1855:Kars: In the year up to May 1855 Turkish forces in the east were reduced from 120,000 to 75,000, mostly by disease. The local Armenian population kept Muravyev well-informed about the Turks at Kars and he judged they had about five months of supplies. He therefore decided to control the surrounding area with cavalry and starve them out. He started in May and by June was south and west of the town. A relieving force fell back and there was a possibility of taking Erzerum, but Muravyev chose not to. In late September he learned of the fall of Sevastopol and a Turkish landing at Batum. This led him to reverse policy and try a direct attack. It failed, the Russians losing 8000 men and the Turks 1500 (29 September). The blockade continued and Kars surrendered on 8 November.

What caused the number of Turkish soldiers to decrease?