Friday, February 20, 2009

Dogs on the run: Giardia infections

What are these drawings you wonder? No, it is not something I came up with while talking on the phone with a concerned pet owner telling me about her dog suffering from diarrhea. Though I have to agree it looks like something I, with my very much limited artistic talent could come up with. But give me a minute, you will see what it is.
Dogs and diarrhea: If I would have ten Dollars for every inquiry I get about it, I probably would be getting close to become a millionaire. The other day I said to my wife: It is getting to a point where I almost start hating what I am doing for a living, there are just too many of this particular inquiry. I am sure you agree, it is not the most pleasant subject to talk about either.
Of course, when it happens the first thing owners blame the cause on is the food what they purchased from us. “Are you aware of any issues related to this with the food you sold me?” Like I am sitting there selling all day long food knowing that it will be harmful to the dog. It does not work like that. If I would know of such a problem, chances are nobody will find out about it since I will simply not sell such a product. So the continuation of the discussion is usually a long investigation of what has happened to the dog before the problem came up. I.e., what did the dog eat? Trust me, this is a problem. Because most dog owners assume they know to 100% exactly what their dog ingested. Those people I have to tell, keep dreaming or wake up. Let me tell you, you do not know the answer to that question unless you keep a very close eye on your pet 24/7. Most dogs will just eat whatever comes into their sight. And they will do it quickly and fast too, before you can blink with an eye. I hear very often about finicky cats. Seldom however I have a dog owner characterizing his pet as being picky. Reminds me kind of that joke this comedian made one day: Being a dog owner, when his wife tells him to clean up the back yard of all the excrements laying around there coming from his own dog, he has no problem following her orders. Because all he does is inviting the neighbor’s dog to come over. That guy cleans up really good. Joking aside, Ingestion of the strangest things can become a problem.
In one case, after unsuccessful and over hasted diet changes, I had to find out that the dog for fun was chewing paint off the doors. Another one was caught drinking very excessive amounts of waste oil from a turkey fryer. My neighbor admitted to feeding my dog fried bacon every morning for weeks until I prohibited Brandy’s tasty morning snack. Quite often it is a change in diet forced too fast onto the dog rather than slowly transitioning. With the same popularity rank veterinarian ordered medical treatments. But most of the times we never figure out what actually caused the problem. We take some simple steps (like feeding rice with added fiber such as for example whole pumpkin or carrots only for a couple days) and after a few days it goes away and things return to normal. Very often it also can be the water which caused a contamination of the dog’s system. Related to this subject I did a little searching and figured I share with you what I found on an infection of the intestine by a commonly occurring single cell organism called giardia, causing severe diarrhea.
The USDA Forest Service says about giardia: “Cool, clear mountain streams may appear clean and safe, but they often harbor a hidden danger. Giardia lamblia, is a microscopic, single celled animal protected by an outer shell called a cyst. If ingested, it can cause a disease known as giardiasis. Giardiasis is not fatal but it can cause great discomfort. All water should be considered potentially contaminated because even contaminated water may look, smell, and taste clean. Cool, clear mountain streams may appear clean and safe, but they often harbor a hidden danger. Most water becomes contaminated by infected animals that live nearby. Beavers and muskrats are easily infected with giardia and, once infected, if they release fecal material in or near water, it becomes contaminated. Many hundred million cysts may be shed at one time by one animal, and it takes as few as ten cysts to cause an infection.”
Now we know why giardia is also commonly know as beaver fever. Beavers are known carriers of giardia. These are also the most commonly diagnosed protozoa in humans. Coccidia is yet another, similar parasite affecting the intestinal tract is coccidian. Unlike the causes of giardia in dogs from lakes and streams, coccidiosis is contracted by eating feces directly.
About the signs and symptoms USDAFS says: “Chronic symptoms will appear from seven to ten days after ingesting the cysts. They include: Abdominal cramps, diarrhea, increased gas, bloating, fatigue, and sometimes weight loss due to nausea and loss of appetite. These symptoms last for several days only and the body can naturally rid itself of the parasite in one to two months. However, for people with weakened immune systems the body often cannot rid itself of the parasite without medical treatment. Most water becomes contaminated by infected animals that live nearby.”
The Dog Health Guide describes signs and symptoms as follows: “Giardia interferes with the absorption of nutrients from food. As can be expected, when you don't get the nutrients you need, you lose weight and appear to have less energy. Dogs with giardisis may have no symptoms or diarrhea. Diarrhea tends to be bad smelling and very watery. Diarrhea may be bad or light and occur frequently or far apart.”
Maggie Fisher, creator of the two drawings, is a veterinary surgeon with a special interest in parasitology. She describes the infection and how it can be treated and controlled as follows:
“The division of Giardia into groups according to species is still somewhat confused; the organisms that infect mammals look very similar but it remains unclear to what extent they form one or a number of species. It is for this reason that, while Giardia infection in some mammals, including dogs, is suspected of being infectious to man (a zoonosis), it has not been conclusively shown that the species in, for example, dogs and man is the same.
The Giardia trophozoite (mystery drawing on the top to the left), which is the active stage of the organism, inhabits the small intestine of the dog. It attaches to the cells of the intestine with its adhesive disc and rapidly divides to produce a whole population of trophozoites. As they detach they may be swept down the intestine. If intestinal flow is fast then they may appear in the feces. However, if they have time, they will develop into the inactive, more durable, cyst form of the organism and these will be passed in the feces. The cyst (mystery drawing on the top to the right) is more able to survive in the environment than the trophozoite, which is very fragile.
Like all infectious agents, in order to cause disease giardia depends on being able to overcome the dog's defense against infection, either by its virtulence or by the number of the organisms becoming established. It has been observed that as few as 10 cysts can cause disease in humans. Different animals may respond to infection in different ways, which may be due to different strains of the same giardia population, with varying levels of pathogenicity. Another explanation for observed differences in the host response to infection is that protective immunity changes with age and/or exposure. This may be temporarily lost if the animal is stressed or immuno-suppressed, for example with corticosteroid treatment.
What is the source of infection for dogs?
The original source of an outbreak may be cysts in contaminated water or the environment. In addition, infected dogs which may be either carriers (show no clinical signs but continue to harbor infection and pass cysts into the environment) or dogs that have diarrhea associated with infection may act as the source. Surveys have shown that about 14% of the adult dog population and over 30% of dogs under one year of age were infected. Once passed, the cysts can survive in cold water for several months.
The cysts are infective as soon as they are passed, unlike other parasites where a lag period is necessary before the organism is infective. The most common route of infection is oral. For example, dogs may accidentally eat cysts as they lick around the environment or lick other dogs' coats (particularly if the other dog has diarrhea). Another major source of infection is drinking contaminated water. Once ingested, the cyst breaks open in the animals' intestine and releases two new trophozoites to initiate infection. If a dog is left in a dirty environment it may act as its own source of further infections it eats cysts passed in its own feces.
What are the clinical signs associated with infection?
The trophozoites divide to produce a large population, then they begin to interfere with the absorption of food, so feces from affected animals are typically light colored, greasy and soft. These signs, together with the beginning of cyst shedding, begin about one week post infection. There may be additional signs of large intestinal irritation, such as straining and mucus in the feces, even though giardia do not colonize the large intestine. Usually the blood picture of affected animals is normal, though occasionally there is a slight increase in the number of eosinophils, one of several types of white blood cells, and mild anemia. Without treatment, the condition may continue, either chronically or intermittently, for weeks or months.
How can infection be diagnosed? Diagnosis is based on demonstration of the infection and the elimination of other possible causes of diarrhea (Salmonella or Campylobacter). Giardia cysts may be observed directly in fecal samples or indirectly using an elisa technique. Direct examination of feces, using zinc sulfate centrifugal flotation. followed by staining has been found to be up to 70% effective at detecting infection from a single fecal sample. The cyst output is very variable from day to day so the detection rate may be improved by pooling fecal samples collected over three days. Fecal examination is the cheapest method but is time consuming and requires an experienced technician for reliable results. The elisa technique requires a kit and some method of reading a color change or some method of production of fluorescent. Studies examining the reliability of some immuno-fluorescent kits have found them to be over 90% accurate, with relatively few false negatives or false positives. However, the tests are costly and probably only worthwhile where there are a large number of samples to be processed. Another option your vet may choose is to take a swap and wipe it at your dogs rectum. It is possible that the swap will not show any causes of giardia in dogs, yet your dog still has the disease. Your doctor will take 3 samples collected at least 2 days apart.
Infection may be treated using one of a number of prescription drugs. There are a number of treatments your vet may order you to use. The Metronidazole, traded as Flagyl, is effective against giardia and is given over 5 to 7 days. This drug should not be given to pregnant dogs as it is known to cause problems with the fetus. Metonidazole also has a positive effect on other causes of diarrhea. The list of options includes: Metronidazole (Flagyl,25-30 mg/kg, 7 days), Furazolidone (Neftin, 4 mg/kg, 10 days), Tinadazole (44 mg/kg once daily, 7 days), Fenbendazole (Panacur 50 mg/kg once daily, 3 days) and Albendazole (Valbazen, 25 mg/kg, 2 days). Other treatments include adding fiber to your dogs diet. Dogs do not acquire immunity to giardia after treatment, so they can contract the disease again. There is a vaccine to prevent the disease. Whatever treatment is chosen, it is very unlikely to eliminate 100% of the infection in all dogs. Adaptations that may be made to try to improve the success rate of a treatment regime include extending the duration and dose of the treatment. Care must obviously be taken with this approach to make sure that an adequate safety margin is always maintained. Another approach is to retreat after an interval of one week. Alternatively, repeat fecal samples may be collected one week after the treatment and dogs still passing cysts can be identified and treated. It should be recognized that, when treating a number of dogs, whichever of these treatment strategies is adopted, there may be one or two dogs that remain as carriers of infection that will act as a potential sources of infection in future.
Dogs should be prevented from access to foul water that may contain large numbers of cysts. Small numbers of cysts may occasionally be present in the potable water supply but the risk of this being a major source of infection is small. It also should be noted that removal of Giardia in contaminated water is difficult. They survive chlorination of drinking water and freezing temperatures up to –9 degrees F, therefore the best solution is disposal.

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