It takes a week or so though. The Herpesvirus that causes this is always around pigeons. Most are exposed and overcome Herpesvirus. The younger ones are more susceptible so this is where it shows up the most. I have seen it in one yearling, but by far, it is usually in the younger young birds.
Treatment is limited.
It is difficult to do anything for the virus per se. Supporting the nutritional needs is most important. Using an anti-trichomonas drug and an antibiotic can help as secondary infection is a problem. The main concern is to stop the spread. Most spread occurs through the water and contaminated feed.