Giardia duodenalis<\/em> is a protozoan parasite that is distributed worldwide and commonly identified in companion animals. The Giardia<\/em> life cycle consists of 2 distinct stages: trophozoites (which are flagellated and motile and parasitize the small intestine) and cysts (which are the infective stage passed in feces). New and improved diagnostic methods continue to come on the market, improving veterinary professionals\u2019 ability to diagnose infected patients. However, treatment of giardiasis continues to be challenging, and even when clinical signs are resolved, treatment often fails to completely eliminate cyst shedding. This article briefly provides an overview of giardiasis with a focus on advancements in diagnostic options, treatment strategies, and management of subclinical, persistent cyst shedders.<\/p>\n Take-Home Points<\/strong><\/p>\n The protozoan parasite Giardia duodenalis <\/i>is transmitted in a fecal\u2013oral cycle when cysts shed into the environment by infected hosts are ingested by na\u00efve hosts. Cysts shed in feces are immediately infectious and extremely robust in the environment, making control of environmental contamination difficult. After cysts have been ingested, they excyst in the duodenum, where they become trophozoites that colonize the small intestine using a structure known as the ventral disc to adhere to the epithelial cells. In addition to causing physical damage to the gut epithelium, trophozoites induce molecular changes, which in combination disrupt nutrient absorption and barrier function of the gut epithelium.1<\/sup> Trophozoites encyst as they enter the large intestine; cysts usually become detectable within 3 to 10 days of infection. Occasionally, trophozoites may be passed in the feces during acute episodes of diarrhea if organisms do not have time to encyst before being voided; however, trophozoites cannot persist in the environment.2<\/sup><\/span><\/p>\n The\u00a0Parasitology series<\/a>\u00a0is brought to you by Merck Animal Health, the makers of Bravecto\u00ae (fluralaner) and Sentinel\u00ae (milbemycin oxime\/lufenuron).<\/p>\n Giardiasis more frequently affects young dogs<\/a> and cats<\/a> (<1 year of age) than adults.2-4<\/sup> The most common clinical signs associated with Giardia<\/i> infection are malabsorption, malodorous feces, chronic diarrhea, and weight loss or lack of weight gain. Apparently healthy animals (usually adults) may harbor chronic subclinical infections and persistently shed cysts; due to the absence of clinical signs, the incidence of this phenomenon is likely underdiagnosed.4-6<\/sup> <\/span><\/p>\n G duodenalis<\/i> is found in all parts of the world and infects a variety of hosts, which leads to some concern regarding Giardia<\/i> infection in companion animals and the possibility of zoonotic pet-to-owner transmission. <\/span><\/p>\n Within the past few decades, it has been determined that despite having identical morphology, Giardia<\/i> recovered from different host species tend to differ genetically.7<\/sup> These genetic differences have led to the classification of Giardia<\/i> into 8 distinct genetic assemblages (A\u2013H), most of which are highly host specific. In the United States, assemblages C and D are thus far limited to dogs, assemblage F is limited to cats, and assemblages A and B are considered to have zoonotic potential.7,8<\/sup> However, even within these potentially zoonotic assemblages, some subassemblages seem to have a broader host range and therefore carry greater zoonotic potential than others. Assemblage A-II is found almost exclusively in humans; A-III and A-IV are found in animals; and A-I has a wider host range, which includes humans, dogs, and cats.9-11<\/sup> <\/span><\/p>\n Of note, recent molecular data indicate that cats may carry zoonotic assemblages more frequently than their canine counterparts. Although nationwide, overall Giardia<\/i> prevalence among surveyed cats was nearly half that among dogs (7.48% and 14.18%, respectively) and 19.1% of Giardia<\/i>-positive cats carried potentially zoonotic assemblages, compared with only 3.7% of Giardia<\/i>-positive dogs.11<\/sup> However, current evidence indicates that although zoonotic risk exists and may be of greater concern with regard to children or immunocompromised persons, most Giardia<\/i> infections are host specific and it is unlikely that transmission between companion animals and owners is a common source of Giardia<\/i> infection in humans.12-14<\/sup><\/span><\/p>\n There are several tests for diagnosing Giardia<\/i> infection in companion animals, although to optimize diagnosis, <\/span>they may need to be used repeatedly or in combination.15<\/sup><\/p>\n Fecal flotation is less sensitive than molecular-based testing16<\/sup>; it is commonly used to screen apparently healthy animals and may also be used to diagnose giardiasis in animals with suspected infection. Giardia<\/i> cysts are best recovered after centrifugal flotation in zinc sulfate solution; addition of Lugol\u2019s iodine stain may enhance visualization of cysts (<\/span>FIGURE 1<\/b><\/span>).17<\/sup> Although sodium nitrate and sugar solutions can also be used for flotation, they can collapse or completely destroy cysts, making identification of any remaining cysts more difficult.18<\/sup> Direct smears can also be used to detect trophozoites in diarrheic feces.<\/span><\/p>\n\n
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\nPublic Health Concerns<\/h2>\n
Diagnosis of Giardiasis<\/h2>\n
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