72 



MISCELLANEOUS PUBLICATION NO. 10 65, U.S. DEPARTMENT OF AGRICULTURE 



Infectious Agents and Allergens 



A real milestone in civilized progress occurred 

 in 1864. Louis Pasteur announced as a result of 

 his beautiful experiments on fermentation that 

 very minute organisms were the active agents in 

 the process. Organisms — yeasts — involved in the 

 development of good wine were found to be quite 

 different from those that cause wine to go bad. 



In 1865, Pasteur isolated bacilli of two distinct 

 diseases that were killing the silkworms and ruin- 

 ing the silk industry in southern France. 



Pasteur became the first distinguished research 

 investigator on the diseases of farm animals. He 

 isolated the causative organisms and developed 

 vaccines for chicken cholera, animal anthrax, and 

 hydrophobia. 



Thomas J. Burrill of the University of Illinois 

 became fascinated with Pasteur's findings while 

 traveling in Europe in the early 1870's. He was the 

 first to show that a plant disease — fire blight of 

 pears and apples — is transmitted by bacteria 

 (21). Even before the discoveries of Pasteur and 

 Burrill, DeBary in Germany had shown that 

 microscopic fungi caused rust and smut diseases 

 of plants. 



Animal Disease Agents Contaminating the En- 

 vironment 



Before 1843, animal diseases were a minor prob- 

 lem in the United States. By 1883, the year before 

 the establishment of an organized animal disease 

 eradication program, there were 146,388,329 do- 

 mestic animals on farms, valued at $2,338,241,519. 

 Hog cholera killed $25 to $30 million worth of 

 hogs annually. Sheep raising was precarious in 

 many sections because of scab and parasitic dis- 

 eases. Tuberculosis and brucellosis were spreading. 

 Anthrax and blackleg were on the increase in 

 most States. Texas fever was feared by cattle 

 raisers. The causes of most of these destructive 

 diseases were unknown, or in dispute, and live- 

 stock owners were largely defenseless. Nothing was 

 known of the extent to which a contaminated en- 

 vironment abetted transmission. 



Contagious pleuropneumonia was such a prob- 

 lem that our export cattle and sheep were denied 

 admission into Great Britain. Our pork was pro- 

 hibited in most of the markets of Europe. 



The Bureau of Animal Industry of the U.S. 



Department of Agriculture was established in 

 1884. The wording of the act indicated that the 

 first duty of the Bureau was to take charge of the 

 eradication of pleuropneumonia — disseminated by 

 contaminated air — in cooperation with authori- 

 ties in the States where the disease existed. The 

 disease was eradicated in 5 j'ears at a cost of 

 $1,509,100.72 {122, p. 2) in Federal moneys. 



D. E. Salmon, the first Chief of the Bureau of 

 Animal Industry, U.S. Department of Agricul- 

 ture, isolated Salmonella bacteria in 1885. There 

 are over 1,000 strains of these bacteria that cause 

 salmonellosis in man and animal. This infectious 

 agent, transmitted by water and food, is still very 

 much with us. 



To find the cause of tick fever was the next task 

 of the Bureau of Animal Industry. While study- 

 ing the cause and control of a cattle fever at the 

 turn of the century, Department scientists dis- 

 covered that ticks were carriers of the disease. To 

 the average citizen this might seem to be a bit 

 of routine information, but it was much more than 

 that. It was the first positive proof that arthropods 

 could carry a disease from one animal to another. 



Brucellosis organisms may contaminate the en- 

 vironment. The disease is widespread and costly ; 

 it mainly affects cattle, swine, and goats. The pre- 

 dominant clinical signs of the disease in pregnant 

 females are abortions, birth of weak calves, re- 

 tained placentas, and vaginal discharge, often 

 followed by a temporary or permanent infertility. 

 Exposure to infection takes place by ingestion of 

 contaminated feed and water. Treatment of brucel- 

 losis in cattle has not been successful. It can be 

 prevented only by sanitation, good herd manage- 

 ment, or vaccination, or any combination of them 

 that may be necessary (76). 



Cattle, poultry, swine, and other animals may 

 be affected by tuberculosis. Theobald Smith dis- 

 covered that the human tubercle bacteria are not 

 the same as bovine tubercle bacteria. Tubercle 

 bacilli usually enter the body via contaminated 

 food or water. Sometimes they are breathed di- 

 rectly into the lungs. Control of the disease in 

 cattle includes environmental sanitation and the 

 prevention of contamination of healthy animals. 

 A Federal-State program started in 1917, in which 

 cattle were tested with tuberculin, infected ani- 

 mals were killed, and an indemnity paid for 

 slaughtered animals, has successfully reduced 



