Skin and Fur
Checking through the fur, you will be able to spot little black fleas running for cover. Also you maybe able to find a bunch of the small black pebbles bunched together. This is the eggs. Remove the eggs by cutting them out. You can use kitten or cat flea powder to get rid of the fleas. You can also completly shave the rabbit, but that would probably make it cold and lead to snuffles.
This is probably Papillomatosis if they are around the mouth. It is a virus, and there is no cure. The rabbit should be culled and bedding burned, to keep it from having an outbreak. If the warts are not around the mouth, then it is probably nothing but a wart.
This is more common in babies who are about a week to 2 weeks old who have been nesting in their own feces and urine. The best thing to do is to keep the nestbox clean and make sure the mother isn't soiling it. I get this alot with my Fuzzy Lops, I try to keep the boxes clean. Dirty nest boxes often lead to "Nest box eye" when the babies get to the age when their eyes open, their eyes are sealed shut and are filled with pus. Their eyes should be opened carefully and cleaned with warm water, and the nest box should be cleaned out and the hay gone. Babies should be out of the nest box, no later then 2 weeks of age.
This isn't a disease, just a condition seen in older rabbits. It's sometimes confused with rabbit syphilis, and is hard to differentiate without a microscope. The fur around the bottom falls off to the skin. Urine stains are usually on the rabbit, and the strong smell of it everywhere. If the fur is still on the rabbit, it will usually be wet. This often comes from the use of urine guards. They may sound good, but often times the urine bounces back up to the cage, onto the rabbit, causing this. Other times it is a very messy rabbit who goes on himself. Very dirty cages can also cause this when they have wet floors. Antibiotic ointments seem to work well on this but the condition will keep returning if the cages aren't cleaned. If it is from the urine guards, remove them or get a new cage without them.
If left untreated, it could very well lead to disease and mass infection and maggots everywhere. (ew.)
This could be from the rabbit pulling their own fur out, for different reasons. It could be because they are hot, or in does, a false pregnancy, where they think they are pregnant and attempt to make a nest with the fur from their chest and belly.
If there are alot of rabbits in one cage they usually pull the fur off of eachother. Often times if they aren't getting enough fiber they eat their own fur and others fur to get it. It could also be a sign of Hutch burn if the remaining fur is urine soaked. Increase the fiber, keep rabbits seperated, and always keep the cages clean.