Roundworms

Roundworms are probably the most common worms to be found in your dog's intestines.  Toxocara canis (T. canis) and Toxascaris leonina. T. canis are the two 'flavours' of this species and are more common in puppies.  These worms can be transmitted to humans.

Most puppies are born with roundworms as they can float through the placenta and into the puppy.
 

Tapeworms

Tapeworms are a serious intestinal parasite that dogs acquire by eating infected fleas or other animals infected with tapeworms or fleas that are carrying them.

Dipylidium caninum is the most common type of tapeworm.

Whilst you're unlikely to find roundworms in your dog's stools, you may find segments of tapeworms stuck to the fur around your dog's bottom or on its stools. 

These worms can be transmitted to humans.
 

Hookworms

Hookworm larvae can pass from the bitch to her puppies via her milk and can live in the soil for as long as several months.  They are very small (about 1/8 inch) but can make puppies very poorly as they drink a large amount of blood which could cause anaemia. 

These worms can be transmitted to humans.
 

Whipworms

Whipworms can be caught from food, soil, water, other animals poop and animal flesh.  Their eggs are passed from the dog via its poop to the soil where they can live for up to five years given warm moist conditions. (Start praying for freezing weather for a couple of weeks to kill them all off).

These worms can be transmitted to humans.
 

Heartworms

Heartworms are thankfully not found in the UK but are a serious risk for dogs that travel abroad. Transmitted by mosquitos, these parasites can cause serious illness and even death, so precautions should be taken for any dogs who leave the UK.
 

Lungworms

Lungworms are thankfully rare here in the UK, however, they can cause serious illness.  They require a slug or a snail as an intermediary host and are caught by dogs who have played with toys that have been left out overnight or drunk from puddles water bowls that have been left outside. 

What can you do?

As you all know I'm not a big fan of pumping "preventative" chemicals into your dog to treat parasites that they haven't got.
 

Know Thy Enemy!

The first place I would go to is Wormcount.com.  Simply sending off for one of their packs and sending them back a sample will let you know WHAT (if anything) your dog has in its system.  I do this twice a year.
 

Treatments?

I treat my dogs with Diatomaceous Earth.  This is a very fine talcum powdery substance which is actually the fossilised remains of tiny sea creatures called Diatoms.  The outer edges of each fossilised diatom are razor sharp.  This substance does no harm to us or our dogs if ingested not inhaled, but acts as lethal shrapnel to all internal parasites in the gut.  Since there is no chemical involved, the parasites are unable to develop a resistance, which is the problem with so many products on the market today. 

And remember too pick up all poop promptly.  Don't give larvae the opportunity to sneak off into the grass to infect another dog or even a child.