Chapter 16
MOULD TOXICOSES AND POISONOUS FUNGI
(excluding ergotism)
Besides ergot (Claviceps purpurea), certain other fungi are known to produce substances toxic to animals. One group of toxicoses is due to the ingestion of food damaged by the growth of moulds and another is due to eating toxin-containing fruit-bodies of larger fungi. A variety of symptoms are exhibited by the affected animals but internal haemorrhage, nervous disturbance, vomiting and hyperkeratosis are the most frequently reported, and occasionally sudden death. Only fifteen toxicoses have been definitely associated with specific fungi and for few of these has any attempt been made to identify the toxin involved.
The poisoning of animals by fungi may take place in a number of ways including:
The only comprehensive review of mycotoxicoses is the one in Russian by Sarkisov (1954) and this is not available for easy reference. The work deals with many aspects of the conditions recognized in the U.S.S.R. and devotes other chapters to unspecified types of poisoning not yet proved to be due to fungi. The toxicoses are described under 10 separate headings according to their causal fungi and there are 268 references in Russian and 32 in other languages. Apart from this study few attempts have been made to gather together the scattered accounts of fungus poisoning in animals. The most notable contribution to the literature in the English language has been by Steyn (1933), who has given an excellent introduction to the subject as well as including details of feeding experiments on 86 animals carried out with mouldy feedingstuffs at Onderstepoort.
Poisoning by Feedingstuffs, Grazing, and Inhalation
(For convenience these toxicoses are considered alphabetically under specific and unidentified fungi.)
Diagnosis
Diagnosis of this type of poisoning presents many difficulties, and the authentic cases reported have almost always entailed a detailed investigation of the fungi present in the sample of food and toxicity tests with the individual species. Sufficient information however is now available for cases of internal haemorrhage, nervous symptoms and severe intestinal disturbance not attributable to any other causes, to be regarded as suspected fungal poisoning, and undoubtedly less exacting methods of diagnosis will be devised.
The methods of testing feedingstuffs for the presence of fungal toxins are given by Sarkisov(1954) but are also described by Carll et al. (1953), They consist of the oral dosage of experimental animals with known quantities of the suspected food and dermal testing using extracts obtained after refluxing in a Soxhlet apparatus. In addition it is necessary to isolate and identify the moulds present in the foodstuff and to test individually each species by feeding and skin tests using extracts from both the mycelium from pure culture and the substrate on which the fungus has been grown. Dermal testing has chiefly been carried out on rabbits in which the skin of the flank is shaved and an ether extract applied in olive oil. The degree and progress of the reaction over the next few days is then noted. Further tests have sometimes been carried out on the toxin including its toxicity for mice by various routes and examination for antibiotic activity (Forgacs et al. , 1954), but only in very few cases have the toxins been chemically identified.
Microbiological Aspects.
The colonization of the soil and of plant and animal substrates by fungi inevitably leads to intense microbial competition for the different complex organic nutrients available and it seems that the excretion and accumulation of substances antagonistic to other micro-organisms is of considerable advantage in obtaining maximum growth against competitors. The antagonistic substances are now termed antibiotics and their production by fungi is sufficiently well known to be considered the rule rather than the exception. Many antibiotics are known which are too toxic for therapeutic use and it seems likely that it is substances of this nature which are basically responsible for outbreaks of poisoning attributed to mouldy food.
A feature of this type of poisoning is that it is sporadic and appears to be largely dependent on the occurrence of weather favourable for the growth of the toxin-producing fungus. Outbreaks of the fusario-toxicoses, cornstalk disease and vulvovaginitis in sows, have almost always followed bad harvesting seasons whilst it is clear that the degree of mouldiness of hay varies from year to year according to prevalence of wet conditions during harvesting. The weather prevailing at the time of gathering the crop therefore seems to play a major part in its subsequent spoilage by moulds and hence to both the occurrence of the toxicoses described here and of several of the respiratory mycoses described in other sections.
Identified species of Fungi
Aspergillus - Perhaps because of their importance as pathogens, the toxin production by species of this genus has been studied more closely than most others. The earlier records of toxicity centred around the investigations of Ceni & Besta (1902), whose interest was in the pathogenic mechanism of A. fumigatus infection. They obtained toxic substances by alcohol and ether extraction of the spores of this fungus, but their significance was not pursued further. A. fumigatus is probably the most abundant of all toxin-producing species found in mouldy food and Carll et al. (1955) experimentally produced extensive internal haemorrhage in a calf after feeding with artificially infected maize for 20 days. Extracts of the maize also showed toxicity for the skin of rabbits. Outbreaks of hyperkeratosis in calves were attributed by Forgacs et al. (1954) to the growth of toxin-producing strains of A. clavatus in pelleted foodstuffs. They isolated this fungus and caused the death of two calves by feeding them on whole grain inoculated with the isolate. Characteristic lesions of internal haemorrhage were produced whilst sub-lethal doses led to hyperkeratosis. Similar results were obtained by Carll et al. (1954) for certain isolates of A. chevalieri. Levitski & Koniukhova (1947) added A. flavus, A. nidulans and A. niger to the list of toxin-producing species. Carll et al. (1954) failed to obtain results with strains of A. flavus and A. tamarii also isolated from mouldy food concentrate but Burnside et al. (I957) found that their strains of A. flavus produced substrates which were toxic for pigs.
Dendrodochium toxicum -Toxicosis due to Dendrodochium toxicum has been described only in the U.S.S.R., where it was first observed in 1937 among horses in the Ukraine. The fungus infects straw and chaff and the disease runs a very rapid, fatal course (Sarkisov, 1954; Karpova- Benua, 1954).
Diplodia zeae -Mitchell (1918a) found that maize infected by Diplodia zeae could cause incoordination and paralysis when fed to cattle. Symptoms appeared within two days of feeding 20lb. of experimentally inoculated maize to one animal. Theiler (1927) considered that cattle and sheep were affected, and gave catarrhal enteritis and hyperaemia of the lungs and kidneys as characteristics of this toxicosis. Mitchell & Beadles (1940) have repeated the earlier work on the impaired feeding value of maize damaged by this fungus.
Fusarium -The fusariotoxicoses are fairly well known and four species of Fusarium and their varieties have been found to produce toxins. Toxin-producing strains of F. sporotrichioides have been recognized only in the U.S.S.R., where they were found growing on grain which had overwintered in the field under snow. Such affected grain fed to animals produced "alimentary toxic anaemia" characterized by haemorrhages in the alimentary canal. Horses, pigs and dogs have been affected, but the most serious outbreaks have occurred in man (Sarkisov (1954) lists 92 references on this toxicosis). Loginov (1958) isolated F. sporotrichioides var. minus from mouldy wheat bran fed to newly-weaned piglets which had died with catarrhal inflammation of the naso-pharynx, stomatitis, oedema of the lungs and liver dystrophy.
Steyn (1933) made an extensive series of experiments using F. moniliforme var. subglutinans by feeding the fungus and its substrates to rabbits. Only two died, but these showed paralytic symptoms for the previous two days.
F. graminearum (syn. F. roseum), the imperfect state of Gibberella saubirietii (syn. G. zeae ?), causes scab of barley and other cereals, forming the perithecia of its perfect state on the grains. Affected barley has proved toxic when fed to most species of domestic animals and also to man but the toxicosis is best known in pigs. Although its toxic properties were known previously, it was the extensive infection of the North American barley crop in 1928 that led to outbreaks of poisoning in pigs both in that region and in Europe, to which quantities of the same grain were exported. Some 20 papers on the disease in pigs appeared during the subsequent three years, and nearly all described symptoms of vomiting, refusal to eat and foetid diarrhoea which occurred within a short time of feeding. Schroeter & Strassberger (1931) considered cholin or a hydrolysed ester to be the toxin but the precise nature of the substance was not established. It was apparently not formed in pure cultures on artificially infected grain and Moore et al. (1934) stated that "the toxic principle results from the interaction of parasite and host during the active growing period". In man there is a distinct effect on the central nervous system giving rise to staggering and hence to the name "drunken bread" for loaves prepared from infected barley (Sarkisov, 1954).
Stachybotrys alternans (syn. S. atra ?) - Although species of Stachybotrys are common saprophytes on plant substrates and are world-wide in distribution, one strain has been found to produce stachybotryotoxicosis. This is S. alternans Bon. var. jateli and it has so far been found only in Eastern Europe and the U.S.S.R. The earliest records of the disease came from Russia in 1938 and the disease was studied extensively by Vertinskii (1940) but most of the information here is taken from Sarkisov's account. S. alternans var. jateli when growing on straw or hay produces a toxin in 2-3 weeks just about the same time as spore formation occurs. When affected fodder is fed to horses symptoms of the disease appear in 1-4 days and consist of cracking and swelling of the lips and inflammation of the oral mucosa (1st stage). Continued feeding leads to extensive changes in the blood including a fall in the leucocyte count and a loss of clotting power, whilst later necrotic foci appear in the mouth (2nd stage). The 3rd and final phase of the disease follows with a sudden rise in temperature to 40° - 41°C., increased heart action, further deterioration of the blood, and death in 1-3 days. Post-mortem examination reveals extensive haemorrhages in many organs including the brain, and necrosis of the alimentary tract. The disease has received considerable attention in the U.S.S.R. and measures for its control have been devised, largely based on the recognition of affected fodder and its destruction.
Penicillium - The penicillia are by far the best known antibiotic producing fungi, but several of the antibiotics are highly toxic for animals as well as being active against bacteria. Among these is patulin isolated originally from P. patulum, but considered by Hori et al. (1954) to be the cause of mass deaths in cows which had eaten malt feed affected by a Penicillium sp. of the urticae series. Sippel et al. (1954) described a haemorrhagic disease of pigs and cattle which followed the feeding of mouldy corn (maize) and they were later able to reproduce the condition by feeding maize on which the fungi isolated from the original sample had been grown (Burnside et al., 1957). These authors found that only two of the 13 species of moulds which they isolated from the mouldy maize produced any toxins, viz. Aspergillus flavus and Penicillium rubrum. Four pigs force-fed 8 ounces of maize infected by the latter species, died within 24 hours and similar rapid results were obtained in a goat, mice and horses. Non-toxic strains of the same species were also isolated.
Puccinia graminis -The rust fungi (Uredinales) have occasionally been responsible for reports of poisoning in livestock (Friedberger & Frohner, 1905), and recently Lapcevic et al. (1953) have given an account of how five of 16 horses died suddenly following the feeding of severely-rusted wheat straw infected with Puccinia graminis; the remaining 11 animals had salivation and stomatitis. Attempts at the experimental reproduction of the condition resulted in the death of one of three horses.
Ustilago and Tilletia -The spores of the smut fungi (Ustilaginales) occur in large quantities in affected grain and have occasionally been found to cause disease which might possibly be termed a toxicosis but is probably more correctly classed as an allergy which may possibly develop into a true mycosis. Steyn (1933), quoting Pammel (1911), refers to the feeding of maize infected with Ustilago maydis (syn. U. zeae) as a cause of loss of condition in cattle. Hutyra & Marek (1922) say that the same fungus was responsible for gout in birds, whilst Ivanov (1949) has shown that inhalation of the spores of this smut led to extensive outbreaks of pneumonia in cattle in Bulgaria. The animals in these outbreaks had emphysema of the lungs with nodule formation, each focus being centred on a single spore or group of spores surrounded by asteroid projections together with histiocytes, giant cells and peripheral fibrosis. In contrast allergic reaction appeared to be responsible for a curious case of skin trouble in a farmer who had slept in a corn field where much of the crop was infected with smut, (Preininger, 1937), and actual pathogenicity by U. maydis was shown by Moore et al. (1946) to have occurred by the presence in the central nervous system of a man, who died after showing chronic nervous symptoms, of the budding yeast-like phase of the fungus. Experimental work has been carried out on rats by Tichomirov & Bogdanovic (1941). Bunt of wheat (Tilletia caries) has also been held responsible for the poisoning of dogs by Greig (1924). The three animals affected had convulsions and in one of these there was marked cerebral meningitis with spores actually present in the brain and other organs. The trouble was thought to have originated from the ingestion of food containing the spores. However when Dobson (1926) tried to confirm these observations by experimental feeding with large quantities of bunt spores, he was unable to find any deleterious effect on dogs, guinea-pigs, rabbits or fowls.
Unidentified Species of Fungi.
The toxicoses included under this heading may possibly be due to the presence of some of the fungi already mentioned but in most cases the connexion with mouldy feeding stuffs is largely circumstantial and no further investigation of outbreaks has been made. The category is therefore rather unsatisfactory and the symptoms described may well be due to unrelated causes such as infectious or other diseases not recognized at the time.
Cornstalk Disease - First noticed by Mayo (1891), the effect of feeding mouldy cornstalks (maize) to horses was shown experimentally by Butler (1902) to be a leucoencephalitis or acute haemorrhagic encephalitis (Buckley & MacCallum, 1901). Further attention was directed to the condition after extensive outbreaks, again in the U.S.A., in 1934 as described by Graham (1936) and several references to the disease have appeared since that time. Generally nervous symptoms appear some four weeks after feeding has commenced and consist of staggering, lethargy and sometimes paralysis followed by death in 6-7 weeks. Postmortem findings include softening and liquefaction of the brain and haemorrhage, congestion of the liver and swelling of the kidneys (Schwarte et al., 1937; Biester et al., 1940). Experimental feeding of mouldy corn stalks has confirmed theIr toxicity but as yet no specific fungi have been isolated from them. Various attempts to demonstrate the presence of the virus of equine encephalomyelitis in the brains of affected animals were unsuccessful.
Darnel (Lolium temulentum) poisioning -The poisoning of animals by this grass, one of the best known toxic plants, may possibly not be connected in any way with fungi, but there is some evidence that fungi are intimately concerned in the toxicity of the grass. Darnel is an annual plant, at one time a common weed of cereal crops, having most probably been the "tares" of the Bible. According to Leemann (1933) it is not toxic in its early stages of growth and only the seeds contain the toxin. Support for this comes from the majority of outbreaks of suspected darnel poisoning having been reported after hay containing the seeds had been fed or, in man, after bread made from flour from contaminated grain had been consumed. Nervous disturbance is a characteristic sign with giddiness, trembling, staggering followed by convulsions, delirium and death. Post-mortem examination rarely reveals any abnormality.
The connexion of darnel poisoning with fungi is long-standing but still shrouded in uncertainty .Lolium temulentum seeds usually contain a symbiotic fungus outside the aleurone layer but a certain proportion are free from infection. Freeman (1902) presumed that the seeds infected by the fungus were toxic and those without were not, but this suggestion is still not confirmed.
The identity of the fungus has never been established but it seems likely that it is the endophytic one known to be present in several species of Lolium and which does not seem to have any adverse effect on the vigour or palatability of the grass (Neill, 1952). In addition to this organism however there is an ascomycete parasitic on rye-grasses (Gloeotinia temulentum, syn. Phialea temulentum) which causes so-called "blind seed disease" and infects the inflorescences in a similar way to ergot (Claviceps purpurea), The ovary is replaced by a mass of hyphae and the imperfect spores (Endoconidium temulentum) are formed on the outside of this mass (Sampson & Western, 1954). Whether or not this fungus is the endophyte of Lolium temulentum is still not clear (Neill, 1941).
Mouldy hay poisoning -The feeding of mouldy oat hay to cattle was thought by Newsom et al. (1937) to cause trembling, staggering and cyanosis of the lips leading eventually to death. The following year Thorp (1938) made further observations on the condition by experimentally feeding cattle with mouldy hay from the top and middle of a stack. The former group of animals died with typical symptoms whilst the latter were not affected, the hay from this part of the stack being of much better quality. Changes reminiscent of hydrocyanic acid poisoning were seen on post-mortem examination. Thorp fed the same hay samples to guinea- pigs, rabbits and sheep without adverse effects.
Sweet clover poisoning -- Mouldy hay with a high content of sweet clover (Melilotus alba) has been shown to be the cause of a particular type of poisoning associated with severe haemorrhage and outbreaks of the condition in the U.S.A. have been termed "sweet clover disease". Roderick & Schalk (1931) monographed the disease in cattle after making a detailed study of field and experimental cases. The earliest sign of the trouble following the feeding of mouldy hay was a delay in coagulation time of the blood which occurred at about 15 days. Internal haemorrhage was found at about three weeks and death either occurred suddenly or followed progressive weakening and took place at about 30 days. Postmortem examination revealed extensive haemorrhages in different parts of the body, chiefly in the thoracic region and in the serosa of the rumen, but also intramuscularly. Toxicity of the hay for sheep and rabbits was demonstrated but horses were not found to be susceptible.
Roderick and Schalk were not successful in their many attempts to extract and identify the toxic substance but subsequent work on the disease by Campbell, Link and others some ten years later (Campbell et al., 1940) led to the isolation, identification and synthesis of the haemorrhagic agent as dicoumarin 3,3-- methylenebis (4-hydroxycoumarin) (Stahmann et al. 1941). A later derivative was eventually developed as the rodenticide warfarin (see Garner, 1957). The fungi associated with the original outbreaks of sweet clover disease were apparently not identified.
Vulvovaginitis in pigs -The first reports of vulvovaginitis in sows associated with the feeding of mouldy maize were made by Buxton (1927) and McNutt et al. (1928) in Iowa, involving maize harvested during the very wet autumn of 1926. The condition at first resembled normal oestral changes but occurred in piglets from six weeks to four months of age in which the vulva swelled considerably with occasional vaginal prolapse. Experimental feeding of the same mouldy maize resulted in similar symptoms within six days. Ten years later Pullar & Lerew (1937) described an almost identical outbreak in Victoria (Australia) also with maize harvested after heavy rain, and another report came from the U.S.A. in 1945 when Koen & Smith noted enlargement of the prepuce and mammary glands of castrated male piglets as an additional sign. The only other similar outbreaks recorded are those of McErlean (1952) in Ireland, but there the food was mouldy barley. The symptoms noted in these outbreaks indicate that the toxic substances were oestrogenic and therefore probably different from any of those already mentioned. In each outbreak the withdrawal of the mouldy food resulted in great improvement and eventual recovery.
Poisoning by larger fungi
Compared with the vast literature on mushroom and toadstool (the gill-fungi or agarics - Basidiomycetes) poisoning in man, there is little information even on the effect of the more deadly of these fungi on animals. Rabbits for instance have been said to be immune to the effects of the toxin of the Death Cap (Amanita phalloides) and this had led to the use of their stomach contents (chopped up with sugar or jam) as an antidote for human cases. In his invaluable book on these fungi Ramsbottom (1953) points out that rabbits will succumb to Amanita phalloidps if it is eaten in reasonable quantities. Other poisonous species may also frequently be found in a partly eaten condition, obviously grazed by small rodents, slugs etc. Of the species thought to have been involved in outbreaks of poisoning in animals Amanita verna was incriminated by Piercy et al. (1944) in cases of severe intestinal disturbance in which two cows died following convulsions. Pieces of the fruit bodies of the fungus were found in the stomach of one animal. Russula emetica, an attractive bright red species, was thought to have been involved in the death of a reindeer bull in Scotland by Utsi (1956). Two extremely interesting cases of poisoning due to the morel (Morchella esculenta, an ascomycete) were described by Herms (1950) in two pet dogs in Germany. One of these animals had been allowed to drink the water in which a gathering of these fungi had been cooked and some hours later had attacks of vomiting, shivering, diarrhoea and haematuria whilst the other simply ate a few pieces of the cooked fungus. Both animals recovered quickly. This record seems to confirm the observation that it is not desirable to use the cooking water of morels which are otherwise considered edible.
Miscellaneous conditions
It is not possible in this review to cover all the literature on mycotoxicoses but there are a number of further instances of suspected poisoning of livestock with mouldy food which deserve a brief mention. Among these Forgacs & Carll (1955) have suggested, in a preliminary note, that more attention might be paid to fungi as a cause of haemorrhagic disease in poultry, for they were able to reproduce the field condition by feeding grain artificially infected with various species of Aspergillus, Penicillium and Alternaria. Eckles et al. (1924) investigated the significance of moulds in silage but considered that the evidence for poisoning was inconclusive, although they still advised against the feeding of badly moulded samples. Contrary to most other workers, Borchers & Peltier (1947) fed 10% of artificially moulded starter ration to chicks and actually found an improved growth rate over the controls, possibly foreshadowing the widespread present day inclusion of antibiotics in feedingstuffs. However the fungi used were not specified and it is unlikely they included any toxin-producing strains.
List of fungi known to produce substances toxic to animals