Viv: Wikipedia indicates there was a smallpox epidemic in 1860 which affected the HMS Hannibal while in Italy - could be relevant?
en.wikipedia.org/wiki/HMS_Hannibal_(1854)

Also, this site which you might not have previously seen( www.archive.org/details/royalnavyhistory06clow) has a online readable book with info re the HMS Hannibal - Author: Clowes, W. Laird (William Laird), Sir, 1856-1905; Markham, Clements R. (Clements Robert), Sir, 1830-1916; Mahan, A. T. (Alfred Thayer), 1840-1914; Wilson, Herbert Wrigley, 1866-1940
Volume: 6
Subject: Great Britain. Royal Navy
Publisher: London : S. Low, Marston, Co.

Good luck.