Prototheca wickerhamii

Prototheca wickerhamii is a species of algae belonging to the genus Prototheca. Unlike most algae, which are photosynthetic, Prototheca wickerhamii is achlorophyllous, meaning it lacks chlorophyll and does not perform photosynthesis. This organism is of medical significance because it is one of the few algal species known to cause a rare infection called protothecosis in humans and animals.

Characteristics

Prototheca wickerhamii is a unicellular organism that reproduces asexually by endosporulation, where new cells form within the parent cell. The cells are round to oval in shape and can form colonies. They are typically found in environments such as soil, sewage, and water bodies, where they can survive and multiply. Due to their lack of chlorophyll, these organisms rely on organic material for nutrition, making them more similar to fungi in their ecological niche.

Pathogenicity

Prototheca wickerhamii can cause protothecosis, an infection that primarily affects the skin, but can also involve the eyes, central nervous system, and disseminate to other body parts in immunocompromised individuals. Cutaneous protothecosis presents with nodules, ulcers, or pustules that can be mistaken for other dermatological conditions. Ocular protothecosis may lead to keratitis, conjunctivitis, or endophthalmitis, posing a risk of significant vision loss.

Diagnosis and Treatment

Diagnosis of protothecosis is challenging and often requires a combination of clinical suspicion, histopathological examination, and culture of the organism. Prototheca wickerhamii appears as spherical to oval yeast-like cells in tissue, which can be visualized using special fungal stains. Treatment options are limited due to the organism's resistance to many common antifungal agents. Amphotericin B, itraconazole, and voriconazole have been used with varying degrees of success.

Epidemiology

Infections caused by Prototheca wickerhamii are rare and have been reported in both immunocompetent and immunocompromised hosts. Cases have been documented worldwide, with no specific geographical distribution. The exact mode of transmission to humans is not well understood, but it is thought to occur through direct contact with contaminated environmental sources.

Prevention

Preventive measures against protothecosis are not well established due to the rarity of the infection and the ubiquitous nature of the organism. However, individuals with compromised immune systems should avoid contact with potential environmental reservoirs such as soil and stagnant water.

See Also

• Algae
• Infectious disease
• Immunocompromised host
• Antifungal resistance