In the year the ability of tsetse flies to vector trypanosomes was demonstrated ( use numerals). ento

I believe the answer is in the year of 1909.
The Tsetse has largely influenced economic situation in sub-Saharan Africa as the biological vectors of trypanosomes that enable it to spread various type of diseases,  such as animal trypanosomiasis and  human sleeping sickness, which cause a huge cost in government spending.

Existing to a lot of people