Massey mapped the occurrence of African sleeping sickness (trypanosomiasis) in the Belgian Congo, showing that the disease was spreading along the banks of rivers.

[8] In 1876, Mrs. Levi Massey was the founding president of the Woman's Missionary Society of the Methodist Episcopal Church in Canada, in Belleville, Ontario.

[12]: 355, 360 Massey left Montreal, Canada on July 26, 1899, and arrived at the port of Benguella in Portuguese Angola on September 17, 1899.

[2] On October 25, 1899, Massey arrived at the mission station in Chisamba to begin work as a missionary doctor.

[17] In 1905, Massey reported the presence of sleeping sickness among Baluba porters who had been recruited to work from the Bukama Territory of the Democratic Republic of the Congo.

[18] Sleeping sickness was a devastating fatal disease that would not be treated successfully until 1920, when Louise Pearce tested arsenic-based drugs.

[22] Subsequently, Massey studied at University College Hospital in London, receiving his Licentiate in Medicine and Surgery of the Society of Apothecaries (L.M.S.S.A.Lond.)

[23] Throughout his career, Massey continued to study, treat and write about infectious and tropical diseases such as encephalitis, onyalai, and tuberculosis, becoming highly regarded.

[3][1] Massey corresponded with Edwin Ray Lankester[26] and sent specimens of ticks to members of the London School of Tropical Medicine.