Other bacteria that are found around horses and in the soil that are able to cause infection when transmitted during sexual intercourse include Pseudomonas, Staphylococci, E.coli and Klebsiella. One bacterium that is not usually a resident in horses of either sex is Hemophilus equigenitalis. CEM is very important because it is highly contagious and it is difficult to identify mares and stallions that have the disease but are not showing symptoms. These asymptomatic horses pass the infection on to their partners. Most CEM mares are unable to conceive and if they do conceive they usually abort.
Symptoms usually appear within three to five days after exposure in mares.
The signs include large amounts to gray to creamy discharge that mats the hindquarters and tail. However, some mares show no signs or symptoms of the disease even though they carry the bacteria and can pass it along. These mares are asymptomatic carriers. A stallion who carries Hemophilus equigenitalis generally does not show any signs of infection. The first signs that a stallion is infected usually are a high rate of reproductive failure in mares that the stallion services and a large number of mares that show signs of infection after being serviced.