Texas longhorn are descendants of the first cattle in the Americas which were brought over from Europe by Christopher Columbus and the Spanish Conquistadors in the fifteenth century. Over the intervening centuries, they became extremely well adapted to their environment and their hardiness included resistance to a scourge which, among other names, was called the Texas Fever.
Texas Fever caused more recently imported cattle to fall sick with anaemia, high fever, red urine and severe lethargy which very often ended in death. Only cattle which came into contact with longhorns or which grazed pasture after they’d passed through were affected – so the longhorns were obviously to blame. Farmers rose up in arms – their livelihood was in danger and indeed many of them were financially ruined by the disease. Their reaction was to block the passage of longhorns being driven along established trails, and sometimes to shoot the cattle on sight. They also killed cowboys in their vigilante excesses.
Legislation was passed eventually. It stated that diseased cattle were not to be driven through the State of Missouri. Unfortunately the law was no help at all to the farmers because the longhorns showed no signs of being affected by the disease they were clearly carrying. They could keep on coming, perfectly legally.
Various quarantine laws redirecting the longhorns or restricting the droving to winter months did little to help. Theories about the origin of Texas fever abounded. It was believed by some that the longhorns ate poisonous plants which didn’t harm them but which caused their dung to be so toxic that it killed the other cattle.
Finally in 1893 Theobald Smith and Fred Lucius Kilborne of the Bureau of Animal Industry in Washington announced that they’d solved the mystery. The disease was due to a protozoan that lived in and destroyed red blood cells. Just as importantly, they’d worked out that the disease was transmitted by ticks, which fell off the longhorns, reproduced in the grass, and infected the resident cattle.
The other part of the mystery was why longhorns weren’t affected to the same degree as other cattle. The most likely explanation is that longhorn calves were born with a natural partial resistance which was then consolidated by a mild attack of the disease at an early age giving it enough immunity to prevent illness but not enough to stop it from being a carrier.
The modern, technical name for Texas Fever is Babesiosis after the name of the protozoan which causes it. It has been eradicated almost entirely in the United States thanks to a vigorous programme of cattle dipping to kill the ticks. The protozoan is now only present in a small strip of land along the Mexican border which has been quarantined since 1938. However white-tailed deer can carry the tick responsible for the disease and they’re of course free to move across any quarantine lines. It isn’t known yet whether this may represent a danger.