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Giardiasis

VetBooks.ir ABOUT THE DIAGNOSIS cysts that have been passed by infected animals; this route of
infection is called fecal-oral transmission, and the giardiasis occurs
primarily in puppies and kittens, animals with weakened immune
Giardiasis (also called Giardia infection or “beaver fever”) is an
infection caused by a microscopic protozoan organism called Giardia. systems (immunodeficient), and animals that live in crowded housing
Giardia organisms infect the intestines of animals and humans, environments such as animal shelters, breeding facilities, kennels,
causing varying degrees of digestive problems, especially diarrhea. catteries, and so forth, where the Giardia organisms accumulate in
These organisms are found all over the world. There are many the animals’ surroundings. Still, Giardia infection occurs routinely in
different kinds or species of Giardia. Giardia can infect mammals, healthy pets living in home environments with access to the outdoors.
birds, reptiles, and amphibians. When they are present, symptoms of giardiasis are centered
Giardia has two main stages of development: Giardia cysts on the digestive system. Most infected animals seem healthy and
and Giardia trophozoites; both are too small to be seen with the do not show any signs of illness (asymptomatic carriers). Some
naked eye and require microscopic identification. Cysts are passed animals, especially puppies and kittens, will develop diarrhea
in the feces (excrement, stool) of infected animals and humans. caused by giardiasis. Vomiting sometimes occurs. The diarrhea
These cysts can contaminate the environment. When an animal or a can be variable in degree, from very mild to severe. It can occur
human comes in contact with these Giardia cysts in such a way as every time that animal has a bowel movement or only occasionally.
to allow them to enter the digestive system (for example, drinking Sometimes it may go away on its own, and return with intermittent
contaminated water), Giardia trophozoites emerge from the cysts flare-ups. The diarrhea usually does not contain any blood. If the
and infect the intestines of the animal or person. The trophozoites condition is not properly treated, the diarrhea can continue for a
then multiply in the intestines and afterward enclose themselves in long period of time (i.e., become chronic) and lead to the improper
a protective shell, forming new Giardia cysts. These cysts are once processing and digestion of nutrients (malabsorption), decreased
again passed in the stool (feces) when the animal or person has appetite, and weight loss. The diarrhea may then start to smell very
a bowel movement, where they can then be taken up by another bad and look pale in color; it is usually soft rather than watery.
individual, perpetuating the spread of Giardia. It takes about 1 to None of these signs of illness is specific to giardiasis. Many other
2 weeks for a person or an animal to begin passing (shedding) intestinal conditions can cause these same symptoms, which explains
cysts in the stool after first taking the cysts in. Both trophozoites the need for Giardia testing when these types of symptoms arise.
and cysts can be passed in the stool, but only cysts can infect Humans can also be infected by Giardia. People most often
other animals or people; trophozoites usually die outside the host become infected by drinking water from contaminated sources or
(animal or person). The protective shell of the cyst allows the Giardia from direct contact with other infected humans. It is not known if
organism to survive in the environment for long periods of time, dogs and cats can directly transmit Giardia to people, but because
which explains the widespread existence of giardiasis in nature. the same strains of Giardia have been found in humans, dogs and
Several tests are available to screen for giardiasis in pets, but in cats, it is recommended that giardiasis in cats and dogs be treated
some cases the diagnosis can be difficult to make because Giardia as a potentially communicable (zoonotic) disease. This means close
cysts are shed only intermittently. Therefore, your veterinarian may attention needs to be paid to basic hygiene, such as wearing
need to perform more than one type of test or repeat a particular gloves or washing hands after handling a pet with diarrhea of any
test to confirm giardiasis. Some veterinarians will treat an animal cause, and confirmed giardiasis in particular, to reduce the risk
with medication for giardiasis in the absence of a conclusive result if of pet-to-human transmission. Any suspicion of human Giardia
the symptoms and circumstances make giardiasis a likely possibility infection should be discussed with a medical doctor.
and the veterinarian suspects that giardiasis is present but just
escaping detection. A positive response is diagnostically useful: if TREATMENT
the symptoms improve after treatment, it is likely that the animal Pet: Giardia infection is treated with one of several available drugs.
had giardiasis. The animal’s fecal (stool) sample can be checked Most are safe, but some treatments have caused mild to severe
directly for Giardia trophozoites under the microscope (direct smear) side effects in some dogs and cats. Tell your veterinarian if your
or may be analyzed biochemically for giardial proteins (enzyme-linked pet is or may be pregnant because some medications should
immunosorbent [ELISA] test and immunofluorescent antibody [IFA] not be used in pregnant animals. Treatment of giardiasis is highly
test). A more recently developed test, polymerase chain reaction effective in some individuals and only partially so in others. A dog
(PCR) test may also assist the diagnosis of giardiasis. Fecal samples or cat that has received a course of treatment for giardiasis could
from the animal can be microscopically examined for cysts using a still harbor Giardia because the organism may be quite resistant.
technique called zinc flotation. It may be necessary to repeat this Also, reinfection can occur because the cysts can survive in the
test at least three times over a period of 10 days for increased environment for weeks and can be picked up by the same dog or
effectiveness because of intermittent passing of the organism in cat who passed them. Therefore, it is important to follow up with
stool. Rarely, when results are still negative after performing some your veterinarian. Immunodeficient animals and animals with other
or all of the available tests discussed above, Giardia organisms disease conditions can have more difficulty clearing the infection
may ultimately only be found as the source of the problem during and eliminating symptoms. Because dogs and cats infected with
more advanced procedures, such as endoscopy or even intestinal Giardia can be a source of contamination of the environment and
surgery if an altogether different disorder was suspected, warranting may possibly transmit the infection to people, veterinarians will usually
intestinal biopsies. recommend treatment of infected dogs and cats even when these
animals are not showing any overt symptoms of illness (for example,
LIVING WITH THE DIAGNOSIS treating with antiparasitic drugs based on a finding of Giardia on
Giardiasis is common in dogs. This infection occurs less frequently microscopic fecal examination, even if there is no diarrhea). A vaccine
in cats. Dogs and cats become infected when they swallow Giardia is available, but it is not recommended for general use because it

From Cohn and Côté: Clinical Veterinary Advisor, 4th edition. Copyright © 2020 by Elsevier Inc. All rights reserved.