TpeL-producing strains of Clostridium perfringens type A are highly virulent for broiler chicks.

Clostridium perfringens type A and type C are causative agents of necrotic enteritis (NE) in poultry. TpeL, a recently-described novel member of the family of large clostridial cytotoxins, was found in C. perfringens type C. Others have since reported TpeL in type A isolates from NE outbreaks, suggesting that it may contribute to the pathogenesis of NE. The virulence of TpeL-positive and -negative C. perfringens strains from cases of NE was examined by challenge of broiler chicks. Gross lesions typical of NE were observed in all challenged birds, and those inoculated with TpeL(pos) strains had higher average macroscopic lesion scores than those inoculated with a TpeL(neg) strain. Infection with TpeL(pos) strains may yield disease with a more rapid course and higher case fatality rate. Thus, TpeL may potentiate the effect of other virulence attributes of NE strains of C. perfringens. However, TpeL(pos) and Tpel(neg) strains compared here were not isogenic, and definitive results await the production and testing of specific TpeL mutants.

Clostridium perfringens alpha toxin is produced in the intestines of broiler chicks inoculated with an alpha toxin mutant.

Poultry necrotic enteritis (NE) is caused by specific strains of Clostridium perfringens, most of which are type A. The role of alpha toxin (CPA) in NE has been called into question by the finding that an engineered cpa mutant retains full virulence in vivo[9]. This is in contrast to the finding that immunization with CPA toxoids protects against NE. We confirmed the earlier findings, in that 14-day-old Cornish × Rock broiler chicks challenged with a cpa mutant developed lesions compatible with NE in >90% of birds inoculated with the mutant. However, CPA was detected in amounts ranging from 10 to >100 ng per g of gut contents and mucosa in birds inoculated with the cpa mutant, the wildtype strain from which the mutant was constructed, and our positive control strain. There was a direct relationship between lesion severity and amount of CPA detected (R = 0.89-0.99). These findings suggest that the role of CPA in pathogenesis of NE requires further investigation.

Enterotoxigenic Escherichia coli infection in captive black-footed ferrets.

Enterotoxigenic Escherichia coli with genes for heat stabile toxins Sta and STb was isolated from the gastrointestinal tract and multiple visceral organs of three adult and three juvenile black-footed ferrets (Mustela nigripes) that died in a captive breeding colony between 24 May 1998 and 2 July 1998. Similar isolates were obtained from rectal swabs of one adult and one juvenile that were clinically ill. All were fed a diet composed of mink chow, raw rabbit meat, beef liver powder, blood meal and lard. Escherichia coli of the same toxin genotype was isolated from the mixed ration. Clinical signs included sudden death, dehydration, anorexia and diarrhea. Necropsy lesions included acute enteritis with large numbers of rod shaped bacteria microscopically visible on intestinal villi.

An outbreak of type C botulism in 12 horses and a mule.

A USDA Early Response Team investigated deaths of several horses and a mule in northern Arizona at the request of local animal health officials. Thirteen animals (12 horses and 1 mule) housed at 5 facilities in a 7.4 square mile area died between August 1998 and January 1999. Clinical signs consisted of muscular weakness that rapidly progressed to lateral recumbency. Ten animals had paresis of the tongue, throat, or lips. Affected animals appeared alert and were interested in eating and drinking, even while recumbent. All 13 animals were euthanatized. Clostridium botulinum type C was isolated from feces or intestinal contents from 3 affected horses. Preformed toxin was detected in samples of soil and bird droppings collected from a nearby horse burial site. It was hypothesized that the outbreak was a result of birds, presumably ravens, feeding at the burial site and at horse facilities in the area that transferred toxin to the affected animals.

Diagnostic and feedlot pathology.

Common feedlot diseases are discussed with emphasis on pathology and diagnosis. Differential lesions are discussed. Diseases are categorized by body systems.

Sudden death of feedlot cattle.

Sudden deaths or the sudden death syndrome are perceived as major concerns in cattle feedlots because most of these deaths occur in cattle near market weight. Etiology and preventive measures are poorly defined. The current literature indicates that sudden deaths are associated most commonly with digestive upsets. Death is thought to be the result of interactions between factors including acidosis, bloat, and endotoxemia. Trauma, peracute interstitial pneumonia, and other identifiable events are specifically defined but relatively uncommon. Enterotoxemia is of questionable significance as a cause of sudden deaths.

Induction of gross and microscopic lesions of porcine proliferative enteritis by Lawsonia intracellularis.

OBJECTIVE: To evaluate experimental induction of porcine proliferative enteritis (PPE), using cell cultured Lawsonia intracellularis (ileal symbiont intracellularis), and to determine whether dexamethasone administration or age of the host or both affects susceptibility to L intracellularis infection. ANIMALS: Thirty-two 3- or 7-week-old pigs. PROCEDURES: Lawsonia intracellularis was extracted from tissue with lesions of PPE and was subcultured in a continuous Henle 407 cell line at 37 C under an atmosphere of 5% CO2. Three- or 7-week-old pigs were inoculated orally with 100 ml of a 10-day-old cell culture preparation of the bacterium or infective intestinal homogenates. Control pigs were inoculated with uninfected Henle cells. Pigs were observed daily for clinical signs of infection and necropsied at death or at termination of the study. Lesions in the small and large intestines were recorded. RESULTS: Diarrhea was observed in pigs 4 to 7 days after inoculation with the pure culture agent or homogenates and lasted throughout the study period. Histologic lesions consistent with PPE were detected in pigs inoculated with pure culture. Intestinal lesions were absent in control pigs inoculated with uninfected Henle cells. Differences in lesions were not significant between treatment groups that varied in age or were receiving dexamethasone. Tissue specimens from pigs at necropsy were culture negative for Salmonella spp and Serpulina hyodysenteriae. CONCLUSION AND CLINICAL RELEVANCE: Gross and microscopic lesions typical of acute PPE were induced in pigs by use of a cell culture agent. Age differences and the stress induced by administration of dexamethasone had no effect on development of intestinal lesions.

Injection-site lesions: incidence, tissue histology, collagen concentration, and muscle tenderness in beef rounds.

The national incidence and extent of injection-site lesions in the muscles of the round were determined via audits conducted at retail stores and in purveying establishments. Two additional experiments were conducted to examine the subsequent effects of pharmaceutical administration on tissue histology, soluble and insoluble collagen concentration, and muscle tenderness in beef bottom-rounds. Injection-site lesion incidence in beef round cuts audited at retail (n = 3,538) and in steak-cutting facilities (n = 15,464) was 8.45 and 10.04%, respectively, with an average lesion-trim of 314.7 and 191.59 g, respectively, in these two studies. Lesion classification revealed that 93.20 and 99.91% of lesions reported for the retail and purveyor audits, respectively, were chronologically aged lesions. Overall, 19,002 round cuts were examined, and injection-site lesion incidence (nationally) was 9.74%, whereas lesion-trim averaged 211.8 g. Warner-Bratzler shear measurements taken near lesions and in areas 7.62 cm from the lesions were higher (P < .001) for lesioned, than for control bottom-round steaks. Warner-Bratzler shear values for lesion cores were 3.5 times greater than those in paired control (non-affected) steaks. Concentrations of insoluble and soluble collagen were much higher (P < .001) at the site of the lesion center in lesion-afflicted vs control steaks. Histological determinations of the relative proportions of muscle, connective tissue and fat to a distance of 5.08 cm from the site of the lesion center confirmed that severe disruption of muscle tissue constituents and architecture had occurred. Injection-site lesions occur at an unacceptable frequency in the muscles of the round, and severe tissue changes accompany these lesions that can dramatically affect tenderness of those cuts.

Injection-site lesions in carcasses of cattle receiving injections at branding and at weaning.

Crossbred steer and heifer calves (n = 84) were given injections at branding and at weaning (using a completely randomized block design); 225 to 376 d later, pairs of two subprimal cuts from each animal were evaluated for incidence and severity of injection-site lesions. The four products compared were 1) a 2-mL clostridial, 2) a 5-mL clostridial, 3) vitamin AD3, and 4) a long-acting oxytetracycline antibiotic (OTC). Branding-age calves (mean 48.3 d of age) received intramuscular injections of two of the four products, in the semimembranosus (inside round) muscles (one in the left muscle and one in the right); at weaning age (mean 199.3 d of age), calves received injections of the remaining two products in the gluteus medius (top sirloin butt) muscles (one in the left and the other in the right). Injections at branding of 2 mL of clostridial, 5 mL of clostridial, vitamin AD3, and OTC caused injection-site lesions in 72.5, 92.7, 5.3, and 51.2%, respectively, of inside rounds from slaughter cattle. Incidence of injection-site lesions was lowest (P < .05) among inside rounds and top sirloin butts from animals given vitamin AD3 (as calves, and at both branding and weaning times) and was highest (P < .05) in inside rounds from cattle given, as calves, injections of 5 mL of clostridial at branding or of OTC at weaning. Less trimming was required to remove the lesions resulting from injections of all four products when they were given at weaning time. Before completion of the present study, it was thought that injection-site lesions were from damage that subsisted only briefly following an inoculation; these results make it abundantly clear that intramuscular administration of clostridials and certain antibiotics will cause damage so severe that it will be evident in beef muscle 7.5 to 12 mo later.

Incidence of injection-site blemishes in beef top sirloin butts.

The occurrence of damaged muscle tissue resulting from intramuscular injections of animal-health products represents a "quality control" problem and an economic loss to the beef industry. Five individual and sequential national audits of injection-site blemishes in beef top sirloin butts have been conducted at the steak-cutter level. During the most recent audit (March 1993), the incidence of injection-site blemishes in top sirloin butts was determined to be 10.87 +/- 2.99%, with an average weight per blemish of 123.39 +/- 5.48 g. A 5-point classification system used to partition the blemishes into chronological stages of the healing process suggested that the majority of the blemishes originated at the cow-calf or stocker levels, or early in the finishing period. Evaluation of blemish data by geographic location of plant-of-origin suggests that the problem occurs throughout the beef production sector.

Abomasal erosions in feedlot cattle.

The abomasa of 1,949 slaughtered feedlot cattle, 45 necropsied feedlot cattle that died 2 to 45 days after arrival, and 45 necropsied pastured cattle were opened and examined. Of these organs, 484, 1, and none, respectively, contained erosions. The slaughtered cattle were fattened at 3 locations: 1,305 with 430 eroded abomasa were fed a ration of corn in northeastern Colorado; 144 cattle with 4 affected abomasa fed a ration of milo in south-central Arizona; and 500 cattle with 50 affected abomasa fed a ration of milo and corn in northwestern Texas. The red-brown lesions developed late during the second semester of fattening and were located mostly on fundic folds. Those on fold edges were linear and were 2 to 15 cm long, whereas those on fold sides were punctate and were 2 to 15 mm in diameter. Normal fold edges contained fewer goblet cells and less surface mucus than did fold sides. Eroded folds had disruption of surface epithelium, damage to endothelial cells, and dilated, thrombosed, congested, and ruptured capillaries. Mean pH values of 16 normal and 17 eroded abomasa were 4.7 and 3.9, respectively. Necrosis of all tissue toward the mucosal surface of erosions was extensive. The cause of gastric erosion in cattle is not known.

Experimental reproduction of porcine proliferative enteritis.

Conventional crossbred pigs from different sources and of different weights were examined for susceptibility to porcine proliferative enteritis. The ileal mucosa of pigs with the disease was emulsified and suspended in Mueller-Hinton broth. Pigs weighing 15, 120 and 200 lb (6.8, 54.5 and 91 kg) (four pigs per group) were stressed and inoculated orally with 80 ml of emulsified proliferative ilea. Severe lesions of porcine proliferative enteritis were detected in three of the four pigs weighing 6.8 kg. Mild lesions were detected in two of the four pigs in each of the other two groups. Gross lesions consisted of reticulation of the serosa, and hyperaemia and thickening of the mucosa with either fibrin or blood clots adherent to the mucosal surface. Inflammation, numerous mitotic figures and epithelial cell proliferation were observed microscopically in the crypts. Silver stained sections revealed numerous comma-shaped organisms in the crypts of infected epithelial cells. Using this method, serial reproduction of the disease was accomplished through the passage of fresh and previously frozen inocula. The virulence of the freshly prepared inoculum increased with passage through the host, whereas the inoculum prepared from tissue that had previously been frozen showed a decrease in infectivity and virulence. These data provide strong evidence for the infectious nature of this disease.

Passive protection of segmented swine colonic loops against swine dysentery.

Swine-ligated loops were used to demonstrate passive protection against swine dysentery. Loops inoculated with immune sera containing complement and with homologous Treponema hyodysenteriae were normal at necropsy. Loops inoculated with heat-inactivated immune sera and heterologous T hyodysenteriae were not protected. Loops inoculated with heat-inactivated immune sera and homologous T hyodysenteriae were partially protected. Positive control loops inoculated with isolate B204 (88%) or B234 (44%) T hyodysenteriae and normal sera developed lesions typical of swine dysentery, whereas negative control loops inoculated with nonexposed sera only were normal.

Eliminating swine dysentery from selected herds.

In attempts to eliminate swine dysentery from a herd, the total cost of nitroimidazole medication in the water can be estimated at 16/gal over 3-4 weeks and for carbadox in the feed at 70/100 lb over 6-8 weeks. Use of dimetridazole or ipronidazole in the water for 3-4 weeks or carbadox in the feed for 6-8 weeks eliminates Treponema hyodysenteriae from the porcine gut. A 30-day (10 weeks with carbadox) preslaughter withdrawal time should be provided. Impervious surfaces should be thoroughly sanitized, while permeable surfaces and lots should be cleaned, dried and aired well for 2-3 weeks in warm, dry weather and for at least 60 days in cool, damp weather. Animal vectors and fomites must be controlled. Isolation of new breeding stock for 3-4 weeks helps prevent recontamination. While elimination of swine dysentery is not practical in many herds because of poor facilities or lack of producer commitment, a properly designed program can result in economic benefits.

The effects of challenge on the humoral and cellular immune responses in pseudorabies vaccinated swine.

The effects of challenge exposure on the humoral and cellular immune responses in pseudorabies vaccinated swine were studied in 84 barrows. The pigs were divided into seven groups and challenge exposed to a virulent strain of pseudorabies virus on months 1, 3, 5, 8, 10, 12 and 14 after vaccination. The pigs were vaccinated with commercial attenuated and inactivated pseudorabies virus vaccines. The protection conferred by vaccination was equally effective with both types of vaccines. The levels of cellular and humoral immunity after challenge exposure in pigs vaccinated with either type of vaccine were similar. The cell-mediated immune response can be effectively used for the early detection of pigs exposed to pseudorabies virus. Virus isolation attempts from the brain and spleen in most of the vaccinated pigs were unsuccessful.

Involvement of lipopolysaccharide in the pathogenicity of Treponema hyodysenteriae.

Treponema hyodysenteriae, the etiologic agent of swine dysentery, caused gross and microscopic lesions in the large intestines of C3HeB/FeJ mice. No gross lesions were observed in the intestines of the closely related, but lipopolysaccharide-resistant, C3H/HeJ strain of mice, and microscopic lesions were mild, if present at all. In the presence of actinomycin D, 1 mg of T. hyodysenteriae lipopolysaccharide (LPS) was lethal for C3HeB/FeJ but not for C3H/HeJ mice. Also, the treponemal LPS was chemotactic for macrophages from C3H/HeJ mice but not for macrophages from C3HeB/FeJ mice. The difference between the two mouse strains in lesion development may be due to the nondestructive nature of LPS in C3H/HeJ mice, which suggests that the treponemal LPS is involved in the pathogenicity of T. hyodysenteriae. T. hyodysenteriae may prove to be a useful bacterium in the study of LPS-resistant C3H/HeJ mice, because resistance to the treponemal LPS and to the treponeme itself appear to correlate.

Effects of vaccination on lesion development in pseudorabies virus-challenged swine.

The effects of vaccination against pseudorabies virus (PRV) infection were studied in 93 barrows. Commercial attenuated and inactivated PRV vaccines were used. The protection provided was evaluated by the comparison of clinical signs, gross lesions, and microscopic lesions among vaccinated and nonvaccinated pigs after challenge exposure with a sublethal dose of PRV. Histopathologic changes are described for the CNS and other tissues. Neither the modified live- nor the inactivated-PRV vaccines prevented clinical signs or microscopic lesions in pigs after challenge exposure. However, both vaccines diminished the severity of clinical signs and microscopic lesions in the animals for a period of up to 8 months after they were vaccinated. Protection against clinical signs and microscopic lesions was absent in the pigs 10 months after the vaccination.

Serotype-specific protection against Treponema hyodysenteriae infection in ligated colonic loops of pigs recovered from swine dysentery.

Resistance to Treponema hyodysenteriae (serotypes 1, 2, 3, and 4) infection was evaluated in ligated colonic loops in pigs recovered from swine dysentery. Lesions were present in most loops from recovered swine inoculated with heterologous serotypes; however, lesions were not present in loops of recovered swine inoculated with homologous serotypes.

Naturally occurring porcine proliferative enteritis: pathologic and bacteriologic findings.

The lesions of porcine proliferative enteritis were studied by light and electron microscopic techniques in feeder pigs, fattening hogs, bred gilts, sows, and boars. The characteristic microscopic feature common to all age groups was proliferation of immature crypt epithelial cells, primarily in the ileum and the distal part of the jejunum. Similar changes were also observed in the midjejunum, cecum, and colon of a new swine. The earliest detectable microscopic lesion was focal proliferation of crypt epithelial cells with accompanying inflammation of the lamina propria and leukocytic exudate within affected crypt lumina. Lesions progressed to diffuse crypt cell proliferation, elongation of crypts, and loss of villi. Immature epithelial cells contained variable numbers of intracytoplasmic, nonmembrane-bound, curved organisms resembling Campylobacter sp bacteria. Similar organisms were within phagolysosomes of macrophages in the lamina propria and within the cytoplasm of crypt epithelial cells undergoing mitosis. Campylobacter sputorum subsp mucosalis was isolated from the ileal mucosa in 30 of 58 swine.