Equine Venereal Disease
Causes of Equine Coital Exanthema
This disease which affects the external genitalia is caused by the Equine Herpes 3 virus. Being that it is a virus, this is a disease that will be with the horse for all its life. Equine Coital exanthema is believed to only be transmitted during the acute phase of the diease through serous fluid from the blisters.
Transmission of EHV-3
This virus is transmitted through sexual intercourse, breeding tools, handlers, etc.
Equine Coital Exantema: This is seen in mares and stallions with the appearance of acute small lesions, no bigger than 2mm in diameter. They are seen around the vulva in mares, and on the sheath in stallions. The small bumps will blister and then rupture leaving raw, ulcerated, painful sores.. While the majority of the symptoms are external studies show that the presence of the virus can cause small and large plaque variants in tissues. 
Contagious Equine Metritis: Acute symptoms include acyine inflammtion of the uterus causes an obvious think, milky, mucioud vulvar discharge 10 to 14 days after live, covering a stallion. Chronis symptoms include milder uterine inflammtion that will cause less obvious vulvar discharge and at this time the infection may be more difficult to eliminate. Carrier mares can occur once the bacteria become stable within the reproductive tract. There mares can be asymptomatic for months and still remain infectious 
The First Case of CEM was diagnosed in England in 1977.
It has infected horses in 26 Countries:
Austria, Belgium, Bosnia-Heregovina, Croatia, the Czech Republic, Denmark, Finland, France, Germany, Great Britiain, Greece, Guinea-Bissau, Ireland, Italy, Japan, Luxembourg, the former Yugoslavian Republic of Macedonia, Montenegro, the Netherlands, Norway, Serbis, the Slovak Republic, Slovenia, Sweden, Switerland, and the United States.
Animal and Plant Health Inspection Service. (2005, June). Contagious Equine Metritis. Retrieved from United Ststes Department of Agriculture Animal and Plant Health Inspection Service: http://www.aphis.usda.gov/publications/animal_health/content/printable_version/fs_ahcem.pdf
Michael Ball, D. (1997, September 1). Equine Herpes Virus. Retrieved December 2, 2009, from The Horse: http://www.thehorse.com/Print.aspx?ID=668
Zoologix. (n.d.). Equine herpesvisur type III (EHV-3). Retrieved December 10, 2009, from Zoologix: http://www.zoologix.com/horse/Datasheets/EquineHerpesvirusTypeIII.htm