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Wien Klin Wochenschr. 2002 Jul 31;114(13-14):479-81.

Theobald Smith--the discoverer of ticks as vectors of disease.

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  • 1Clinical Institute of Hygiene and Medical Microbiology, University of Vienna, Vienna, Austria.


The cause of Texas fever in cattle, which is characterised by lysis of erythrocytes leading to anaemia, icterus, haemoglobinuria, and death, remained unsolved for many decades and assorted theories were proposed as an explanation for a disease being transmitted by apparently healthy animals. From 1889 to 1893, Theobald Smith and Frederick L. Kilbourne could demonstrate in elegantly conducted experiments how the disease was spread from cattle to cattle by ticks serving as the vector of transmission. Furthermore, they were able to identify the pathogen of Texas fever, an intra-erythrocytic protozoan which Smith named Pyrosoma bigeminum. Today it is recognised that either of two species of the now renamed genus Babesia, Babesia bigemina and Babesia bovis, may be involved in Texas fever and that babesiosis is generally transmitted by ticks. In animals, genera like Boophilus spp., Dermacentor spp. and Rhipicephalus spp. are possible vectors. The first case of tick-transmitted babesiosis in a human was reported by Skrabalo and Deanovic in 1957 and occurred near Ljubliana in the small town of Strmec, Croatia. In humans, the vectors of most reported cases are ticks of the genus Ixodes, which are among the most predominant ticks in Austria. However, cases of human babesiosis in Austria remain to be studied. Smith and Kilbourne's work was the first demonstration that ticks transmit disease of any kind. Furthermore, by proving that ticks carry Babesia microti--which causes babesiosis in animals and humans--this is the first account of a zoonotic disease and the foundation of all later work on the animal host and the arthropod vector.

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