This tells about giardia:
Giardia (Giardia canis)
Holly Nash, DVM, MS
Veterinary Services Department, Drs. Foster & Smith, Inc.
Giardia are protozoa (one-celled organisms) that live in the small intestine of dogs and cats. Giardia are found throughout the United States and in many other parts of the world. Infection with Giardia is called 'giardiasis.'
There are many things we do not know about this parasite. Experts do not agree on how many species of Giardia there are and which ones affect which animals. Veterinarians do not even agree on how common Giardia infections are and when they should be treated. Generally, it is believed that infection with Giardia is common but disease is rare. There is much about the life cycle we do not know either.
How do Giardia reproduce and how are they transmitted?
Giardia multiply by dividing.
A dog becomes infected by eating the cyst form of the parasite. In the small intestine, the cyst opens and releases an active form called a trophozoite. These have flagella, hair-like structures that whip back and forth allowing them to move around. They attach to the intestinal wall and reproduce by dividing in two. After an unknown number of divisions, at some stage, in an unknown location, this form develops a wall around itself (encysts) and is passed in the feces. The Giardia in the feces can contaminate the environment and water and infect other animals and people.
What are the signs of a Giardia infection?
Most infections with Giardia are asymptomatic. In the rare cases in which disease occurs, younger animals are usually affected, and the usual sign is diarrhea. The diarrhea may be acute, intermittent, or chronic. Usually the infected animals will not lose their appetite, but they may lose weight. The feces are often abnormal, being pale, having a bad odor, and appearing greasy. In the intestine, Giardia prevents proper absorption of nutrients, damages the delicate intestinal lining, and interferes with digestion.
Can Giardia of dogs infect people?
This is another unknown. There are many species of Giardia, and experts do not know if these species infect only specific hosts. Sources of some human infections have possibly been linked to beavers, other wild animals, and domestic animals. Until we know otherwise, it would be wise to consider infected animals capable of transmitting Giardia to humans.
You may have heard about Giardia outbreaks occurring in humans due to drinking contaminated water. Contamination of urban water supplies with Giardia is usually attributed to (human) sewage effluents. In rural settings, beavers most often get the blame for contaminating lakes and streams. Giardia outbreaks have also occurred in day care centers fueled by the less than optimal hygienic practices of children.
How do we diagnose giardiasis?
Giardiasis is very difficult to diagnose because the protozoa are so small and are not passed with every stool. Tests on serial stool samples (one stool sample every day for three days) are often required to find the organism. Special diagnostic procedures, beyond a routine fecal examination, are necessary to identify Giardia. The procedures we use to identify roundworms and hookworms kill the active form of Giardia and concentrate the cyst form.
To see the active form, a small amount of stool may be mixed with water on a microscope slide and examined under high magnification. Because these forms have flagella, you can see them move around on the slide. The active forms are more commonly found in loose stools. If you ever have the opportunity to see the active form of Giardia under the microscope, take it! It is an interesting-looking creature. It is pear-shaped and its anatomy makes it look like a cartoon face, with eyes (which often look crossed), nose, and mouth. Once you see it, you will not forget it.
Cysts are more commonly found in firm stools. Special solutions are used to separate the cysts from the rest of the stool. The portion of the solution that would contain the cysts is then examined microscopically.
In spring, 2004, a diagnostic test using ELISA technology became available. This test uses a very small fecal sample, and can be performed in 8 minutes in a veterinarian's office. It is much more accurate than a fecal examination.
We have done the tests, now what?
Now we come to how to interpret the test results. It can be a dilemma for your veterinarian. What you see (or do not see) is not always a correct indication of what you have. A negative test may mean the animal is not infected. However, few, if any, laboratory tests are 100% accurate. Negative test results can also occur in some infected animals. If a negative test occurs, your veterinarian will often suggest repeating the test.
What about a positive test? That should not be hard to interpret, right? Wrong. Giardia can be found in many dogs with and without diarrhea. If we find Giardia, is it the cause of the diarrhea or is it just coincidence we found it? The animal could actually have diarrhea caused by a bacterial infection, and we just happened to find the Giardia. Test results always need to be interpreted in light of the signs, symptoms, and medical history.
If we find Giardia, how do we treat it?
Here we go again; treatment is controversial too. There is a question about when to treat. If Giardia is found in a dog without symptoms should we treat the animal? Since we should not know if G. canis can infect man, we often err on the side of caution and treat an asymptomatic infected animal to prevent possible transmission to people.
If we highly suspect infection with Giardia, but can not find the organism, should we treat anyway? This is often done. Because it is often difficult to detect Giardia in the feces of dogs with diarrhea, if there are no other obvious causes of diarrhea (e.g.; the dog did not get into the garbage several nights ago) we often treat the animal for giardiasis.
There are several treatments for giardiasis; some of them have not been FDA approved to treat giardiasis in dogs. Metronidazole is one of these, but is the old standby. The nice thing about this drug is that it also kills some types of bacteria that could cause diarrhea. So if the diarrhea was caused by bacteria, and not Giardia, we still kill the cause of the diarrhea and eliminate the symptoms. Makes us look pretty sharp! Unfortunately, metronidazole has some drawbacks. It has been found to be only 60-70% effective in eliminating Giardia from infected dogs. In some dogs, it can cause vomiting, anorexia, and some neurological signs. It also can be toxic to the liver in some animals. It is suspected of being a teratogen (an agent that causes physical defects in the developing embryo), so it should not be used in pregnant animals. Finally, it has a very bitter taste and many animals resent taking it.
Quinacrine hydrochloride has been used in the past, but is not very effective and can cause side effects such as lethargy, vomiting, anorexia, and fever.
A newer drug, albendazole, has been shown to be 50 times more effective than metronidazole and 10-40 times more effective than quinacrine hydrochloride in killing Giardia in the laboratory. It has not been approved for use in dogs. Some serious side effects of albendazole have been noted, including injury to the bone marrow. Since it may also cause birth defects, it should not be used in pregnant animals.
In a small study, fenbendazole, which has been approved for treatment of roundworm, hookworm, and whipworm infections in dogs, has been shown to be effective in treating giardiasis in dogs. It is safe to use in puppies.
A combination of praziquantel, pyrantel pamoate, and febantel has also been shown to decrease cyst excretion in infected dogs.
This table summarizes the information above.
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