The most common types of fungal infections that infect the brain are Candida albicans, Mucor, Cryptococcus neoformans and Aspergillis fumigatis but depending on the geographical area, other types of fungi can infect the brain. These include Histoplasma capsulatum, Coccidiodies immitis and Blastomyces dermatitidis. Fungi in general do not infect people with healthy immune system, but for those whose immune system is compromised for whatever reason, they can be a constant threat as they are opportunistic in nature.
- Type of fungi: Spores
- Areas infected: Blood vessels
Aspergillus is a particularly nasty fungus, as it can cause systemic infection within patients with weakened immune systems. It is designed to survive at normal human body temperature (37 degrees C, or 98.5 degrees F for you Americans). It can also infect the brain through the ascending blood vessels up the neck, and can lead to septic haemorrhagic infarctions (a condition combining blockages of the blood vessels leading to death of tissue and bleeding out at the same time: this is triggered by the invasion of the Aspergillus fungi into the blood vessels.)
- Type of fungi: Dimorphic: mycelial/yeast
- Areas infected: Lungs, skin, nervous system, bones
At the human body temperature of 37 degrees C, Blastomyces dermatitidis is in yeast form. The condition that the yeast causes is blastomycosis. It originates in soil, and if a human picks it up, the yeast first invades in the lungs and then can spread to the nervous system, where the yeast can cause either epidural or brain abcesses or meningitis. Another neurological symptom associated with blastomyces is headaches.
- Type of fungi: Dimorphic: Yeast/filamentous
- Areas infected: Nail plates
Candida albicans is dimorphic in nature: that is, it can exist in two different states: either in the form of a yeast or in a filamentous form. The yeast form is used when it is outside of the host as it both relatively small and protective, and the filamentous form is used inside of the body. It is part of the normal gut flora, however in those with weakened immune systems, it can be a real nuisance. Candida albicans is also the organism responsible for the condition known as thrush. In the brain, it produces multiple abcesses smaller than the naked eye, and it may also produce granulomas, although that is not always the case.
- Type of fungi: Mould
- Area/s infected: Lungs
Like Aspergillus, Coccidiodes tends to reside in the soil. It gets into humans via inhalation of their particles. When it is present in humans, it tends to cause Valley fever or coccidiomycosis, which presents as a flu-like illness with several symptoms, including fever, muscle and joint pain, rash, headaches and a cough. It usually doesn’t infect the central nervous system, but it can lead to meningitis, which can be fatal.
- Type of fungi: Yeast (encapsulated)
- Areas infected: Lungs, central nervous system
Cryptococcus neoformans tends to originate in pigeon faeces: it gets inhaled and infects the lungs. However, in AIDS patients, the infection can spread into the central nervous system, causing fungal meningitis and encephalitis. Cryptococci themselves do not tend to infect people with healthy immune systems, but only those with weakened immune systems.
- Type of fungi: Dimorphic:
- Areas infected: Lungs
Histoplasma capsulatum tends to be located within bat guano and bird faeces. The disease associated with histoplasma fungi is called histoplasmosis, and in most cases, it is asymptomatic, but in chronic cases it can resemble TB (tuberculosis.)
- Type of fungi: Mould
- Areas infected: brain
Infections by fungi from the Mucor genus are quite rare, but when they do happen, they are severe. It tends to happen most often in diabetics who have ketoacidosis, as Mucor fungi favour a relatively acidic environment. Non-diabetic patients’ internal environments are relatively alkali. When someone becomes infected with Mucor fungi, it is known as mucormycosis, and this presents with thrombosis (formation of a blood clot) and necrosis (cell death).