This is a rust disease, probably European pear rust. I have linked to two articles below, but it is not necessary to remove the tree or prune out branches, or even use fungicides as suggested in the articles. I will see about getting an updated article. Rust is primarily a cosmetic disease common on members of the rose family, including apple and pear. It requires a primary host ( a juniper) and an alternate host in the rose family to complete its lifecycle. I have also included information on cedar-apple rust, which is very similar. 

Pear rust:

https://www.canr.msu.edu/news/scout_your_bradford_pears_now_for_european_pear_rust

https://www.gpwmi.us/sites/default/files/fileattachments/public_works/page/14667/pear_tree_trellis_rust.pdf

Cedar-apple rust for comparison:

https://www.canr.msu.edu/news/cedar_apple_rust_a_tale_of_a_fungal_disease_with_two_hosts