Journal of Ethnopharmacology Poisonous Plants of Veterinary and Human Importance in Southern Africa
Total Page：16
File Type：pdf, Size：1020Kb
Journal of Ethnopharmacology 119 (2008) 549–558 Contents lists available at ScienceDirect Journal of Ethnopharmacology journal homepage: www.elsevier.com/locate/jethpharm Poisonous plants of veterinary and human importance in southern Africa C.J. Botha a,∗, M.-L. Penrith b,c a Department of Paraclinical Sciences, Faculty of Veterinary Science, University of Pretoria, Private Bag X04, Onderstepoort 0110, South Africa b TADScientific, 40 Thomson Street, Colbyn 0083, South Africa c Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, University of Pretoria, Private Bag X04, Onderstepoort 0110, South Africa article info abstract Article history: Southern Africa is inherently rich in flora, where the habitat and climatic conditions range from arid Received 9 April 2008 environments to lush, sub-tropical greenery. Needless to say, with such diversity in plant life there are Received in revised form 14 July 2008 numerous indigenous poisonous plants, and when naturalised exotic species and toxic garden varieties Accepted 17 July 2008 are added the list of potential poisonous plants increases. The economically important poisonous plants Available online 25 July 2008 affecting livestock and other plant poisonings of veterinary significance are briefly reviewed. In addition, a synopsis of the more common plant poisonings in humans is presented. Many of the plants mentioned Keywords: in this review are also used ethnobotanically for treatment of disease in humans and animals and it is Human Livestock essential to be mindful of their toxic potential. Poisoning © 2008 Elsevier Ireland Ltd. All rights reserved. Poisonous plants Southern Africa Veterinary 1. Introduction While the active principles and mode of action are known for many plants, many others are known to induce poisoning, but the Southern Africa has a rich and varied flora that includes a wide mechanism of intoxication has yet to be elucidated. variety of plants with the potential to cause poisoning of animals Diagnosis of plant poisoning of livestock depends on the history, and humans. Heavy stock losses caused by plant poisoning have clinical syndrome observed, post-mortem lesions, evidence that occurred throughout the history of the region, and have given rise plants have been grazed, and remains of toxic plants in the gastro- to considerable research. Although there is a large amount of infor- intestinal tract. Where the toxic principle is known, confirmatory mation in the veterinary field, human poisoning appears to be less laboratory tests may be possible. well documented. Only a proportion of plant poisonings results from the presence Plant poisoning in animals is usually accidental, and most fre- of toxic principles in the plant itself. Poisoning can result from con- quently occurs during unfavourable conditions when pastures are tamination of non-toxic food plants with mycotoxin synthesizing poor due to drought, veld fires and overstocking and trampling fungi and from other interactions with organisms including insects, of the grazing. Consumption of hay contaminated with poisonous helminths and bacteria that result in the elaboration of toxins. It plants also occurs. In humans it may be accidental or intentional. can also result from mineral imbalances that are linked to the con- Accidental poisoning in humans may be due to confusing poisonous sumption of certain plants under particular circumstances, such as with edible plants, contamination of food with poisonous plants, or enzootic icterus in sheep, which is a form of chronic copper poison- by the use of plants as remedies. ing. In this review, only poisoning due to toxins in the plant tissue Poisonous plants can affect the entire spectrum of organ sys- itself will be discussed. tems, with some plants having several toxic principles that affect Many of the plants mentioned in this review are also used eth- different systems. The dominant effect may depend on the condi- nobotanically for treatment of disease in humans and animals. tion, growth stage or part of the plant, the amount consumed, and The interrelationship of pharmacology and toxicology is important the species and susceptibility of the victim. as therapeutic efficacy occurs at a lower dose, where overdos- ing can induce poisoning. However, poisonous plants may contain active compounds with useful biological activities (McGaw and Eloff, 2005). With the current emphasis on research and devel- ∗ Corresponding author. Tel.: +27 12 5298023; fax: +27 12 5298304. opment of phytomedicines in southern Africa it is imperative E-mail address: [email protected] (C.J. Botha). to be aware of and have some information at hand regarding 0378-8741/$ – see front matter © 2008 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.jep.2008.07.022 550 C.J. Botha, M.-L. Penrith / Journal of Ethnopharmacology 119 (2008) 549–558 the more common plant poisonings occurring in man and live- Chronic bufadienolide poisoning is caused by a group of suc- stock. culent plants of the family Crassulaceae (plakkies) of the genera When plants are to be utilized ethnobotanically it is essential to Tylecodon, Cotyledon and Kalanchoe. Their bufadienolides have a be mindful concerning their toxic potential. As it is not the intention cumulative, neurotoxic effect that produces a syndrome known of this review to include all aspects of ethnobotanical usage the as ‘krimpsiekte’ (=shrinking disease), a paretic syndrome of sheep interested reader is referred to the complete and comprehensive and goats (Botha, 2003). Consumption of these plants can result reference works compiled by Watt and Breijer-Brandwyk (1962), in acute cardiac glycoside poisoning, as the manifestation depends Hutchings et al. (1996), Neuwinger (1996) and Van Wyk and Gericke on factors such as dose, duration of exposure, the bufadienolides (2000). involved and predisposing factors. Hungry animals that consume Upon selecting plants for ethnopharmacological studies, large amounts of the plants in a short period of time may die sud- researchers are encouraged to search available literature for known denly or develop an acute syndrome that can include depression, toxic properties of plants of interest, prior to conducting biological bloat, regurgitation, paralysis of the tongue, salivation and recum- activity studies. Where toxic effects are unknown, parallel cytotox- bency. This may progress to the typical chronic form of poisoning, icity studies, or inclusion of a panel of unrelated micro-organisms, which can also develop in animals that are exposed to the plants are useful in detecting potential toxicity when screening plant over a protracted period that allows low but continuous intake. extracts or isolated natural products for antibacterial, antifungal, Affected animals lag behind the flock, walk with the neck dangling antiviral and antiparasitic activity (Cos et al., 2006). and assume the characteristic ‘shrinking’ posture, with the back arched, the feet drawn together under the body and the head hang- 2. Major plant poisonings of livestock in southern Africa ing down. Affected small stock tire quickly and lie down with the neck extended sometimes twisted to one side (torticollis). Mortal- The plant poisonings that cause major stock losses in southern ity can be as high as 90%. Poisoning has also been reported in horses Africa have been thoroughly reviewed by Kellerman et al. (1996) and domestic chickens. Relay toxicosis or secondary poisoning has and Naudé et al. (1996). been described in dogs that have eaten the flesh of goats and horses that have died of krimpsiekte (Henning, 1926). 2.1. Cardiac glycosides 2.2. Gousiekte Plants that contain cardiac glycosides are considered to be the most important cause of livestock poisoning (Kellerman et al., Various plants of the family Rubiaceae (Pachystigma spp., Fado- 1996). Cardiac glycosides affect a wide range of species, includ- gia homblei and Pavetta spp.) induce a syndrome known as ing humans, but cardiac glycoside poisoning in southern Africa ‘gousiekte’ (=quick sickness). Large numbers of domestic rumi- is most frequently reported in cattle and sheep. Chemically, two nants can die suddenly without any premonitory signs 6–8 weeks forms of cardiac glycosides’ are contained by plants, viz. car- after ingestion of these rubiaceous plants. These plants occur in denolides and bufadienolides. Plants that contain cardenolides the north-eastern and central parts of southern Africa and may be include Nerium oleander (oleander), Thevetia peruviana (yellow grazed when they sprout before the new grass appears, or in the late oleander), Strophanthus spp. (poison rope), Acokanthera spp. (bush- summer when the grass becomes dry. Affected animals usually drop man’s poison bush), Gomphocarpus spp. (milkweeds), Cryptostegia dead after exercise or other stimulation, although a few may mani- grandiflora (rubber vine) and Adenium multiflorum (impala lily). fest signs of congestive heart failure. Histopathological examination As these are unpalatable plants they are rarely eaten by stock of the heart reveals typical lesions of degenerative cardiomyopathy and therefore of little veterinary importance. Major stock losses and replacement fibrosis that affect mainly the endocardium of the are, however, recorded due to consumption of plants containing heart. Both cattle and small stock are affected. A polyamine has been bufadienolides. Poisoning by bufadienolides falls into two major isolated and purified relatively recently and has been identified as categories, acute poisoning