I wouldn't worry too much about the hay right now as long as you blitz out the cage and wash anything that might be carrying eggs. Personally I just get Pets at Home hay because a guy in the shop once told me that it's probably sprayed at some point because it's mass produced and pretty cheap! I'm happy with that. I had an incident with local organic farm hay where some little harmless things crawled out and were all over my downstairs so we had to have a bit of a purge and for my indoor pigs it just wasn't worth the risk again. The pigs were fine, but little beetles were in all my cupboards!
It's thought that quite a few pigs just carry a few mites here and there but for some reason they can occasionally take hold and cause problems. I've found it's kind of ongoing - a bit like cats/dogs and occasionally getting them flea treated. Every time a new pig is introduced here there is a risk of them bringing something in - they don't always of course but sometimes they have. But I've gotten used to looking for the signs of scratching and shedding now. They all shed some, and when it warms up in summer or the heating comes on in winter they all shed more, but the shedding from a piggy suffering with a mite infestation is something else. You notice more and more hair everywhere, sudden bouts of intense scratching, sensitive skin, bald patches and just general not-very-happy looking. But if you can treat your 2 boys effectively you might never have this problem again!
We get prescribed the 450 and it comes in boxes like this
View attachment 207064 and a single 'pipette' looks like this
View attachment 207065 a tiny tube: and a box contains 6 pipettes but the vet might not always prescribe by the boxful. Going by my previous vet experiences your vet should have ideally given you 3 pipettes for Rusty and 3 pipettes for Pete (if he knew there was another pig living in contact with him). Some vets follow the rule that if a piggy doesn't have symptoms there's no need to treat but that's a bit like finding your kid has nits and assuming that the rest of the class doesn't so usually a more senior vet at the practice will have a word. The companion can harbour mites and the cycle starts again. If your friend is happy to phone the vet and explain that mites were diagnosed, there are two pigs, but only one pipette was given they should hand over more xeno. You will pay for each tube but you shouldn't have to pay for another consultation as it was down to them!
If it helps, here is a link to the product data sheet
https://www.dechra.co.uk/Files/Files/ProductDownloads/uk/Xeno450_Datasheet_UKIE.pdf and if you look on page 2 you will see it says "For the treatment of an existing infestation, repeat doses are required two weeks and four weeks after the initial application".
Use that tube on Rusty anyway if you haven't already, because he's obviously suffering at the moment and it
will clear any mites he has. The only thing is the symptoms will reappear a few weeks down the line as any eggs hatch and grow. If Pete can't be treated now because you are going away there's not too much point treating him more than a few days later. So if you are going to be a week or 10 days away just start from scratch when you get back. But if your friend can prise at least one more tube out of the vet and dob it onto Pete's skin they should because then you can just tackle the repeat doses in 2 weeks - you have a bit of time. Don't rub it through the fur - you are trying to dob it onto the skin at the roots and it is then absorbed through the skin and goes all round the system - this is why it depends on body weight. Good luck - your friend is welcome to either join the forum or (if it's allowed) log on as you if they need any support.
