Rhinocladiella mackenziei

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Rhinocladiella mackenziei is a dark, pigmented mold that can cause a serious brain infection called cerebral phaeohyphomycosis. It was first described in 1993 as Ramichloridium mackenziei after eight patients developed brain abscesses. In 2007, genetic studies moved it to the genus Rhinocladiella.

Geography and people affected
- This fungus was long thought to be mainly found in the Middle East, with cases reported in Saudi Arabia, Kuwait, and Qatar. Infections have also been seen in Afghanistan, Iran, and India, and more cases are now being reported in other regions.
- Unlike many fungi that mainly affect people with weak immune systems, most infections with R. mackenziei have occurred in people with normal immune function.

How it likely causes brain disease
- People usually become infected through inhaling spores or, less commonly, through skin injuries. The fungus can travel through the bloodstream to the brain and form abscesses.
- Melanin, a pigment in the fungus, may help it evade the immune system and cross into the brain, contributing to its ability to cause disease and making treatment harder.

Environmental niche and diagnosis
- The exact environmental habitat of R. mackenziei is not well understood, which makes it hard to isolate from the environment. Special techniques, such as using high temperatures or certain chemical enrichments, are sometimes needed to recover the fungus in the lab.
- It prefers hot, dry climates, and growth in the lab is slow. In culture at 30°C, it forms dark colonies that are tough and cottony; it grows poorly at 25°C and does not have a known sexual state.
- Diagnosis is based on finding pigmented fungal elements in affected tissue and confirming the organism by culture or genetic sequencing.

Clinical features and treatment
- Cerebral phaeohyphomycosis caused by this fungus leads to symptoms such as headaches, fevers, neurological problems, seizures, weakness on one side of the body, and sometimes changes in behavior.
- If not treated, this infection has a very high mortality rate. The fungus is often resistant to Amphotericin B, a common antifungal drug.
- Some strains are susceptible to triazole antifungals such as itraconazole, posaconazole, and isavuconazole, but responses can be variable. A combination of antifungal drugs, sometimes together with surgical removal of infected brain tissue and immune system support, is commonly used.
- Overall outcomes remain poor, and treatment plans are usually complex and individualized.

Summary
Rhinocladiella mackenziei is a rare but deadly brain-infecting fungus, historically linked to the Middle East but now found in other regions as well. It often affects people with normal immune systems and presents major diagnostic and treatment challenges. Early recognition, accurate lab identification, and aggressive combined therapy are crucial, but the prognosis is frequently guarded.