Skin scrapes are taken to identify both mange mites (which burrow and lay eggs beneath the skin) and some fungal infections. They can however show a negative result despite the fact there is actually something present.
Where the skin scrape has been taken, you can bathe the area with boiled and cooled salt water, or use diluted F10 disinfectant (these is also anti-fiungal) or dilute hibiscrub.
I would not use savlon unless you are intending to use the dry antiseptic spray (which is povidine iodine).
A topical spot on is not always suitably effective for mange mites (although it will work for hay mites and lice which live on the surface of the skin). If a spot-on is used, it should be a prescription strength variety (eg Xeno) and not an over-the-counter low dose treatment which may not be strong enough to deal with an active infection. A course of 3 injections of ivermectin spaced 10-14 days apart to break the mite life cycle would be more effective for mange mites than a topical treatment. Some insects are now developing resistance to ivermectin and for a persistent case of mites, doramectin injections would be a suitable alternative.
It is useful to bathe a piggie 48 hours after a mite treatment to get rid of the insect debris which can be irritating. At this point, many opt to use a fungal treatment (Imaverol) as part of the bathing regime where diluted imaverol is syringed through the fur and left to dry. It can also be applied around the eyes with a cotton bud. After 3 rounds of mite treatment/bathing and dipping/syringing through imaverol, there should be a full recovery.
The above does not apply to piggies who have serious wounds from self-mutilation as a result of a severe mange mite infection - injections combined with spraying open wounds with dilute F10 are a better option (see my posts on this thread
https://www.theguineapigforum.co.uk/threads/2-more-dying-piggies.122408/
Finally hygiene is also critical to eradicating a fungal or mite infection. Wear surgical gloves when handling and be careful about touching your skin as some fungal infections can be transferred to humans.
The cages/bedding/hideys etc need to be regularly cleaned/disinfected/treated.
For mite infections:
Fabrics (duvets, towels, fleeces, cosies etc) should be washed at 60degC or above with a biologcal detergent and if possible iron them afterwards.
Hard surfaces including plastic cages can be treated with eg Johnsons insecticidal cage spray (but be aware they contain permethrins - cats should be kept away and the spray should not be breathed in by any animal including yourself - best done outside). Leave for 30mins and then wash off thoroughly with a good animal disinfectant such as F10.
Carpets should be vacuumed thoroughly
Bin anything you can't clean that has been in contact with the guinea pigs.
In addition - For fungal infections
Add some type of peroxide to the wash cycle (eg Vanish)
F10 disinfectant can be used to clean hard surfaces including cages etc. It is the only disinfectant I have found where the manufacturers show efficacy against ringworm spores.
HTH
x
Edit - cross-posted with Wiebke!