Are modern day diseases made in labs?

For example the Swine Flue virus could not exist in nature and a sample of it was made in a lab (that went missing supposedly but yet turned out to infect everyone) as it as a combo of pig, 2 types of bird and another animal's combination of viruses which could never combine in nature without a lab. There's also Aids and that never existed before the 1900's. Are these all made in labs and if so why?