The Russo-Circassian War  involved a series of battles and wars in Circassia, the northwestern part of the Caucasus, in the course of the Russian Empire's conquest of the Caucasus. Fighting lasted approximately 101 years, starting in the reign of Empress Catherine the Great and finishing in 1864. Although the Russian conquest of the Caucasus started at least as early as the Russo-Persian Wars, the term Caucasian War commonly refers only to the period 1817-1864. Those who use the term Russian-Circassian War take its starting date as 1763, when the Russians began establishing forts, including at Mozdok, to be used as springboards for conquest. The Caucasian War ended with the signing of loyalty oaths by Circassian leaders on 2 June  1864. Afterwards, the Ottoman Empire offered to harbour the Circassians who did not wish to accept the rule of a Christian monarch, and many emigrated to Anatolia, the heart of the Ottoman territory and ended up in modern Turkey, Syria, Jordan, Israel, Iraq and Kosovo. Different smaller numbers ended up in neighbouring Persia. Various Russian, Caucasus, and Western historians agree on the figure of ca. 500,000 inhabitants of the highland Caucasus being deported by Russia in the 1860s. A large fraction of them died in transit from disease. Some of those that remained loyal to Russia were settled into the lowlands, the left-bank of the Kuban River.
Question: How did many inhabitants of the highland Caucasus die?
Answer: in transit from disease