They are called cottontails or cottontail rabbits. They are especially susceptible to the myxomatosum virus.

See http://en.wikipedia.org/wiki/Cottontail_rabbit.

Sep 30, 2010 ... in Sylvilagus rabbits as a climax associ- ..... coelho do mato (Sylvilagus minenses), ... virus myxomatosum in cottontail rabbits, ...
aje.oxfordjournals.org/content/77/2/213.full.pdf

It has been suggested by Fenner (1952) that just as Sylvilagus is the ... related to myxoma is the fibroma of Shope (1g32a, b), found in cottontail rabbits (the species ..... 0 virus do mixoma no coelho do mato (Sylvilagus minenses) sua ...
onlinelibrary.wiley.com/doi/10.1111/j.1744-7348.1954.tb01130.x/pdf

Laboratory transmission of fibromas (Shope) in cottontail rabbits by means of ... H.B. Aragao, O virus do mixoma no coelho do mato (Sylvilagus minenses), ...
linkinghub.elsevier.com/retrieve/pii/004268225790065X