Prototheca

Prototheca wickerhamii

Prototheca is a genus of algae that is unique because it includes species that are not photosynthetic and are known to cause a rare infection called protothecosis. This condition affects humans, dogs, cats, and cattle, manifesting in a variety of clinical presentations ranging from cutaneous lesions to systemic infections. The organisms belonging to this genus are closely related to green algae of the family Chlorellaceae, but unlike their photosynthetic relatives, Prototheca species have lost their chlorophyll and thus their ability to perform photosynthesis.

Classification

Prototheca is classified within the kingdom Algae, despite its non-photosynthetic nature. It is part of the family Chlorellaceae, which includes mostly photosynthetic green algae. The loss of photosynthesis in Prototheca is an example of reductive evolution, where an organism loses complex traits over time. The most commonly encountered species in human and animal infections are Prototheca wickerhamii and Prototheca zopfii.

Pathogenesis

Prototheca species cause disease by invading the skin, soft tissues, or, less commonly, the bloodstream. The mechanism of pathogenicity is not fully understood but is thought to involve the production of enzymes that break down host tissues, allowing the organism to invade and cause infection. Immunocompromised individuals, such as those with HIV/AIDS, cancer, or those on immunosuppressive therapy, are at higher risk of developing protothecosis.

Clinical Manifestations

Protothecosis can present in several forms, depending on the route of infection and the immune status of the host. Cutaneous protothecosis, the most common form, presents as skin lesions that may be ulcerative or nodular. Systemic infection can occur, leading to more severe conditions such as meningitis, endocarditis, or disseminated disease affecting multiple organs. Ocular protothecosis, affecting the eye, can lead to keratitis or endophthalmitis.

Diagnosis

Diagnosis of protothecosis involves the isolation of Prototheca species from clinical specimens such as skin lesions, blood, or cerebrospinal fluid. Microscopic examination of these specimens can reveal the presence of spherical to oval yeast-like organisms. Culture of the organism on specific media can help in identifying the species, which is crucial for determining the appropriate treatment.

Treatment

Treatment of protothecosis is challenging due to the limited susceptibility of Prototheca to antifungal agents. Amphotericin B, itraconazole, and voriconazole have been used with varying degrees of success. Surgical removal of localized lesions may be necessary in some cases. The overall prognosis depends on the site and severity of the infection and the immune status of the host.

Prevention

Preventive measures against protothecosis are not well established due to the rarity of the infection. However, general recommendations include avoiding contact with contaminated water sources and maintaining good hygiene practices, especially in immunocompromised individuals.