A study of the pathology and pathogensis of myocardial lesions in gousiekte, a cardiotoxicosis of ruminants

Trials were performed in sheep and rats to elucidate the pathogenesis of the myocardial lesions in gousiekte. In the first trial the macro- and lightmicroscopical lesions and myofibre morphometrical changes were studied in ten sheep exposed daily to Pachystigma pygmaeum at 10 g/kg live body weight for 23 to 31 days. All the treated animals either died or were euthanased in extremis between 31 and 51 days after the commencement of dosing. In the second trial the myocardial ultrastructural lesions were studied in six sheep dosed with Fadogia homblei at a dosage rate of 10 g/kg per day live body weight for 22 to 23 days. All the treated animals either died or were euthanased in extremis between 34 and 57 days after the commencement of dosing. The main objective of the third trial was to compare the myocardial lesions in rats exposed to pavetamine with lesions recorded in sheep exposed to P. pygmaeum and F. homblei plant material. Seven rats were injected intraperitoneally with pavetamine at a dosage rate of 5 mg/kg on day 0 and three were killed on day 6. The remaining four were injected with a second dose of pavetamine at a dosage rate of 3 mg/kg on day 27 and euthanased on day 42. In the sheep exposed to P. pygmaeum pulmonary oedema and hydropericardium were present in eight, hydrothorax in four and ascites in two cases. In two sheep cardiac dilatation was associated with subendocardial pallor (fibrosis) and transmural myocardial mottling. Myofibre hypertrophy was recorded in all the sheep, myofibre necrosis and replacement fibrosis occurred in seven animals the latter being particularly evident in animals with medium to long latent periods. A mononuclear cellular infiltration that varied from mild to severe was evident in all the cases and endocardial thickening, which is an indication of cardiac dilatation, was present in seven animals. Myofibre atrophy occurred in eight animals and was the most striking lesion in a sheep with a short latent period. “Typical” gousiekte lesions, characterised by myofibre necrosis and atrophy, replacement fibrosis and an associated round cell infiltration in the subendocardial region, were present in eight of the sheep. “Atypical” lesions, characterised by hypertrophy of myofibres with multifocal coagulative necrosis or myofibre atrophy, were recorded in two sheep, both of which had short latent periods. The myofibre diameter and nuclear area in the affected animals differed statistically from those of the controls (larger) and anisocytosis and anisonucleosis were particularly striking in sheep with intermediate to long latent periods. The most striking ultrastructural lesions included breakdown of myofibrils, involving in particular what appeared to be thick (myosin) filaments; selective proliferation of organelles such as mitochondria and sarcoplasmic reticulum in areas previously occupied by myofibrils; excessive folding of the myofibre sarcolemma; and advanced myocardial injury characterised by complete loss of myofibrils with loss of intercellular connections and necrosis of myocardial cells. No lesions were present in the rats exposed to a single dose of pavetamine, although they became anorexic and lost weight. Rats exposed to pavetamine twice became anorexic within two to three days after the first exposure and regained weight within a few days (on about day 7). However, they kept on losing weight after the second exposure and continued to do so until termination of the experiment. As a general rule the myocardial lesions were mild in the rats dosed twice with pavetamine. Transmural multifocal myocardial necrosis, with an associated round cell infiltration and replacement fibrosis, was the most striking light- microscopical lesion. The lesions were comparable with “atypical” lesions in ruminants. Ultrastructural lesions in degenerative/necrotic fibres included karyolysis, swelling of the mitochondria and focal lysis of myofilaments. In rats exposed to pavetamine twice there was statistical evidence of myofibre atrophy. Based on the information emanating from this study and previous research the following deductions are made to explain the pathogenesis of the myocardial lesions: 1. Pavetamine has a prolonged effect on the myocardium owing to inhibition of protein synthesis, and also influences the energy production system, which affects the function of myocytes. The structure of the myocytes is not affected during the early stages of the latent period but eventually myofibre hypertrophy, atrophy, degeneration and necrosis are seen. 2. Replacement fibrosis in the subendocardial region is a sequel to the effect of pavetamine on myofibres and the consequence of ischaemia owing to impaired myocardial perfusion of, particularly, the subendocardial region, as a result of decreased myocardial contraction, increased diastolic pressure, tachycardia and myofibre hypertrophy. 3. Cardiac dilatation is a compensatory mechanism, a result of the myofibre damage inflicted by pavetamine and ischaemia (pathological dilatation). 4. Lesions in animals with gousiekte represent a final common pathway of cellular damage rather than a manifestation of a specific type of heart disease. Animals may die during any stage in the development of the lesions. “Atypical” lesions represent a manifestation of the disease in a progression that terminates with dilated cardiomyopathy if the animal does not die during the early stages. These deductions provide an explanation, for the first time, for the latent period between ingestion of the plant and the onset of illness in gousiekte. They also explain the wide range of lesions seen in experimental cases. It furthermore demonstrate that the “typical” lesions of gousiekte are not pathognomonic, and that the absence of “typical” lesions does not rule out a diagnosis of gousiekte in situations where exposure to the causative plants and the clinical history support such a diagnosis.Thesis (PhD)--University of Pretoria, 2008.Paraclinical Sciencesunrestricte

A study of the pathology of lumpy skin disease in cattle

Microscopic lesions in cattle infected with the virus of the Neethling form of lumpy skin disease comprised a granulomatous reaction in the dermis and hypodermis which extended to the surrounding tissue. During the early stages of the lesions a vasculitis and lymphangitis with concomitant thrombosis and infarction resulted in necrosis and oedema. A hallmark of the acute to subacute stages of the lesions was the presence of intracytoplasmic eosinophilic inclusions in various cell types. The inclusions consisted of the viroplasm which was identified as aggregates of electron-dense, finely granular to fibrillar deposits in which membrane-enclosed virions and occasional groups of tubular structures were observed. Various cytopathogenic changes were observed in cells exhibiting viral proliferation. The morphogenesis of the virions is discussed in relation to the cytopathogenic changes.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format

Diarrhoea in pigs induced by rotavirus

Electron microscope examination of the faeces of scouring pigs revealed virus particles which were morphologically indistinguishable from rotavirus (reo-like), a virus associated with diarrhoea in neonatal pigs (Leece, King & Mock, 1976). This is the first record of this virus in the Republic of South Africa.The articles have been scanned in colour with a HP Scanjet 5590; 300dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format

Amaurosis in sheep resulting from treatment with rafoxanide

Amaurosis occurred in sheep on various farms in the Republic of South Africa after treatment with rafoxanide. Histopathological examination revealed a status spongiosus of varying severity in the central nervous system in all the cases, having a predilection for certain areas such as the periventricular area of the lateral ventricles, optic tracts, lateral geniculates and optic fasciculi. The retina was the only ocular tissue affected and lesions observed in the retina included necrosis of nerve cells in the ganglionic layer. In chronic cases of amaurosis this layer showed a complete absence of nerve cells. The possible pathogenesis of the lesions and their differentiation from those found in certain plant toxicoses are discussed.The articles have been scanned in colour with a HP Scanjet 5590; 300dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format

The pathology of heartwater. I. A study of mice infected with the Welgevonden strain of Cowdria ruminantium

Gross and microscopical lesions in mice intravenously infected with the Welgevonden strain of Cowdria ruminantium closely resembled the lesions described in cattle, sheep and goats. A high concentration of organisms was present in alveolar endothelial cells. Cytopathic changes in parasitized and non-parasitized endothelial cells and the morphology of the organisms are described and compared with the Ball₃ strain of C. ruminantium. Possible mechanisms in the development of the lung oedema are considered and the role of mice as animal model is discussed.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format

Heartwater in Angora goats. II. A pathological study of artificially infected, treated and untreated goats

Pathological lesions in untreated Angora goats infected with the Ball₃ strain of Cowdria ruminantium corresponded with those previously reported. A severe nephrosis was the most prominent pathological lesion in the animals treated after the 1st day of the febrile reaction. Renal ischaemia appears to be central to the pathogenesis of the kidney lesions.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format

The pathology of heartwater. II. A study of the lung lesions in sheep and goats infected with the Ball₃ strain of Cowdria ruminantium

Lung lesions in sheep and goats infected with the Ball₃ strain of Cowdria ruminantium corresponded with those reported in mice infected with the Welgevonden strain of Cowdria ruminantium. Ultrastructural changes in the alveolar endothelial and epithelial cells are described and the pathogenesis of the lung oedema is briefly discussed.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format

The isolation and cultivation of calf rotavirus in the Republic of South Africa

Calf rotavirus was cultivated and propagated in tissue culture from faeces of 3-week-old calves suffering from severe diarrhoea. Criteria for viral involvement were: production of cytopathic effects in primary foetal calf kidney cells, specific fluorescence, and identification of the agent by means of electron microscopy. In a limited serological survey the majority of the cows on an infested farm were found to possess neutralizing antibodies to the local rotavirus strain.This article has been scanned in colour with a HP Scanjet 5590; 300dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-Format

Paralysis in lambs caused by overdosing with parbendazole

An experiment was undertaken to determine whether an overdose of the anthelmintic parbendazole could cause paralysis in lambs when given to ewes during the early stages of pregnancy. Out of a total of 68 lambs, born from ewes treated at various stages of gestation with parbendazole at 180 mg/kg, 5 showed the paralysis syndrome, 5 showed skeletal deformities, 2 were ataxic, while 1 foetus was aborted. The ewes giving birth to paralysed lambs had been treated with parbendazole at 30, 32, 37 and 53 days of gestation. Cerebral hypoplasia was observed in 2 of these lambs, while 2 others showed internal hydrocephaly. Histopathological lesions observed in the lambs with cerebral hypoplasia included gliosis and areas of encephalomalacia in the cerebral white matter. Lesions present in the spinal cords of the 2 ataxic lambs included pydromyelia, syringomyelia, duplication of the spinal canal and an abnormal position of the canal. This is the first report describing brain lesions in lambs as a result of an overdose of parbendazole.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format

Etude sur la diarrhee post-natale du veau au virus rota: transmission de la malad!£ et tentative de vaccination des veaux prives de colos-trum

Mild to severe scouring could be produced in colostrum-deprived calves with tissue culture adapted rota virus and faecal material from field cases of calf diarrhoea. The faeces of experimentally infected calves contained rotavirus for at least 3 days. Pathogenic bacteria were present in one calf only and this calf also showed the most severe gastroenteritis. Eight calves were vaccinated with a live rota viral calf diarrhoea vaccine and subsequently challenged with infective rota virus. Mild scouring was observed after vaccination, but the calves remained normal after challenge. Rotavirus particles were detectable in the faeces for a few days after vaccination and challenge.The articles have been scanned in colour with a HP Scanjet 5590; 300dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format