From what I've seen on TV, Alberta where I live, is hardly like Afghanistan. But it is dry here and often dusty in summer. I also use my camera well below freezing sometimes...as recently. I take care of my stuff, but not scared to take it out under some fairly harsh conditions.
For sure, changing lenses in a sandstorm would not be a good plan. But under more"everyday" conditions, I see nothing wrong with changing lenses in the field. Obviously some common sense is necessary. I'd be more concerned about using a zoom lens in a dust storm and pulling dust into the lens guts when zooming in and out.
I'd take my A77 there in a heartbeat ... not think twice. My KM 7D, A700 and A77 combined have been to several countries including Northern China and Inner Mongolia (IMAR, part of China), Mexico, Chile, Cuba, Belize, Arizona, Kauai and the Big Island. In 2006, I took my KM 7D with only one lens (Tamron 24-135mm) on a tour in Mexico. I knew conditions would be dusty...we were in mountainous, rural areas. I never had to change lenses and that was good. Mainly I took just one lens because we had a severe weight restriction on the trip. I longed for a second lens on occasion. I was the "trip" photo guy and took a couple of thousand photos in 5 days...was a hoot.
Whatever you decide, good luck!