Residual Viruses in Pork Products P
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0099-2240/78/0035-0142$02.00/0 APPLIED AND ENVIRONMENTAL MICROBIOLOGY, Jan. 1978, p. 142-145 Vol. 35, No. 1 Copyright (© 1978 American Society for Microbiology Printed in U.S.A. Residual Viruses in Pork Products P. D. McKERCHER,* W. R. HESS, AND F. HAMDY Plum Island Animal Disease Center, Northeastern Region, Agricultural Research Service, U.S. Department ofAgriculture, Greenport, New York 11944 Received for publication 9 August 1977 Partly cooked canned hams and dried pepperoni and salami sausages were prepared from the carcasses of pigs infected with African swine fever virus and pigs infected with hog cholera virus. Virus was not recovered from the partly cooked canned hams; however, virus was recovered in the hams before heating in both instances. Both African swine fever virus and hog cholera virus were recovered from the dried salami and pepperoni sausages, but not after the required curing period. Animals in certain stages of infection may ing and thawing. This prolonged survival is true escape detection by the usual ante- or post-mor- even in lymph nodes and residual blood vessels tem inspection at abattoirs. Meat from such of carcasses in which rigor mortis has been com- animals may inadvertently be included in com- plete (5-7). mercial products. Such contamination may be Pork products imported into the United called primary contamination as compared with States that might be potential hazards for the secondary contamination, which occurs during spread of such diseases as SVD and FMD in- processing, storage, or distribution of the prod- clude partly cooked canned hams, dry salami uct (3). In primary contamination, one considers sausage, dry pepperoni sausage, and processed animal products because animals become in- intestinal casings. Cured and dried products fected with a great variety of viruses, and some such as salami and pepperoni sausage originat- ofthese viruses inevitably occur in food products ing from countries where SVD is present are no prepared from such animals. Some of these vi- longer permitted entry into the U.S. except for ruses, such as those of foot-and-mouth disease further processing by heating to an internal tem- (FMD), hog cholera (HC), African swine fever perature of 74.5°C (166°F) (12). Perishable (ASF), and Newcastle disease, although of great canned meat products, e.g., partly cooked hams, economic importance, are of little or no concern have been found to be free of SVDV and FMDV to human health (3). when the internal temperature of processing Investigations of outbreaks of swine vesicular reaches 690C (156°F) (6). disease (SVD) have incriminated feeding of gar- The following experiments were performed to bage contaminated with SVD virus (SVDV)-in- determine whether the viruses of ASF and HC fected meat scraps. Infectivity is reduced only could remain viable in such products. slightly or not at all in cold storage, so uncooked pork and pork products could remain a hazard MATERIALS AND METHODS indefinitely (2). Virus. The ASF virus (ASFV) used was from an FMD virus (FMDV), however, will survive outbreak in Portugal in 1960 (10). It was a 1:10 sus- only if the pH remains above 6.2. Bacon car- pension of spleen and blood from the fifth laboratory passage in domestic pigs and was designated as ASF casses treated by wet or dry salting and un- L'60, batch 5. It was titrated by the hemadsorption treated bone marrow sometimes contain virulent reaction (9) in swine buffy coat cultures prepared as virus for at least 42 days. The inactivation of described elsewhere (8), and the titers were expressed FMDV in the muscles of a carcass is generally as the log of 50% hemadsorption (Had50) per milliliter. brought about by the production of lactic acid. The HC virus (HCV) used was NADL VIII PIADC Quick freezing of beef stops acid formation, and 1, 1:10 suspension of spleen and blood. It had a titer FMDV has been recovered as long as the meat of 105.3 plaque-forming units per ml. is kept frozen. However, thawing of this quick- Source of meat. Four cross-bred Tamworth swine frozen meat allows acid formation to resume at weighing 125 pounds (56.8 kg) each were inoculated an accelerated rate that with ASFV (5 ml intravenously and 5 ml intramuscu- rapidly produces an larly [i.m.]). All swine had fever ranging from 40.4°C environment unsuitable for FMDV survival. (104.8°F) to 41.6°C (106.8°F) in 24 h. Swine were Acid formation is not as great in lymph nodes slaughtered 48 h after inoculation, and the carcasses and blood as in muscle, and the virus is likely were hung at 4°C (39°F) for 48 h. to survive longer there even with delay in freez- Two cross-bred Tamworth swine weighing approx- 142 Vol.. 35, 1978 RESIDUAL VIRUS IN PORK PRODUCTS 143 imately 125 pounds each were inoculated i.m. with before and after smoking and at intervals as shown in HCV. Both swine were killed on day 5 at peak of Tables 1, 2, and 3: whole (unground) meat samples temperature, and the carcasses were hung at 4°C in a from the carcasses, ground meat samples, brined ham, cold room for 48 h. The pH of the meat for both heated ham, and pepperoni and salami sausages. groups was 5.6. Virus assay. The samples for ASFV detection Product preparation. All meat, including hams, were ground with alundum with a mortar and pestle was deboned, and excess fat was removed. Fifty and suspended in Hanks balanced salt solution with pounds (22.7 kg) of meat was ground with a %ii;-inch lactalbumin hydrolysate culture fluid to give a 20% (4.8-mm) plate for preparation of salami sausage, and suspension. The suspension was thoroughly mixed in 50 pounds of meat was ground with a '/s-inch (3.2- a Vortex mixer and then centrifuged for 5 min at 1,000 mm) plate for preparation of pepperoni sausage. x g. The supernatant fluid was diluted serially in (i) Hams. Hams weighing about 2 pounds (0.80 kg) lactalbumin hydrolysate and assayed in swine buffy each were injected with a 16% by weight brine solution coat cultures; four cultures were used per dilution. and submerged in the same solution for 24 h at 4°C. The cultures were examined for hemadsorption at 24, The hams were then tightly packed in cans, and the 48, and 72 h. In samples in which negative or uncertain cans were sealed. Some of the canned hams were reactions were obtained at 72 h, fluids from cultures submerged in a 37.8°C (100°F) water bath, and a inoculated with the 10-' and 10-2 dilutions were sub- similar number were kept as unheated controls at passaged to fresh buffy coat cultures. All cultures were 4°C. The internal temperature of the ham was 2.5°C retained for a final reading at 7 or 8 days postinocu- (37°F) at the start of the experiment. The bath tem- lation (DPI). perature was slowly increased so that in about 3.5 h, A 20% (wt/vol) suspension of each HC sample was the internal temperature of the ham was 69°C. The made in Eagle minimum essential medium containing hams (Perishable Keep Under Refrigeration) were antibiotics (100 units of penicillin, 100 ytg of strepto- then placed in a cooling bath at 4°C for about 2 h and placed in a cold room at the same temperature. TABLE 1. Recovery ofASFV in meat samples by (ii) Salami sausage. The ground meat was thor- oughly mixed with the recommended amounts of salt, animal inoculation sugar, dextrose, white pepper, garlic, sodium nitrite, Days and sodium nitrate (4, 11). After a 48-h curing period Sample after Virus recovery at about 4°C, a lactic acid starter culture (Lactacel, slaugh- (Had5o/g) ter Merck and Co., Inc.) was thoroughly mixed with the meat. The pH at this time was 5.5. The mixed meat Whole meat 2 lo325lo0375 was then packed into 1.5-inch (37.5-mm) diameter Ground meat 2 10325_103.75 casings and kept in an environmental control chamber Salami + ingredients + 3 1020-102.5 at 20°C (68°F) and a relative humidity of 68% for 48 starter h. The salami sausages were then placed in the smok- Pepperoni + ingredients + 3 1030_10325 ing chamber and exposed to smoke produced from starter hickory chips for 12 h at 32°C (89.6°F) and a relative Ham brined 2 102.5_i103.75 humidity of 80% and for an additional 12 h at 49°C Ham heated 5 Negative (120°F) and a relative humidity of 58%. Pepperoni sausage 8 102.75_103 The sausages were then removed from the smoking Salami sausage 9 10- chamber, washed with warm water to remove surface Pepperoni sausage 30 Negative juices and fat, and placed in a drying room at 11.7°C Salami sausage 30 Negative (52°F) and 72% relative humidity for not less than 25 days. The pH of the meat was determined at the time of grinding, after mixing, and in the finished product. TABLE 2. Recovery ofHCV in meat samples by (iii) Pepperoni sausage. The ground meat was animal inoculation thoroughly mixed with recommended amounts of salt, Response of sugar, dextrose, sodium nitrate, sodium nitrite, cay- Days inoculated enne pepper, pimento, aniseed, garlic powder, and Sample after animalsa pepperoni pepper and was kept for 48 h at 4°C (4, slaughter 11). Lactic acid starter culture (Lactacel) was thor- Pig I Pig 2 oughly mixed with the meat. The mixture was packed Whole meat 1 + + into casings of 1-inch (25-mm) diameter and kept in Ham brined 2 + + an environmental control chamber at 20°C and a Pepperoni + ingredients + 2 + + relative humidity of 60% for 48 h.