The most recognizable parasites are external freeloaders such as ticks and fleas, although some culprits can't be detected with the naked eye, like intestinal worms, an example of internal parasites.
Your pet can be allergic to anything from pollen to an insect bite or even a type of protein. Signs and symptoms may vary from individual to individual but usually range from mild to severe. Some allergies can be fatal if not given medical attention in time.
Depending on what you intend on doing with your new pal, you can either go the rescue or registered breeder route. Please do not support pet shops or commercial mills - the animals live in misery and you are not helping by giving them your money!
If you want to get into protection sports or compete seriously in any canine sport, then your best bet is to start researching dog breeds that excels in your chosen sport. Once you've found your match, the next step is to find an ethical breeder with bloodlines proven to produce competitive dogs.