Pathologic features of polybrominated biphenyl toxicosis in the rat and guinea pig.

Young male rats were fed a diet containing 0, 1, 10, 100, or 500 ppm of a commercial mixture of polybrominated biphenyls (PBB) that had been accidentally incorporated into a mineral mixture and fed to Michigan livestock and poultry. After 30 days, 9 of the 12 rats in each group were killed and tissues were examined. Liver weight to body weight ratios were significantly increased at all feeding levels; at 500 ppm, liver weight had more than doubled. Kidney weight was not affected. Microscopic lesions were mostly confined to the liver and consisted of extensive swelling and vacuolation of hepatocytes in rats fed diets containing 100 and 500 ppm of PBB. Slight swelling and vacuolation were seen in rats fed the diet containing 10 ppm, and lesions were not found at 0 or 1 ppm. There was a significant increase in hepatic mitochondrial size at 1 ppm, and smooth endoplasmic reticulum was markedly increased at 100 and 500 ppm. Myelin bodies were present at 100 and 500 ppm, and vacuoles were numerous. Rats killed at 60 days had similar lesions. The activity of hepatic microsomal enzymes increased at all levels of feeding of PBB. Rat pups nursing dams fed a diet containing 10 ppm of PBB had microscopic and ultrastructural hepatic lesions. When guinea pigs were fed PBB at the same amounts as were rats, the results were strikingly different. Guinea pigs fed a diet containing 500 ppm of PBB died within 15 days; at 100 ppm, only 2 of 6 survived for 30 days. Effects on liver weight were inconsistent, but 2 of 6 fed a diet containing 10 ppm had enlarged livers.     

Pathology of experimentally induced polybrominated biphenyl toxicosis in pregnant heifers.

Toxicosis was induced in pregnant Holstein-Friesian heifers by giving polybrominated biphenyls a in gelatin capsules at the rate of 25 g/day. Initially, this dosage was approximately 67 mg/kg of body weight. Clinical signs were anorexia, excessive lacrimation and salivation, diarrhea, emaciation, dehydration, depression, and abortion. Fever was not evident during the experiment. Values for serum glutamic-oxalacetic transaminase, lactic dehydrogenase, blood urea nitrogen, and bilirubin were increased. Changes in packed cell volume, hemoglobin content, total erythrocyte and leukocyte counts, and differential leukocyte counts were minimal and reflected dehydration and secondary infection. The principal urine changes were decreased specific gravity and moderate proteinuria. Gross necropsy findings included dehydration; subcutaneous emphysema and hemorrhage; atrophy of the thymus; fetal death with concomitant necrosis of cotyledons; kidneys that were enlarged, pale tan to gray; thickened wall of the gallbladder; inspissated bile; edema of abomasal folds; mucoid enteritis; linear hemorrhage and edema of the rectal mucosa; and secondary pneumonia. Microscopic changes were most marked in the kidneys, gallbladder, and eyelid. In the kidney, the principal changes were extreme dilatation of collecting ducts and convoluted tubules, with epithelial degenerative changes of cloudy swelling, hydropic degeneration, and separation from the basement membrane. Common changes in the gallbladder were moderate to marked hyperplasia and cystic dilatation of the mucous glands in the lamina propria. The changes in the eyelids were characterized by hyperkeratosis, with accumulations of keratin in hair follicles of the epidermis and squamous metaplasia with keratin cysts in the tarsal glands. Clinical signs and lesions of toxicosis did not develop in heifers given the polybrominated biphenyls at the rate of 0.25 mg and 250 mg/day for 60 days. Initially these rates were approximately 0.00065 mg/kg and 0.65 mg/kg of body weight, respectively.     

Serum isocitrate dehydrogenase during polybrominated biphenyl toxicosis in dairy cattle

Bovine serum isocitrate dehydrogenase (sICDH) was investigated in dairy cattle as a clinical measurement indicative of hepatic injury. Conditions for optimization of isocitrate dehydrogenase assays for bovine serum are described. Assays of sICDH in normal cattle show average activities of .814 (SD = .202) units/ml serum with a range of .316 to 1.268 for 83 samples taken from 32 animals. Investigation of sICDH in pregnant dairy cattle experimentally dosed with polybrominated biphenyl (PBB) showed no discernible elevations until doses were sufficient to cause toxicosis (25,000 mg PBB/d). Cows lethally dosed with 25,000 mg PBB/d had moderate elevations of sICDH (approximately a twofold increase) concomitant with severe toxicosis in some but not all animals. This PBB dose also caused abortion or fetal death in pregnant animals; elevation of sICDH in these animals was coincident with fetal trauma. This suggests that sICDH may be influenced by fetoplacental contributions in pregnant animals. Non-pregnant cows, intoxicated with PBB, had minimal sICDH elevation as compared with 10-fold in a calf with experimentally induced hepatotoxicity (thioacetamide). This observation was consistent with histopathological findings of minimal, if any, hepatic involvement in dairy cattle lethally intoxicated with PBB. Serum isocitrate dehydrogenase appears to be a useful adjunct to the ordinary complement of serum chemistries used for clinical diagnosis; however, it does not appear to reflect exclusively hepatic injury.     

Toxicologic disease of the digestive tract.

There is a diverse and long list of toxicants that can affect the digestive system of food-producing animals. The plants and other natural toxicants discussed in this article are those primarily affecting the GI system. A number of other plants may also affect the digestive tract, but the effects from these are considered secondary and less pronounced. Often, plant poisonings affecting the digestive tract present with similar clinical signs, and a good thorough history is necessary to help differentiate between them. Moreover, a careful walk through the pasture with a keen eye to note plants that have been browsed or grazed may greatly assist the history. In cases where toxins are suspected as the cause of a GI disorder, consultation with a veterinary toxicologist at a diagnostic laboratory may be indicated. These professionals are knowledgeable about a wide variety of natural and other toxicants that may be present in your area. They can help with developing a differential diagnosis and the selection of appropriate samples to confirm the diagnosis.     

Toxicologic evaluation of chlorpyrifos in cats

Twenty-four male domestic shorthair cats were used to evaluate the acute and chronic effects of a single, toxic but sublethal, orally administered dose of chlorpyrifos. A dosage of 10 mg/kg of body weight did not induce clinical signs of toxicosis, but a dosage of 40 mg/kg induced clinical signs of toxicosis, and 1 of 12 cats died. Chlorpyrifos given at a dosage of 0.1 mg/kg to 2 cats reduced whole blood and plasma cholinesterase (Che) activities to values obtained after cats were given doses that induced clinical signs of toxicosis. Regeneration time for whole blood and plasma Che activities ranged from 7 to 28 days. Brain Che activity was considerably decreased in 1 cat that died 4.5 hours after dosing, but was normal in all others at 28 days after dosing. Other than decreased Che activity, significant changes were not seen in hematologic or serum biochemical values. Toxin-related lesions were not seen during macroscopic or microscopic examination.     

Toxicologic effects of ribavirin in cats

Ribavirin, a broad-spectrum antiviral agent active in vitro against a number of RNA and DNA viruses, has been associated with moderate toxicity in laboratory animals and humans. Clinically, ribavirin has been used effectively in persons primarily to treat life-threatening viral diseases such as acute haemorrhagic fever or viral pneumonia of infants. In order to evaluate the feasibility of using this antiviral agent in cats, the effects of oral (p.o.), intramuscular (i.m.) and intravenous (i.v.) doses of ribavirin in 27 9-month-old specific-pathogen-free cats were evaluated by haematology, clinical chemistries, bone marrow biopsies and histopathology. Ribavirin was administered once daily for 10 consecutive days at a dose of either 11, 22, or 44 mg/kg after which all cats were euthanatized and necropsied. Most cats receiving 22 or 44 mg of ribavirin/kg became anorectic and suffered some degree of weight loss (0.2 to 0.6 kg), and about one-third of the cats developed diarrhoea and/or mucous membrane pallor. Icterus or haemorrhage was not observed. The most profound and consistent haemato-logic change, particularly among the moderate and high dosage groups regardless of route of administration, was a significant and severe thrombocytopenia (range, 33–78% reduction in mean platelet counts vs. baseline). Other changes, particularly reductions in total WBC and neutrophils and reductions in RBC and PCV, tended to occur at lower ribavirin dosages, but generally they were not statistically significant. Cats given 44 mg of ribavirin/kg i.v. showed significant decreases in leukocyte variables, including total WBC (P = 0.016), neutrophils (P= 0.026) and lymphocytes (P= 0.047). Mild-to-moderate increases in serum alanine aminotransferase and alkaline phosphatase activities occurred at doses of 22 and 44 mg/kg. Evaluation of bone marrow biopsies before and after treatment revealed that cats given 11 mg of ribavirin/kg had mild megakaryocytic (MK) hypoplasia, whereas cats receiving 22 or 44 mg/kg had progressively severe degrees of MK hypoplasia and dysplasia, asynchronous MK maturation, and increased myeloidrerythroid ratio. Pathologic changes in ribavirin-treated cats generally were mild and included primarily enteritis (seven cats) and hepatocellular vacuolation and/or centrilobular necrosis (seven cats). Results of this study in cats indicated that daily administration of ribavirin at a dose range of 11 to 44 mg/kg induced a dose-related toxic effect on bone marrow, primarily on megakaryocytes and erythroid precursors, and at the higher dosages it suppressed numbers of circulating leukocytes.     

The Role of the Toxicologic Pathologist in the Post-Genomic Era#

An era can be defined as a period in time identified by distinctive character, events, or practices. We are now in the genomic era. The pre-genomic era: There was a pre-genomic era. It started many years ago with novel and seminal animal experiments, primarily directed at studying cancer. It is marked by the development of the two-year rodent cancer bioassay and the ultimate realization that alternative approaches and short-term animal models were needed to replace this resource-intensive and time-consuming method for predicting human health risk. Many alternatives approaches and short-term animal models were proposed and tried but, to date, none have completely replaced our dependence upon the two-year rodent bioassay. However, the alternative approaches and models themselves have made tangible contributions to basic research, clinical medicine and to our understanding of cancer and they remain useful tools to address hypothesis-driven research questions. The pre-genomic era was a time when toxicologic pathologists played a major role in drug development, evaluating the cancer bioassay and the associated dose-setting toxicity studies, and exploring the utility of proposed alternative animal models. It was a time when there was shortage of qualified toxicologic pathologists. The genomic era: We are in the genomic era. It is a time when the genetic underpinnings of normal biological and pathologic processes are being discovered and documented. It is a time for sequencing entire genomes and deliberately silencing relevant segments of the mouse genome to see what each segment controls and if that silencing leads to increased susceptibility to disease. What remains to be charted in this genomic era is the complex interaction of genes, gene segments, post-translational modifications of encoded proteins, and environmental factors that affect genomic expression. In this current genomic era, the toxicologic pathologist has had to make room for a growing population of molecular biologists. In this present era newly emerging DVM and MD scientists enter the work arena with a PhD in pathology often based on some aspect of molecular biology or molecular pathology research. In molecular biology, the almost daily technological advances require one’s complete dedication to remain at the cutting edge of the science. Similarly, the practice of toxicologic pathology, like other morphological disciplines, is based largely on experience and requires dedicated daily examination of pathology material to maintain a well-trained eye capable of distilling specific information from stained tissue slides - a dedicated effort that cannot be well done as an intermezzo between other tasks. It is a rare individual that has true expertise in both molecular biology and pathology. In this genomic era, the newly emerging DVM-PhD or MD-PhD pathologist enters a marketplace without many job opportunities in contrast to the pre-genomic era. Many face an identity crisis needing to decide to become a competent pathologist or, alternatively, to become a competent molecular biologist. At the same time, more PhD molecular biologists without training in pathology are members of the research teams working in drug development and toxicology. How best can the toxicologic pathologist interact in the contemporary team approach in drug development, toxicology research and safety testing? Based on their biomedical training, toxicologic pathologists are in an ideal position to link data from the emerging technologies with their knowledge of pathobiology and toxicology. To enable this linkage and obtain the synergy it provides, the bench-level, slide-reading expert pathologist will need to have some basic understanding and appreciation of molecular biology methods and tools. On the other hand, it is not likely that the typical molecular biologist could competently evaluate and diagnose stained tissue slides from a toxicology study or a cancer bioassay. The post-genomic era: The post-genomic era will likely arrive approximately around 2050 at which time entire genomes from multiple species will exist in massive databases, data from thousands of robotic high throughput chemical screenings will exist in other databases, genetic toxicity and chemical structure-activity-relationships will reside in yet other databases. All databases will be linked and relevant information will be extracted and analyzed by appropriate algorithms following input of the latest molecular, submolecular, genetic, experimental, pathology and clinical data. Knowledge gained will permit the genetic components of many diseases to be amenable to therapeutic prevention and/or intervention. Much like computerized algorithms are currently used to forecast weather or to predict political elections, computerized sophisticated algorithms based largely on scientific data mining will categorize new drugs and chemicals relative to their health benefits versus their health risks for defined human populations and subpopulations. However, this form of a virtual toxicity study or cancer bioassay will only identify probabilities of adverse consequences from interaction of particular environmental and/or chemical/drug exposure(s) with specific genomic variables. Proof in many situations will require confirmation in intact in vivo mammalian animal models. The toxicologic pathologist in the post-genomic era will be the best suited scientist to confirm the data mining and its probability predictions for safety or adverse consequences with the actual tissue morphological features in test species that define specific test agent pathobiology and human health risk.     

Experimental polychlorinated biphenyl toxicosis in germfree pigs.

The effects of polychlorinated biphenyls were studied in eight germfree pigs. Beginning at fourteen days of age, two pigs each were fed daily 12.5, 25, 50 and 100 mg/kg body weight of polychlorinated biphenyls as Aroclor 1254. Three germfree pigs were negative controls. Clinically the treated pigs had inappetance, a hemorrhagic diarrhea, erythema of the nose and the anus, retarded growth, distended abdomen and at the higher dose levels, incoordination and coma followed by death. Deaths occurred in 11 to 35 days after exposure. At necropsy, the piglets exhibited grossly enlarged mottled liver, erosions of the gastric mucosa, hemorrhages through the mesentery and the intestinal wall, a fibrinous pericarditis, a hypoplastic thymus and congested swollen thyroid glands. The histopathological lesions included hepatic centrolobular necrosis, interstitial myocarditis, endocarditis, myopathy of the muscles, gastric erosions and colitis. All of the organs examined for polychlorinated biphenyls had elevated residue levels which were particularly high in the fat, liver, psoas muscle, brain and kidney and were higher than has been reported in conventional pigs fed approximately equal concentrations of polychlorinated biphenyls. The severity of clinical signs, pathological changes and tissue concentrations were directly related to the dose administered and were more pronounced in the germfree pigs than has been described in conventional pigs.     

Pharmacologic-endocrinological findings in animal experiments with TURISYNCHRON and SUISYNCHROM. 2. Toxicologic findings

Acute, subacute and chronic toxicity of TURISYNCHRON and its zinc complex (SUISYNCHRON) was tested in mice, rats and dogs. The acute toxicity of SUISYNCHRON was lower than that of TURISYNCHRON in mice and rats. Ulcerative lesions in the duodenum produced by high doses of SUISYNCHRON were quantitatively less pronounced than those produced by similar doses of TURISYNCHRON. Subacute toxicity testing in rats showed that neither preparation had any toxic effect on haematological, clinical chemical or histological criteria in the dosages selected. Chronic toxicity testing of TURISYNCHRON in dogs did not reveal any evidence of toxic damage.     

Dynamics of Salmonella contamination in a commercial quail operation.

Control of carcass contamination requires knowledge of the source and dynamics of spread of Salmonella in commercial poultry production. We examined Salmonella contamination at a U.S. commercial quail operation. Pulsed-field gel electrophoresis (PFGE) was used to type isolates in order to trace Salmonella throughout this production environment. During a 6-mo survey, Salmonella serotypes hadar, typhimurium, typhimurium variant Copenhagen, and paratyphi were encountered within this poultry operation. Ninety-four percent of the Salmonella isolated from breeder and production houses and from carcass rinses belonged to Salmonella serotypes typhimurium variant Copenhagen and hadar. There were six distinct S. typhimurium variant Copenhagen genetic types, as identified by PFGE, present within this particular poultry operation. Seventy-nine percent of S. typhimurium variant Copenhagen identified from the environment of the breeder and production houses produced the same PFGE pattern. Thirty-eight percent of S. typhimurium Copenhagen isolated from carcass rinses and the breeder house shared the same PFGE DNA pattern. This study demonstrates the transmission of salmonellae throughout this production environment, from the breeders to their progeny and to the birds ultimately processed for human consumption.     

Acute depigmentation of fertile brown eggs in a commercial layer operation.

Rapid depigmentation of brown eggs is an infrequent but startling event in the commercial egg industry that can result in significant economic losses. Loss of shell pigment in brown-shelled eggs is caused by various factors. In many cases, the exact cause of flock-wide pigment loss remains undetermined. A rapid decline in shell pigmentation was observed in 2 flocks of Hyline brown layers. The lack of evidence of an infectious disease process suggested a feed or management problem. On the basis of a small-scale, "in-house" feeding trial, the feed was identified as the cause of depigmentation. Feed analysis by liquid chromatography with mass spectrometry confirmed the presence of 4,4'-dinitrocarbanilide, a major component of nicarbazin (NCZ). There was no evidence of increased mortality, and only a slight but transient drop in the egg production was observed. Depigmentation effects were rapidly reversed after replacing the feed with NCZ-free feed.     

Toxicologic evaluation of a microencapsulated formulation of methyl parathion applied dermally to cattle

Acute toxicity studies in newborn calves and 2- to 3-year-old cattle were conducted with methyl parathion (O,O-dimethyl O-(p-nitrophenyl) phosphorothioate) in the form of a 22% microencapsulated slurry used in a manually operated sprayer. Twelve calves and 9 cattle were tested. The minimal toxic dosages were 4 L of a 0.5% concentration for calves and 10 L of a 0.25% concentration for mature cattle. At all toxic dosages, cholinesterase activities were decreased--that of the calves to 0 and that of the cattle to 50% of base line or less. Weight losses 2 weeks after single exposures to the treated cattle ranged from 6.5% to 11.5% of total body weight. Absorption of the formulation in its entirety or its metabolic products resulted in a possible interference with feed utilization.     

Influenza in commercial broiler breeders.

Influenza was detected in a flock of broiler breeders during routine serological monitoring. Although there were no clinical signs, egg production may have been affected in hens on one story of a two-story breeder house. Intensive measures were taken to avoid transmission to other farms. Two months after the flock was found to be serologically positive, sentinel hens were placed in the flock, and they became serologically positive 1 month later. In spite of this evidence for virus being present in the flock, no detectable transmission to any other farm occurred.