698 Modern Food Microbiology Figure 29–2 Trichinella spiralis in muscle, magnification: 350× Source: From S.H Abadie, J.H Miller, L.G Warren, J.C Swartzwelder, and M.R Feldman, Manual of Clinical Microbiology, 2d ed.; copyright c 1974 by American Society for Microbiology, used with permission pork contained trichinae in diaphragm muscles examined postmortem in the United States For the 5-year period 1977–1981, 686 cases with deaths were reported in the United States.91 The CDC survey data for the years 1983–1987 show 33 outbreaks with 162 cases and death, which represents a mean of around 32 cases per year for this 5-year period.5 For the 15-year period 1973–1987, the CDC recorded 128 outbreaks and 843 cases for an average of 56 per year.4 However, the actual number of cases in the United States in 1985 had been estimated to be 100,000.7 Only three cases were recorded in Canada in 1982, with none in 1983 and 1984.103 For the 3-year period 1987–1989, fewer than 50 annual cases were reported, but 120 were reported in 1990 Ninety of these occurred in Iowa among 250 immigrants from Southeast Asia who consumed raw pork sausage An additional 15 cases occurred in Virginia; pork sausage was the vehicle food Pork was incriminated in 79% of the cases for the years 1975–1981, with bear meat in 14% and ground beef in 7% Studies on pork in retail ground beef have revealed that from to 38% of beef samples contained pork The presence of pork in ground beef may be deliberate on the part of some stores, or it may result from using the same grinder for both products The reported cases in the United States (Fig 29–3) for the 4-year period 1997–2001 are listed in Table 28–3.88 Of the 33 cases, the average number per year was about 6, with 21 traced to bear meat Although T spiralis is best known as the cause of trichinosis, this disease can be caused also by T pseudospiralis and T nativa In 1999, four cases by T pseudospiralis were traced to undercooked, barbecued wild boar meat in France, and the incubation period was between and 14 days T nativa causes trichinellosis in arctic and near-arctic regions, and the organism is freeze resistant.37 Foodborne Animal Parasites 699 Figure 29–3 Reported cases of trichinellosis by year, United States, 1970–2000 (CDC, 02) Symptoms and Treatment One to days after the ingestion of heavily encysted meat, trichinae penetrate the intestinal mucosa, producing nausea, abdominal pain, diarrhea, and sometimes vomiting When only a few larvae are ingested, the incubation period may be as long as 30 days The symptoms may persist for several days, or they may abate and be overlooked The larvae begin to invade striated muscles about 7–9 days after Table 29–3 Outbreaks of Trichinellosis Among Patients, by Year, State, Number of Cases, Month of Illness Onset, and Implicated Meat—United States, 1997–200188 Year State No of Cases Month of Illness Onset Implicated Meat 1997 1998 1999 2000 2000 2001 2001 2001 2001 Total Montana Ohio Illinois Illinois Alaska California California California California 2 2 33 December October–November March–May January August–September May May–June August November Bear jerky Bear roast, ground bear meat Pork sausage, pork jerky Pork sausage, smoked pork Bear steak (fried) Home-raised pork Home-raised pork (raw) Bear Bear 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 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 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 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 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 weeks after smoking, but none could be detected after weeks The effect of NaCl concentration, water activity (aw ), and fermentation method on viability of T spiralis in Genoa salami Foodborne Animal Parasites 701 Table 29–4 Required Period of Freezing at Temperatures Indicated Temperature (◦ C) Group (days) Group (days) −15 −23 −29 20 10 30 20 12 Note: Group = less than 15.24 cm in depth; group = more than 15.24 cm in depth From Sec 18.10 Regulations Governing the Meat Inspection of the United States Department of Agriculture (9 CFR 18.10, 1960) Source: From A.W Kotula, K.D Murrell, L Acosta-Stein, L Lamb, and L Douglass J Food Sci 48:765–768; copyright c 1983 by Institute of Food Technologists was evaluated by Childers et al.20 Pork from experimentally infected pigs was used to prepare salami The trichinae larvae were completely destroyed at day 30 and thereafter in salami made with 3.33% NaCl and given high-temperature (46.1◦ C) fermentation treatment, irrespective of product pH No larvae were found in products made with 3.33% NaCl and given low-temperature fermentation after 30 days In salami made with no salt, 25% of larvae were found at days 15–25, but none thereafter A summary of the main control steps of prevention, detection, and inactivation are illustrated in Figure 29–4 Microwave Cooking The efficacy of microwave ovens in destroying T spiralis larvae has been investigated by several groups In a homemaker-oriented study in which most trichina-infected pork roasts were cooked in microwave ovens by time rather than product temperature, Zimmerman and Beach107 found that of 51 products (48 roasts and pork chops) cooked in different ovens, remained infective Six of the did not attain a midroast temperature of 76.7◦ C, whereas the other exceeded this temperature at some point in the cooking cycle The investigators noted that the experimentally infected pork used Figure 29–4 Various stages in the movement of pork from the farm to consumer at which control efforts may be applied Source: From K.D Murrell 1985 Food Technol 39(3):65–68, 110; copyright c Institute of Food Technologists 702 Modern Food Microbiology in the study came from pigs infected with 250,000 T spiralis, which produced around 1000 trichina per gram of tissue compared to about trichina per gram in naturally infected pigs Although the large number of trichinae per gram may have been a factor in their survival at the cooking procedures employed, the inherent unevenness of cooking in microwave ovens is of concern In another study, whereas trichinae larvae were not inactivated at 77 or 82◦ C in microwave ovens, cooking to an internal temperature of 77◦ C in a conventional convection oven, flat grill, charbroiler, or deep fat did inactivate the larvae.64 Further, infected larvae survived rapid cooking that involved thawing pork chops in an industrial microwave oven followed by cooking on a charbroiler to 71 or 77◦ C.65 The cooking of pork in microwave ovens is clearly a matter of concern relative to the destruction of trichinae larvae, and two factors may explain the greater efficiency of convection ovens over microwave ovens First, microwave cooking is rapid, and herein may lie the problem Oven heat has been shown to be more destructive to trichinae larvae in roasts when slow-cooked in conventional ovens at 200◦ F (93.3◦ C) than when fast-cooked at 350◦ F or 176.7◦ C.11 Second, a convection oven is more uniformly heated than some microwave ovens This is minimized if the product is rotated in the latter type ovens or if the oven is equipped with an automatic rotating device Otherwise, uneven heating occurs, leading to undercooking of some parts of a roast while other parts may be overcooked It has been shown that a set of criteria that leads to consistent doneness of pork products in microwave ovens will result in safe products.106 Anisakiasis This roundworm infection is caused by two closely related genera and species: Anisakis simplex (the herringworm or whaleworm) and Pseudoterranova decipiens (formerly Phocanema; codworm or sealworm) Both of these organisms have several intermediate hosts and generally more than one definitive host Humans are not final hosts for either, and human disease occurs as the result of humans being accidental interlopers in the life cycles of these worms The definitive hosts are marine mammals—whales in the case of A simplex and gray (and other) seals in the case of P decipiens Feces of these animals contain thousands of eggs, which when they enter water undergo their first molt (stage L1 to stage L2) The free-swimming larvae that result are ingested by small crustaceans (copepods), and they, in turn, are ingested by larger crustaceans, which serve as intermediate hosts during the second molt (stage L2 to L3) A final host may ingest L3 larvae along with the crustacean intermediate, but more often, L3 is ingested by fish or squid, which may, in turn, be ingested by larger fish before reaching the final host The last two molts (L3 and L4) lead to adults that mate, and these events take place in the final host The infectious larva is L3, and it is usually found in tight, flat coils in or on fish viscera, and some larvae may occur in the belly flap muscles of fish Because of its preference for whale hosts, A simplex is found more often in fish from the northern Pacific In the case of P decipiens, eggs in seal feces are ingested by copepods, and L2- or early-L3-stage larvae are ingested by the first intermediate host—fish In fish, they penetrate the stomach wall, enter the body cavity, and many burrow into fish muscles In fish, the L3 larvae grow to 25–50 mm in length and are red to brown in color The final host, seals, tends to ingest the organisms principally from smelt and other small fish Human infections occur upon the ingestion of fish that contain L3- and L4-stage larvae Thus, anisakids not mature in humans Disease symptoms arise from the activities of the juvenile worms A simplex larvae are more harmful than those of P decipiens because they often penetrate the mucosal lining, whereas most P decipiens larvae are passed in feces or are coughed up or vomited after irritating ... Pork sausage, smoked pork Bear steak (fried) Home-raised pork Home-raised pork (raw) Bear Bear 700 Modern Food Microbiology the initial symptoms Where 10 or fewer larvae are deposited per gram of... Institute of Food Technologists 702 Modern Food Microbiology in the study came from pigs infected with 250,000 T spiralis, which produced around 1000 trichina per gram of tissue compared to about... 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◦