686 Modern Food Microbiology
2. Eleven of 35 medical students in New York City in 1968 had an increase in toxoplasma antibodies
following the consumption of hamburger cooked rare at the same snack bar, and 5 contracted
clinical toxoplasmosis.
58
3. In 1974, a 7-month-old infant who consumed unpasteurized goat’s milk developed clinical
toxoplasmosis. Although T. gondii could not be recovered from milk, some goats in the herd
had antibody titers to T. gondii as high as 1:512, and the child had a titer of over 1:16,000.
83
4. In 1978, 10 of 24 members of an extended family in northern California contracted toxoplasmosis
after drinking raw milk from infected goats.
89
5. In S˜ ao Paulo, Brazil, 110 university students suffered acute toxoplasmosis after eating undercooked meat.
19
Since most of the above cases have been traced to meats, the consumption of raw or undercooked
meats carries the risk of this infection. Other documented meatborne outbreaks have been reviewed.
95
Control
Toxoplasmosis in humans can be prevented by avoiding environmental contamination with cat feces
(from cat litter boxes, for example) and by avoiding the consumption of meat and meat products that
contain viable tissue cysts. The cysts of T. gondii can be destroyed by heating meats above 60
◦ C or by
irradiating at a level of 30 krad (0.3 kGy) or higher.
33 The organism may be destroyed by freezing, but
because the results are variable, freezing should not be relied on to inactivate oocysts. See reference
8 for a detailed review of the life cycle of Toxoplasma gondii.
Sarcocystosis
Of more than 13 known species of the genus Sarcocystis, two are known to cause an extraintestinal disease in humans. One of these is obtained from cattle (S. hominis) and the other from pigs
(S. suihominis). Humans are the definitive hosts for both species: the intermediate host for S. hominis
is bovines, and pigs for S. suihominis.
When humans ingest a sarcocyst, bradyzoites are released and penetrate the lamina propria of
the small intestine, where sexual reproduction occurs that leads to sporocysts. The latter pass out of
the bowel in feces. When sporocysts are ingested by pigs or bovines, the sporozoites are released
and spread throughout the body. They multiply asexually and lead to the formation of sarcocysts in
skeletal and cardiac muscles. In this stage, they are sometimes referred to as Miescher’s tubules. The
bradyzoite-containing sarcocysts are visible to the unaided eye and may reach 1 cm in diameter.
19
Several studies have been conducted to determine the relative infectivity of Sarcocystis spp. Of 20
human volunteers in five studies who ate raw beef infected with S. hominis, 12 became infected and
shed oocysts, but only 1 had clinical illness.
34 Symptoms occurred within 3–6 hours and consisted of
nausea, stomachache, and diarrhea. In 15 other volunteers who ate raw pork infected with S. suihominis,
14 became infected and shed oocysts, and 12 of these had clinical illness 6–48 hours after eating the
pork.
34 Six who ate well-cooked pork did not contract the disease. In another study of another species
of Sarcocystis, dogs did not become infected when fed beef cooked medium (60
◦ C) or well done
(71.1–74.4
◦ C), but the beef was infective when fed raw or cooked rare (37.8–53.3
◦ C). Dogs fed the
same raw beef after storage for 1 week in a home freezer did not become infected.
35 In another study,
two human volunteers passed sporocysts for 40 days after eating 500 g of raw ground beef diaphragm
muscle infected with Sarcosporidia.
85
2. Eleven of 35 medical students in New York City in 1968 had an increase in toxoplasma antibodies
following the consumption of hamburger cooked rare at the same snack bar, and 5 contracted
clinical toxoplasmosis.
58
3. In 1974, a 7-month-old infant who consumed unpasteurized goat’s milk developed clinical
toxoplasmosis. Although T. gondii could not be recovered from milk, some goats in the herd
had antibody titers to T. gondii as high as 1:512, and the child had a titer of over 1:16,000.
83
4. In 1978, 10 of 24 members of an extended family in northern California contracted toxoplasmosis
after drinking raw milk from infected goats.
89
5. In S˜ ao Paulo, Brazil, 110 university students suffered acute toxoplasmosis after eating undercooked meat.
19
Since most of the above cases have been traced to meats, the consumption of raw or undercooked
meats carries the risk of this infection. Other documented meatborne outbreaks have been reviewed.
95
Control
Toxoplasmosis in humans can be prevented by avoiding environmental contamination with cat feces
(from cat litter boxes, for example) and by avoiding the consumption of meat and meat products that
contain viable tissue cysts. The cysts of T. gondii can be destroyed by heating meats above 60
◦ C or by
irradiating at a level of 30 krad (0.3 kGy) or higher.
33 The organism may be destroyed by freezing, but
because the results are variable, freezing should not be relied on to inactivate oocysts. See reference
8 for a detailed review of the life cycle of Toxoplasma gondii.
Sarcocystosis
Of more than 13 known species of the genus Sarcocystis, two are known to cause an extraintestinal disease in humans. One of these is obtained from cattle (S. hominis) and the other from pigs
(S. suihominis). Humans are the definitive hosts for both species: the intermediate host for S. hominis
is bovines, and pigs for S. suihominis.
When humans ingest a sarcocyst, bradyzoites are released and penetrate the lamina propria of
the small intestine, where sexual reproduction occurs that leads to sporocysts. The latter pass out of
the bowel in feces. When sporocysts are ingested by pigs or bovines, the sporozoites are released
and spread throughout the body. They multiply asexually and lead to the formation of sarcocysts in
skeletal and cardiac muscles. In this stage, they are sometimes referred to as Miescher’s tubules. The
bradyzoite-containing sarcocysts are visible to the unaided eye and may reach 1 cm in diameter.
19
Several studies have been conducted to determine the relative infectivity of Sarcocystis spp. Of 20
human volunteers in five studies who ate raw beef infected with S. hominis, 12 became infected and
shed oocysts, but only 1 had clinical illness.
34 Symptoms occurred within 3–6 hours and consisted of
nausea, stomachache, and diarrhea. In 15 other volunteers who ate raw pork infected with S. suihominis,
14 became infected and shed oocysts, and 12 of these had clinical illness 6–48 hours after eating the
pork.
34 Six who ate well-cooked pork did not contract the disease. In another study of another species
of Sarcocystis, dogs did not become infected when fed beef cooked medium (60
◦ C) or well done
(71.1–74.4
◦ C), but the beef was infective when fed raw or cooked rare (37.8–53.3
◦ C). Dogs fed the
same raw beef after storage for 1 week in a home freezer did not become infected.
35 In another study,
two human volunteers passed sporocysts for 40 days after eating 500 g of raw ground beef diaphragm
muscle infected with Sarcosporidia.
85