Worms are the most common internal parasites.

In Colorado, the pine bark beetle is a common parasite.

Many are common parasites of freshwater fish.

These protozoa are common parasites of many invertebrates including insects and polychete worms.

Mammomonogamiasis is a very rare human infection yet a common veterinary parasite.

Giardia affects humans, but is also one of the most common parasites infecting cats, dogs and birds.

In cases of onchocerciasis, another common filarial parasite, the drug is not used.

The genus Trichuris is particularly well known for being a common parasite of domestic animals and less usually humans.

It is one of the most common parasites of fish.

The most common parasites in fish are roundworms from the family Anisakidae and fish tapeworm.