Microbiology
Summary
Aspergillus spp. are catalase-positive, opportunistic fungi that have several distinguishing features and potential health impacts. Aspergillus flavus, specifically, produces harmful aflatoxins, which can contaminate nuts, legumes, wheat, and other crops. These aflatoxins have been linked to hepatocellular carcinoma. Morphologically, Aspergillus has septate hyphae that branch at acute 45-degree angles. The fungus is primarily transmitted through the inhalation of spores present in its fruiting bodies. Once in the body, it can lead to various clinical manifestations. Allergic bronchopulmonary aspergillosis, a type I hypersensitivity reaction, is seen in patients with conditions like cystic fibrosis and asthma and is characterized by increased serum IgE, migratory pulmonary infiltrates, and wheezing.
Aspergillus can colonize the lungs, forming "fungus balls" in old pulmonary cavities, leading to symptoms such as fever, hemoptysis, and cough. These aspergillomas are often observed in cavities left behind from conditions like tuberculosis, sarcoidosis, and emphysema. Notably, these fungus balls can be seen on chest X-rays as radiopaque structures that shift when a patient changes position. In patients who are immunocompromised or neutropenic, Aspergillus can cause invasive pulmonary aspergillosis. If not contained, the fungus can invade blood vessels and spread to other organs, leading to complications like kidney infarction, endocarditis, CNS lesions, and necrosis in the paranasal sinuses. Treating aspergillosis typically involves antifungal agents such as voriconazole and amphotericin B.
Lesson Outline
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FAQs
Aspergillus fumigatus and Aspergillus flavus are both types of filamentous, catalase-positive fungi. They are part of the Aspergillus genus, which includes around 180 species. However, they have different implications for human health. A. fumigatus is the most common species that causes infection in individuals with weakened immune systems, resulting in conditions such as aspergillomas and angioinvasive aspergillosis. On the other hand, Aspergillus flavus produces aflatoxins, which are potent carcinogens and can lead to hepatocellular carcinoma.
Allergic bronchopulmonary aspergillosis (ABPA) is an allergic reaction that occurs in response to the inhalation of spores from Aspergillus fumigatus. It typically affects individuals with asthma or cystic fibrosis. The inhaled spores induce an immune response that can lead to inflammation and scarring of the lungs.
Both aspergillomas and angioinvasive aspergillosis are diseases caused by Aspergillus fumigatus. An aspergilloma, also known as fungus ball, is a cluster of fungus fibers, blood clots, and white blood cells that manifest in lung cavities formed by pre-existing diseases, like tuberculosis. Angioinvasive aspergillosis is a severe and often fatal form of invasive aspergillosis where the fungus invades the blood vessels, obstructing blood supply and leading to tissue death.
Amphotericin B and voriconazole are common antifungal medications used to treat infections caused by Aspergillus fumigatus. Amphotericin B has been used for a long time but often has serious side effects. Voriconazole, however, is now often the drug of first choice for invasive Aspergillus infections due to its better efficacy and fewer side effects.
Aspergillus flavus produces aflatoxins, which are potent carcinogens. When ingested, often via contaminated food, these toxins can cause DNA mutation in liver cells, potentially leading to hepatocellular carcinoma. Chronic exposure to high levels of aflatoxins is recognized as a major risk factor in the development of this specific type of liver cancer.
