Dear Princess Celestia

"So, we've got to inform everypony of this? And somehow expect all of them to follow with these 'guidelines' that you're going to magically know about?" Luna questioned scepticism resonating with each word, her voice sounded condescending however the look in her eyes emits the feeling of genuine concern about the potential harm they might cause to the ponies of Canterlot with a single use used word. "Well, we haven't got the time to try and construct some brilliant speech, now. Go and gather everypony, I'll join you when I'm finished here. I need to sent Twilight a scroll so she's aware of the situation" Celestia stated, then she shoos Luna towards the balcony so she could conjure herself a quill and scroll, Celestia's pushing made Luna frown only to turn around and gallop out onto the balcony before ascending into the sky with her midnight blue wings flapping through the air. "Excellent. Hopefully things are well with you, my dear Twilight." Celestia wished, then she telekinetically places the quill against the blank scroll, her eyes narrowed with consideration at the letter she could write until she took a deep breath and exhaled out the air she had inhaled before beginning to write.

Dear Princess Twilight Sparkle

My former student, my dearest friend, I have the worst news I can reveal at this moment.
Canterlot has been breached by this unknown infection, I was informed by my adviser Raven Inkwell, I hope to prevent continued infection swiftly, but I must inform somepony else
Luna is aware of the situation and has revealed that the infected ponies do not have any connection with the Dream Realm, we fear that the infection disconnects their spirits from their body
This is possibly confusing but I can explain to you, the spirit of an entity is what allows Luna to connect with them and their mind within the Realm of Dreams.
This infection, it is somehow managing to strip those it infects of their souls.
We must acquire a cure for this plague as soon as possible.
I and my sister will be arriving in Ponyville as soon as possible to bring whatever aid we can.
Please, inform me that something has gone well in Ponyville, I don't think I could handle discovering that something has happened to you.

-Sincerely, your former mentor and dearest friend
Princess Celestia

Celestia stared down at the scroll, her regel demeanour swiftly began to crumble as she began to quietly cry at the mere thought of Twilight somehow succumbing to this unknown and potentially apocalyptic plague, Celestia wipes her eyes using her wings then she took yet another deep breath. "Control yourself Celestia. Your ponies need you. Everypony needs you." Celestia spoke commandingly, she had forced her authoritarian composure to re-emerge with her eyes beginning to glimmer with royal power, then she rolled the scroll up until she could conjure one of her royal seals which she placed around the scroll to hold it closed. "Please. Take care of yourself Twilight, I don't think I could lose another member of my family..." Celestia whispered to herself, then she struck the scroll with a beam of pure solar magic causing the scroll to disburse into a wisp of golden magic, the wisp flew itself out through the balcony with Celestia rushing after it closely and desperately. "Please my dear Twilight...We need you..." Celestia pleaded out into the air, part of her was hoping that her words would touch the ears of destiny itself, somehow gifting Twilight with some kind of protection but she could already tell that the world around them was not so willing to help them.