Zooprophylaxis is the use of animals to protect human health. The ideas of zooprophylaxis have been around for centuries: for example, Edward Jenner's use of the cattle disease cowpox to inoculate humans against the related but much more dangerous smallpox. However, the name of the field is relatively recent in English (though the Italian "Istituto Zooprofilattico" is over 70 years old).

Some historians have suggested that cattle caused the disappearance of malaria from the British Isles. There are certainly mosquitoes there, but once large numbers of cattle started being raised for food after the Industrial Revolution, the mosquitoes fed on cows' blood, and the malaria germ does not reproduce in cows' blood the way it does in other animals. Since the cattle were not serving as reservoirs of disease, the disease was much less prevalent than in the Mediterranean Sea coast of Europe, where fewer cows were raised.

Raising cattle to serve as a dead end for disease vectors, instead of insecticides and medication, is being tried out in several parts of the world, as drug-resistant strains of malaria make the old methods less effective. Other diseases such as Japanese encephalitis may also be made less common by the same tactics. One article suggests that even lizards may provide zooprophylaxis against some tick-borne diseases; it is a field which deserves more study.

Sources:
Carlson, Laurie Wynn. Cattle: An Informal Social History. Chicago: Ivan R. Dee, 2001.
http://www.izo.it/comune/Istzoo.html
http://www.nps.ars.usda.gov/programs/programs.htm?npnumber=104&docid=268
http://www.lshtm.ac.uk/itd/dcvbu/malcon/Techvector.html
http://www.rockefeller.edu/pubinfo/news_notes/100501/100501h.html
http://wonder.cdc.gov/wonder/prevguid/p0000008/p0000008.asp
http://ehpnet1.niehs.nih.gov/docs/2001/suppl-2/223-233gubler/gubler-full.html