Cat Parasites - Giardia


Cat Parasites - Giardia

Giardia contamination in well water

Question: Hi, I do not know if this is the type of question to ask, but if not maybe you can direct me to the right place. Our water has giardia in it. It doesn't bother us too much, but it does the cats. Especially the kittens. We had a filtration system installed. My question is, I have to wash the water bowls etc in tap water. Am I contaminating the drinking water by doing this? I either let the bowls air dry or towel dry them before filling with filtered water. Thanks!

Answer: Julie- Giardia contamination of well water is unusual but can occur in several circumstances - most commonly after flooding but also in situations in which the well is subject to fecal contamination for other reasons, like heavy exposure to livestock contamination, poor location (low spots, bottom of a hill) or if the well is shallow. Deeper wells are an unlikely source of contamination. Giardia contamination of public water supplies is uncommon but definitely occurs. Filtration can control this but the filter must be a 1 micron pore size or designated as capable of removing cysts by NSF standards. Most home filtration systems have larger pore sizes than this. A good site for information on this: In multiple cat households the most common cause for recurrent giardia infection is the presence of one or more carriers -- cats who may not display symptoms but are infected and shedding giardia cysts. It is very hard to clear giardia in this situation. Giardia organisms do require some moisture to survive and are susceptible to dying simply by air drying. They will die if exposed to temperatures above 130 degrees Fahrenheit, so using a dishwasher will usually kill them, as well. Disinfectants containing quaternary ammonium are considered to be the best disinfectants for controlling giardia but chlorine bleach diluted 1:32 or less with water are also reported to be effective (Zimmer, et. al, 1988). The recommendations for eliminating giardia from a multiple cat household are somewhat forbidding. It is considered to be best to treat all the cats with fenbendazole (Panacur Rx) at 50mg/kg once a day for 3 days. Then move the cats to an area that has been cleaned thoroughly and disinfected with quaternary ammonium disinfectant or steam cleaned. Then steam clean or disinfect the part of the house the cats were previously living in. Bathe all the cats, clipping long haired cats if necessary to ensure removal of all fecal material from their hair. It is supposed to be safe to disinfect cats with the quaternary ammonium disinfectant (Barr et. al., May 1994 Compenium on Continuing Education) but I have to admit that I wouldn't want to recommend that to most of my clients. Put the cats back into the original area several days after it is cleaned and allowed to dry thoroughly. Administer fenbendazole again. Repeat the process until the infection is permanently cleared from the household. If cats can become re-exposed from a contaminated water source it may be impossible to completely control giardia infection. You might want to consider the vaccination for giardia in that circumstance (cuts down on shedding, decreases diarrhea, doesn't prevent infection in most cats) and/or routine use of fenbendazole on a schedule that seems reasonable to you and your vet. Any new cats should be treated with fenbendazole prior to their introduction into the household. The briefer answer to your question is that if you clean the bowls well then really air dry them thoroughly, they should not be a contamination source. If you want to be extra careful, pour boiling water in them, wash them in the dishwasher and/or use disinfectants on them. Unless there is something really strange going on in your water system, there should be no way that washing the bowls contaminants the rest of the household water supply --- although it theoretically might expose you to infection directly and the sink could be contaminated and serve as a method of spreading the infection. I hope this is helpful. Mike Richards, DVM 4/6/2002

Giardia, L-Lysine and Metronidazole

Question: Dear Dr. Richards,

I am a new subscriber to your web site, which I found extremely useful, and which has opened my eyes on many things that neither me nor our vet knew! I have two cats. Both of them (obviously) have herpes virus, but only one of them (5 months old) is on L-Lysine (great results, I should say: his awful conjunctivitis has disappeared completely, although I am not sure for how long - he is still at the end of his treatment!). The other cat (the elder one - 3 years old) has inflammatory bowl disease and takes prednisone, that's why our ophthalmologist did not suggest taking L-Lysine for this elder cat as his immune system is already down. To add to this "pretty" bouquet of diseases, the elder cat recently was also diagnosed with Giardia (although both cats are strictly indoor ones) and is going to be on metronidazole. Since there's a possibility that the younger cat also has Giardia, our vet has recommended to give metronidazole to him too. My question is: what do you think about treating a cat with both medications - L-Lysine and metronidazole? Is it OK to take both at the same time? Is it really necessary to treat him with metronidazole (he seems to be very healthy with a strong immune system, and unlike the other cat, has no diarrhea at all)? Thank you very much for your time, Corinne

Answer: Corinne-

L-lysine is an amino acid, one of the building blocks of protein. It does not have much effect on the cat's body. It works for herpes virus because the virus is an RNA based virus. Due to this, the virus has to fool the body into making DNA. L-lysine interferes with this process because it resembles the amino acid the body really needs for the conversion. This interferes with virus reproduction and in chronic cases of herpes virus it helps to inhibit the virus and allow the body to deal with it. So it really doesn't have much effect on the immune system and it doesn't interfere with other medications much. It is generally safe to use this amino acid for treatment of herpes virus while using other medications or while treating other conditions.

Lots of cats with giardia have no clinical signs. Most of them never get treated for the illness. But they can be carriers and since your older cat appears to be susceptible to the giardia organism it is probably best to treat both of them to try to prevent recurrences.

Hope this helps. I am sorry for the delay in responding to your question.

Mike Richards, DVM 1/22/2001

Resistant Giardia

Question: Dear Dr. Mike: I have three Maine Coon cats, one of which was diagnosed with giardia several months ago by our veterinarian. His only symptom was foul smelling diarrhea. He was originally treated with furazolidone for 10 days, which stopped the symptoms. Approximately 1 month later, the symptoms started again. At this time, all three cats were treated with furazolidone. The symptoms reoccurred sometime after the treatment was completed. Then all three were treated for ten days with metronidazole. We also began changing and disinfecting the litter boxes twice per day. Then the same scenario; a reoccurance of the symptoms in the same cat. All three are currently on another 10 day treatment regimen of metronidazole. Our veterinarian plans another 10 day treatment for the cat with the recurring diarrhea.

My questions are: 1. Is this the most effective treatment for giardia? 2. Where could my cats come in contact with this? (They are inside cats, their only contact with the outside world is when they go to the groomer, which I discontinued after the first round of treatment.) The youngest, who has the recurring symptoms, was bought from a reputable breeder in February 1995. Could he have had the parasite without symptoms since then? 3. Is it possible for giardia to be transmitted to my family? 4. How long does it usually take to eradicate this parasite? We are becoming frustrated by the constant pilling and litter box disinfecting. This has gone on for months. My loving cats now avoid me for fear that I may open their mouth and push an unpalatable pill down their throat. Thank you for any advice that you can give. A.

Answer: A- There are five medications that I know of that can be used to treat giardia. Quinacrine, which is not available in the United States, is used in dogs for giardiasis but may not be effective in cats. Furozolidone (Furox Rx), metronidazole (Flagyl Rx), albendazole (Valbazen Rx) and fenbendazole (Panacur Rx) have all been recommended for use against Giardia in dogs and cats. There are many more reports of resistance to medication for giardiasis in cats than in dogs, so it may not be that unusual to have such a hard time treating the problem, although we seem to have been lucky and have not had a case similar to yours for resistance.

We have not used furazolidone and have no personal experience with success rates using it. We have not used albendazole, either. We usually start treatment with metronidazole at 50mg/kg/day for 5 days. Most of the time that has worked well for us but we have seen a few resistant cases. We have used fenbendazole at 50mg/kg/day for 5 days to treat these cases and it has worked effectively for us in this situation so far. We have tried using fenbendazole first and have had one case where it didn't work as the initial agent but metronidazole helped. I am not sure that there is a "best" medication for giardia. I think that it just seems necessary to start with one of the recommended medications and use others if that one doesn't work.

Giardia have a cystic stage which is excreted in the feces. The cysts can live for several months if they are not exposed to sunlight or dried out. Quaternary ammonium disinfectants (like Roccal Rx) may be the best disinfectants but live steam cleaning of infected catteries has been suggested and I am sure I have seen at least one reference which suggested that chlorine bleach diluted 1:30 was reasonably effective, as well. Obviously most people are not going to be able to steam clean their house. Giardia have a direct infective cycle (no intermediate host). The cysts are picked up orally from contaminated surfaces or water. We have had one client who reported that giardia was found in their well water.

It does seem a little odd that your inside only cats are affected with this parasite but due to the problems with resistance any one of your cats may have been a carrier of the organism. Immune incompetency (cats infected with feline leukemia or feline immunodeficiency virus or stressed severely in some manner) may contribute to resistance or ease of infection. It may be a good idea to check for these diseases.

I think I'd also consider the possibility that something else is going on unless giardia have been isolated from the stool again after the treatments.

I don't think anyone knows for sure whether or not giardia can be transferred from pets to humans. There is some variation among strains of giardia and this may mean that there is a lower probability of infection between species than some people think. On the other hand, it makes it possible for the traits of the strains to overlap enough that perhaps infection between species is possible. I'd be cautious and wash hands after handling the cats, cat toys, litterpans and food bowls. Clean the house as well as you can, disinfecting surfaces for which that is possible with quaternary ammonium (preferably) or chlorine bleach disinfectants.

Mike Richards, DVM

Last edited 08/06/03


Michael Richards, D.V.M. co-owns a small animal general veterinary practice in rural tidewater Virginia. Dr. Richards graduated from Iowa State University's College of Veterinary Medicine in 1979, and has been in private practice ever since. Dr. Richards has been the director of the PetCare Forum...