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Why can fungal infections be especially dangerous for people with weakened immune defenses?

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Diagram showing the West Nile virus transmission cycle: a mosquito bites an infected bird (the primary reservoir host), then transmits the virus to humans or horses (incidental hosts) through subsequent bites. — infectious disease Birds are the primary reservoirs of West Nile virus. The virus is transmitted to humans and horses by mosquitoes that have bitten infected birds.

Fungal infections, or mycoses, can be particularly dangerous for individuals with compromised immune systems because their bodies lack the necessary defenses to control fungal growth. While many fungi exist in balance with the human body, factors such as malnutrition, cancer, or the use of immunosuppressive drugs can weaken the immune system, allowing these organisms to proliferate unchecked.12

In healthy hosts, the body typically maintains an ecological balance that prevents opportunistic pathogens from causing harm. However, in immunosuppressed individuals—such as those with AIDS or transplant patients—fungi can transition from localized, manageable issues to devastating, systemic diseases. These infections can invade the bloodstream and damage vital organs, including the heart, brain, eyes, and kidneys, often leading to life-threatening complications. Because these patients cannot mount an effective response, fungal pathogens that are otherwise harmless can become primary causes of mortality.213