# Fungal Pathogen Fungal pathogens are fungi that cause diseases in humans or other organisms... Collectively, infectious fungi and fungus-like pathogens are the most devastating disease agents known on the planet. Few among the millions of fungal species fulfill four basic conditions necessary to infect humans: high temperature tolerance, ability to invade the human host, lysis and absorption of human tissue, and resistance to the human immune system. In previously healthy individuals, invasive fungal disease is rare because animals’ sophisticated immune systems evolved in constant response to fungal challenges. In contrast, fungal diseases occur frequently in immunocompromised patients. Paradoxically, successes of modern medicine have put increasing numbers of patients at risk for invasive fungal infections. Among the estimated 1.5–5.0 million fungal species on planet Earth (O’Brien et al. 2005), only several hundred cause disease in humans, and very few are able to affect healthy people. The remarkable resistance of mammals to fungal pathogens has been hypothesized to be responsible for emergence of mammals as the dominant land species, when proliferation of fungi at the end of the Cretaceous era created a “fungal filter” that selected for this animal group (Casadevall 2005, 2012). [The Spectrum of Fungi That Infects Humans](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4292074/) * Estimated 1.5–5.0 million fungal species on planet Earth * Only several hundred cause disease in humans * Very few are able to affect healthy people Only 150,000 fungal species have been described to date D.L. Hawksworth in 1991 in which he estimated that there were roughly 1.5 million species. In the last ten years, new DNA sequencing technologies have revolutionized studies of fungal taxonomy and diversity, leading to changes in the estimates of fungal species numbers ranging from 2.2 to 3.8 based on host association and 11.7 to 13.2 million species using high-throughput sequencing. Few among the millions of fungal species fulfill four basic conditions necessary to infect humans: * high temperature tolerance (37°C and above) * ability to invade the human host (i.e., reach, penetrate, or access tissues it will parasitize) * lysis and absorption of human tissue (i.e., digest and absorb tissue) * resistance to the human immune system Unlike plants, insects, and ectothermic vertebrates, mammals are highly resistant to invasive fungal diseases. Fungal infections today are among the most difficult diseases to manage in humans immunocompromised—more susceptible to infections with fungi ectothermic vertebrates (animals whose body temperature fluctuates with their surroundings) aka cold-blooded animal Currently, only four classes of systemic antifungal medicines (azoles, echinocandins, pyrimidines and polyenes) are used in clinical practice, and only a few others are under development (17, 18, 19, 20). Although existing antifungal medicines are effective, they are associated with a plethora of adverse effects. The use of these medicines also requires expertise, and drug–drug interactions are particularly common (21). ### Candida Auris Candida auris, a drug-resistant fungus first identified in 2009 resistant to disinfectants and antifungal drugs 3.8 million people die each year of infections caused by C. auris and other fungi ### Coccidioidomycosis Coccidioidomycosis or cocci, Valley fever, as well as California fever, desert rheumatism, or San Joaquin Valley fever, is a mammalian fungal disease caused by Coccidioides immitis or Coccidioides posadasii. ### Cat Fungus "It is a mold in the cold and a yeast in the beast." sporothrix brasiliensis The cat-infecting fungus is a relative of Sporothrix schenckii fungi that cause skin infections , called sporotrichosis or rose growers’ disease. Like many other soil-dwelling fungi, Sporothrix fungi are dimorphic, meaning they have two forms. “It is a mold in the cold and a yeast in the beast,” S. brasiliensis can spread in its yeast form, Lockhart said. “That doesn’t happen with any of the other dimorphic fungi.” https://www.sciencenews.org/article/deadly-fungus-cats-people-spreading