“For the first time in history it was proved conclusively that the essential factor of an infectious disease may be a microparasite that reaches its victims only through an intermediate host, and this revealed why a truly infectious disease may in no respect be contagious.”  Ulysses Grant Houck, 1924


Dorsal and ventral views of replete female Boophilus annulatus

Desperate measures

By the 1860s, livestock producers in the U.S. had long been concerned with cattle fever.  The disease took huge tolls on their herds, but its causes and means of spreading were not well-understood. It had arrived in North America in the 1600s, brought by cattle imported from the Spanish colonies of the West Indies and Mexico. It spread throughout the southern United States and then began working its way northward as infected herds were driven across the plains to cattle markets. By 1877, northern ranchers were determined to stop southern herds from contaminating their own. Without organized control efforts or government intervention, cattlemen fended for themselves.  Sometimes they sent armed parties to turn back herds on their trip north through Missouri, Kansas, Arkansas, and Indian territory.

Texas cattle fever caused an uproar. No one knew what caused the disease, how southern cattle spread it, or why it disappeared in the winter. It was time to find a solution.


Dorsal and ventral views of male Boophilus annulatus

Linking ticks to disease

The investigation of cattle fever was among the top priorities at the fledgling BAI. Salmon decided to take a risky and controversial step—he approved a plan to investigate a common theory among cattlemen that ticks were responsible for cattle fever. Many scientists dismissed the BAI’s pursuit of a layman’s theory as nonsense. However, Salmon believed the idea had merit, because his own observations showed a strong correlation between areas of tick infestation and cattle fever.

Three young veterinary scientists on Salmon’s staff were given charge of the investigation. Theobald Smith, a trained microscopist and Salmon’s laboratory assistant, studied the microbial cause of Texas fever. Frederick L. Kilborne, who supervised the BAI’s experiment station, was responsible for testing the theory that ticks transmitted the disease. Cooper Curtice, head of the bureau’s zoological laboratory, turned his attention to the biology of the tick.

Lasting impact of cattle fever research

Control of ticks made possible many improvements in cattle production and facilitated the transport of cattle throughout the U.S. and Canada. Tick eradication revolutionized the agricultural economy of the American South. With cattle fever under control, the South gained open access to northern markets and became an important beef cattle producing region by the mid-20th century.


Andrews, John S. 1987. “Animal Parasitology in the United States Department of Agriculture, 1886-1984.” In 100 Years of Animal Health 1884-1984, edited by Vivian D. Wiser, Larry Mark, H. Graham Purchase, and Associates of the National Agricultural Library, 113–65. Beltsville, MD: Associates of the National Agricultural Library, Inc.

Cattle Fever Tick Eradication Program –Tick Control Barrier: Maverick, Starr, Webb, and Zapata Counties, Texas: Draft Environmental Impact Statement.” 2013. www.aphis.usda.gov/animal_health/animal_diseases/tick/downloads/draft_eis_document.pdf.

Houck, U. G. 1924. “History of the Bureau of Animal Industry and Zoological Division.” U.S. National Animal Parasite Collection Records. Box 98, Folder 5. Special Collections, National Agricultural Library.

Schwabe, Calvin W. 1981. “A Brief History of American Parasitology: The Veterinary Connection between Medicine and Zoology.” In The Current Status and Future of Parasitology: Report of a Conference Sponsored Jointly by The Rockefeller Foundation and the Josiah Macy, Jr. Foundation, edited by Kenneth S. Warren and Elizabeth F. Purcell, 21–43. New York: Josiah Macy, Jr. Foundation.