The animal responsible for causing the most human deaths each year is neither lions, sharks, nor snakes. By far, the world's deadliest animal is the mosquito (Gatesnote). The majority of these deaths are caused by malaria, a major disease transmitted by mosquitoes. At the Department of Tropical Medicine and Parasitology, Juntendo University School of Medicine, we are conducting research on malaria.

1. Malaria and the Problems It Causes_

• ・What is Malaria?_
• ・Efforts Toward Malaria Elimination and the Challenges to Overcome_
• ・Drug Resistance—When Treatments No Longer Work_

2. Our Ongoing Research: "Offensive" Malaria Drug Resistance Research_

• Field Research_

___1) What we have discovered so far – Discovery of Artemisinin-resistant Parasites in Africa______
___2) Moving forward – Expanding on Our Field Discoveries
______

• Laboratory Research_

__ 1) Validating Field Findings and Developing New Techniques for Early Detection of Resistant Parasites
　　 2) Predicting the Future – Developing a System to Predict Future Drug-resistant Parasites in the Field
______
3. Conclusion_

1. Malaria and the Problems It Causes

・What is Malaria?
Malaria is one of the world's three major infectious diseases, alongside HIV/AIDS and tuberculosis. It is caused by a parasite called the malaria parasite, transmitted through the bite of an infected mosquito. Of the types of malaria parasites that infect humans, the ones most likely to cause death are widely distributed in Africa and around the world. Malaria once existed in Japan, but after the implementation of malaria eradication programs focusing on controlling mosquito vectors, as well as infrastructure improvements such as roads and waterways, malaria epidemics ended in the 1950s. However, malaria continues to cause significant issues in many countries. In Africa, malaria is as common as the cold or flu in Japan. Worldwide, there are hundreds of millions of new malaria cases annually, with 420,000 deaths. Malaria hinders economic development, which in turn exacerbates the spread of the disease. Malaria and development are inextricably linked. Eradicating malaria breaks this vicious cycle and contributes significantly to sustainable development.

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・Efforts Toward Malaria Elimination and the Challenges to Overcome
Various global efforts are underway to eliminate malaria. Malaria spreads through the bite of infected mosquitoes. To control this, effective methods include distributing insecticide-treated nets (ITNs) and spraying long-lasting insecticides indoors (IRS). Additionally, malaria can be prevented through early treatment, and the effectiveness of current treatments has led to a decline in malaria-related deaths since the mid-2000s.
However, there are limitations in combating the mosquito vectors, which dominate the ecosystem on a much larger scale than the malaria parasite. The malaria parasite, which has been in an evolutionary battle with humans for hundreds of thousands of years, is highly intelligent and uses various strategies to ensure its survival. If an effective vaccine is developed, it could shift the paradigm of malaria elimination strategies. However, the malaria parasite has evolved numerous mechanisms to escape human immunity, making the development of a vaccine extremely difficult. To date, no sufficiently effective vaccine has been developed. Furthermore, a more serious situation is emerging in the form of drug resistance—malaria parasites that are no longer affected by current treatments. We are advancing basic and innovative applied research to address this issue. Details are provided below.

・Drug Resistance—When Treatments No Longer Work
The emergence of drug-resistant pathogens is one of the most troublesome issues in the battle against diseases. In addition to malaria, drug-resistant microorganisms are a significant global problem, and it is predicted that by 2050, drug-resistant infections will cause more deaths than cancer. The same issue applies to malaria. Even when new drugs are developed, drug-resistant parasites eventually emerge. For example, chloroquine, once a highly effective malaria treatment, saw resistance emerge by the late 1950s, and by the 1980s, the resistant parasites had spread throughout Africa.

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2. Our Ongoing Research: "Offensive" Malaria Drug Resistance Research

To solve the problem of drug resistance, it is essential to discover new insights through research and develop new technologies. Since our lab restructured in 2012, we have focused on malaria drug resistance as the cornerstone of our research and have made significant achievements. Our goal is to use basic research to clarify the mechanisms of resistance and the evolutionary mechanisms of resistance, and based on these insights, to develop effective countermeasures against drug resistance. Our research is based on two main pillars: field research, which involves surveys in the affected regions, and laboratory- based molecular biological research. Here, I will briefly explain what we are doing in both areas.

・Field Research
Field research allows us to explore solutions to drug resistance from a macro perspective. Our lab regularly conducts drug resistance surveys in Uganda and Papua New Guinea. Together with other universities and research institutes, we form teams that stay on-site for 1-2 months, conducting ongoing surveys to evaluate the effectiveness of malaria drugs in these regions. These surveys have been ongoing since 2013 in Uganda and since 2016 in Papua New Guinea. Both are tropical countries located along the equator, with a large number of malaria patients.

1) What we have discovered so far – Discovery of Artemisinin-resistant Parasites in Africa
Our field surveys have led to several new discoveries. One such discovery, achieved through our ongoing surveys in Uganda, is the identification of Artemisinin- resistant parasites. Artemisinin, an anti-malarial drug, quickly eliminates the malaria parasite and alleviates symptoms. It is currently used as the first-line drug in all malaria- endemic countries, and its introduction has led to a decline in malaria-related deaths since the mid-2000s. The Nobel Prize in Physiology or Medicine was awarded to Tu Youyou in 2015 for her remarkable contribution to tropical medicine.
However, in countries along the Mekong River, such as Cambodia and Myanmar, Artemisinin-resistant parasites have already emerged. Special testing methods are required to detect resistant parasites, which exploit the parasite's unique properties. We adopted and refined this method early on to enable its use in tropical regions, and through this approach, we became the first to identify Artemisinin-resistant parasites in Africa. Moreover, by using next-generation sequencing, we sequenced the entire genome of these parasites and compared them with malaria genomes from other regions. We found that the resistance did not originate from Southeast Asia, as previously thought, but emerged independently in Africa (Publication and press release in 2018). This discovery of Artemisinin-resistant parasites in Africa has garnered global attention.

2) Moving forward – Expanding on Our Field Discoveries
Building on this discovery, our research is now progressing to the next stage. The most important step is to clarify the clinical effectiveness of Artemisinin treatment in patients with resistant parasites in the areas where we discovered them. It’s a complex issue, but the Artemisinin-resistant parasites we identified were found using an in vitro resistance test, where we cultured parasites from infected patients alongside Artemisinin in a laboratory to assess their resistance. However, it’s not just the drug that kills the parasites inside a patient’s body. The patient’s own resistance and immune response also play a role. The strength and nature of this “force” vary depending on the patient and the endemic area. Therefore, we are conducting a study to treat patients with Artemisinin and determine the clinical effect of this treatment. This study will reveal whether clinically resistant parasites have emerged in the regions where we first identified them.


We are also working to improve the in vitro testing method to detect Artemisinin-resistant parasites. The current method requires skilled technicians to distinguish malaria parasites under a microscope, which can lead to inconsistent results. We are improving this method to make it simple and reliable for anyone to use, as well as developing a way to evaluate resistance in a continuous (quantitative) manner. Since 90% of malaria cases occur in Africa, it is crucial to detect resistant parasites early to prevent a major issue. Currently, no malaria drug with the same effectiveness as Artemisinin is available, so it’s essential to identify resistant parasites as early as possible and take preventive action. This is why developing a “simple, stable, and universally applicable test method” is vital.

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・Laboratory Research
In order to validate the findings from our field research, laboratory research is indispensable. Simultaneously, we are developing laboratory systems to predict what will happen in the field. Below, I will explain the research activities we are engaged in at the Department of Tropical Medicine and Parasitology, Juntendo University School of Medicine.

1) Validating Field Findings and Developing New Techniques for Early Detection of Resistant Parasites
As mentioned earlier, our regular field surveys have led to new discoveries. If these can be reproduced in the laboratory, they become more reliable findings. Moreover, we aim to develop new technologies based on these discoveries. With approval from the Ugandan government, we have been collecting malaria parasites from patients in the field, freezing and transporting them to Japan. In our lab, we revive these parasites and study how they became resistant to Artemisinin. By understanding the mechanisms of resistance, we aim to develop drugs that target resistant parasites and technologies that delay the emergence and spread of drug resistance. We are also using population genetic methods to identify candidate genes related to Artemisinin resistance in Africa. Once we identify mutations in the malaria genome that are linked to resistance, we can introduce these mutations into susceptible parasites and test whether they become resistant. This allows us to confirm whether specific mutations are related to resistance. If they are, these genetic markers can be used for epidemiological studies of drug resistance. These markers can be detected from just a drop of blood, allowing for large-scale testing. By developing such new technologies, we can quickly and affordably detect resistant parasites. When combined with the new in vitro methods mentioned above, this will improve the accuracy of resistance detection.

2) Predicting the Future – Developing a System to Predict Future Drug-resistant Parasites in the Field
We are developing a laboratory system to predict future events in the field. One method we use is laboratory evolution experiments, which have been employed in several research labs with bacteria, viruses, and malaria to create drug- resistant pathogens. By culturing malaria parasites with anti-malarial drugs, drug-resistant strains will emerge. This method allows us to create resistant parasites that may appear in the field in the future.
However, this method has a significant drawback: it can take several years to develop drug- resistant malaria parasites. For instance, it took five years to generate Artemisinin-resistant parasites using this approach.






To overcome this, we have introduced minor genetic modifications to malaria parasites to make them evolve much faster than normal ones. These modified parasites, called mutator malaria parasites, can develop resistance in a matter of weeks to months when exposed to anti-malarial drugs. This innovative technique has already allowed us to isolate drug- resistant parasites. We are using these isolated parasites to explore the mechanisms of resistance and identify the responsible genes. This will enable us to prepare effective diagnostic tools and treatments before resistant parasites emerge in the field.

3. Conclusion

As mentioned above, our lab takes an integrated approach from both the field and the laboratory, conducting comprehensive research that can contribute to malaria control efforts. We are always accepting PhD and master's students, and we open recruitment for postdoctoral researchers and professional staff when positions become available. We prioritize diversity within our lab and recruit individuals with achievements in other research fields. If you are interested, please contact us at tmita[at]juntendo.ac.jp.