Page 81 - VHSA - Onderstepoort 100 Years - Part 3

information on them could be obtained from overseas literature. South Africans were therefore forced to look to themselves for answers to the problems posed by these plants.
Reviewing the history of research on plant poisoning at Onderstepoort over the last century, in the limited space allowed, is a daunting task. A complete record would fill a book. In view of this, we have decided to only briefly outline some of the research on the major problems listed in the 1996 study referred to above.
ONDERSTEPOORT 100
plants, including several plak- kies (Tylecodon, Cotyledon and Kalanchoe spp.), tulp (Moraea spp.), slangkop (Drimia spp.), kruidjie-roer-my-nie (Melian- thus spp.) have been shown to also contain bufadienoli- des. Perhaps it is appropriate here to acknowledge the signal contribution made by Anderson, who probably iso- lated more cardiac glycosides from plants than anyone else in the world.
Having gained a clear understanding of the cause and mechanics of cardiac glycoside poisoning – though it niggles that we still do not
know how a bufadienolide can cause krimpsiekte (a paretic nervous condition) without
affecting the heart and other organs – our thoughts turned to its treatment and control. Several therapeutic agents were tested without notable success until Joubert (1976-1982 and 1990-2004) demonstrated that drenching poisoned animals with activated charcoal gave excellent results. This simple,
According to this study,
poisoning of stock with cardiac
glycoside-containing plants
(as an entity) is the single
most important plant poisoning in South Africa. The study estimated that in an average year 33% of all cattle deaths from plant poisonings and mycotoxicoses in the country could be ascribed to plant-associated cardiac glycosides. No wonder then that this poisoning has been assiduously studied for more than a 100 years.
Yellow tulp
The first account of research on a cardiac glycoside-containing plant dates back to 1891, when J.F. Soga – the first South African born veterinarian – succeeded in reproducing krimpsiekte by dosing a ‘plakkie’, Tylecodon ventricosis, to goats. Regrettably, his findings were greeted with scepticism, because amongst others, the influential Prof P. MacOwen of the University of the Cape of Good Hope could not find a precedent for a member of the Crassulaceae being toxic! Eventually it fell to M.W. Henning, some two decades later, to confirm to every one’s satisfaction that Tylecodon spp. were indeed the cause of krimpsiekte.
(Moraea pallida
(
(
a
), a major cause of acute cardiac glycoside poisoning of stock
“The first account of research on a cardiac glycoside containing-plant dates back to 1891, when J.F. Soga – the first South African born veterinarian – succeeded in reproducing krimpsiekte by dosing a ‘plakkie’, Tylecodon ventricosis, to goats.”
practical and economical treatment has saved the lives of untold numbers of stock. Satisfied that an effective treatment was
available, we then began investigating ways
and means of preventing plant-induced
cardiac glycoside poisoning. The current 171 measures for controlling plant poisonings
– e.g. by the mechanical or chemical eradication of plants, the latter being par- ticularly distasteful from an ecological
point of view – all involved changing the environment in some way. But changing
the environment is not always feasible, especially in the communal and extensive commercial farming areas, where both the
capital and labour for doing so are lacking.
Since the environment could not easily be
The next notable milestone in the saga of krimpsiekte and cardiac glycoside poisoning was the isolation in 1965 of the toxic principle (a bufadienolide) from a tulp (Moraea pallida) by Naudé and D.J. Potgieter. Although the work was not done at Onderstepoort, this landmark was followed in 1971 by the isolation of a bufadienolide from Tylecodon wallichii by van Rooyen and Pieterse. Knowing the nature of these toxic principles was very important, as this allowed us to gain access to applicable information (such as modes of action) on extensively researched cardiac glycosides, e.g. digitalis, abroad. Following this pioneering work, many
changed, we decided that the only other way of controlling plant poisonings would be by manipulating the animal to resist them. The most obvious method for doing this was to immunize stock against plant poisonings. Joubert according- ly attempted to prepare a vaccine against cardiac glycoside poisoning by conjugating various cardiac glycosides with bovine serum albumin. Although sheep developed strong im- munity to the particular cardiac glycoside in the vaccine, little cross-immunity could be demonstrated against challenges with non-homologous cardiac glycosides or cardiac glyco- side-containing plants.
Toxicology
1908-2008
Years