Practice Essentials
Protothecosis is an uncommon infection with an achlorophyllic algae of the genus Prototheca that may present as a localized infection of the skin, olecranon bursitis, or disseminated infection.
Background
Localized infection of the skin is most common and typically results from primary inoculation through a wound or abrasion. In immunocompromised individuals, infection with Prototheca can become widespread. Currently, six species are included in the genus Prototheca: Prototheca wickerhamii, Prototheca zopfii, Prototheca blaschkeae, Prototheca cutis, Prototheca ulema, and Prototheca stagnora. The first four species are known to cause infections in humans, most commonly P wickerhamii. Prototheca infections have also been reported in cattle, cats, and dogs, with boxer dogs being the most represented canine breed noted to have cutaneous Prototheca infection. [1]
Pathophysiology
Prototheca is an achlorophyllic variant of the green alga Chlorella. The organism is ubiquitous but especially prevalent in aqueous environments. Infection usually results from inoculation into the dermis or subcutis by a penetrating injury associated with contaminated or swampy water. Traumatic inoculation with no water exposure has also been reported. [2] Infection has also been described as a complication following surgery. [3, 4] Person-to-person transmission has not been reported, but Prototheca has been cultured from underneath fingernails as well as from other cutaneous sites in healthy individuals.
When healthy individuals become infected, the organism has low virulence and may remit on its own without treatment. Reported cases of protothecosis are more commonly described in patients who are immunosuppressed, have a hematologic malignancy, or a history of organ transplantation. The more widespread use of immunosuppressive drugs also increases the risk of protothecosis infections. [5] Of all possible immunosuppressants, glucocorticoids, whether topically applied, taken orally, or locally injected, are the most specifically associated with the onset of protothecosis. [6] In healthy individuals, the infection is localized and curable, but cases of disseminated disease in individuals who are severely immunocompromised can be fatal. Cases of disseminated disease have involved the blood, the peritoneum, the GI tract, the liver, and the meninges.
Etiology
Infection is usually caused by P wickerhamii. Less commonly, infection occurs with P zopfii. Prototheca is ubiquitous in the environment. It has been cultured from a wide variety of aqueous sources, including lakes, streams, ponds, and even tap water. Prototheca species have also been cultured from animal feces, soil, and a variety of other sources.
This organism is widely encountered in the environment, but it does not produce infection in most individuals. Most reported cases have occurred in patients who are severely immunosuppressed (eg, long-term immunosuppression for organ transplantation, [7, 8] autoimmune disease, graft versus host disease, chemotherapy or radiation therapy, [9] AIDS/HIV infection, [10, 11, 12] diabetes mellitus, [13] chronic renal failure, or Cushing disease). Another association reported included hypogammaglobulinemia (most likely resulting from common variable immunodeficiency. [14]
Epidemiology
Frequency
United States
Protothecosis is a rare infection, with the majority of reports involving the skin and nails. [15] Most cases in the United States are from the Southeast, although cases from virtually all geographic regions have been reported.
International
Protothecosis is seen worldwide, with cases reported on every continent except Antarctica. [6]
Race
No racial predilection is noted.
Sex
No sexual predilection is evident.
Age
Protothecosis typically affects those older than 30 years or elderly persons, although pediatric cases have been reported.
Prognosis
Patients with localized disease have an excellent prognosis and can expect cure. The prognosis of patients with severe disease and immunosuppression is poor.
Localized infection
In immunocompetent individuals, the infection usually remains confined to the skin at the site of inoculation. Olecranon bursitis can develop from protothecosis. Rarely, tenosynovitis can occur secondary to protothecosis and has been reported following injection of a sclerosing agent for varicose vein treatment. [16] Infection of a corneal graft has been reported. [17] Biological agents are being used with increased frequency, and it is important to note that cutaneous protothecosis has been noted in the setting of ustekinumab therapy for psoriasis. [18]
Systemic infection
Rare cases of systemic infection occur almost exclusively in patients who are severely immunocompromised, as in patients receiving chemotherapy, or immunosuppressed patients, such as those on infliximab. Involvement of the meninges has been reported in a few cases of patients with AIDS.
Patient Education
Immunocompromised patients as well as healthy individuals should avoid bathing or swimming in swampy or stagnant bodies of water. Individuals diagnosed with prothecosis should undergo evaluation for underlying immunosuppression if an obvious predisposing factor is not already known.
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This subtle lesion of cutaneous protothecosis on the shoulder shows an ill-defined, slightly erythematous, thin plaque.
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Periodic acid-Schiff–stained sections of protothecosis reveal rounded endospores that form characteristic moruloid structures in the dermis.
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Electron photomicrograph of Prototheca wickerhamii shows a central rounded endospore surrounded by a corona of molded endospores.
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Biopsy reveals morula structures surrounded by lymphocytes and histiocytes (hematoxylin and eosin–stained sections; 200x).
