Protozoal Infections
December, 1997
Protozoa are microscopic organisms that consist of a single
cell, but are larger than bacteria. Free-living protozoa, like
amoebas, are found in ponds and rivers and rarely cause disease
in animals and humans. Two kinds of protozoan parasites, giardia
and coccidia, have the potential to cause disease, and occur in
animals nearly as commonly as the intestinal worms.
Giardiasis is contracted by ingestion of feces or contact with an
environment or body of water contaminated with feces from an
animal with the disease. Signs, if they occur, may show up in as
little as 5-7 days, but the organism may not be detected in a
stool sample for several weeks. Signs usually include chronic or
intermittent diarrhea, poor appetite and weight loss. Diagnosis
is usually accomplished by identifying the organism in stool.
This can be difficult, due to the fact that they are not excreted
in every stool produced during the disease, even when a severe
diarrhea is present. Also, the typical sugar flotation solution
used most commonly to identify intestinal worms can distort
giardia, and other tests on the stool may be recommended for
positive identification. Treatment is usually accomplished with
the drug Metronidazole (Flagyl), but the disease is also
responsive to a broad spectrum wormer, Albendazole (Valbazen).
Good sanitation practices are also important to help prevent
recurrence. Giardia is apparently not too selective about the
species it may inhabit, and we must always consider the potential
for spread from animals to humans.
Coccidiosis, on the other hand, is more species specific, so that
each species of coccidia usually cause disease in only one
species of animal. Similar to giardia, infection is usually
achieved by a fecal-oral route. However, coccidia have the
potential to form cysts in the host animal’s intestines and
other organs, sometimes animals of different species. This means
that small mammals, including rabbits, may act as carriers of
canine coccidia. As with giardia, coccidia infection can exist
with no clinical signs. Disease signs are most common in young
animals, animals with other illness, or animals that are
immunosuppressed or stressed. Typical signs are diarrhea, poor
appetite and weight loss. Diagnosis is usually reliable with a
routine fecal floatation exam. Coccidiosis is usually treated
with a Sulfa drug and may require 2-3 weeks of therapy.
As previously mentioned, these organisms are usually species
specific. A few notable exceptions to this rule are
Cryptosporidium and Toxoplasmosis. Cryptosporidium causes
diarrhea, is rare in dogs and can be spread directly to people.
Toxoplasmosis is a concern mostly to pregnant women and can be
picked up by contact with cat feces and uncooked meats.