What is Giardiasis?
Giardia lamblia is a protozoan (single-celled organism) parasite which is found in the small intestine of vertebrates including mammals. Infection with Giardia lamblia causes giardiasis.
Giardia causes severe diarrhea, dehydration and stomach cramps.
How do cats become infected with Giardia?
The most likely transmission in cats is direct animal to animal (fecal-oral route). Cats can also become infected by drinking water containing the infective cysts. Once inside the intestine the cyst opens releasing two trophozoites.
There are two stages to the life cycle. Trophozoites are the active motile (swimming) form and it is at this stage that it lives in the intestines feeding and reproducing. The trophozoites have flagella, which are long hair like structures which enables toe protozoa to move around. During the feeding stage, the parasite replicates in the small intestine by binary fission (this is the asexual reproductive process where one cell divides into two cells.
The trophozoites move towards the colon where they produce a cyst wall. The trophozoite within the cyst divides once, and this mature cyst now contains two trophozoites. This cyst is carried away by the passing fecal stream and leaves the body.  These cysts are extremely hardy and can survive for long periods in water.
What are the symptoms of Giardia in cats?
The parasite has a one to two week incubation period. Most cats are asymptomatic, although they may keep passing on cysts for months or years. Clinical signs are most likely to be seen in younger animals from multi-cat households/environments.
If large numbers of trophozoites develop the cat will develop symptoms which include;
- Foul smelling stools, often yellowish, foamy/frothy.
- Weight loss
- Abdominal distension
- Abdominal pain
How is Giardia diagnosed?
Fecal flotation (zinc sulfate solution) may be used to detect cysts. Cysts may not be present in the stool of a cat with diarrhea.
Fecal smears may detect the active trophozoites. These are more likely to be seen moving around in watery stools and cysts are more commonly found in firm stools. A negative sample doesn't necessarily rule out giardiasis. Three stool samples should be studied over a period of 7 - 10 days before a definite diagnosis is made.
ELIZA is another method of testing for giardiasis. This may either be performed in your veterinarian's office of sent off to a laboratory for testing.
How is giardiasis in cats treated?
There are a number of medications which may be used to treat giardia in cats, however no drugs been approved for treatment of giardia in cats in the USA.
|Metronidazole||Flagyl||Antibiotic which is most commonly used to treat giardiasis in cats. This medication also has the benefit of having anti inflammatory properties also. This medication is suspected of being teratogenic (can increase the risks of congenital malformation) so should not be used in pregnant cats. Side effects may include loss of appetite and hypersalivation, presumably due to the bitter taste of this medication.||15-25mg/kg|
|Fenbendazole||Drontal Plus, Panacur||An
anthelmintic (antiparasitic drug to kill worms), this may be used
particularly if concurrent infection with parasitic worms is suspected.
Metronidazole and Fenbendazole may be used in conjunction with each other.
|Furazolidone||Furoxone||This is another antibiotic and antiprotozoal which may be used to treat giardiasis in cats. This medication can cause vomiting and diarrhea and should not be used in pregnant cats.||4mg/kg twice daily|
Your veterinarian will prescribe whichever drug they feel is best to treat giardiasis in your cat.
Additional supportive care may also be required such as fluids to treat dehydration and nutritional support.
Can I catch giardiasis from my cat?
This answer is still not entirely known so it is safe to err on the side of caution and presume it is possible to catch giardiasis from cats and practice strict hygiene.
 The Cornell Book of Cats (page 311).