There are various intestinal worms that can infect dogs and cats, with hook worms, round worms (ascarids), whip worms (mainly in dogs) and tapeworms being the main groups. Symptoms can include diarrhoea, bloody stools, weight loss, anaemia, pot belly, dry hair and/or general poor appearance. If left untreated, worm infestations can be fatal. Worms can be picked up from the mother (either in utero or via milk), from the environment (infected stools), from eating infected prey (lizard or mouse), or, in the case of tapeworms, from fleas. Worms can also be transmitted to humans.
However, if you decide to keep your dog outdoors, it is important to consider how you'll ensure it receives the appropriate amount of human contact (particularly during those cold winter months in which we'd all much rather stay snuggled inside rather than playing fetch with our pals in the cold!). An option could be to enlist the service of a dog walker. Also, if you work long hours or are sometimes forced to take overnight trips, it may be useful to consider "doggy day care" facilities to ensure that your dog receives the TLC and companionship it will need in your absence.
Puppy Roundworms can infect humans. To prevent this infection, puppies should be wormed regularly throughout their first year of life, and owners should be thorough with their own personal hygiene after having interacted with the dog. Tapeworms, Hookworms, and Whipworms can also infect dogs, and your veterinary surgeon can advise when to worm the dog.