||Theobald Smith, MD, is known for discovering that ticks are the vectors of Texas cattle fever. (Courtesy of the New York Academy of Medicine Library)
The discovery that insects can transmit disease was among the many accomplishments of a man who contributed much to veterinary medicine, although he was never a veterinarian.
Theobald Smith, MD, and colleagues discovered in the late 1800s that ticks are the vectors of Texas cattle fever, a finding that presaged the discovery of insects as vectors of other diseases. The pioneering researcher would go on to publish a total of about 300 papers with many key findings in pathology during a career that spanned half a century.
Dr. Smith was an active member of the United States VMA, later the AVMA, for five years before becoming an honorary member in 1897. He served as a chairman of the Committee on Diseases.
“While he never had a veterinary degree, except those awarded as honors, he spent his lifetime in devoted pursuit of veterinary disease problems,” wrote Dr. Ellis Pierson Leonard in “A Cornell Heritage: Veterinary Medicine 1868-1908.”
Born in 1859 in Albany, N.Y., Dr. Smith earned a bachelor’s degree in natural science from Cornell University in 1881 and a medical degree from Albany Medical College at Union University in 1883.
From 1884-1895, Dr. Smith worked within the Department of Agriculture’s new Bureau of Animal Industry. His time there was extremely productive, according to a 2008 article by Dr. Myron Schultz in Emerging Infectious Diseases.
According to the article, during his first two years at the BAI, Dr. Smith discovered a species of bacteria that he mistakenly thought to be the cause of hog cholera—later shown to be caused by a virus. The genus Salmonella
took its name from the head of the BAI, Dr. Daniel E. Salmon.
Among his accomplishments while working at the BAI, Dr. Smith collaborated with Dr. Salmon to demonstrate that sterilized cultures of dead bacteria can confer immunity.
In 1888, Dr. Smith and colleagues began studying the scourge of Texas cattle fever. They identified a protozoan (Babesia bigemina) as the cause of the disease, but had not solved the mystery of transmission. A 1914 article by James Middleton in the magazine The World’s Work described the course of the investigations.
Southern farmers pointed to the cattle tick as the cause of all the trouble. Unlike many other scientists, Dr. Smith and his colleagues decided to make a trial of the idea.
According to the article: “He collected several animals whose bodies were covered with the usual multitude of ticks and placed them in an enclosure occupied by a tickless herd. In about thirty days the latter animals fell ill with the disease. He then carefully removed by hand all the ticks on the first group, and mixed the cattle with another healthy herd. This time there resulted no trace of the disease. His next experiment was to scatter a field with ticks removed from Southern steers. Healthy cattle, led to browse in this place, promptly contracted cattle fever.”
The Emerging Infectious Diseases article notes that Dr. Smith collaborated with Drs. Fred L. Kilborne and Cooper Curtice, both veterinarians, in discovering that ticks are the vectors of Texas cattle fever.
In 1893, Dr. Smith published a 301-page monograph about their laboratory and field experiments. These experiments also demonstrated that in ticks, the infection could pass from adults to nymphs.
According to the 1914 The World’s Work article: “He has shown the way—by destroying the ticks: but the ticks still ravage almost unchecked.” Nevertheless, according to the 2008 EID article: “Delineation of the tick’s life cycle soon paved the way for control of the disease by dipping cattle to kill the ticks.”
The EID article continues: “The discovery by Smith et al. that insects can transmit disease represents one of the fundamental steps forward that altered the entire course of medical science and public health. It presaged the discovery in the next few years of the insect transmission of trypanosomiasis of cattle (nagana) in 1895 by David Bruce, malaria in 1897 by Ronald Ross, yellow fever in 1900 by Walter Reed and his colleagues, and typhus in 1909 by Charles Nicolle.”
For most of his time at the BAI, Dr. Smith also taught at George Washington University.
In 1895, Dr. Smith moved to Massachusetts to become director of the state’s antitoxin and vaccine laboratory and a professor of applied zoology and then comparative pathology at Harvard University.
“He wasted no time in applying his meticulous approach to the production of biologics, increasing the potency of diphtheria antiserum fourfold, while the annual number of free doses distributed in Massachusetts rose from 1,724 in 1895-96 to 40,211 in 1901-02, sparing an estimated 10,700 lives,” according to a 2009 article by Dr. Steven M. Niemi in Harvard Magazine. “This endeavor also produced the first description of immune-mediated hypersensitivity—anaphylaxis, known for years as the ‘Theobald Smith phenomenon.’”
In 1914 or 1915, depending on the source, Dr. Smith joined the Rockefeller Institute for Medical Research as director of the branch in Princeton, N.J., for the study of animal pathology. He remained there until his retirement in 1929, and he died in 1934.
A 1935 obituary by J. Howard Brown, PhD, in the Journal of Bacteriology provided an overview of Dr. Smith’s career. According to the obituary: “The subjects of his many publications include: the method of transmission of infectious agents from one individual host to another, as in the insect transmission of the parasite of Texas fever; the role of Heterakis in the production of enterohepatitis of turkeys; the differentiation of closely related organisms, as the varieties of tuberculosis bacilli, the Brucella, the paratyphoid bacilli, the streptococci and the anaerobes; simple and ingenius methods of cultivating and differentiating bacteria, as the use of the fermentation tube, the use of bits of fresh unheated animal tissue in media and the differential value of sugar fermentation; comprehensive studies of infections natural to animals; the production of immunity by heat killed cultures; the transmission of antibodies in utero and through the colostrum.”
The obituary observes: “It is difficult to say whether Dr. Smith’s devotion to comparative pathology was more the result of choice or opportunity but he soon recognized that disease is a natural biological phenomenon common to all living things.”
In a 1933 letter to a colleague, Dr. Smith discussed his philosophy of research. He wrote: “In general a fact is worth more than theories in the long run. The theory stimulates but the fact builds. The former in due time is replaced by one better but the fact remains and becomes fertile. The fertility of a discovery is perhaps the surest measure of its survival value.”