Well, they can get fleas – here’s a very good article from a vet in Texas and why she does not recommend letting your rabbit play outside.
The Indoor Bunny
by Loretta Pantenburg, DVM
Summertree Animal & Bird Clinic
I know rabbit owners often think that their rabbits would love to be able to play outside, but is that what your bunny really wants? And, more importantly, is that what is best for your bunny? As a veterinarian, I see the sad side of what happens when pet rabbits are allowed outside. I see the rabbits with heat stress that die because their owners did not realize that rabbits do not tolerate temperatures over 80 degrees for long. Rabbits that are kept inside in the cool air conditioning, then put outside to “play” in temperatures they are not accustomed to, often get heat stress, or worse, heat stroke. The few rabbits that survive heatstroke must be monitored for days afterwards for signs of kidney failure.
Sometimes when rabbits are let outside the neighborhood dog or cat gets in the yard, resulting in injuries or heat stress from being chased, or bite wounds from the dog or cat. Anything that frightens a rabbit (ie: dog, cat, loud noises, etc.) can result in the bunny kicking and hurting, or even possibly breaking, its back.
What other problems do we see when rabbits are kept outside? Rabbits are very good at escaping from very small gaps in a fence and they almost never survive to return home. External parasites are a big problem, especially in Texas and other warm states. The most common parasites we see are fleas and mites. These can lead to skin irritation and, in severe cases, significant blood loss or anemia. Fleas are a host for tapeworms.
We also see fly larvae (Cuterebra) and tapeworm infestation. This begins as eggs or larvae in the soil which then migrates through the skin to cause local abscesses and infection. In severe cases, brain or neurological damage may occur. Treatment often requires surgery or prolonged antibiotic therapy. Fly bites may carry pox virus, which can cause lesions that occlude the rabbits sight or breathing and make them vulnerable to infection. Shope’s fibroma is a tumor caused by a virus, carried by vectors (like flies), that is seen in rabbits.
By far the most common, and worst, thing we see is the bunny that comes in with maggots in its skin. This is usually around the rectal area, secondary to urine or feces getting on the fur, and flies laying eggs on the area. The result is usually a very sick rabbit with severe skin wounds and infection. Treatment usually involves anesthetizing the rabbit, removing the maggots, cleaning and debriding the wounds, treating with antibiotics, and LOTS of follow-up care by both the owner and the veterinarian.
So what do I, as a veterinarian, recommend? Try setting up a play area inside your house. Include a variety of play toys, items to chew on, and ideally a companion rabbit. Provide a rabbit-safe environment, free from the worries of heat stress, injury, trauma, and parasites, and your bunny won’t miss the outside. He will also enjoy a longer, healthier, happier life.
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Just as he should be LOL.
Mine aren’t allowed tilw e get a house though… too many dogs here, and who knows what they use on the grass here 
