Hookworms:

Hookworms can infect pets and/or humans in a number of ways: 
Ingesting larvae from contaminated water or soil;
Eating an infected host (mouse, vole, rabbit etc.);
Via larvae penetrating the skin;
Through larvae infecting fetuses or through milk.

Hookworms in Pets
In pets, hookworms feed on the host’s blood and can quickly cause anemia.  The gums will be pale, and vomiting/diarrhea can occur.  As the larvae migrate through the lungs, the pet can even develop pneumonia.  Animals may become emaciated and can eventually die from the infection.

Hookworms in Humans
In people, hookworm larvae penetrate the skin (usually through bare feet).  The larvae then migrate, causing a disease known as “cutaneous larva migrans” or “creeping eruption.”   “Red line” lesions appear on the skin, causing severe itching.  Usually the larvae die in a few weeks, and the condition disappears. 


Roundworms:
Roundworms can enter a host in a number of ways
Eating an infected host.  For example, a mouse ingests the eggs, which hatch and then migrate through the tissue of the host-mouse.  If a carnivore (cat or dog) then eats the mouse, the larvae are released into the digestive system of the mouse, where they take up residency in the intestine.
Ingesting eggs.  A dog eats the eggs, which then hatch and the larvae enter the wall of the small intestine.  The larvae then migrate through the circulatory system, going either to the respiratory system or to other organs. 
In utero.  A pregnant dog infected with Roundworms can pass them to her puppies in utero.  (Note:  Cats cannot pass Roundworms in utero, but can pass them via nursing.)
Via mother’s milk.  Larvae can also invade female mammary tissues and enter the young during nursing. 

Diseases Caused by Roundworms in Pets
    In the intestine, Roundworms steal nutrients, interfere with digestion, and can damage the lining of the intestine.  In young puppies, these parasites can migrate to the lungs and cause pneumonia.