Animal Diseases

• Heartworm Society
  Everything you ever wanted to know about heartworm disease can be found here!
• USDA Animal and Plant Health Inspection Service 
  The USDA maintains this website with information on a variety of animal health related topics, including the latest news on such things as Mad Cow Diseases, foot and mouth disease, and many other things.
• West Nile Virus
  This site is maintained by the Centers for Disease Control in Atlanta, and has the latest information on the spread of West Nile Virus in the US, as well as information on disease transmission, symptoms, etc.
• American Veterinary Medical Association
  This site is a good starting point to learn more about a variety of topics, including feline injection-site sarcomas and the latest subjects in veterinary medicine.
• Companion Animal Parasite Council
  Guidelines for controlling parasites in dogs and cats.