Page 88 - VHSA - Onderstepoort 100 Years - Part 3

OND
ERSTEPOORT 100
of facial eczema in sheep by dosing pure cultures of the causal fungus (Pithomyces chartarum) obtained from a toxic field clearly fell in the ambit of diagnostics. The position with regard to maldronksiekte and Aspergillus clavatus tremors, for example, is not quite so clear. Pienaar in collaboration with Kellerman and others (1976) incriminated Solanum tetense in the disease of cattle in the Limpopo Province characterized by epileptiform seizures. Later, similar disorders in the USA and South America were ascribed to other Solanum spp. With regard to A. clavatus tremors, Kellerman and his co-workers (1976) showed that this highly fatal nervous disorder of cattle was caused by as yet unidentified mycotoxins produced by the fungus growing saprophytically on feeds such as sorg- hum beer residue and sprouted maize. Since then, outbreaks of A. clavatus tremors have been reported in Israel, Scotland and elsewhere.
One of the major problems facing South African diag- nosticians has been the lack of a laboratory test for plant- associated cardiac glycoside poisoning. These poisonings have traditionally been diagnosed on circumstantial evidence such as the clinical signs, and the presence of appropriate plants showing signs of being eaten and/or leaf fragments in the rumen. Schultz and her co-workers in the early 1990s tried to address this problem by adapting the fluorescence
During the late 1970s and 1980s the diagnostic laboratory was upgraded by the acquisition of modern instruments such as a gas chromatograph mass spectometer
quite true. In each case, the active principles have been identified and thorough investigations have been carried out on their botanical, clinical, toxicological, pathological and other aspects. One instance that deserves to be highlighted, though, was the landmark identification by J.S.C. Marais at Onderstepoort in 1944 of monofluoroacetate, the active
polarization immunoassay (FPIA), a tech- nique for monitoring digoxin therapy in humans, for use in animals. Digoxin plasma concentrations are monitored by demonstrating these cardenolides in human serum, based on antigen/antibody reac- tions and competitive binding. They found that many phytogenous bufadienolides showed cross-reactivity with a commercial- ly available fluorophore for digoxin, a cardenolide. Using this technique, positive reactions have been obtained in rumen/ stomach contents and organs of cattle, ostriches, suni antelope and even a dog that mouthed a toad. Another problem bedevilling us is that gousiekte cannot be diagnosed until stock start dying, and once they do so, there is no means of identifying the affected (but clinically normal) ones in latency. There is now some light in the tunnel, as Fourie and his co-workers (1989) found that of all the clinical pathological
principle of gifblaar. In-depth studies of gifblaar poisoning and seneciosis were not undertaken largely because their active principles (monofluoroacetate and pyrro- lizidine alkaloids) had been exhaustively studied abroad.
Much the same situation applied to 178 Lantana poisoning and vermeersiekte. One should note, perhaps in the passing, that Snyman and his co-workers demonstrated that the aversion factor in Senecio latifolius was the active principle of the plant, a pyrrolizidine alkaloid. Many other plants were also investigated. One incident that springs to mind, is that when Anderson isolated a neurotoxin, a 4-methoxy deriva- tive of pyridoxine, from the pods of Albizia versicolor, he pointed out the close chemical relationship between his toxin and vitamin B6, and proposed that administering vita- min B6 might be a treatment for Albizia
“One of the major problems facing South African diagnosticians has been the lack of a laboratory test for plant-associated cardiac glycoside poisoning. These poisonings have traditionally been diagnosed on circumstantial evidence such as the clinical signs, and the presence of appropriate plants showing signs of being eaten and/or leaf fragments in the rumen.”
poisoning. Trials by B. Gummow and his co-workers (1992) at our laboratory subsequently proved his suspicion correct; vitamin B6 is indeed very effective. Here was a rare instance where the structure of a toxin revealed the treatment of a poisoning.
Diagnostics
When it comes to plant poisonings, the line that divides research and diagnostics is somewhat blurred. The induction
parameters they tested, elevation of aspartate transaminase activity in the serum was the most reliable indicator of cardiac involvement during latency.
In the first 60 years of the last century, the diagnoses in our laboratory were dominated by inorganic poisonings. Dip attendants regularly monitored the arsenic content of plunge dips all over the country and no veterinarian travelled with- out his dip test kit. Arsenic was the standard acaricide used to control the ticks responsible for diseases such as East Coast
PART 3
History of Individual Disciplines
1908-2008
Years