satisfy regulatory requirements and commit to substantial community engagement. The NMDC will discuss its approach with the central and local governments, plan to conduct small-scale field trials, and conduct educational promotion and communication risk assessment with the community. The NMDC expects that over the next few years evidence for the effectiveness of this new vector-control tool will accumulate and that this can provide epidemiological evidence on the prevention of mosquito-borne diseases.

Figure 3. Wolbachia mosquito factory

Establish a dengue epidemic early-warning system and information platform with geographic information

  Factors that should be considered when planning epidemic prevention are increasingly diverse, such as the number of dengue cases, the distribution of local and imported cases, climatic factors, the location of hot and cold areas, and the distribution of the population. Years of information are needed before it is possible to predict where and when a dengue epidemic will occur. Therefore, the establishment of a complete information platform can help local governments effectively use epidemic-prevention resources in a timely and appropriate manner and avoid dengue outbreaks. The NMDC has successfully assisted Tainan, Kaohsiung, and Pingtung in establishing a customized information platform for epidemics. In 2018, the NMDC expanded its assistance to New Taipei City and Chiayi City. These platforms can help local governments accumulate relevant monitoring information during non-epidemic periods as well as assist with the prevention and treatment of disease when outbreaks do occur. In addition, NMDC has also established an early-warning system for dengue fever and a risk-prediction model through statistical analysis. Through the application of GIS satellite positioning technology, a dynamic risk map of the entire epidemic area was successfully created. The early-warning system can provide important epidemic prevention information for the public as well as the government’s command centers.

Figure 4. Dengue epidemic early-warning system and geographic information platform

Comments are closed.