A Passion for Global Parasitic Diseases — The Path to Tunga Penetrans Research
Yasunaka:
Could you tell us about your career path and what led you to study Tunga penetrans?
Hyuga:
After graduating from the School of Veterinary Medicine at Nihon University’s College of Bioresource Sciences, I spent five years working at the Food Additives Laboratory and Parasitology Laboratory of the Tokyo Metropolitan Institute of Public Health. There, I was involved in testing and research on food additives in Tokyo, countermeasures for foodborne parasitic diseases, infectious disease control, and public awareness activities related to emerging topics.
However, I wanted to expand my work beyond Tokyo and engage in parasitic diseases at a global level. That led me to enroll in the Graduate School of Biomedical Sciences at Nagasaki University, specializing in Emerging Infectious Diseases. At that time, I joined the Department of Eco-Epidemiology at the Institute of Tropical Medicine, Nagasaki University. Although the laboratory was collecting epidemiological data on Tunga penetrans, the data had not yet been analyzed. This prompted me to begin Tunga penetrans research domestically.
Tungiasis, the disease caused by Tunga penetrans, is known to be unevenly distributed even within the same village, despite sharing similar climate, vegetation, and economic conditions. To understand why hotspots of tungiasis exist, I analyzed environmental and household-level spatial risk factors using data collected from Kenya’s coastal regions.
As my research progressed, I became more deeply interested in Tunga penetrans, leading me to apply for a postdoctoral fellowship that supports overseas study. This enabled me to study at the International Centre of Insect Physiology and Ecology (ICIPE) in Kenya. After returning to Japan, I became an Assistant Professor in the Department of Parasitology at the Institute of Tropical Medicine, Nagasaki University, where I was also involved in dengue and malaria vaccine research. From April 2025, I will be moving to the School of Veterinary Medicine at Nihon University. I hope to continue Tunga penetrans research in collaboration with international partners whenever possible.
Yasunaka:
What initially motivated you to get involved in tropical medicine?
Hyuga:
It all started when I was a junior high school student and read books like ‘The Flying Parasite’ and ‘Laughing Kaichu.’ I was fascinated by the world of parasites. By the time I decided to pursue graduate studies, I already wanted to work on parasitic diseases worldwide. Since most parasitic diseases are prevalent in tropical and subtropical regions, that naturally led me to tropical medicine.
Developing Tunga Penetrans Traps — Field Investigations in Kenya
Yasunaka:
What kind of work are you currently doing?
Hyuga:
I am currently researching Tunga penetrans, the insect that causes tungiasis. My aim is to develop traps that can effectively capture Tunga penetrans and reduce their population. I’m investigating what factors attract Tunga penetrans and intend to use those findings to develop a trap.
Yasunaka:
How do you plan to create the Tunga penetrans trap?
Hyuga:
Initially, I conducted research in Kenya to determine what attracts adult Tunga penetrans. Unlike other insects, we cannot maintain the life cycle of Tunga penetrans using laboratory animals. Therefore, to obtain larvae, I collected soil samples from the bedrooms of households affected by tungiasis. When Tunga penetrans infests a person, the parasite lays eggs in the soil around the dwelling. These eggs hatch into larvae, which eventually pupate and become adults under natural conditions. Since the bedrooms are where the parasites remain the longest, the soil there contains higher concentrations of larvae. By collecting and isolating larvae from the soil, I was able to rear them into adults for experimental use.
Yasunaka:
What attracts Tunga penetrans?
Hyuga:
Like other blood-feeding insects, they are likely attracted to body heat and odors. However, I found that light was the most promising attractant for developing traps. Just as moths, butterflies, and mosquitoes are drawn to light, Tunga penetrans also respond to light.
Yasunaka:
Are you considering combining multiple attractants like light, heat, and odors for the trap?
Hyuga:
Initially, I thought about combining multiple attractants to strengthen the lure effect. However, considering the simplicity required for field applications, I am currently focusing on a trap that uses only light.
Yasunaka:
Apart from traps, what other measures can be taken against tungiasis?
Hyuga:
Capturing Tunga penetrans alone may not be sufficient as a countermeasure. In addition to traps, using insecticides to reduce the number of Tunga penetrans is another method. Treating tungiasis is also essential. Ideally, I would like to develop an integrated approach that includes trapping along with other measures.
Yasunaka:
How is tungiasis treated?
Hyuga:
The common practice involves using safety pins, razors, or plant thorns to extract the parasite from the skin. According to people in Kenya, crushing the flea during extraction increases the risk of inflammation, so the key is to remove the entire flea intact. However, this method carries risks of bloodborne infections and secondary infections, so it is not recommended.
WHO recommends the use of an oil called NYDA*, which is primarily used for treating head lice. When applied to tungiasis, the dimethicone in NYDA suffocates the embedded fleas by blocking their respiratory system. Unfortunately, NYDA is not readily available in regions where tungiasis is endemic.
*NYDA: A commercial product containing two types of dimethicone that physically blocks the respiratory system of Tunga penetrans, leading to asphyxiation.
Yasunaka:
It’s surprising that such a promising treatment is not readily available in the regions where it is most needed.
Experiencing Tunga Penetrans Firsthand?!
Yasunaka:
I heard that you were infected with Tunga penetrans during your fieldwork. What symptoms did you experience?
Hyuga:
By chance, three fleas embedded themselves in my heel. I managed to remove two of them quickly, but I overlooked one and left it untreated. For the first week, there were no symptoms. Then, I started experiencing pain and itching as the flea burrowed deeper into my skin. Over time, I developed a blister-like swelling at the site due to a strong allergic reaction, making it difficult to wear shoes and walk. The pain and itching also kept me up at night.
Yasunaka:
Did you receive treatment at a local hospital?
Hyuga:
Yes, at the hospital, they punctured the blister and drained the fluid. Then, they prescribed an antibiotic cream.
The Appeal of Tunga Penetrans — Cute but Troublesome?!
Yasunaka:
What do you find fascinating about Tunga penetrans in terms of appearance, behavior, or biology?
Hyuga:
The adult Tunga penetrans flea has a distinct appearance with a sharp, pointed face that makes it look as if it is pouting. There’s a certain charm in its appearance. Unlike other fleas, they are very small (0.5-1.0 mm in length) and have fewer spines and setae, giving them a more delicate and dainty look — or maybe that’s just me (laughs).
Most fleas reproduce on the surface of the host’s body without embedding themselves in the skin. However, female Tunga penetrans burrow into the epidermis to mate and lay eggs. This skin invasion is what causes tungiasis, leading to severe itching, pain, and secondary infections. From a biological perspective, the lifecycle of Tunga penetrans is unique, but it is also the very reason why the disease can be so severe.
Helping Those Suffering from Tungiasis
Yasunaka:
What do you find rewarding about your work?
Hyuga:
To collect research materials (soil from bedrooms), I had the opportunity to visit the homes of people affected by tungiasis and talk to them about their daily lives. Seeing firsthand the burden that tungiasis places on these individuals and knowing that my research could ultimately help them is very motivating.
Yasunaka:
How did you gain the cooperation of local residents during fieldwork?
Hyuga:
In Kenya, there are community health volunteers who are like health commissioners for each area. They are well-informed about the health status of local residents. Before visiting households affected by tungiasis, I explained the purpose of the research to the health volunteers and asked them to act as guides in their areas. When requesting residents to participate, Kenyan staff members communicated in Swahili or local tribal languages to obtain informed consent. The health volunteers also helped facilitate communication, ensuring that the participants clearly understood the research objectives. Before collecting samples, we obtained ethical approval at the national and local government levels in Kenya and secured consent from each participant.
Yasunaka:
It sounds like gaining local cooperation involves many steps. What do you prioritize when working with local residents and staff?
Hyuga:
Since the Kenyan staff and I come from different backgrounds, misunderstandings can occur. Therefore, whenever I noticed a potential miscommunication, I made it a point to double-check to ensure we were on the same page. Additionally, during sampling, I was careful to respect local customs and cultural practices, such as being mindful of the timing of calls and visits.
Yasunaka:
That’s a thoughtful approach. Were there any challenges you faced while conducting research in Kenya?
Hyuga:
Yes, on days with heavy rain or strong winds, power outages and internet disruptions occurred frequently. Additionally, there were several instances where demonstrations over the rising cost of living or road closures related to presidential elections disrupted commuting routes. These situations are common in Kenya, but for a Japanese researcher, they were unexpected challenges that required quick adaptation.
Yasunaka:
What are your future goals and dreams?
Hyuga:
Tungiasis is a zoonosis, meaning it affects both humans and animals. Currently, my focus is on humans, but I’d like to expand my research to include animals using Tunga penetrans traps. If the traps prove effective, I dream of distributing them free of charge through international cooperation, similar to how bed nets were distributed for malaria control.
Yasunaka:
What do you think is the significance of Japanese researchers engaging in tropical medicine?
Hyuga:
With global warming and recent climate changes, tropical medicine may no longer be limited to “tropical” regions. The challenges faced in tropical areas are not just local issues; they are global problems. Thus, rather than focusing on ‘Japanese’ researchers, I believe that engaging in tropical medicine is a way to address global challenges regardless of nationality or origin.
Yasunaka:
Lastly, do you have any advice or comments for the student section members of the Japanese Society of Tropical Medicine?
Hyuga:
The great thing about J-Trops* is that it provides opportunities to connect with professors engaged in tropical medicine. It might feel intimidating to approach prominent professors at conferences, but through interviews like these, you can ask about their work in depth and foster connections. I hope you all continue to take advantage of such opportunities.
*J-Trops: Japanese Society of Tropical Medicine Students’ Branch
Clockwise from top left: Kento Oshiro, Yuma Yasunaka, Dr. Ayako Hyuga, and Aika Kitamura.
Profile of Interview Participants
Dr. Ayako Hyuga
Lecturer, Laboratory of Veterinary Food Hygiene, School of Veterinary Medicine, Nihon University (from April 2025). After graduating from the School of Veterinary Medicine at Nihon University, she worked as a public health officer in Tokyo before obtaining her PhD in Emerging Infectious Diseases at the Graduate School of Biomedical Sciences, Nagasaki University. She then conducted research on Tunga penetrans at the International Centre of Insect Physiology and Ecology (ICIPE) in Kenya and developed traps for the parasite as an Assistant Professor at the Department of Parasitology, Institute of Tropical Medicine, Nagasaki University. From April 2025, she will return to Nihon University. Hobbies include handicrafts, skating, and swimming. Her motto is a quote from Uesugi Yozan: ‘If you try, you can do it. If you don’t, nothing will get done. The reason things don’t get done is because people don’t try.’
Yuma Yasunaka
Fourth-year medical student at the School of Medicine, University of Occupational and Environmental Health, Japan (from April 2025). Originally from Kanagawa Prefecture. Became interested in parasitology during a lecture in his second year, particularly intrigued by the life cycle of Strongyloides stercoralis. Currently researching the inhibitory effects of rodent malaria parasites on collagen-induced arthritis in the Parasitology Laboratory. Member of the university’s yacht club. His motto is: ‘If you think of it, today is a lucky day; every day after is an unlucky day.’
