Some very brief answers to your questions on brucellosis.
1. Number of human cases per year in the US. Actually diagnosed -
very few, usually less than a couple of dozen. Problem - the
overwhelming number of cases either go undiagnosed & untreated, or
are misdiagnosed. Estimates of properly diagnosed cases-less than
2. Humans (and animals) are infected via exposure and contact with
contaminated tisssues. Milk (unpasteurized), aborted fetuses, and
birthing fluids/tissues are the most common. Meat (muscle) from
Brucella infected animals is safe for human consumption after aging
process and cooking.
3. Severity of disease in humans - extremely variable, from a mild
to severe recurrent flu like syndrone ( fever, sweats, muscle and
joint aches) to more severe disease such as crippling arthritis,
orchitis, and meningitis, can even be life threatening.
4. Vaccines ( for animals) - not perfect. Cattle - the vaccines
historically and currently utilized are not very protective against
infection but lower abortion rates. There are no currently vaccines
licensed for elk and or bison. Some are being evaluated for elk and
bison but preliminary data indicates that the vaccines will not be as
effective in bison and elk. Delivery in free-ranging populations is
also more difficult. Similar problems exist with diagnostics. But
brucellosis eradication programs in most areas of industrialized
countries in traditional livestock and public and private bison herds
with the available technology.