1893 – Tick to cattle transmission of Texas Tick fever described

  A few years after beginning his work at BAI, Theobald Smith turned his attention to Texas cattle fever, a devastating disease that destroyed 90% of herds in some affected areas. It occurred in northern cattle that came in contact with cattle from Texas during cattle drives to stockyards in Kansas, Missouri, Iowa, and Illinois. It was a problem of great economic and political importance. Cattle ranchers had long held a vague but persistent impression that ticks were in some manner the cause of the disease. Smith had the good sense to listen to the cattle ranchers and formulate a hypothesis based on these impressions that he tested with searching experiments to subject it to scientific scrutiny. Some confusion exists about the part that Smith played in the Texas cattle fever discovery. Smith is widely cited as the sole person who discovered that ticks were the vectors of Texas cattle fever, when in fact, it was a collaborative effort of Smith with his colleagues, Fred L. Kilbourne and Cooper Curtice, both veterinarians. Smith never claimed this work as solely his own, even though popular accounts entirely credited him.

 

In 1889, Smith described little bodies in the erythrocytes of infected cattle; he later recognized (1891) them as protozoa, which he eventually named Piroplasma bigeminum (now called Babesia bigemina). Following this discovery, Smith and Kilbourne conducted experiments in which they placed southern cattle in pens with northern cattle. In some instances, ticks were left on the infected animals; in other enclosures, the ticks were removed. The researchers also kept native cattle in fields in which infected ticks had been left on the ground. These transmission experiments established beyond question the role of ticks (Boophilus spp.) as the carrier of this disease. Smith’s 301-page monograph about the laboratory and field experiments, BAI Bulletin No. One (1893), is regarded as one of the classics of medical literature. In these experiments, it was also demonstrated that the infection could pass in ticks from adults to nymphs, a new and extraordinary phenomenon of parasitism. This research was conducted by Curtice. Delineation of the tick’s life cycle soon paved the way for control of the disease by dipping cattle to kill the ticks.

 

References:

• Chernin E A unique tribute to Theobald Smith, 1915. Rev Infect Dis 1987;9:625–35
• Dolman CE Theobald Smith, 1859–1934, life and work. N Y State J Med 1969;69:2801–16
• Dolman CE Texas cattle fever, a commemorative tribute to Theobald Smith. Clio Med 1969;4:1–31
• Dolman CE Theobald Smith (1859–1934), pioneer American microbiologist. Perspect Biol Med1982;25:417–27
• Schwabe CW Cattle priests, and progress in medicine. Minneapolis: University of Minnesota Press; 1978. p. 177–82.
• Zinsser H Biographical memoir of Theobald Smith, 1859–1934. Rev Infect Dis 1987;9:636–54

Photo: https://en.wikipedia.org/wiki/Babesia