Five years ago, during the first North American outbreak of the cattle disease CXC, the death rate from the disease was 5 percent of all reported cases, whereas today the corresponding figure is over 18 percent
It is clear, ttherefore, that during these past 5 years, CXC has increased in virulence
During the first North American outbreak of the disease, many of the deaths reported to have been caused by CXC were actually due to other causes.