Synonyms: Cercomonas intestinalis, Lamblia intestinalis, Giardia intestinalis, Megastoma entericum, Giardia enterica. European writers still call this species Giardia intestinalis, but there was so much confusion about the availability of the specific names intestinalis and enterica that Stiles (1915) established the present name.
Hosts: Man, Old and New World monkeys, pig. Hegner (1930) and Armaghan (1937) infected laboratory rats and Bonestell (1935) infected woodrats (Neotoma fuscipes) with G. lamblia from man. Haiba (1956) infected wild and laboratory Rattus norvegicus, but failed to infect wild R. rattus and laboratory mice with G. lamblia from man.
Location: Duodenum, jejunum, upper small intestine.
Geographic Distribution: Worldwide.
Prevalence: G. lamblia is common in man. In 86 surveys of 134,966 people thruout the world summarized by Belding (1952), its prevalence ranged from 2.4 to 67.5% with a mean of 10.4%. It was found in 7.4% of 35,299 persons in 24 surveys in the United States, and in 6.9% of 65,295 persons in 20 surveys in the rest of the world. It is about 3 times as common in children as in adults. G. lamblia was reported from a pig in Tennessee by Frye and Meleney (1932). Its prevalence in swine is unknown.
Morphology: The trophozoites are 9 to 21 u long, 5 to 15 u wide and 2 to 4 u thick; they are usually 12 to 15 u long. The median bodies are curved bars of the duodenalis type. The cysts are ovoid, 8 to 12 u long and 7 to 10 u wide, and contain 4 nuclei.
Pathogenesis: There was considerable controversy for many years whether Giardia is pathogenic in man, but it is now generally agreed that it may be in some individuals. Most infections are symptomless, but in a fairly small number there is a chronic diarrhea. The feces contain a large amount of mucus and fat but no blood. The diarrhea is accompanied by dull epigastric pain and flatulence. Affected persons have a poor appetite and lose weight. In some cases the gall bladder may be invaded and cholecystitis may be present, but there is no proof that the protozoa caused this condition. Pizzi (1957) reviewed some of the literature on the pathogenicity of G. lamblia and concluded that in heavy infections it may also interfere with fat absorption and produce a deficiency in fat-soluble vitamins. It is more often pathogenic in children than adults. The pathogenicity of G. lamblia for swine is unknown.
Diagnosis: Giardia infections can be diagnosed by recognition of trophozoites or cysts in stained fecal smears. Fixation with Schaudinn’s fluid and staining with iron hematoxylin are recommended. Trophozoites alone are generally found in diarrheic stools. The cysts can be concentrated by the flotation technic. Zinc sulfate solution should be used for flotation; sugar and other salt solutions distort the cysts and make them unrecognizable.
Cultivation: Neither G. lamblia nor any other species of Giardia has been cultivated in artificial media. Karapetyan (1958) cultured it in chicken fibroblast tissue cultures along with the yeast, Candida guilliermondi. The protozoon did not develop without the yeast, which led him to believe that there may be a synergistic relation between the 2 organisms.
Treatment: Giardia infections in man can be successfully treated with either quinacrine or chloroquine. Three oral doses of 0.1 g each are given daily for 5 days. Amodiaquin is considered even better than these (Lamadrid-Montemayor, 1954); a single dose of 0.6 g is given to adults.
Prevention and Control: These depend on sanitation. Cerva (1955) found that 2 to 5% phenol or lysol would kill G. lamblia cysts, but that chloramine, mercuric chloride, formalin and a number of other disinfectants were ineffective in the concentrations commonly used. The cysts were killed by temperatures above 50° C and, after 10 hours, by freezing below -20° C. They remained viable in water for over 3 months.