If the infection passes through the placenta to the fetus, plagues or crusts of fungus will develop on the skin of the fetus. Diagnosis is made by culturing the organism from aborted tissues. To prevent mycotic abortions, do not abruptly change the diet of pregnant cattle from all forage to one that includes a large amount of grain, and avoid moldy feeds when possible. The bacterium, Listeria monocytogenes , is widespread in nature. It is often associated with a dirty environment because it is found in animal, bird and human stool.
Infection occurs primarily by eating or inhaling the organism.
The infected cow may have a brief fever and depression but abortion will only follow after a stressful event, so a long time may pass before an abortion occurs. After L. monocytogenes enters the body, it travels through the blood stream to the reproductive tract. Once there, it infects the placenta. If large numbers of L. monocytogenes bacteria are present, they may invade the fetus and cause it to die. Abortion usually follows within two to three days.