Lice are passed on by one of two manners. Either by direct contact or indirect contact with someone who is infected with lice.
The chances of coming in contact with lice in the wilderness is exceedingly remote. A camp site that has been abandoned for several days would be free of lice if it was actually occupied by an infested person.
First of all, there is no need to spray your home and belongings with potentially dangerous insecticides. Lice are known as “obligate parasites,” meaning they don’t survive very long without their human host. They need us to live, and they die within 24 to 48 hours after removal from a human host. - How to Keep Lice from Spreading—and Coming Back!
Here is how people actually get lice:
Head lice move by crawling; they cannot hop or fly. Head lice are spread by direct contact with the hair of an infested person. Anyone who comes in head-to-head contact with someone who already has head lice is at greatest risk. Spread by contact with clothing (such as hats, scarves, coats) or other personal items (such as combs, brushes, or towels) used by an infested person is uncommon. Personal hygiene or cleanliness in the home or school has nothing to do with getting head lice. - Who is at risk for getting head lice?
If one really encounters lice in the great outdoors, either someone in the group brought the infestation with them or one is camping (very remote possibility) in camp that had been infested by others within 48 hours of the infested person leaving.
Basically what I am saying is that someone in a hiking group brought the lice into the wilderness with them if an infestation occurred at all.
Update: My same thought still holds for body lice.
Without a constant source of blood, the lice perish within 2-5 days. In hot weather, when several layers of infested clothing are worn, the lice may move to an outer layer where the temperature is cooler. Lice are very rarely seen crawling on the outside of infested clothes, if they are visible it is an indication the individual is heavily infested. Normally body lice are sensitive to light and if disturbed will quickly move to a seam or crease for cover. - Department of Medical Entomology
Body lice too are transmitted by contact:
Body lice are spread through direct physical contact with a person who has body lice or through contact with articles such as clothing, beds, bed linens, or towels that have been in contact with an infested person. In the United States, actual infestation with body lice tends to occur only in persons, such as homeless, transient persons, who do not have access to regular (at least weekly) bathing and changes of clean clothes, such as homeless, transient persons. - How are body lice spread?
In a truly wild area, I believe such an infestation would not be found, regardless of what type of lice is involved.