Mycotoxins: what to expect next year?

Madrid (Spain) set a new July record high on July 6, topping out at 39.9°C (103.8°F), exceeding the previous July record from July 24, 1995 (39.5°C). Germany’s all-time heat record was toppled on July 5 in Kitzingen where a maximum temperature of 40.3°C (104.5°F) was recorded.

According to Meteo-France, several monthly and all-time records were either tied or broken during the first weekend of July in France. Temperatures as high as 36°C (97°F) were reported in western Poland while in the western Czech Republic topped out at 37.8°C. Temperatures reached 32 °C (89.6°F) in parts of southern Sweden.

The temperature at London’s Heathrow Airport skyrocketed to 36.7 °C (98.1°F), a July  record high, not only there but for anywhere in the UK, according to the UK Met Office. It was also the hottest day in Wimbledon history, topping the previous record of 34.6°C on June 26, 1976. The temperature in Maastricht, in the far southeast of The Netherlands rose to 38.2 °C (100.8°F), setting a new national July heat record, topping the 37.1 oC reading in Westdorpe in 2006.

Extremely high temperatures ideal for aflatoxin formation

Higher-than-usual temperatures and a reduced snowpack have been affecting Alaska and Canadian territories this season. In Alaska, 562 fires have scorched more than 250.000 hectares of land with a record of 6 active fires in one day. All these extremely high temperatures and weather conditions (high humidity and drought, high precipitation, big difference between day and night temperatures) are ideal for aflatoxin formation. These conditions can be devastating in corn producing states. The impact of aflatoxin due to lost maize yield in the USA has been estimated to be around $225 million/year. In general, drought increases the amount of aflatoxin found in corn. A hot, dry year such as the current one in which the plants are stressed may have much higher levels of aflatoxin than would be found in a ‘normal’ year.

Fungal interactions

Mycotoxins and predominantly aflatoxins are a constant concern for agriculture. Some seasons and weather conditions such as this year’s puts industry on high alert. Aflatoxins are potent mycotoxins that reduce development, impair the immune system, and cause cancer and death. Several Aspergillus species produce aflatoxins during crop infection, which is greatly influenced by weather conditions including freezes, droughts, rainfall, and shifts in temperature. Weather also influences the average aflatoxin-producing potential of the fungi. Contamination occurs both during crop development and after crop maturation.

Interactions of aflatoxin-producers with agronomic practices and weather events at specific crop stages determine the magnitude of contamination through effects on pests, crops, and timing of activities. Weather events that favor high contamination during crop development may suppress contamination after crop maturation either prior to harvest or during post-harvest handling and storage. Different fungi require different growth conditions but the risk of mycotoxin contamination to crops is the same.  Warm weather results increased deoxynivalenol production in crops, although temperatures higher than 32°C are supposed to be safer (Paterson, 2011).

Fusarium head blight (FHB) intensity is associated with weather conditions during flowering (anthesis) and up to the hard dough stage of kernel development. Rainfall and humidity in the wheat-field contribute to infection by Fusarium sp. (Kiecana et al. 1987). In favorable weather conditions, more than 10% of ears may become infected, resulting in severe disease. Severe head blight occurrence decreases not only the grain yield but also the grain quality . The UK crop monitor developed a Smartphone app which monitors quality of wheat based on several criteria. Risk factors for development of Fusarium species which produce deoxynivalenol in grain are shown in table 1.

Competition with other nutrients

Another important factor is the ability of A. flavus and A. parasiticus to compete with other fungal species for nutrients. In particular, F. verticillioides appears to compete with A. flavus on the maize ear; A. flavus can be dominant for years in temperate weather conditions and high temperature and drought conditions respectively (EFSA, 2013). Fusarium verticillioides as well as F. proliferatum are producers of fumonisins with fumonisin B1 being the most predominant among this group of mycotoxins. Besides temperature, there are several factors known to affect the occurrence of F. verticillioides ear rot of corn such as drought stress, insect damage, other fungal diseases, planting dates and corn genotype (Parsons and Munkvold, 2010). Fumonisin-producing fungi can be found wherever maize is grown. In North America, the risk is higher in Texas and the south-eastern states, compared to the central and Midwestern states; however, fumonisins remain the most common mycotoxin in the ‘corn belt’ states (Wu, 2011). Nevertheless, the most important conditions favoring fumonisin risk are insect damage to grain and moisture.

Aflatoxin contamination can be divided into two distinct phases with infection of the developing crop in the first phase and increases in contamination after maturation in the second phase (Cotty, 2001). Developing crops are often very resistant to infection by Aspergillus flavus and subsequent aflatoxin contamination unless environmental conditions favor both fungal growth and crop susceptibility.

During the first phase of contamination, wounding of the developing crop by birds, mammals, insects, mechanically (e.g. hail) or the stress of hot dry conditions results in significant infections (Cotty and Lee, 1990). The second phase of contamination may occur at any time from crop maturation until consumption (Cotty, 2001). During this phase, toxins increase in both components infected during the first phase and those infected after maturation. The second phase occurs when the mature crop is exposed to warm, moist conditions either in the field or during transportation and storage, or use (i.e. on the feedlot floor) (Cotty, 1991).However, every year is a different event, and the amount of aflatoxin contamination will depend on that particular year’s weather and not on broader changes alone.

Economic losses due to aflatoxins are huge

Aflatoxin B1, produced by Aspergillus molds, is metabolized into aflatoxin M1 in ruminants. Sources of Aflatoxin B1 include corn, peanuts, and cottonseed. When a lactating cow consumes feed with high level of aflatoxins, it will metabolize the aflatoxin B1 into aflatoxin M1 and excrete it in urine and milk. Due to the constant global climate change and varying weather conditions in different regions of the world, the economic losses from discarded contaminated milk are unpredictable, yet real and significant.

Aflatoxin B1 is the most carcinogenic natural compound known (EFSA, 2004). Aflatoxin M1 has a high carry-over rate to animal products such as milk. Fresh milk is regularly checked for aflatoxin M1; concentrations above 0.5 μg/kg (0.5 grams in 1000 tons of milk) in the USA or 0.05 μg/kg (0.05 grams in 1000 tons of milk) in the EU are considered undesirable and such milk cannot be used for products that go into the human food chain. Contaminated milk must be discarded, and apart from the cost of lost milk revenue, the dairy producer also incurs the cost of proper disposal of the contaminated milk. Many loads of corn have been rejected at grain elevators due to unsafe aflatoxin levels. Processors have been known to dump tankers of milk when milk contamination levels exceed safe levels of aflatoxin M1 (0.05 ppb EU; 0.5 ppb USA).

Prevention

Farmers who are particularly sensitive to aflatoxin contamination if it is a problem, might consider an alternative crop, such as grain sorghum. Grain sorghum is a lot less prone to aflatoxin contamination than corn but produces grain that can often be substituted for corn in feeds and other products. When aflatoxin M1 is detected in milk at elevated levels, there are two practical ways to combat this problem:

1) The contaminated feed should be replaced with aflatoxin-free feed. Importantly, with respect to aflatoxin, generally the EU and FDA currently  do not permit feed or feed material containing aflatoxin to be blended with uncontaminated feed to reduce the aflatoxin content of the resulting mixture to levels acceptable for use as human food or animal feed.

2) Specific feed additives should be added in the existing feed of dairy cows to effectively adsorb aflatoxin B1 during digestion inside the gastrointestinal tract. Effectiveness of such feed additives is related to reducing the total intake of aflatoxins and conversion to aflatoxin M1.

Conclusion

Routine crop monitoring provides large sets of geographically referenced data which is useful in describing influences of weather on contamination across regions, states, and even continents. Knowledge of weather influences facilitates both better monitoring and improved cost-benefit ratios through weather-based adjustment of management strategies. Recent episodes of severe contamination of maize and cottonseed highlights the importance of weather influences and the need to adjust cropping cycles and management practices in order to avoid losses associated with aflatoxins. Although extensive efforts and preventive actions are taken during growing, harvesting and storage periods, the chances of mycotoxin contamination are high. Therefore successful detoxification procedures after harvest are important. The addition of specific feed additives to animal feeds is a very common method to prevent mycotoxicosis.

References are available on request