Myxomatosis (sometimes shortened to  myxo  or myxy) is a disease that affects rabbits and is caused by the myxoma virus.It was first observed in Uruguay in laboratory rabbits in the late 19th century. It was introduced into Australia in 1950 in an attempt to control the rabbit population (see Rabbits in Australia).t was first observed in Uruguay in laboratory rabbits in the late 19th century. It was introduced into Australia in 1950 in an attempt to control the rabbit population (see Rabbits in Australia).