Fleas and ticks are not the only parasites that plague our small dogs. These external bloodsuckers can sometimes pass along internal parasites, like worms or protozoa. Fleas carry tapeworm; ticks carry protozoal diseases, such as when these bugs take a bite. If you live in an area where mosquitoes are present, you should use a monthly heartworm medication, such as Heartguard, or regularly apply a wide-spectrum topical product like Revolution.