I am not a professional.
Links are provided below.
If you have horses, and you suspect any of the following, do not rely on myself or the Internet. Call your veterinarian immediately and let a paid professional advise you. Also, please realize that most of what you read and see on the Internet are "worst case" scenarios.
The article below, posted by K-State has one of the best pictures that I have seen online of a "typical example" of pigeon fever. It also gives a visual explanation of why it is called "pigeon fever". Noting again that it has nothing to do with pigeons or birds.
Also, please note and take care when reading to understand the relation of the disease to flies. The best article explaining the relation is by Texas A & M. Dr. Amy Swinford, head of diagnostic bacteriology for the Texas Veterinary Medical Diagnostic Laboratory, says, "Flies can serve as mechanical vectors to transmit the organism from the environment to horses."
After confirming with my own veterinarian office, flies are used as the "machine" to "transport" to horses. You can think of it this way, mosquitoes carry the West Nile Virus, then by biting can transmit the disease. In the case of pigeon fever, when a horse has an abscess that opens or is lanced, as with any open wound, flies will be attracted to the site. With the disease on the fly, they can then go to another horse and either by collecting on eyes, nose or a possible wound or abrasion, transfer the disease there.
This is one blessing in having this occur this time of year. There are no flies at this time. In summer or fall, it becomes important to use a wound dressing that repels flies on a pigeon fever abscess, such as SWAT, and to also take measures of fly control to protect other horses.
Pigeon fever: Confirmed cases in Texas horses have soared in six years, TVMDL data shows
Pigeon Fever 2012: an emerging disease in Kansas
Pigeon Fever in Horses-A re-emerging disease
Horse Owners Urged to Guard Against Pigeon Fever
Hope this is helpful.