700 Modern Food Microbiology
the initial symptoms. Where 10 or fewer larvae are deposited per gram of muscle tissue, there are usually
no symptoms. When 100 or more per gram are deposited, symptoms of clinical trichinosis usually
develop, whereas for 1000 or more per gram of tissue, serious and acute consequences may occur.
Muscle pain (myalgia) is the universal symptom of muscle involvement, and difficulty in breathing,
chewing, and swallowing may occur.
69 About 6 weeks after the initial infection, encystment occurs,
accompanied by tissue pain, swelling, and fever. Resistance to reinfection develops, and it appears to
be T cell mediated. Thiabendazole and mebendazole have been shown to be effective drugs for this
disease.
Diagnosis
Because the trichinae exist as coiled larvae in ovoid capsular cysts in skeletal muscles, biopsies
are sometimes performed on the deltoid, biceps, or gastrocnemius muscles. A significant eosinophilia
usually develops during the second week of the disease. Antibodies can be detected after the third week
of infection; immunological methods that may be used include bentonite flocculation, cholesterollecithin flocculation, and latex agglutination. A bentonite titer of 1:5 is significant, but this test is not
positive until at least 3 weeks after infection. This disease is positively diagnosed if a serologic test
(e.g., ELISA) is positive for IgG and/or IgM antibodies to Trichinella in the serum of victims.
Prevention and Control
Trichinosis can be controlled by avoiding the feeding of infected meat scraps or wild game meats
to swine, and by preventing the consumption of infested tissues by other animals. The feeding of
uncooked garbage to swine helps to perpetuate this disease. Where only cooked garbage is fed to pigs,
the incidence of trichinosis has been shown to fall sharply.
This disease can be prevented by the thorough cooking of meats such as pork or bear meat. In
a study on the heat destruction of trichina larvae in pork roasts, all roasts cooked to an internal
temperature of 140
◦ F (60
◦ C) or higher were subsequently found to be free of organisms.
11 Larvae
were found in all roasts cooked at 130
◦ F (54.4
◦ C) and lower, and in some roasts cooked at 135
◦ F.
The USDA recommendation for pork products is that the product be checked with a thermometer after standing and if any part does not attain 76.7
◦ C (170
◦ F), the product should be cooked
further.
105
Freezing will destroy the encysted forms, but freezing times and temperatures depend on the thickness of the product and the specific strain of T. spiralis (Table 29–4). The lower the temperature of
freezing, the more destructive it is to T. spiralis, as was demonstrated in the following study. Four selected temperatures were chosen for the freezing of infected ground pork that was stuffed into casings
and packed into boxes. When frozen and stored at −17.8
◦ C, the trichinae lost infectivity between 6
and 10 days; at −12.2
◦ C, infectivity was lost between 11 and 15 days.
91 When frozen at −9.4
◦ C, they
remained infective up to 56 days, and for up to 71 days when frozen at −6.7
◦ C.
108 Freezing in dry
ice (−70
◦ C) and liquid nitrogen (−193
◦ C) destroys the larvae.
63 The destruction of trichina larvae by
irradiation is discussed in Chapter 15.
The effect of curing and smoking on the viability of trichina in pork hams and shoulders was
investigated by Gammon et al.
38 They employed the meat of hogs experimentally infested with T.
spiralis as weanling pigs. After curing, the meat was hung for 30 days, followed by smoking for
approximately 24 hours at 90–100
◦ F, with subsequent aging. Live trichinae were found in both hams
and shoulders 3 weeks after smoking, but none could be detected after 4 weeks. The effect of NaCl
concentration, water activity (a w ), and fermentation method on viability of T. spiralis in Genoa salami
the initial symptoms. Where 10 or fewer larvae are deposited per gram of muscle tissue, there are usually
no symptoms. When 100 or more per gram are deposited, symptoms of clinical trichinosis usually
develop, whereas for 1000 or more per gram of tissue, serious and acute consequences may occur.
Muscle pain (myalgia) is the universal symptom of muscle involvement, and difficulty in breathing,
chewing, and swallowing may occur.
69 About 6 weeks after the initial infection, encystment occurs,
accompanied by tissue pain, swelling, and fever. Resistance to reinfection develops, and it appears to
be T cell mediated. Thiabendazole and mebendazole have been shown to be effective drugs for this
disease.
Diagnosis
Because the trichinae exist as coiled larvae in ovoid capsular cysts in skeletal muscles, biopsies
are sometimes performed on the deltoid, biceps, or gastrocnemius muscles. A significant eosinophilia
usually develops during the second week of the disease. Antibodies can be detected after the third week
of infection; immunological methods that may be used include bentonite flocculation, cholesterollecithin flocculation, and latex agglutination. A bentonite titer of 1:5 is significant, but this test is not
positive until at least 3 weeks after infection. This disease is positively diagnosed if a serologic test
(e.g., ELISA) is positive for IgG and/or IgM antibodies to Trichinella in the serum of victims.
Prevention and Control
Trichinosis can be controlled by avoiding the feeding of infected meat scraps or wild game meats
to swine, and by preventing the consumption of infested tissues by other animals. The feeding of
uncooked garbage to swine helps to perpetuate this disease. Where only cooked garbage is fed to pigs,
the incidence of trichinosis has been shown to fall sharply.
This disease can be prevented by the thorough cooking of meats such as pork or bear meat. In
a study on the heat destruction of trichina larvae in pork roasts, all roasts cooked to an internal
temperature of 140
◦ F (60
◦ C) or higher were subsequently found to be free of organisms.
11 Larvae
were found in all roasts cooked at 130
◦ F (54.4
◦ C) and lower, and in some roasts cooked at 135
◦ F.
The USDA recommendation for pork products is that the product be checked with a thermometer after standing and if any part does not attain 76.7
◦ C (170
◦ F), the product should be cooked
further.
105
Freezing will destroy the encysted forms, but freezing times and temperatures depend on the thickness of the product and the specific strain of T. spiralis (Table 29–4). The lower the temperature of
freezing, the more destructive it is to T. spiralis, as was demonstrated in the following study. Four selected temperatures were chosen for the freezing of infected ground pork that was stuffed into casings
and packed into boxes. When frozen and stored at −17.8
◦ C, the trichinae lost infectivity between 6
and 10 days; at −12.2
◦ C, infectivity was lost between 11 and 15 days.
91 When frozen at −9.4
◦ C, they
remained infective up to 56 days, and for up to 71 days when frozen at −6.7
◦ C.
108 Freezing in dry
ice (−70
◦ C) and liquid nitrogen (−193
◦ C) destroys the larvae.
63 The destruction of trichina larvae by
irradiation is discussed in Chapter 15.
The effect of curing and smoking on the viability of trichina in pork hams and shoulders was
investigated by Gammon et al.
38 They employed the meat of hogs experimentally infested with T.
spiralis as weanling pigs. After curing, the meat was hung for 30 days, followed by smoking for
approximately 24 hours at 90–100
◦ F, with subsequent aging. Live trichinae were found in both hams
and shoulders 3 weeks after smoking, but none could be detected after 4 weeks. The effect of NaCl
concentration, water activity (a w ), and fermentation method on viability of T. spiralis in Genoa salami