An update: After several months we are no further forward with Spud and his health. The vet is leaning towards injury to the inside of the intestines from such a heavy worm load when he came in. He also isn’t regenerating his red blood cells effectively at the moment, so can get severely anemic very quickly. His blood count was 6 and even getting him to vets within half hour he was gravely ill and had to stay in vets for 5 days. Possibly due to more bleeding from the intestine . Long term he will probably need blood tests and lab work every month to start off and possibly ongoing for life. He has to take antacids and Iron Tablets.