On the surface, both strains of Anopheles arabiensis look the same, and inside their bodies, both types of mosquitoes have the potential to carry the malaria parasite—killer of at least one million people each year. But public health student Randolph Cheung knows that the difference between the two strains of mosquitoes is significant: one type always dies when sprayed with DDT, while the other type sometimes survives.

In July, Cheung went to South Africa to identify some of the genetic variations between the two strains of A. arabiensis. He was one of 13 Yale graduate students who did research abroad last summer with funding from a Downs International Health Student Travel Fellowship. “They have gone literally to the four corners of the world,” said Serap Aksoy, Ph.D., associate professor of epidemiology and public health, at a symposium in October featuring talks and posters on research by the fellows.

Cheung’s corner of the world was the insectary at the Department of Medical Entomology at the National Health Laboratory Service in Johannesburg, where he spent three months analyzing genetic differences between the two strains of malaria mosquito. Entomologists can use this genetic information to figure out which strains of mosquitoes are genetically similar to the newly resistant strain—and therefore most likely to develop resistance themselves. Once they know where those strains are located, South Africa’s public health officials can give priority to killing resistance-prone mosquitoes.

Cheung searched for genetic differences between the strains by extracting their DNA and comparing polymorphisms at eight sites on the gene. When Cheung finishes characterizing those differences for his master’s thesis, entomologists will be able to use that information to classify different types of mosquitoes. The only way to tell the difference without genetic methods, according to Cheung, is to see if two mosquitoes that mate produce healthy offspring. If not, they probably belong to different strains.

Cheung spent his hours outside the lab volunteering in the emergency department of a public hospital and enjoying the differences between South Africa and his native California. “Everything was interesting: the weather, the people, the language, the architecture, the music, the food.” He described as “surreal” the radical disconnection between the impoverished Hillbrow neighborhood where he worked and the deluxe shopping malls 15 minutes’ drive away in Santon.

Last summer’s Downs fellows came from the schools of public health, medicine and nursing and from the graduate school. Fellows included Jessica Kattan, a second-year medical student who analyzed medical records in Paraguay to research patterns of leprosy transmission to children; public health student James Moore, who surveyed teenagers in South Africa to study how drinking alcohol affects their nutrition; and Gladys Y. Ng, also at the School of Public Health, who spent the summer in a laboratory in China to find out whether mice could serve as animal models for testing potential hookworm vaccines.

The fellowship was established in 1965 and later named in honor of its founder, Wilbur G. Downs, M.D., M.P.H., who died in 1991. Downs was a specialist in tropical medicine and infectious diseases, a champion of international travel for students and a formidable fly fisherman who was a professor at the School of Public Health from 1962 to 1971.