Nobody can guarantee to you that you have, or have no parasites.
Read recommended messages in this forum to get some insight.

For your wife, few links:

Alphabetical Listing of parasitic animals in humans:
http://www.cdc.gov/ncidod/dpd/parasites/listing.htm
Centers for Disease Control (CDC.gov)

Excerpts:
http://www.biosci.ohio-state.edu/~parasite/ascaris.html
It is estimated that 25% of the world's population is infected with Ascaris Lumbricoides.
25% = more then 1.5 billion people in the world
Source: Dr. P.W. Pappas, Ohio State University


http://www.cdc.gov/ncidod/dpd/parasites/ascaris/factsht_ascaris.htm
What is an Ascaris infection?
An ascarid is a worm that lives in the small intestine. Infection with ascarids is called ascariasis (ass-kuh-rye-uh-sis). Adult female worms can grow over 12 inches in length, adult males are smaller. Adult worms can live 1 to 2 years.


Pinworms:
http://www.biosci.ohio-state.edu/~parasite/enterobius.html
It is estimated that pinworms infect more than 400,000,000 people throughout the world (10% of humans), and in many areas of the world (e.g., North America and Europe) it is the most common nematode parasite of humans. On a world-wide basis, however, Ascaris lumbricoides ranks #1 infecting more than 1,000,000,000 people (25% of humans).

Image of pinworms around anus:
http://www.biosci.ohio-state.edu/~parasite/pinworms_anus.html


Giardia lamblia (giardiasis)
http://www.biosci.ohio-state.edu/~parasite/giardia.html

One person can pass millions of G. lamblia cysts each day, and most infections probably result from ingestion of water or food contaminated with human sewage. Open sewers in city streets and contamination of drinking water with this sewage undoubtedly results in many infections. However, in some countries the use of human fecal material ("night soil") as a fertilizer is also an important source of infection. Many cases of "traveler's diarrhea" are caused by Giardia. Even in developed countries potable water can be contaminated with small amounts of sewage, especially when septic systems are built too close to wells. Thus, it is not surprising that G. lamblia is found throughout the world.

Every year many people return from camping trips to find that they are suffering from giardiasis, but the source of these infections remains uncertain. Some authorities believe that Giardia infects a number animals other than humans, particularly beavers, and that campers contract giardiasis from drinking stream water contaminated with cysts from beavers (hence, "beaver fever"). Other authorities, however, believe that these cases result from streams contaminated with human feces. Although mountain streams may appear to be "sparkling clean," some camper upstream may be using your drinking water as a toilet! Thus, no matter what it looks like, stream water should be treated before drinking. Boiling will kill Giardia cysts, and there are commercially available filters that will remove the cysts from water.


http://www.biosci.ohio-state.edu/~parasite/toxoplasma.html
Toxoplasma gondii has very low host specificity, and it will probably infect almost any mammal.
In most humans infected with Toxoplasma, the disease is asymptomatic. However, under some conditions, toxoplasmosis can cause serious pathology, including hepatitis, pneumonia, blindness, and severe neurological disorders. This is especially true in individuals whose immune systems are compromised (e.g., AIDS patients). Toxoplasmosis can also be transmitted transplacentally resulting in a spontaneous abortion, a still born, or a child that is severely handicapped mentally and/or physically.

http://www.cdc.gov/ncidod/dpd/parasites