Foodborne Animal Parasites 681
G. lamblia is generally noninvasive, and malabsorption often accompanies the symptomatic disease.
96
Growth of the organism is favored by the high bile content in the duodenum and upper jejunum.
79
From an outbreak of giardiasis among 1400 Americans on the Madeira Island in 1976, the symptoms, along with the percentage incidence among victims, were as follows: abdominal cramps (75%),
abdominal distention (72%), nausea (70%), and weight loss (40%). The median incubation period
was 4 days, and G. lamblia was recovered from 47% of 58 ill patients. The consumption of tapwater
and the eating of ice cream or raw vegetables were significantly associated with the illness.
66 The
29 victims of the 1979–1980 outbreak traced to home-canned salmon (see below) displayed the following symptoms: diarrhea (100%), fatigue (97%), abdominal cramps (83%), fever (21%), vomiting
(17%), and weight loss (59%), among others.
77 From another study of 183 patients, the five leading
symptoms (and percentage complaining) were diarrhea (92%), cramps (70%), nausea (58%), fever
(28%), and vomiting (23%).
96 Weight loss of about 5 lb or so is a common feature of giardiasis, and
it was associated with the 1985 outbreak traced to noodle salad.
78
Giardiasis is a highly contagious disease. It has been documented in daycare centers where unsanitary
conditions prevailed. The human infection rate ranges from 2.4 to 67.5%.
19 The minimum infectious
dose of G. lamblia cysts for humans is 10 or less.
82
Giardiasis is diagnosed by the demonstration of trophozoites in stool specimen by microscopic
examinations using either wet mounts or stained specimens. G. lamblia can be grown in axenic
culture, but this does not lend itself to rapid diagnosis. Effective enzyme-linked immunosorbent assay
(ELISA) tests have been developed. Both circulating antibodies and T lymphocytes are elicited during
infection by G. lamblia. Because no enterotoxin has been demonstrated, diarrhea is caused by other
factors.
96
The drug of choice for the treatment of giardiasis is quinacrine, an acridine derivative. Also effective
are metronidazole and tinidazole.
96
Incidence in Foods and Foodborne Cases
Giardia has been shown to occur in some vegetables, and it may be presumed that the organism occurs
on foods that are washed with contaminated water or contaminated by unsanitary asymptomatic
carriers. Of 64 heads of lettuce examined in Rome, Italy, in 1968, 48 contained Giardia cysts, and
cysts were recovered from strawberries grown in Poland in 1981.
3
As early as 1928, it was suggested that hospital food handlers were the likely source of protozoal
infections of patients. Of 844 private patients in an urban center, 36% contracted giardiasis, and it was
believed the infections were acquired by eating cyst-contaminated raw fruits and vegetables. These
and some other early incidences of possible foodborne giardiasis have been discussed by Barnard and
Jackson.
3 Following is a list of suspected and proved foodborne giardiasis:
1. Three of four members of a family who in 1960 ate Christmas pudding thought to have been
contaminated by rodent feces became victims.
21 Giardia-like cysts were found.
2. In their surveillance of foodborne diseases in the United States for 1968–1969, Gangarosa and
Donadio
39 recorded an outbreak of giardiasis with 19 cases for 1969 but provided no further
details.
3. In December 1979, 29 of 60 school employees in a rural Minnesota community contracted the
disease from home-canned salmon prepared by a worker after changing the diaper of an infant
later shown to have an asymptomatic Giardia infection.
77 This was the first well-documented
common-source outbreak.
G. lamblia is generally noninvasive, and malabsorption often accompanies the symptomatic disease.
96
Growth of the organism is favored by the high bile content in the duodenum and upper jejunum.
79
From an outbreak of giardiasis among 1400 Americans on the Madeira Island in 1976, the symptoms, along with the percentage incidence among victims, were as follows: abdominal cramps (75%),
abdominal distention (72%), nausea (70%), and weight loss (40%). The median incubation period
was 4 days, and G. lamblia was recovered from 47% of 58 ill patients. The consumption of tapwater
and the eating of ice cream or raw vegetables were significantly associated with the illness.
66 The
29 victims of the 1979–1980 outbreak traced to home-canned salmon (see below) displayed the following symptoms: diarrhea (100%), fatigue (97%), abdominal cramps (83%), fever (21%), vomiting
(17%), and weight loss (59%), among others.
77 From another study of 183 patients, the five leading
symptoms (and percentage complaining) were diarrhea (92%), cramps (70%), nausea (58%), fever
(28%), and vomiting (23%).
96 Weight loss of about 5 lb or so is a common feature of giardiasis, and
it was associated with the 1985 outbreak traced to noodle salad.
78
Giardiasis is a highly contagious disease. It has been documented in daycare centers where unsanitary
conditions prevailed. The human infection rate ranges from 2.4 to 67.5%.
19 The minimum infectious
dose of G. lamblia cysts for humans is 10 or less.
82
Giardiasis is diagnosed by the demonstration of trophozoites in stool specimen by microscopic
examinations using either wet mounts or stained specimens. G. lamblia can be grown in axenic
culture, but this does not lend itself to rapid diagnosis. Effective enzyme-linked immunosorbent assay
(ELISA) tests have been developed. Both circulating antibodies and T lymphocytes are elicited during
infection by G. lamblia. Because no enterotoxin has been demonstrated, diarrhea is caused by other
factors.
96
The drug of choice for the treatment of giardiasis is quinacrine, an acridine derivative. Also effective
are metronidazole and tinidazole.
96
Incidence in Foods and Foodborne Cases
Giardia has been shown to occur in some vegetables, and it may be presumed that the organism occurs
on foods that are washed with contaminated water or contaminated by unsanitary asymptomatic
carriers. Of 64 heads of lettuce examined in Rome, Italy, in 1968, 48 contained Giardia cysts, and
cysts were recovered from strawberries grown in Poland in 1981.
3
As early as 1928, it was suggested that hospital food handlers were the likely source of protozoal
infections of patients. Of 844 private patients in an urban center, 36% contracted giardiasis, and it was
believed the infections were acquired by eating cyst-contaminated raw fruits and vegetables. These
and some other early incidences of possible foodborne giardiasis have been discussed by Barnard and
Jackson.
3 Following is a list of suspected and proved foodborne giardiasis:
1. Three of four members of a family who in 1960 ate Christmas pudding thought to have been
contaminated by rodent feces became victims.
21 Giardia-like cysts were found.
2. In their surveillance of foodborne diseases in the United States for 1968–1969, Gangarosa and
Donadio
39 recorded an outbreak of giardiasis with 19 cases for 1969 but provided no further
details.
3. In December 1979, 29 of 60 school employees in a rural Minnesota community contracted the
disease from home-canned salmon prepared by a worker after changing the diaper of an infant
later shown to have an asymptomatic Giardia infection.
77 This was the first well-documented
common-source outbreak.