Yes, Jeanne, we have 'spread it around' - a lot - by selling/moving cattle around the country. Misconceptions, misinformation, and poor diagnostic tests in the past have contributed to the problem.
We used to think that 2 doses of long-acting oxytetracycline (LA-OTC) would 'clear' the infection, and that animals that survived the infection would 'clear' on their own. Truth is that neither of those are the case. Clinically-affected cattle that are treated and survive, as well as animals that are infected as calves (which don't become ill because their immune and blood-forming systems are in high-gear since they're rapidly growing) will not be 'cleared', but rather will be chronically infected, with low-level parasitemia, and can serve as a source of infection for naive animals.
The old Complement Fixation test that we used to use to test probably missed as many as 80-85% of those chronic low-level carriers - resulting in a lot of false-test-negative animals being sold around. The newer cELISA test is, however, very sensitive, and quite specific.
Anaplasma strains present in most of the US are tick-vectored, and biting flies like horseflies are of minimal importance in spreading it within a herd.
Whole-herd treatment with a LA-OTC is a double-edged sword, though I'm not sure that it's necessarily falling out of favor. You can't get enough OTC in a cow to kill/clear the organism... you're just slowing it down, hopefully long enough for the cow to kick up production of new red blood cells and survive... but if you treat an animal early in the incubation phase, as soon as the drugs wear off, the parasite picks up right where it left off, and you'll have new clinical cases 3-6weeks later. I saw cases from one herd that lasted from August into December one year, because every time they had another clinical case, they treated everything... and they kept suppressing the pathogen in those animals that were freshly infected... but as soon as the drugs wore off... here we go again.
