From Fungal Threat to Scientific Triumph: The Aflatoxin Challenge

    You might have heard of “aflatoxins, " often related to food poisoning. We must say, this is a real serious issue under the category of food poisoning, beginning with common indigestion symptoms, but may end up with death. So, what are aflatoxins??

    Before the specific topic, let's see a much broader name, “mycotoxin”, the secondary fungal metabolic byproduct. According to the research findings, around 25% of global crop production is affected by mycotoxin contamination and which leads to an annual economic loss of above $900 million. The ingestion of mycotoxins is generally called mycotoxicosis, which is different from the term “mycosis” (fungal infection). Usually, filamentous fungi or microfungi are behind the mycotoxicosis, and are not similar to the macrofungal (mushroom) toxins.

    Among the vast variety, there are three mycotoxigenic fungal genera

1.     Aspergillus

2.     Fusarium

3.     Penicillium

    Mycotoxins are classified based on the fungal genera that produce them, as shown in Table 1.

    Table 1: Different types of mycotoxins and the crops commonly affected

    The fungal toxin production is affected by many factors

·       Physical factors (moisture, humidity, temperature, mechanical damage)

·       Chemical factors (carbon dioxide, oxygen, composition of substrate, pesticide, fungicide, etc).

·       Biological factors (plant variety, stress, insects, spore load).

Figure 1: List of factors leading to multiple mycotoxin contamination

    Due to their structural integrity, most mycotoxin varieties persist through conservative food processing techniques, such as milling, drying, and thermal treatments, complicating their complete removal from contaminated food products. The severity of mycotoxin contamination depends on the level and extent of exposure, as well as factors such as species, race, age, sex, nutrition, and other diseases.

Most of the crops, for example, cereals, are susceptible to microfungal contamination during both pre- and post-harvest times; consequently, the animals that consume those crops will suffer from mycotoxicosis, and the effect will extend to the secondary consumers through the milk, eggs, meat, etc., produced from the affected animals. Fortunately, there is no evidence of such secondary mycotoxin contamination reported.

Figure 2: Chronic effects of mycotoxin contamination in humans

Aflatoxins

Aflatoxins, the most harmful mycotoxins, are chiefly secreted by Aspergillus flavus and Aspergillus parasiticus, which contaminate food crops such as peanuts, tree nuts, maize, chillies and dried fruits. This leads to critical health damages to primary consumers and a significant socioeconomic burden on communities. Kachapulula et al. in 2019 reported a severe aflatoxin contamination induced by Aspergillus flavus in various wild fruits in Zambia, which impacted the nation’s economy. These harmful consequences caused by aflatoxin ingestion are collectively called aflatoxicosis; it was initially identified as the etiological factor for Turkey X disease at the end of the 20^th century. Furthermore, recent medical researches identify aflatoxins as potent carcinogens, leading to hepatocarcinoma.

Over eighteen aflatoxin varieties have been identified to date, among which B1, B2, G1, and G2 are the most prevalent and lethal; their nomenclature is based on the characteristic light absorption and emission properties. Furthermore, the carcinogenic metabolites of aflatoxin B1 and B2 – designated as M1 and M2, respectively – have been detected in milk, meat, and eggs of affected animals, and even in the breast milk of affected humans. Considering their high toxicity and lethality, food safety authorities across various countries have established stringent regulations governing the permissible limits of aflatoxin intake in both humans and animals.

The physical damage from insect and bird bites, along with ideal environmental conditions such as temperature and humidity, influence the level of contamination and colonization of aflatoxigenic fungi on crops at the pre-harvest stage; contrarily, improper handling and inappropriate storage conditions are principal causes for the post-harvest fungal threats. Besides, a subsequent exposure to optimum temperature (25 – 37°C) and humidity (>85%) engenders the production of aflatoxins.

Figure 3: Different stages of fungal contamination and the factors leading to aflatoxin biosynthesis 

Aflatoxicosis impacts on human health

Prolonged aflatoxin exposure has been associated with severe health consequences, including hepatocellular carcinoma, immune suppression, impaired growth in children, and permanent liver damage, particularly in the malnourished population. However, the onset of aflatoxicosis is symptomatized by high fever, vomiting, ascites, liver failure, edema of feet, and jaundice, with a high mortality rate compared to chronic aflatoxicosis. Based on recent studies, a pernicious aflatoxin concentration is estimated as 1000μg/kg in humans and 50-300μg/kg in animals; protracted exposure for more than a week can induce adverse consequences at much lower concentrations (>100μg/kg).

The risk of carcinogenicity of aflatoxins is proportional to the duration of exposure in both humans and animals, affecting the kidney, liver, lungs, or colon, thus identified as a group I carcinogen. Prolonged aflatoxicosis is the leading etiological factor for more than 70% of hepatocarcinoma reported globally. The research data proposes a relationship between the age and health condition of the individual with the extent of adverse effects caused by aflatoxicosis, suggesting a poor prospect for irreversible liver damage in affected children than elders.

Figure 4: Adverse effects of aflatoxicosis

Table 2: Scientific evidence of aflatoxin-induced liver damage

    Mitigation and Control Measures

    As we have already discussed, aflatoxin metabolites can even contaminate the breast milk; fortunately, there is no evidence of any adverse effects on babies who consumed the contaminated breast milk. The scientific world proposes that the immature metabolic pathways in infants possibly protect them from the lethal effects of the toxic contaminant. Moreover, WHO support this proposal with the scientific evidence of lower risk of AFM1-induced cancer reports.

The ruminal microorganism-based mycotoxin detoxification is also reported, which has numerous controlling factors including nutrient profile of the food material, aflatoxin category, species and genera of affected animal, etc. But regardless of the efficiency of the natural protective measures discussed above, a standardized (refer Table 4)
mitigation strategy must be implemented to devoid aflatoxin-related complications in all different populations.

Table 3: Mitigation strategies for aflatoxin contamination at different stages of crop harvest

References

1.     FDA (US. Food & Drug Administration). CPG Sec. 683.100 Action Levels for Aflatoxins in Animal Feeds. 2019. Available online: https://www.fda.gov/regulatory-information/search-fda-guidance-documents/cpg-sec-683100-action-levels-aflatoxinsanimal-feeds  (accessed on 19 December 2021).

2.     Commission Directive 2003/100/EC of 31 October 2003 amending Annex I to Directive 2002/32/EC of the European Parliament and of the Council on undesirable substances in animal feed. OJEU 2003, 285, 33–37. Available online: https://eur-lex.europa.eu/legalcontent/EN/TXT/PDF/?uri=CELEX:32003L0100&from=EN. (accessed on 19 December 2021).

3.     Kaale, L.; Kimanya, M.; Macha, I.; Mlalila, N. Aflatoxin contamination and recommendations to improve its control: A review. World Mycotoxin J. 2021, 14, 27–40.

4.     Benkerroum, N. Aflatoxins: Producing-Molds, Structure, Health Issues and Incidence in Southeast Asian and Sub-Saharan African Countries. Int. J. Environ. Res. Public Health 2020, 17, 1215

5.     Abdin, M.; Ahmad, M.M.; Javed, S. Advances in molecular detection of Aspergillus: An update. Arch. Microbiol. 2010, 192, 409–425

6.     Dhanasekaran, D.; Shanmugapriya, S.; Thajuddin, N.; Panneerselvam, A. Aflatoxins and aflatoxicosis in human and animals. In Aflatoxins: Biochemistry and Molecular Biology; Guevara-González, R.G., Ed.; BoD–Books on Demand: London, UK, 2011; Volume 10, pp. 221–254. [CrossRef]

7.     World Health Organization (WHO). Aflatoxins; WHO: Geneva, Switzerland, 2018. Available online: https://www.who.int/ foodsafety/FSDigest_Aflatoxins_EN.pdf (accessed on 19 December 2021)

8.     Grace, D.; Lindahl, J.F.; Atherstone, C.; Kang’ethe, E.; Nelson, F.; Wesonga, T.; Manyong, V. Aflatoxin Standards for Feed. Building an Aflatoxin Safe East African Community Technical Policy Paper 7; International Institute of Tropical Agriculture: Ibadan, Nigeria, 2015. Available online: https://cgspace.cgiar.org/bitstream/handle/10568/75535/Aflatoxin%20standards%20for%20feed.pdf?sequence=1 (accessed on 19 December 2021).

9.     Santini, A.; Ritieni, A. Aflatoxins: Risk, exposure and remediation. In Aflatoxins: Recent Advances and Future Prospects; IntechOpen: London, UK, 2013; pp. 343–376.

10.  Alameri, M.M.; Kong, A.S.-Y.; Aljaafari, M.N.; Ali, H.A.; Eid, K.; Sallagi, M.A.; Cheng,W.-H.; Abushelaibi, A.; Lim, S.-H.E.; Loh, J.-Y.; et al. Aflatoxin Contamination: An Overview on Health Issues, Detection and Management Strategies. Toxins 2023, 15, 246. https://doi.org/10.3390/toxins15040246.

11.  Ezekiel, C.N.; Ayeni, K.I.; Akinyemi, M.O.; Sulyok, M.; Oyedele, O.A.; Babalola, D.A.; Ogara, I.M.; Krska, R. Dietary Risk Assessment and Consumer Awareness of Mycotoxins among Household Consumers of Cereals, Nuts and Legumes in North- Central Nigeria. Toxins 2021, 13, 635.

12.  Arak, H.; Karimi Torshizi, M.A. Comparative consequences of two sources of aflatoxins in ducklings experimental aflatoxicosis.Vet. Res. Forum 2021, 12, 305–311.

13.  De Freitas Souza, C.; Baldissera, M.D.; Descovi, S.; Zeppenfeld, C.; Eslava-Mocha, P.R.; Gloria, E.M.; Zanette, R.A.; Baldisserotto, B.; da Silva, A.S. Melaleuca alternifolia essential oil abrogates hepatic oxidative damage in silver catfish (Rhamdia quelen) fed with an aflatoxin-contaminated diet. Comp. Biochem. Physiol. Part C: Toxicol. Pharmacol. 2019, 221, 10–20.

14.  Rotimi, O.; Onuzulu, C.; Dewald, A.; Ehlinger, J.; Adelani, I.; Olasehinde, O.; Rotimi, S.; Goodrich, J. Early Life Exposure to Aflatoxin B1 in Rats: Alterations in Lipids, Hormones, and DNA Methylation among the Offspring. Int. J. Environ. Res. Public Health 2021, 18, 589.

15.  Morales-Moo, T.; Hernández-Camarillo, E.; Carvajal-Moreno, M.; Vargas-Ortiz, M.; Robles-Olvera, V.; Salgado-Cervantes, M.A. Human Health Risk Associated with the Consumption of Aflatoxins in Popcorn. Risk Manag. Health Policy 2020, 13, 2583–2591.

16.  Hatipoglu, D.; Keskin, E. The effect of curcumin on some cytokines, antioxidants and liver function tests in rats induced by Aflatoxin B1. Heliyon 2022, 8, e09890.

17.  Njombwa, C.A.; Moreira, V.; Williams, C.; Aryana, K.; Matumba, L. Aflatoxin M1 in raw cow milk and associated hepatocellular carcinoma risk among dairy farming households in Malawi. Mycotoxin Res. 2021, 37, 89–96.

18.  Shabeer, S.; Asad, S.; Jamal, A.; Ali, A. Aflatoxin Contamination, Its Impact and Management Strategies: An Updated Review. Toxins 2022, 14, 307. https://doi.org/10.3390/toxins14050307.

19.  Suwarno WB, Hannok P, Palacios-Rojas N, Windham G, Crossa J and Pixley KV (2019). Provitamin A Carotenoids in Grain Reduce Aflatoxin Contamination of Maize While Combating Vitamin A Deficiency. Front. Plant Sci. 10:30. https://doi.org/10.3389/fpls.2019.00030.

20.  Kumar, A., Pathak, H., Bhadauria, S., Sudan, J., 2021. Aflatoxin contamination in food crops: causes, detection, and management: a review. Food Production, Processing and Nutrition. 3(17). 21). https://doi.org/10.1186/s43014-021-00064-y.

21.  Upadhaya, S.D.; Sung, H.G.; Lee, C.H.; Lee, S.Y.; Kim, S.W.; Jo, K.J.; Ha, J.K. Comparative study on the aflatoxin B1 degradation ability of rumen fluid from Holstein steers and Korean native goats. J. Vet. Sci. 2009, 10, 29–34.

22.  Peles, F.; Sipos, P.; Kovács, S.; Gy˝ori, Z.; Pócsi, I.; Pusztahelyi, T. Biological Control and Mitigation of Aflatoxin Contamination in Commodities. Toxins 2021, 13, 104. https://doi.org/10.3390/toxins13020104.

23.  Alshannaq, A.F., Gibbons, J.G., Lee, M-K., Han, K-H., Hong, S-B., Yu, J-H., 2018. Controlling afatoxin contamination and propagation of Aspergillus favus by a soy-fermenting Aspergillus oryzae strain. Nature: Scientific Reports, 8:16871. https://doi.org/10.1038/s41598-018-35246-1.

24.  Kachapulula, P.W., Bandyopadhyay, R., Cotty, P.J., 2019. Aflatoxin contamination of Non-cultivated fruits in Zambia. Front. Microbiol. 10:1840. https://doi.org/10.3389/fmicb.2019.01840. 

25.  Jouany, J.-P.; Yiannikouris, A.; Bertin, G. Risk assessment of mycotoxins in ruminants and ruminant products. Opt. Mediterr. A 2009, 85, 205–224

26.  Kifle, M.H.; Yobo, K.S.; Laing, M.D. Biocontrol of Aspergillus flavus in groundnut using Trichoderma harzianum strain kd. J. Plant Dis. Prot. 2017, 124, 51–56

27.  Asurmendi, P.; Pascual, L.; Dalcero, A.; Barberis, L. Incidence of lactic acid bacteria and Aspergillus flavus in brewer’s grains and evaluation of potential antifungal activity of these bacteria. J. Stored Prod. Res. 2014, 56, 33–37

28.  Hua, S.S.T.; Beck, J.J.; Sarreal, S.B.L.; Gee, W. A major volatile compound 2-phenylethanol from the biocontrol yeast, Pichia anomala, inhibits growth and expression of aflatoxin biosynthesis genes of Aspergillus flavus. Mycotoxin Res. 2014, 30, 71–78

29.  Yılmaz, S., Kaya, E., Comakli, S., 2017. Vitamin E (α-tocopherol) attenuates toxicity and oxidative stress induced by aflatoxin in rats. Adv Clin Exp Med. 26(6), 907-917. https://doi.org/10.17219/acem/66347.

30.  Zhao, L., Feng, Y., Xu, Z-J., Zhang, N-Y., Zhang, W-P., Zuo, G., Khalil, M.M., Sun, L.H., 2021. Selenium mitigated aflatoxin B1-induced cardiotoxicity with potential regulation of 4 selenoproteins and ferroptosis signaling in chicks. Food and Chemical Toxicology, 154, 112320. https://doi.org/10.1016/j.fct.2021.112320.

31.  Alpsoy, L, Yalvac, M.E., 2011. Key roles of vitamins A, C, and E in aflatoxin B1-induced oxidative stress. Vitam Horm., 86, 287-305. https://doi.org/10.1016/B978-0-12-386960-9.00012-5.

32. Ahmadian, F., Nosrati, A.C., Shahriari, A., Faezi-Ghasemi, M., Shokri, S., 2020. Effects of zinc chelating nutrients on Aflatoxin production in Aspergillus flavus. Food and Chemical Toxicology, 137, 111180. https://doi.org/10.1016/j.fct.2020.111180.