Although there are numerous parasites that could affect your dog, when worming we focus on the main culprits.  All are easily avoided using all wormers, Heartwormers, Flea and tick treatments, ear drops, visits to your vet plus diligent care.  If your dog is infected with one or more, they may become very sick.  In my experience prevention is much better than cure. 

Heartworms 

Heartworms are parasites that live in the right side of your dog's heart and in the large blood vessels connected to the heart and lungs.  Mosquitos carry the parasite from dog to dog and all dogs are equally susceptible to heartwom.  The first signs that your dog may be affected are:  a raspy cough, decreases appetite and weight loss, laziness 

http://www.heartwormsociety.org/canine.htm. 

Tapeworms 

Tapeworms are flat worms that consist of several segments that break off to resemble grains of rice.  They attach themselves to your dog's small intestine.  Fleas transmit this worm and all dogs are equally susceptible.  The first signs that your dog may be affected are:  visible segments if the dog passes them, dragging (scooting) it's rear end along the ground and occasionally severe weight loss. 

Whipworms 

Whipworms are whip shaped parasites that live in your dog's large intestine.  Your dog may become infected by eating food contaminated with whipworm eggs or by picking the eggs up from the soil.  It is mainly a problem in dogs over the age of three months.  Symptoms include:  bloody diarrhoea, weight loss and in severe cases seizures. 

http://www.cedarnet.org/taylrvet/whipworms.html 

Hookworms 

Hookworms are parasites that live in the small intestine.  It can be picked up through the soil or can be passed onto a puppy through its mother.  Rodents may also pass the parasite onto dogs.  It mainly affects puppies but all dogs a susceptible.  Signs that your dog may have hookworm include:  pale gums, diarrhoea, weakness, weight loss and itching. 

Roundworm 

Roundworm lives inside the small intestine and feed off digested food.  The most common form of infestation is through the mother to her unborn puppies.  Very young puppies are commonly affected.  Symptoms include:  diarrhoea, unhealthy coat, colicky pain, loss of appetite and a pot belly appearance. 

Ear Mites 

Ear mites are tiny organisms that are barely visible to the naked eye.  They live on the surface of the ear canal but sometimes affect the face or tail.  They are highly contagious and can be caught by merely socialising with other animals that are affected.  All dogs are susceptible and symptoms may include:  vigorous shaking of the head, rubbing head along the ground and scratching at the ear. 

http://www.vetinfo.com/dearmites.html 

http://www.peteducation.com/article.cfm?cls=2&cat=1589&articleid=734 

Paralysis Tick 

The paralysis tick is found mainly along Australia's east coast but are slowly working their way inland.  They attach themselves to the dog and as they feed, inject a powerful neurotoxin into the dog.  If not detected and treated immediately the dog will die.  Dogs can pick the ticks up easily from anywhere (trees, bushes, grass etc) and once the tick has attached itself it will stay on the dog until it has had its fill and then will fall off.  All dogs are equally susceptible and symptoms may be:  vomiting, excessive drooling, change in breathing, loss of voice and paralysis starting at hindquarters and working up the dog. 

http://www.zip.com.au/~suthvet/ticks.htm 

Fleas 

Fleas are tiny parasites that live on your dog.  They reproduce at a rapid rate and have long legs which allow them to jump great distances.  Fleas are found everywhere in the environment and will easily jump from animal to animal including humans.  All dogs are equally susceptible.  You can tell easily if your dog has fleas as they are easily visible with the human eye.   If you cannot see a flea but you do see small black dirt like substance changes are, fleas are there.  In severe cases of flea infestation dogs can suffer from hair loss and anaemia. 

http://www.k9web.com/dog-faqs/fleas-ticks.html