Poisonous plants.

South Africa is blessed with one of the richest floras in the world, which--not surprisingly--includes many poisonous plants. Theiler in the founding years believed that plants could be involved in the aetiologies of many of the then unexplained conditions of stock, such as gousiekte and geeldikkop. His subsequent investigations of plant poisonings largely laid the foundation for the future Sections of Toxicology at the Institute and the Faculty of Veterinary Science (UP). The history of research into plant poisonings over the last 100 years is briefly outlined. Some examples of sustained research on important plant poisonings, such as cardiac glycoside poisoning and gousiekte, are given to illustrate our approach to the subject and the progress that has been made. The collation and transfer of information and the impact of plant poisonings on the livestock industry is discussed and possible avenues of future research are investigated.

The role of fluorescence polarization immuno-assay in the diagnosis of plant-induced cardiac glycoside poisoning livestock in South Africa.

Poisoning with cardiac glycoside-containing plants is collectively the most important plant-associated poisoning of livestock in southern Africa. As a diagnosis of this significant poisoning is currently based on circumstantial evidence, a practical chemical procedure indicating the presence of cardiac glycosides in plants and animal specimens would be of considerable benefit. The fluorescence polarization immunoassay (FPIA) method, used to determine digoxin plasma levels in humans and dogs, was adapted to estimate cardiac glycoside levels in known cardiac-glycoside-containing plants as well as in the rumen and organs of dosed sheep. Positive FPIA values were obtained with bufadienolide-containing plants, while negative results were obtained with plants not known to contain cardiac glycosides. The FPIA has aided in the diagnosis of cardiac glycoside poisoning in livestock and game in 30 outbreaks examined at the Division of Toxicology, Onderstepoort Veterinary Institute. Each outbreak is briefly described. As a result of this assay, a better understanding of cardiac glycoside poisoning has been reached.

Continuous exposure to an aversive mixture as a means of maintaining aversion to vermeerbos (Geigeria ornativa O. Hoffm.) in the presence of non-averted sheep.

Continuous exposure to an aversive mixture was investigated as a means of maintaining aversion to vermeerbos in sheep subjected to the social influence of non-averted sheep. The use of an aversive mixture was based on a hypothesis that continuous exposure to an acceptable aversive mixture (containing both the aversive substance and the identification factors of vermeerbos mixed with maize meal) would tempt sheep to consume small quantities of the aversive mixture each day and that this would keep them averted to vermeerbos, despite the social influence of non-averted sheep. Persistent aversion to a vermeerbos-maize meal mixture (1:99 by mass) by sheep continuously exposed to such an aversive mixture, after an initial aversion conditioning with lithium chloride (LiCl, 160 mg/kg BM), was demonstrated. Aversion in adjacent controls not exposed to the aversive mixture only lasted for some time. A similar result was obtained when sheep were challenged for intake of a pure stand of established vermeerbos. Three sheep continuously exposed to an aversive mixture after an initial aversion conditioning totally refused grazing the vermeerbos during a 42-day trial, despite the social influence of three non-averted control sheep grazing vermeerbos on an adjacent site. These results were confirmed by a second replication the following year. Joint grazing for an hour a day by averted and non-averted sheep during the last seven days of this replication also resulted in total avoidance of vermeerbos by the averted animals, despite continued intake of vermeerbos by the control sheep

Krimpsiekte in a sheep following a single dose of Tylecodon ventricosus (Burm. f.) Toelken and the isolation of tyledoside D from this plant species.

Tylecodon ventricosus induced severe respiratory distress in two penned sheep without any electrocardiographic abnormalities being recorded. Based on the results it appears as if T. ventricosus predominantly induces the neuromuscular syndrome referred to as krimpsiekte. A single, relatively large intraruminal dose of 10.0 g/kg induced krimpsiekte in one sheep. Treatment with 5.0 g/kg activated charcoal on two consecutive days did not prevent the development of krimpsiekte. A bufadienolide, tyledoside D, was isolated from semi-dried plant material.

Neurospecificity of phyto-bufadienolides is not related to differences in Na+/K+ pump inhibition.

The aim of the present study was to investigate the effects of neuro- (cumulative) and cardiotoxic (non-cumulative) bufadienolides originating from plants (phyto-bufadienolides) on the Na+/K+ pump current (Ip) in cardiac (rat and guinea pig) and dorsal root ganglion cells (guinea pig), and on Ca2+ currents in cardiomyocytes (guinea pig). All bufadienolides tested (non-cumulative drugs: thesiuside, tyledoside C; lanceotoxin B and tyledoside F for the neurotoxic group) were potent blockers of Ip at concentrations in the micro- and submicromolar range. K0.5 values for Ip inhibition in dorsal root ganglion neurones were slightly lower compared to cardiomyocytes, but the order of potency was similar in both cell types. Both classes of bufadienolides were equipotent in suppressing Ip, generated by high- and low-affinity pump isoforms. Phenomena related to pump inhibition, as hypercontracture and increase in T-type Ca2+ current in cardiomyocytes, were influenced to the same extent. Therefore, from these results, neurospecificity of some bufadienolides could not be explained by differences in Na+/K+ pump affinity.

Krimpsiekte, associated with thalamic lesions, induced by the neurotoxic cardiac glycoside, cotyledoside, isolated from Tylecodon wallichii (Harv.) Toelken subsp. wallichii.

The specific neurotoxic principle of Tylecodon wallichii (Harv.) Toelken subsp. wallichii, the cause of krimpsiekte in small stock, was isolated and identified as the previously described cumulative bufadienolide, cotyledoside. Krimpsiekte was experimentally induced in two sheep by the repeated intravenous administration of cotyledoside at the rate of 0.01-0.015 mg/kg body mass. On day 9, both animals developed clinical signs typical of krimpsiekte, which is characterized by tremors, paresis and recumbency. Both sheep had difficulty in controlling their hindquarters when attempting to lie down. No significant electrocardiograph abnormalities were detected during the experiment which confirms that cotyledoside at low doses does not overtly affect the electrical activity of the heart. No gross lesions were observed in the sheep. The most significant microscopic lesions comprised mild brain oedema and pronounced vacuolation of the white matter of thalamic nuclei. These lesions might explain some of the motor function deficiencies clinically observed in this syndrome. The previously held contention that these neurotoxic cardiac glycosides are indeed the cause of krimpsiekte is, therefore, confirmed.

Photosensitivity in South Africa. IX. Structure elucidation of a beta-glucosidase-treated saponin from Tribulus terrestris, and the identification of saponin chemotypes of South African T. terrestris.

Saponin C, a beta-glucosidase-treated saponin isolated from ethanol-water extracts of a South African collection of Tribulus terrestris, was shown by one- and two-dimensional NMR spectroscopy to be ruscogenin 1-O-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-6)-acetylglucopyranoside++ +. GC-MS analysis of the hydrolysed ethanol-water (4:1) extracts of T.terrestris specimens from two of four sites, revealed high levels of ruscogenin and potentially lithogenic diosgenin saponins. Specimens from two other sites contained non-lithogenic saponins derived predominantly from tigogenin, neotigogenin, gitogenin and neo-gitogenin.

The distribution, diagnoses and estimated economic impact of plant poisonings and mycotoxicoses in South Africa.

Maps are provided showing the national and provincial distributions of many plant poisonings and mycotoxicoses in South Africa. The various poisonings are briefly described and criteria for their diagnoses are given. The annual mortalities of cattle from plant poisonings/mycotoxicoses in South Africa were calculated as c. 37 665 head with a current cash value of c. R57 627 450, and that of small stock as c. 264851 head with a value of c. R46 878 627. The annual total cost of plant poisonings/mycotoxicoses to the livestock industry of South Africa is conservatively estimated at R104 506 077. These figures do not include hidden losses such as diminished production, reproductive failure, the cost of not utilizing toxic pastures and the fall in price of infested land.

A tremorgenic mycotoxicosis in cattle caused by Paspalum distichum (l.) infected by Claviceps paspali.

This is the first reported outbreak of paspalum staggers in cattle following ingestion of Paspalum distichum (L) infected by Claviceps paspali in South Africa. A day after starting to graze on an ergotised paspalum field, 43 animals exhibited various degrees of generalised tremors and ataxia. Four animals became paretic and went into sternal recumbency. All affected animals recovered. The condition was reproduced by feeding ergotised grass to a calf. Signs of intoxication were observed 48 h after ingestion of c. 30 g/kg of the semi-dry plant material. The calf developed tremors and a slight ataxia, which became more pronounced following light exercise.

Plant poisonings and mycotoxicoses as constraints in livestock production in east Africa: the southern African experience.

The major plant poisonings and mycotoxicoses of southern Africa are discussed in relation to East Africa. As almost all the plant genera and most species responsible for intoxication in southern Africa are present in East Africa, it is postulated that the same intoxications probably also occur in the latter. There is a necessity to diagnose and control these conditions.

In vivo effects of a novel calcium antagonist (R56865) against induced epoxyscillirosidin and tulp poisoning in sheep.

Two anaesthetized sheep were intoxicated with epoxyscillirosidin, the main cardio-active bufadienolide, extracted from Homeria pallida (Natal yellow tulp). The epoxyscillirosidin was injected intravenously as a bolus of 50 micrograms/kg, followed 30 min later by a continuous infusion in a normal saline drip (0.9% NaCl) at 25 micrograms/kg/h. In addition, another two conscious sheep were poisoned by intraruminal dosing of 1,25 g/kg of dried H. pallida plant material. Electrocardiograms, heart and respiratory rates and venous-acid-base levels were recorded prior to and at approximately 30-60 min intervals during the course of the experiment. Additional recordings were made when animals showed signs of intoxication. R56865 (Janssen Pharmaceutica, Pty Ltd), a novel Ca++ antagonist, was administered at the first distinct signs of cardiac disturbances in the sheep given epoxyscillirosidin and after development of tachycardia and dyspnoea in those that received plant material. Activated charcoal was drenched at 3 g/kg to both sheep that received H. pallida about 1 h after the initial administration of R56865. All H. pallida sheep and one of the epoxyscillirosidin sheep survived. The signs of intoxication with H. pallida, namely groaning and tachypnoea, abated within minutes of treatment with R56865, but returned c. 30 min later in both animals. The treatment apparently had little effect on heart rate and EKG changes. One of the epoxyscillirosidin sheep was treated while exhibiting paroxysmal ventricular tachycardia. Although a transient improvement in conduction disturbance was recorded, the animal died soon afterwards. The results of this study indicate that the in vivo response of R56865 against induced bufadienolide cardiac disturbance in sheep is not as evident as that observed with R56865 against similar cardiac disturbance in vitro. The potential use of R56865 together with activated charcoal is discussed.

Two outbreaks of type C and type D botulism in sheep and goats in south Africa.

Two outbreaks of botulism in sheep and goats are described; in one, 329 out of 900 sheep in a feedlot died within 9 d of the onset of the disease and in the other, 100 sheep and goats out of 330 succumbed over a period of about 3 weeks. Animals were found dead or died suddenly, without exhibiting clinical signs. Others stood with lowered heads and showed drooling of saliva or a stiff gait. Paresis and/or paralysis were frequent signs in the terminal stages of the disease. Gross lesions such as the accumulation of fluids in body cavities, pulmonary oedema, foam in the trachea, epicardial haemorrhages and congestion of the mucosa of the small intestine, suggestive of heart failure, were present in animals from both outbreaks. Botulism was confirmed via the mouse toxicity test, by the demonstration of Type C and Type D toxins in the feed and intestinal contents of sheep from the first outbreak and Type D toxin in intestinal contents of sheep from the second. The clinical signs and macropathology in the outbreaks of botulism in sheep and goats in South Africa may resemble "krimpsiekte" and cardiac glycoside and ionophore poisoning, as well as other conditions causing heart failure.

Photosensitivity in South Africa. VIII. Ovine metabolism of Tribulus terrestris saponins during experimentally induced geeldikkop.

Geeldikkop was induced in a sheep by dosing it orally with a crude extract of the steroidal saponins from Tribulus terrestris. GC-MS analysis of the sheep's ruminal contents, bile, faeces and urine for free and conjugated sapogenins, revealed the general features of the metabolic pathway by which diosgenin and yamogenin glycosides were converted into the glucuronides of epismilagenin and episarsasapogenin, the major constituents of the biliary crystals that usually form during geeldikkop. Other steroidal saponins in the T. terrestris extract, including those derived from tigogenin, neotigogenin, gitogenin and neogitogenin appear to be non-lithogenic. The implications of these findings are discussed.

Spinal cord degeneration in adult dairy cows associated with the feeding of sorghum beer residues.

A neurological syndrome in a herd of Friesland cows (n = 100) on a diet including sorghum beer residues is described. Over a period of 8 months, 76 cows developed weakness of the hindquarters, progressively worsening ataxia and, eventually, paralysis and permanent recumbency. The course of the disease varied from 2 to 8 weeks. The lesions were significant in the 2 cows necropsied and included extensive, bilaterally symmetrical dilation of myelin sheaths, axonal swelling and loss with Wallerian degeneration, and depletion of myelin in both ascending and descending tracts at all levels of the spinal cord. Focal neuronal degeneration in the spinal cord grey matter and dorsal root ganglia, and focal loss of axons and ovoid formation in the spinal nerve roots and ischiatic nerves were also evident. The pathogenesis of the spinal lesions appears to involve a primary axonopathy with secondary myelin loss. The epidemiology, clinical signs and pathology suggest that the disease was associated with the fungus Aspergillus clavatus.

Photosensitivity in South Africa. VII. Chemical composition of biliary crystals from a sheep with experimentally induced geeldikkop.

Geeldikkop was induced in a sheep by oral administration of crude saponins from Tribulus terrestris. Centrifugation of the bile from this sheep gave a pale green sediment of crystalloid material which was insoluble in common organic solvents, but soluble in acetic acid. Analysis of the crystalloid material by 1H and 13C NMR, EDXA, TLC, LSIMS, and by acidic hydrolysis followed by TLC and GC-MS, revealed it to be composed principally of a 6:1 mixture of the calcium salts of the beta-D-glucuronides of the steroidal sapogenins epismilagenin and episarsasapogenin. The administered saponin was found to contain glycosides of the steroidal sapogenins diosgenin, yamogenin, epismilagenin, tigogenin, neotigogenin, gitogenin and neogitogenin in the ratio 10:7:1:11:7:35:25. A metabolic pathway for the conversion of diosgenin and yamogenin saponins to the biliary glucuronides is proposed.

Perinatal mortality in lambs of ewes exposed to cultures of Diplodia maydis (= Stenocarpella maydis) during gestation. A study of the central-nervous-system lesions.

Previously published results of dosing trials, involving 82 ewes, revealed that 66% of the offspring of dams exposed to cultures of Diplodia maydis in the second trimester of pregnancy and 87% of lambs of ewes exposed in the third trimester, were born dead or died soon afterwards. Spongiform degeneration of myelin of varying degree was present in the brains of all the stillborn and non-viable lambs in these trials. Myelin lamellae were separated at the intraperiod line. The spongiform degeneration occurred throughout the central nervous system in severely affected animals, whereas in mildly affected lambs the lesions had a predilection for the white matter, particularly of the cerebellum and cerebrum. In 28 lambs the spongiform degeneration progressed to lytic necrosis, and hydrocephalus was recorded in two animals.

A nervous disorder in cattle, caused by the plants Ficus ingens var. ingens and Ficus cordata subsp. salicifolia.

Two outbreaks of neurotoxicoses are reported in cattle browsing on the leaves of Ficus spp. In the first outbreak, three animals died and one became ill. A sheep developed severe nervous signs, including tetanic spasms, when dosed with the leaves of Ficus ingens var. ingens from the toxic camp where the cattle had died. The second outbreak resulted in the death of 12 heifers within 48 h of ingestion of the leaves of F. cordata subsp. salicifolia. Clinical signs included hyperaesthesia, ataxia, muscle tremors and padding motions while in lateral recumbency. Similar signs were reproduced by drenching the incriminated leaves to a steer. The sheep dosed with F. ingens var. ingens and two cattle, one of which had died during the second outbreak and the steer drenched with F. cordata subsp. salicifolia, were necropsied. Light microscopical examination consistently revealed oedema of the central nervous system. In the steer, focal demyelination was evident in localized areas of the brain and spinal cord. Liver lesions ranged from mild degeneration to focal disseminated necrosis of hepatocytes.

Cardiomyopathy of ruminants induced by the litter of poultry fed on rations containing the ionophore antibiotic, maduramicin. I. Epidemiology, clinical signs and clinical pathology.

The epidemiological, clinical and clinical pathological findings in 20 cattle and 4 sheep from 15 outbreaks of poultry litter toxicity in South Africa over the past 6 years are documented. In 6 outbreaks, the litter emanated from batteries where maduramicin had been incorporated into rations of broilers. According to circumstantial evidence the litter involved in the 9 other outbreaks was also derived from broilers which had been fed on rations containing an ionophore. The litter was fed ad libitum to the affected stock or constituted 30-80% by volume of their rations. The principal sign manifested was sudden mortality of up to 70% of the herd or flock, usually within 20-40 days of commencement of feeding of poultry litter. A few cattle developed signs of congestive heart failure, and stiffness was commonly seen in sheep. In a dosing trial with poultry litter involving 1 steer and 6 sheep, the steer and a sheep died suddenly and a second sheep was destroyed in extremis. Tachycardia and/or cardiac arrythmia were recorded in 5 sheep, and the activity of aspartate transaminase (AST) and/or lactate dehydrogenase (LD) in the sera of 4 was elevated. Since the cardiac lesions in field cases were similar to those of ionophore poisoning and broiler rations containing maduramicin was a common factor in several outbreaks, toxic litter from some of these outbreaks were tested for the presence of this compound. Analysis by high performance liquid chromatography of litter from 2 specimens of outbreaks revealed that they contained 2.5 ppm and 6.1 ppm maduramicin.(ABSTRACT TRUNCATED AT 250 WORDS)

Perinatal mortality in lambs of ewes exposed to cultures of Diplodia maydis (= Stenocarpella maydis) during gestation.

During 1987 when cob rot was rife, perinatal losses were reported in flocks and herds that had been exposed to diplodiosis. The affected lambs or calves were either stillborn or died soon after birth. Dosing trials at the Onderstepoort Veterinary Research Institute involving 82 ewes revealed that 66% of the offspring of dams exposed to cultures of Diplodia maydis (= Stenocarpella maydis) in the second trimester of pregnancy and 87% of lambs of ewes exposed in the third trimester were born dead or died soon afterwards. A status spongiosus similar to that of the field cases was present in the white matter of the brains of all the affected lambs. The lambs of ewes that had shown nervous signs and those of ewes that had not shown such signs were equally affected. The experiments also clearly demonstrated that foetuses were much more susceptible to diplodiosis than the adults, e.g. in the third trimester 87% of the lambs were affected compared to only 44% of the dams. No perinatal mortalities were recorded in the group exposed to the culture in the first trimester. Ewes developed significant resistance to intoxication after initial exposure to the culture and both the length of gestation and birth mass of the affected lambs were less than those of their untreated counterparts.

Photosensitivity in South Africa. VI. The experimental induction of geeldikkop in sheep with crude steroidal saponins from Tribulus terrestris.

Geeldikkop was induced in sheep by the oral administration of crude steroidal saponins from Tribulus terrestris. Two of the sheep developed typical lesions of geeldikkop, including birefringent crystalloid material in bile ducts and concentric periductal lamellar fibrosis. The clinical pathological changes in these sheep were also consistent with those of geeldikkop: aspartate transaminase and gamma-glutamyl transferase activities in the sera of both were elevated, and one had bilirubinaemia. A third sheep became photosensitive without typical lesions of geeldikkop in the liver or changes in the activities of liver enzymes before euthanasia. The findings of these trials are consistent with reports from abroad that ovine hepatogenous photosensitization, caused by Agave lechuguilla and Narthecium ossifragum, can be induced with crude saponins from the respective plants.