Gertrud Theiler was the youngest daughter of sir Arnold Theiler KCMG, founder and first director of the Veterinary Institute, Onderstepoort, and his wife, Emma Sophie Jegge. She was born in Pretoria on 11 September 1897. 

After matriculating at Pretoria Girls’ High School Theiler spent a year at Rhodes University College in Grahamstown and from there went to the South African College in Cape Town, from where she graduated with a BSc degree in 1918. She spent a number of years overseas doing postgraduate work in helminthology, initially with Prof. O. Fuhrmann at the University of NeuchÁ¢tel, where she obtained her DSc in 1922. Theiler also spent a number of years at schools of tropical medicine in Liverpool, under Prof. Warrington Yorke, and London, under Prof. R.I. Leiper. She wrote four scientific papers on this research of which the relating to the nematode parasites of South African equines is highly regarded and frequently consulted.

On her return to South Africa in 1924 Theiler taught Biology for 15 years. After two years at Jeppe High School for Girls in Johannesburg she obtained a lectureship at the Hugenot College, Wellington. In 1935 she was promoted to the professorship in Zoology and Physiology. During 1939 she lectured temporarily at Rhodes University College, but the following year accepted a research post in the entomology section at Onderstepoort. The resulting studies on ticks occupied her for some 25 years. She became well known in her field around the world.

Officially Theiler retired in 1967, but she continued her work at Onderstepoort as an honoured guest until 1983, when her deafness and failing sight forced her to stop working. She was awarded the Captain Scott Medal of the South African Biological Society in 1960 and the Elsdon Dew Medal of the Parasitological Society of Southern Africa in 1975. Extremely knowledgeable about all forms of nature she also served on the Council of the Wild Life Protection and Conservation Society of South Africa for 30 years and was chairperson of the editorial committee for their magazine, ‘African Wild Life’.

As a founder of the Austin Roberts Bird Sanctuary in Pretoria she spent Sunday afternoons there. The last three years of her life were spent in Still Bay, where she died on 2 May 1986.

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