The most popular hypothesis in the scientific community is that viruses (Coxsackievirus, Rubella…) induce autoimmune disorders such as Type 1 diabetes. These are ubiquitous viruses and most of the world's population is in contact with them. But only, combination of genetic and environmental factors causes an autoimmune disease such as Type 1 diabetes So, I would not talk about the classic transmission of the causative infective agent as in infectious diseases. Here is also important genetic background; otherwise, most of the world's population would suffer from diabetes.
IDr Zdravkovic is correct and one of the indicators that an infective agent is involved is that there is often a peak of type 1 diabetes at the ages when children change schools ( used to be 5 and 11 years old in the UK) and so are exposed to new viruses and bacteria
Definitely it is not possible to till date. diabetes is due to lifestyle factors or genetic susceptibility. Some viruses are responsible for mild triggering of Diabetes type 1. It might be possible in future due to interaction of Eco-Genomics-Physiological interactions in diabetic patient and viruses or bacteria.