Aspergillus flavus- An Overview


Aspergillus flavus is a fungus that belongs to the genus Aspergillus, which comprises about 250 species of molds that are widely distributed in nature. Aspergillus flavus is one of the most important species of Aspergillus, as it can cause diseases in plants, animals, and humans, and produce a potent carcinogen called aflatoxin.

Aspergillus flavus is a saprotrophic fungus, which means that it feeds on dead organic matter, especially plant debris. It can be found in soil, air, water, and various substrates such as grains, legumes, nuts, spices, and dried fruits. It can also infect living plants and animals, including humans, as an opportunistic pathogen.

Aspergillus flavus has a complex life cycle that involves both sexual and asexual reproduction. The asexual spores, called conidia, are produced on specialized structures called conidiophores, which form clusters of spore-bearing cells called phialides. The conidia are usually yellow-green in color and have a rough surface. They can be dispersed by air currents or insects and germinate under favorable conditions. The sexual spores, called ascospores, are produced within a hard mass of fungal tissue called sclerotia, which can survive in harsh environments for long periods. The sclerotia can also produce conidia under certain stimuli. The sexual reproduction of Aspergillus flavus was discovered only recently and is still poorly understood.

Aspergillus flavus is a major threat to human health and food security, as it can cause various diseases and contaminate food products with aflatoxin. Aflatoxin is a group of toxic compounds that can cause acute poisoning, liver damage, immune suppression, and cancer in humans and animals. Aflatoxin is mainly produced by two strains of Aspergillus flavus: the L strain, which produces large sclerotia and low levels of aflatoxin; and the S strain, which produces small sclerotia and high levels of aflatoxin. Aflatoxin production is influenced by several factors such as temperature, moisture, substrate composition, and stress.

The diseases caused by Aspergillus flavus in humans are collectively called aspergillosis, which can range from mild allergic reactions to invasive infections that affect various organs such as the lungs, sinuses, brain, eyes, skin, bones, and blood vessels. Aspergillosis is more common and severe in people who have weakened immune systems due to diseases such as HIV/AIDS, cancer, diabetes, or organ transplantation. The diagnosis of aspergillosis is based on clinical signs and symptoms, radiological findings, laboratory tests such as microscopy, culture, serology, and molecular methods; and histopathology. The treatment of aspergillosis depends on the type and severity of the infection and may include antifungal drugs such as amphotericin B, itraconazole, voriconazole, posaconazole, or caspofungin; surgery to remove infected tissue; or immunotherapy to boost the host defense.

The diseases caused by Aspergillus flavus in plants are mainly ear rot in corn and yellow mold in peanuts; but it can also affect other crops such as cotton, rice, wheat, barley, sorghum, soybean, sunflower, pistachio, almond, walnut; and fruits such as figs and dates. The infection of plants by Aspergillus flavus can occur before or after harvest; but it is more common during storage or transit when the moisture and temperature are favorable for fungal growth. The infection of plants by Aspergillus flavus can reduce the yield and quality of the crops; and also increase the risk of aflatoxin contamination of food products derived from them. The prevention and control of plant diseases caused by Aspergillus flavus involve good agricultural practices such as crop rotation; pest management; irrigation; harvesting at optimal maturity; drying; cleaning; sorting; storing at low temperature and humidity; using resistant varieties; applying fungicides or biocontrol agents; or using physical or chemical methods to reduce aflatoxin levels.

Aspergillus flavus is a versatile and adaptable fungus that poses significant challenges to human health and food security. Therefore, it is important to understand its biology; ecology; epidemiology; pathogenicity; diagnosis; treatment; prevention; and control.