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Thevetia peruviana: Yellow oleander
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Family
Apocynaceae
Common Names
Yellow oleander, be-still tree, lucky nut, tiger apple - Thevetia peruviana (Cascabela thevetia)
Giant yellow oleander, yoyote - T. thevetiodes
Plant Description
A genus of 8 species of shrubs or small trees native to the tropics of Central America and West Indies, Thevetia species are commonly cultivated for their showy yellow flowers. Typically, the plants are perennial, evergreen, branching shrubs and small trees, with simple, linear, alternate, glossy, green leaves and a milky sap. The flowers are produced terminally, and are funnel-shaped, fragrant, showy, with sepals fused basally, and petals ranging from bright yellow to orange or pinkish-yellow. Fruits are green angular drupes that turn red to black when ripe (Fig. 389 and Fig. 390).
Figure 389. Thevetia thevetiodes.
Figure 390. Thevetia peruviana.
Toxic Principle and Mechanism of Action
All animals, including humans, consuming Thevetia species are susceptible to the potent cardiotoxic glycosides Thevitin A and B and thevetoxin that are present in all parts of the plants and especially the fruits and seeds [1-4]. The glycosides act directly on the gastrointestinal tract causing hemorrhagic enteritis, abdominal pain, and diarrhea [5]. The cardiac glycosides act by inhibiting the cellular membrane sodium-potassium (Na+-K+ ATPase enzyme system) pump with resulting depletion of intracellular potassium and an increase in serum potassium [5]. A progressive decrease in electrical conductivity through the heart causes irregular heart activity, and eventually complete block of cardiac activity. Toxic doses of the glycosides cause a variety of severe dysrhythmias and conduction disturbances through the myocardium that result in decreased cardiac output, heart block, and death.
Risk Assessment
Thevetia species are common garden plants in tropical and sub-tropical areas, and like oleander (Nerium oleander) are one of the more poisonous of plants that people and animals are exposed to. In some parts of the world, the fruits of Thevetia are used for suicidal purposes [6]. Extracts from the leaves of the plant are also toxic to fish [7].
Clinical Signs
Animals consuming Thevetia species may be found dead due to the profound effects of the cardiotoxins. A variety of cardiac dysrhythmias and heart block including first and second degree heart block and ventricular tachycardia may be encountered with cardiac glycoside poisoning. Abdominal pain (colic), and diarrhea are also signs commonly encountered in animals poisoned with cardiac glycosides. If observed early in the course of poisoning, animals will exhibit rapid breathing, cold extremities, and a rapid weak and irregular pulse. The duration of symptoms rarely exceeds 24 hours before death occurs.
In acute cardiac glycoside poisoning, the post mortem findings include hemorrhages, congestion, edema, and cell degeneration of the organs of the thoracic and abdominal cavities. In less acute but fatal poisoning, tissue necrosis resulting from decreased oxygenation may be present in a variety of organs.
Treatment
Gastric lavage or vomiting should be induced in dogs and cats as soon as possible. Activated charcoal orally appears to improve survivability [8]. The cardiac irregularities may be treated using anti-arrhythmic drugs such as potassium chloride, procainamide, lidocaine, dipotassium EDTA, or atropine sulfate [9]. The use of fructose-1,6-diphosphate (FDP) has been shown to effectively reduce serum potassium levels, and irregularities of the heart (dysrhythmias), and will improve cardiac function in dogs experimentally poisoned with oleander and presumably in Thevetia poisoning [10]. The mechanism of action of FDP is not known but it apparently restores cell membrane Na+ and K+ ATPase function [10].
As hyperkalemia is a common feature of oleander poisoning, the administration of potassium containing fluids should be done very cautiously, and not at all unless serum potassium levels can be monitored closely. Intravenous fluids containing calcium should not be given as calcium augments the effects of the cardiac glycosides. Poisoned animals should be kept as quiet as possible to avoid further stress on the heart.
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1. Langford SD, Boor PJ. Oleander toxicity: an examination of human and animal toxic exposures. Toxicology. 109: 1-13, 1996.
2. Ansford AJ, Morris H. Oleander poisoning. Toxicon 3: 15-16, 1983.
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Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO, USA.
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