270 STATE BOARD OF AGRICULTURE. 



Part III 



H. J. STAFSETH. 



On the possibility of differentiating between infected and immune 

 animals in infectious abortion. 



INTRODUCTION. 



In studying the relation between pathogenic microorganisms and 

 their hosts we find that three different conditions may exist, namely: 

 1. presence of microparasites on the skin or mucous membranes; 2. in- 

 vasion of the tissues by the microparasites without the production of 

 any sign of disease; and 3. infection, the condition in which morbid 

 changes have resulted and symptoms of disease may be noticeable. 

 Infection with some organisms results in a short time in the appear- 

 ance of symptoms of a more or less alarming nature. In such cases 

 the disease may be checked and serious consequences prevented. Other 

 infections are insidious in their nature and no symptoms appear be- 

 fore it is too late to ward off the attack. In some of these infections 

 the first sign of abnormality is a manifestation of the actual damage done. 

 Infectious abortion comes under this class of diseases, — the dropping 

 of the fetus is the sign of disease apparent to the owner; but in infec- 

 tious abortion, we can conceive of all three of the above mentioned 

 relationships between invader and host. The calf, the nonpregnant 

 heifer and cows which are exposed to infection must surely be subject 

 to surface contamination or to tissue invasion ; while the pregnant 

 animal probably being in a stage of susceptibility may contract the 

 infection and show no outward manifestation thereof for weeks or 

 months. Then with slight warning, the final manifestation of abor- 

 tion may take place and we have gross evidence of disease. Some 

 animals which are suceptible to a certain disease may develop a re- 

 sistance but continue to harbor and to disseminate the organisms, thus 

 endangering the safety of other animals. This condition is also 

 recognized in infectious abortion. 



In an effort to overcome the confusion that has existed for a long 

 time relative to the naming of abortion disease, Giltner (1) has pre- 

 sented a defense of the term infectioU'S abortion making it appear per- 

 missible to use this term to include all the manifold manifestations 

 of the disease and its complications. 



It is well known that animals infected with abortion bacilli will 

 in most cases develop complement fixing and agglutinating antibodies, 

 but the presence of these substances does not necessarily mean that 

 an animal will expel her calf nor does the absence of such antibodies 

 mean that it will not expel her calf. In the experimental herd, at this 

 station, cows have carried normal calves to full term and yet their 

 blood showed positive reactions to the complement fixation and aggluti- 

 nation tests. On the other hand there are cows in the same herd 

 which showed the first positive test at or about the time of abortion. 

 Then again there are cows which will give positive complement fixation 

 and agglutination tests while there are good reasons to believe that 



