An expert's bad blood with mosquitos in fight against malaria

Dong Xueshu is using a microscope to observe the mosquito, July 14, 2016. (Provided by the Yunnan Institute of Parasitic Diseases)

Dong Xueshu enters his lab and carefully gives some fish food to the mosquito larvae he raises, waiting for them to grow into adults for his research.

Dong, 84, is a mosquito expert with the provincial institute of parasite disease prevention and control in the city of Pu'er, southwest China's Yunnan Province. He has been studying mosquitos since the 1960s and has kept his passion for the insects alive even after retiring in 1996.

"I have followed mosquitos my whole life, and it is hard to stop," said the gray-haired man.

Dong's study has come to the spotlight once again, as China observes malaria day later this week.

BAD BLOOD WITH MOSQUITOS

Dong's study on mosquitos started early.

In 1951, Dong, then 15, entered a local medical college in the southwestern Guizhou Province and began to focus on insects that transmit diseases, including fleas and mosquitos.

Three years later, he was assigned to work in an epidemic prevention station in Yunnan. To help with the fight against malaria, he went to the county of Menghai, where a malaria epidemic broke out.

"We were fighting a war against malaria, and I thought we needed to figure out the details of our enemy: mosquitos," he said.

Dong Xueshu displays mosquito specimens to his students, August 7, 2017. (Provided by the Yunnan Institute of Parasitic Diseases)

Malaria is a disease caused by the parasites in mosquitos or by blood transfusion. Typical malaria symptoms include coldness, fever, sweating, anemia and a swollen spleen.

The world has more than 3,000 types of mosquitos, and China has more than 400 types. Experts have found more than 300 types of mosquitos in Yunnan alone because of the unique weather and landscape in the province. Of them, eight types are the main carriers of parasites that spread malaria.

In the first few years, Dong and his colleagues would go to locals' bedrooms and even pigsties to catch mosquitos for study twice a day.

"The locals were the ethnic Dai people, and most of them were living on the second floors of their unique two-story bamboo buildings. They raised domestic animals on the first floors," he said. "Mosquitos thrived on the first floors during summertime."

But locals would not let them in their bedrooms at first because of ethnic traditions.

"We had to beg some village heads to persuade them," he said.

As their work progressed, Dong also informed locals about how to fight against the insects, including using mosquito nets soaked in medicine. He also carried anti-mosquito medicine to rural areas and gave it out to locals for free.

ARDUOUS ADVENTURES IN SEARCH FOR MOSQUITOS

To study mosquitos, it is necessary to have specimens, including those of the larvae and the adult mosquitos.

Dong and his colleagues would go out to rural villages in the remote Yunnan from March to November each year to conduct field surveys.

Because mosquitos can be found in both river valleys less than 80 meters above sea level and on plateaus more than 2,000 meters above sea level, Dong would visit these areas to catch them.

"The surveys could take more than half a year, and we would not stop until the mosquitos start wintering," he said.

The equipment for catching mosquitos was simple: an iron pot, a wood handle, a net, a tube and some plastic bottles.

Dong usually puts the equipment in a sack and sets out to catch mosquitos. The jingling sounds of the equipment hitting each other makes him look like a beggar, he said.

Dong Xueshu instructs students to catch mosquito larvae in the wild, June 24, 2015. (Provided by the Yunnan Institute of Parasitic Diseases)

After the rain, mosquito larvae could be found inside forests where bamboo trees have been logged. The larvae are usually in the rainwater on the left-over of the bamboo trees. However, some mosquitos are tree-born, so Dong has to climb up the trees to fetch the specimens.

The best time to catch mosquitos is when the insects mate, Dong said.
"They dance in groups when they mate," Dong said.

He usually folds the net to catch the mosquitos, uses the tube to siphon them out one by one, and puts them in the plastic bottles.
"Mosquitos fly, it is not that easy to catch them," he said.

Sometimes there is a price to pay for catching the mosquitos. Wild animals such as snakes, wolves and bears sometimes pose potential threats.

Dong recalls an experience in the 1970s when he was collecting mosquito specimens in the bushes in a village in the county of Mengla. A king cobra of his height suddenly appeared.

"I was scared motionless," he said. "I wanted to tiptoe back, but another king cobra showed up in the backward direction."

A few minutes later, the second cobra snaked through the bushes, and Dong managed to get away safe and sound.

"I still feel frightened in hindsight," he said.

Dong said it is easy to run into snakes during the field surveys, so he even bought a book on how to fight the reptiles.

"It is a tough job, but it is meaningful to me," he said.

Thanks to the efforts of experts like Dong, Yunnan's provincial institute of parasite disease prevention and control has received up to 10,000 mosquito specimens so far, including 26 new mosquito types, making the institute one of the biggest mosquito specimen museums in China. These specimens provided valuable research materials.

RAISING MOSQUITOS

While it is important to catch mosquitos, it is even more important to raise them.

"To get more types of mosquitos, you have to raise them," he said. "Let them reproduce so that there are more to study."

In Dong's mosquito-raising lab, he feeds the larvae fish food three times a day.

"You can't feed too much, otherwise there would be an oil membrane in the water, which could choke the larvae," he said.

Dong Xueshu is observing the mosquitoes in mosquito cages, May 30, 2019.(Xinhua)

The larvae grow into adults in a few days, but they need blood before reproduction. So Dong would lend his arm to the mosquitos to suck at first. Later he chose to use mice for his experiment.

The success in raising the mosquitos saved Dong many field trips.

"I don't have to go out all the time because I have already raised many types of mosquitos," he said.

Besides researching mosquitos, Dong's favorite relaxation tip these days is square dancing in the local park amid a group of dancing grannies.

"Square dancing is a very good exercise," he said.

Though in his 80s, Dong still wants to continue his study on mosquitos.

"Mosquitos can mutate, so our research work can't stop," he said.

Editor: John Li