Archives for posts with tag: mycotoxin

Mycotoxins are small compounds found contaminating several plant products.  They are toxic to animals and humans in small doses and poisonings are often difficult to diagnose.  Symptoms of many mycotoxicoses are similar to each other and to those of other food poisonings and viral or bacterial diseases.

The story of aflatoxin, the first described mycotoxin, begins around 1960 in the United Kingdom.  A mysterious disease was running rampant through poultry farms, leaving upwards of 100,000 turkeys dead.  Veterinarians could not easily diagnose this new affliction labeled “Turkey X Disease”.  After ruling out known parasites, focus shifted to a common food source – a Brazilian peanut meal. The peanuts were found to be contaminated with a toxin they dubbed aflatoxin after the fungus found to produce it, Aspergillus flavus.

Aspergillus flavus fungus colonizing field corn (image: Maize Breeding Program at TAMU)

Aspergillus flavus fungus colonizing field corn (image: Maize Breeding Program at TAMU)

A. flavus colonizes oil-rich seeds, such as peanuts, maize (corn), cotton, ground nuts and pistachios.  Unlike many fungi, A. flavus and aflatoxin production are favored by hot and dry conditions.  In the United States, aflatoxin is a sporadic concern primarily for pets and livestock who consume corn and cottonseed products (See: 2006 and 2010 outbreaks in dry pet food).  However, it is a serious concern for human health in other parts of the world, most notably Kenya.  Highly toxigenic (produce high levels of aflatoxin) strains of A. flavus are native to regions in Kenya.  This combined with a maize-based diet and poor storage facilities (A. flavus can continue to grow and produce more aflatoxin after harvest if the grain is not kept dry) leads to aflatoxin poisonings every year in Kenya (even if they aren’t reported).  Aside from acute poisonings (involving liver failure and death), chronic exposure to aflatoxin can lead to liver cancer, jaundice, weight loss and immune system problems.  Aflatoxin can also pass from mother to baby through breast milk.  2004 marked the worst reported aflatoxicosis outbreak in Kenya and the world with 125 documented deaths.

A maize flour mill in Kenya (image: CDC).

A maize flour mill in Kenya (image: CDC).

What can be done?  Researchers have been focusing on understanding the populations of A. flavus in Kenya.  Atoxigenic (naturally produces no aflatoxin) strains of A. flavus have been identified and are being used as a biological control (A product called “aflasafe”) against more toxin strains.  The goal is for the toxin-free strains to outcompete the poison-producing ones in the maize fields, resulting in a less contaminated crop.  Extension and outreach programs have emphasized aflatoxin awareness for those who grow (management strategies, including the new bio control), store (keep it dry, inspect the grain) and sell maize (inspect before sale and production).

Please take a look at this slide show on aflatoxin management in Kenya.

Up next in this series, I’d like to discuss quantitative and qualitative testing methods for mycotoxins.  Testing is easier said than done (accurately), especially in a field setting.

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Welcome back to our Mycotoxin Series!

With wheat harvest mostly complete for the eastern United States, it only seems fitting that I write about deoxynivalenol (DON).  DON is produced by Fusarium graminearum (amongst others) and can be found in products made with wheat, barley and corn.  DON has been dubbed the “most commonly encountered” mycotoxin.  This is likely due to our diets (wheat and corn are staple crops in many cultures and are used in many food products) and much of the wheat we grow is rather susceptible to F. graminearum.

 FHB wheat head katelynwillyerd

F. graminearum is the causal agent of Fusarium head blight of small grains (also known as Scab).  The disease is characterized by premature “bleaching” of the wheat heads (see above), shriveled kernels, reduced yield and DON contamination.  F. graminearum also causes a disease in corn called Gibberella ear rot (more of a concern for livestock).  DON serves as a virulence factor for F. graminearum which means DON is a powerful “weapon” for this pathogen as it infects the plant.

DON is a mycotoxin that is harmful to both plants and animals (any eukaryotic cell, for that matter).  DON binds to ribosomes, preventing cells from translating genes to proteins (remember, Bio 101: DNA –> mRNA –> amino acids/proteins).  Without essential proteins, cells are unable to carryout basic function and die (e.g. bleached, dead tissue on wheat heads).

DON is also known as “vomitoxin”.  This gives you a pretty specific idea about what sort of symptoms we observe in humans and animals suffering from DON poisoning.  DON may also cause other gastro-intestinal distress, poor nutrient absorption, reduced weight gain, feed refusal and impaired immunity.  Despite being the most commonly encountered mycotoxin, we don’t have a good handle on the effects of chronic exposure to low doses of DON that may be in our breakfast cereals, breads, pretzels, pastas, etc.

DON facts katelynwillyerd

PS – A fact sheet I co-wrote on DON in corn in Ohio

Welcome back to our Mycotoxin Series!

Patulin wouldn’t be the first mycotoxin I’d typically introduce, but it has been in the news recently.  Patulin is produced by species of Penicillium, Aspergillus and Byssochlamys, which are filamentous fungi or “molds”.  Patulin can be found contaminating products like fruit, grains and cheese; however, apple juice is of most concern.  And let’s be real, it’s the bruised, damaged and misshapen apples that go into juice (blemish-free are reserved for fresh market’s picky consumers).  However, apples with rot (see below) should NOT go into juice or cider production due to patulin concerns.

apple with Penicillium expansum

Apple infested with Penicillium expansum, a patulin producer.
[NOTE: The blue-gray growth is the fungus. Patulin (waaaaay too small to be seen by the human eye!) is produced by the fungus and spreads into the rotten apple.]

Photo: Puel et al. 2010. Toxins (Basel). 2(4): 613–631.

In April 2013, Winn Dixie brand apple juice was voluntarily recalled due to patulin levels over 50 parts per billion (ppb).  In June 2013, researchers from the University of Granada reported that more than 50% of commercial apple juices tested contained >50 ppb patulin (50 ppb is the “limit” for patulin in both the US and EU).

Healthy apples

Healthy apples

Patulin in apple juice is of particular concern as this product is frequently served to young children.  In fact, some of the commercial juices tested in the aforementioned study were specifically produced and marketed to children. This toxin is a suspected carcinogen and symptoms of a patulin mycotoxicosis (poisoning) are gastro-intestinal inflammation and ulcers, weight loss, swelling, convulsions and impaired immune response (source).

While I’m not a medical doctor or veterinarian, eliminating the contaminated product from one’s diet often alleviates the symptoms.  However, acute mycotoxin poisonings are rare in the US (especially for humans).  Chronic exposure to low levels of mycotoxins is much more concerning and is difficult to study.  Hopefully, juice producers will step up their mycotoxin testing protocols to reduce the levels of patulin on the grocery shelves.

Optional subtitles: Why should I care? Do I really want to know? Thanks a lot Debbie Downer.

Consumers are becoming increasingly aware of and passionate about food quality and safety.  Not a day goes by that you don’t hear buzz words like “organic”, “GMO”, “hormone-free”, “free range”, etc.  Here in the United States, we have a (relatively) safe and secure supply of food.  However, when that security is compromised, it can be big news:

GMO wheat found in Oregon (2013)

Salmonella (2012) and Listeria (2011) found on cantaloupe

E. coli on salad greens in California (2006)

Over the next few weeks I’d like to talk about another threat that can also sicken humans and animals but doesn’t often receive a lot of press: Mycotoxins.  Mycotoxins are pervasive and fascinating, in my opinion.  However, I did spend much of PhD and post doc studying them…

What is a mycotoxin? “Myco” means fungus and a toxin is a poison; mycotoxins are small compounds produced by some fungi that are harmful to humans and animals in small doses. Symptoms of mycotoxin poisoning in humans and animals are known as mycotoxicoses. Mycotoxins associated with “poisonous mushrooms” are easy enough to avoid (don’t eat them!).  However, mycotoxins are frequently found contaminating food and feed products and are consumed unknowingly.

mycotoxin_katelynwillyerd_wheat

Many species of fungi that produce mycotoxins are also plant pathogens.  As part of their infection and colonization of the plant, they produce these toxins which end up in parts of the plant humans and animals eat. I’ll be profiling specific mycotoxins in the weeks ahead, but (spoiler alert!) some of the crops frequently contaminated with mycotoxins are wheat, corn and peanuts.

Interestingly, we don’t know why fungi produce these toxins.  Hypotheses include antiherbivory (protect a host plant and fungus from being eaten), defense against competitors (a weapon against other fungi or microbes), promotes virulence/aids in causing disease or performs some unknown function in fungal cells.

Stay tuned for more in the Mycotoxin Series.

PS – Fungi are really cool organisms and produce many compounds that have been beneficial for humans, such as dyes, penicillin, statins (for high cholesterol), etc!