* Governments, philanthropists pledge most of needed funds
* So far in 2013, only 19 polio cases seen worldwide
* Dramatic progress "puts us within sight of the endgame"
By Kate Kelland, Health and Science Correspondent
LONDON, April 25 (Reuters) - Health groups said on Thursday they could rid the world of polio by 2018 with a $5.5 billion vaccination and monitoring plan to stop the ...