Deep in the ticks of Texas
A young physician's job in the animal industry led to a new understanding of disease spread.
In New York City, in the summer of 1868, diners were furious that they could not get a good steak. The cattle were all dying in a Jersey City slaughterhouse. New Yorkers were ready to riot. It was apparent that this fatal disease was being transmitted by Texas Longhorns and other southern bovines, but the cause went undiscovered in this premicrobiologic era.
As a student at Albany Medical College, Theobold Smith was disgusted by his classmates' drunken antics and lack of intellectual curiosity. Still, he had trouble finding a job after graduation. He eventually ended up working for the National Bureau of Animal Industry. In 1889, he was handed the seemingly unsolvable Texas fever situation to manage. The only thing he could discover was that western farmers had noticed a relationship between ticks and sick cattle: “No ticks, no Texas fever.”
In June of that year, he and an assistant, Alexander, brought seven cows from North Carolina. These animals were described as being “decorated, infected and plagued by several thousands of ticks of assorted sizes including some splendid females an inch long.” Theobald and Alexander began to remove every last one of the ticks, collecting them in cans.
The first arm of the experiment was to place healthy northern cows in fields with either tick-covered or de-ticked healthy southern cows. Within two months, the northern cows in the infested fields were sick, but the cohort in the tick-free fields were fine. This was evidence it was ticks causing the disease, but how? And why weren't the southern cows sick?
Theobold and Alexander figured out the answer to the latter question by exposing calves to ticks and finding that they only got mild fever, inducing a “calfhood” immunity. They then tried putting baby ticks on healthy cows and figured out that a field that had previously held southern cows remained a risk even after the cows were gone because the ticks remained.
In 1893, Dr. Smith, working with a veterinarian, Fred Lucius Kilborne, published “Investigations into the Nature, Causation and Prevention of Texas Fever” for the U.S. Department of Agriculture. This led to quarantine of cows, as well as “dipping” to remove ticks (which the cows no doubt appreciated), but also spelled the end of the picturesque Texas cattle drive, which had spread the ticks.
More important, Dr. Smith had discovered and proven that an insect could be the vector of a disease. The actual cause appeared to be a protozoa that lived within the tick. In fact, that organism had been identified a few years earlier by Victor Babes. We know the disease now as babesiosis. To combat the problem, cattlemen took to vaccinating cattle with a small amount of infected blood, resulting in mixed success.
It was just a few years later that the first human disease carried by insects was identified, African sleeping sickness, carried by the tsetse fly. Remarkable how these same issues are still plaguing society today, especially given our changing climate: quarantine, vaccination, insect-borne disease, and New Yorkers complaining about their steak.