Poisonous Plants, Fungi, and Algae

1. Poisonous Plants, Fungi, and Algae II – Mycotoxins

2. Fungal toxins • Fungi produce a tremendous diversity of toxic compounds • Mushroom toxins formed in the fleshy fruiting bodies of higher fungi • Mycotoxins formed by hyphae of common molds growing under a variety of conditions

3. Mycotoxins • Mycotoxins produced by many fungi growing in contaminated foods and other substrates. • Generally, the highest levels in substrates with high water activity and warm temperatures. • Can develop in grains or nuts in the field due to activities of pathogenic as well as saprobic fungi on the living plant • Forage grass may contain mycotoxins because of a pathogenic fungus or a fungal endophyte

4. Mycotoxins • More commonly -- mycotoxins develop in storage and remain within the food after processing and cooking • Many common indoor environmental contaminants are toxigenic - able to produce toxins • Some studies revealed significant levels of airborne mycotoxins in occupational settings, offices, and even homes

5. Health effects of mycotoxins • Acute and chronic effects on both humans and livestock • Mycotoxins are believed to be among the most potent known carcinogens • Majority of research focused on health effects following ingestion of contaminated food • Effect range from immediate toxic responses and immunosupression to potential long-term teratogenic, estrogenic, and carcinogenic effects. • Possible health effects due to airborne exposure (exposure to airborne spores with mycotoxins)

6. History of mycotoxins • Turkey X disease killed over 100,000 young turkeys in 1960 in England • Affected turkeys stopped eating, became lethargic, suffered hemorrhages under the skin, and died • Autopsies showed livers had undergone extensive necrosis, kidneys developed lesions • Partridges, pheasants, ducklings, and other animals also affected • Only factor in common with all the cases was Brazilian peanut meal as a feed supplement. • Toxin isolated from feed associated with fungal contaminant Aspergillus flavus

7. Aflatoxins • Aflatoxin: A (aspergillus) - fla (flavus) - toxin • Four toxins soon identified: aflatoxin B1, B2, G1, G2 - (B and G refer to blue or green florescence under uv-light) • Today known to be 10 aflatoxins • Aflatoxin B1 most important - highly carcinogenic and widespread occurrence in foods

8. Sources of aflatoxins • Produced by 3 species of Aspergillus: A. flavus, A. parasiticus, A. nomius • Aspergillus flavus a common fungus that occurs on grains and legumes • A. parasiticus most toxigenic species • Aflatoxins not only toxic but also carcinogenic, mutagenic, and teratogenic

9. Effects of aflatoxins • Toxic effects clearly shown in India in 1974 when hundreds were poisoned by eating corn containing aflatoxins and 106 people died • Even when levels not toxic, prolonged exposure caused liver cancer in every species of lab animal tested • Believed responsible for high rates of liver cancer in population groups in Asia and Africa where contaminated food is often consumed • Most important crops - peanuts and corn

10. Aflatoxin B1 is Mutagenic • Hepatocellular carcinoma (HCC) is a major cause of mortality in certain areas of the world • About 50% of the HCC cases in parts of the world where food is contaminated with AFB1show a mutation in codon 249 of p53 tumor suppressor gene • Mutation consists of transversion of G->T in the third position of codon resulting in serine instead of arginine - lab studies confirm

11. Aflatoxins in corn • Contamination occurs both in the field before harvest and in storage • Most researchers agree is that if the contamination is prevented before harvest the problem can be managed • Emphasis is placed on preventing A flavus infections of the corn by developing disease resistant varieties and also by insect control to prevent initial infections at wound sites

12. Aflatoxin levels • Levels permissible in foods subject to legal limits in many countries • Today, foods most frequently contaminated, routinely screened before processing or sale • Permissible limits generally quite low (15-20 parts per billion in US - lower in Europe) for human food • Some scientists feel that no detectable levels of aflatoxins should be permitted because of the carcinogenic effects

13. Economic impact • Because of enforced limits the presence of aflatoxins can have serious economic implications • In 1980 nearly 66% of random corn samples from North Carolina had concentrations exceeding 20 ppb resulting in a $31 million loss to producers and handlers • When cows and goats are fed grains contaminated with aflatoxins, they produce milk with aflatoxins - as a result, limits exist for livestock feed but not as low

14. Average yearly level of aflatoxin contamination from corn grown along the coastal plain of Georgia

15. Economics and health • In US most corn goes to animal feed so aflatoxin exposure are not as much of a problem as in other countries • In many countries in Africa, Central and South America and Mexico corn is a primary staple for human food and many people are exposed to aflatoxin levels above the standard • In Benin - mean levels 37 ppb • In Nigeria - mean levels 292 ppb

16. Aflatoxin production • Aflatoxins are produced under certain conditions but only by some strains • Nontoxigenic strains of A. flavus used to prepare fermented foods in the orient

17. Other mycotoxins • Today over 400 mycotoxins have been identified from 150 species of fungi with new ones discovered each year • Species of Aspergillus, Penicillium, Fusarium, Alternaria, Cladosporium and Stachybotrys form mycotoxins

18. Mycotoxin production • Can occur in one strain of a species, other strains of the same species not toxigenic • Fungi from air samples in homes tested for mycotoxin production using tissue culture of human fibroblast cells • In multiple isolates of a single species (up to 12) some produced mycotoxins, others did not • Warm temperatures and abundant moisture promote mycotoxin production

19. Aspergillus Common toxigenic fungi Penicillium Stachybotrys Fusarium

20. Ochratoxins • Produced by species of Aspergillus such as Aspergillus ochraceus • Most important is Penicillium verrucosum which occurs on grains • Ochratoxin A a nephrotoxin responsible for nephropathy in pigs and probably humans • It is immunosuppressive and also assumed to be carcinogenic in humans - in animal studies it is one of the strongest carcinogens

21. Patulin • Produced by a number of species of Penicillium, Aspergillus and Byssochlamys. • Most important producer is Penicilliumexpansum. • Fungus causes a soft rot of apples; toxin found in apple juice • Patulin first attracted attention as an antibiotic in 1943; no current interest in antibiotic properties because it is too toxic

22. Trichothecenes • Produced by several species of Fusarium • One of the most toxic is T-2 • Believed T-2 responsible for outbreak of alimentary toxic aleukia (ATA) in Siberia during and after World War II • In some areas 10% of the population developed the disease and in most cases it was fatal

23. Alimentary Toxic Aleukia - ATA • Characterized by nausea, vomiting, hemorrhages in many organs, bleeding from nose and throat, bloody diarrhea, low leukocyte count, exhaustion of bone marrow • About a third of deaths due to strangulation from internal swelling of throat • Years later scientists made the connection between the disease and consumption of moldy grain • Symptoms appeared when people ate 2 kg of moldy grain, 6 kg was lethal. Similar hemorrhagic syndrome in animals called moldy corn toxicosis

24. Vomitoxin (Deoxynivalenol) • A trichothecene produced by some Fusarium spp. • Produces vomiting in pigs at low concentrations • Much less toxic than T-2 but immunosuppressive • Contaminates corn, barley, and wheat • Permissible limits are 0.3 ppm for flour and 0.1 ppm in bread or breakfast cereal • During recent wet growing season, Ontario farmers lost $17 million on a wheat harvest contaminated with vomitoxin.

25. Macrocyclic trichothecenes • More toxic than T-2 • Produced by Stachybotrys chartarum (S. atra) and also by species of Myrothecium • Specific toxins are satratoxins, verrucarins, and roridins • Fungi are cellulose decomposers and found growing on hay or straw stored under poor conditions.

26. Macrocyclic trichothecenes • Responsible for the deaths of many horses, but it can also affect cattle, pigs, sheep, poultry • Complex of unpleasant symptoms like ATA. • Stachybotrys found indoors in many locations growing on ceiling tiles and wallboard • Concern about airborne inhalation of spores

27. Yellow rain • During the Vietnam war, there was concern that the Viet Cong were using chemical weapons against the US as well as the population in Laos and Cambodia • Victims were sprayed with a yellow rain • Symptoms were like ATA (possibly some evidence of trichothecene toxins in some of the victims. However, the issue was not clear cut) • Little evidence Viet Cong using chemical weapons • Samples of the yellow rain deposits later shown to be largely made up of pollen - “cleansing flight theory” • This issue has never been resolved

28. Zearalenone • Produced by species of Fusarium found in moldy corn • Chronic exposure is estrogenic • Female pigs especially sensitive causing vulvovaginitis. • Swelling of the vulva, enlargement of the mammary glands, enlargement of the uterus, and vaginal prolapse. • In lower levels causes infertility, stillbirths, and small litters

29. Fumonisins • Produced by several Fusarium species on moldy corn – possibly other fungi as well • First discovered in 1988 • Implicated in cases of esophageal cancer in humans and other cancer in farm animals • Shown to disrupt sphingolipid metabolism (involved in membrane structure) • Implicated in birth defects relating to neural tube abnormalities

30. Exposure in Contaminated Environments • Beginning in late 1980s scientists began raising the issue of possible inhalant exposure • Mycotoxins are not volatile but they are present in fungal spores • In contaminated indoor environments, people may be inhaling hundreds to thousands of fungal spores per hour • If the spore are toxigenic, risks may occur

31. Indoor Fungi • Indoor spores generally reflects outdoors unless there is a source of contamination • Many different types of fungi occur • Most common genus is Cladosporium - just like it is outdoors • BUTPenicillium and Aspergillus often exist at higher concentrations indoors • Stachybotrys has received most media attention over the past 4 years

32. Cladosporium • Common fungal genus occurring both indoors and outdoors • Most abundant outdoor spore type with a worldwide distribution • Normally exists as a saprobe or weak plant pathogen • Spores are known to be allergenic

33. Cladosporium on diffuser

34. Penicillium • One of the most common soil fungi in natural environment • Over 250 species • Well known allergen • Some species produce mycotoxins • Produce VOCs

35. Penicillium in culture

36. Aspergillus • Also common soil fungus and cause rot of stored grain • Over 150 species • Well known allergens • Several species form mycotoxins • Some species can grow at high temperatures • Several species can cause human infections of lung and hypersensitivity pneumonitis

37. Penicillium and Aspergillus • Small spores passively aerosolized when spore clusters disturbed • Spores extremely buoyant, remain airborne for extended time

38. Stachybotrys • Soil fungus in nature • Commonly found indoors on wet materials containing cellulose, such as wallboard, jute, wicker, straw baskets, and paper materials • Spores in slimy mass • Thought to be allergenic although little is known • May produce potent mycotoxins

39. Stachybotrys

42. Health effects from airborne exposure? • Clinical studies not completed yet • Possible correlations in contaminated buildings but no experimental studies with human exposure • Animal studies suggest effects of respiratory exposure important • Possibleeffects: immune suppression, rash, headache, fatigue, sore throat, pulmonary hemorrhage (in infants) • We need more research