eMedicine Specialties > Dermatology > Parasitic Infections

Protothecosis, Cutaneous

Author: Sarah K Taylor, MD, Staff Physician, Department of Dermatology, Walter Reed Army Medical Center and National Naval Medical Center
Coauthor(s): Jon H Meyerle, MD, Assistant Professor, Department of Dermatology, Johns Hopkins University School of Medicine; Consulting Staff, Laboratory Director, Department of Dermatology, Walter Reed Army Medical Center and National Naval Medical Center; Earl J Glusac, MD, Professor, Departments of Pathology and Dermatology, Yale University School of Medicine
Contributor Information and Disclosures

Updated: Dec 11, 2008

Introduction

Background

The skin is most commonly involved, resulting from primary inoculation through a wound or abrasion. The infection is usually localized to the site of inoculation; however, in immunocompromised individuals, it can become widespread.

Pathophysiology

Prototheca is an achlorophyllic mutant of the green alga Chlorella. The organism is ubiquitous in the environment, particularly in aqueous locales. Infection usually occurs as a result of inoculation into or beneath the skin with subsequent exposure to contaminated water. Person-to-person transmission does not occur. However, Prototheca has been cultured from under the fingernails and other cutaneous sites in healthy individuals.

While healthy individuals can become infected, the organism has low virulence. Protothecosis infections are more commonly described in patients who are immunosuppressed. Use of immunosuppressive drugs also increases the risk of protothecosis infections.¹ Of all possible immunosuppressants, glucocorticoids, whether topically applied, taken orally, or locally injected, are the most specifically associated with the onset of protothecosis.² 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. A neutrophilic response appears to be critical in eradicating the infection; however, reports in the literature dispute this.

Frequency

United States

Protothecosis is a rare infection, with approximately 117 cases reported since the initial report in 1964. Most cases in the United States are from the Southeast, though cases from virtually all geographic regions have been reported.

International

Protothecosis is a rare infection, but it is seen worldwide, with cases reported on every continent except Antarctica.²

Mortality/Morbidity

Patients who are severely immunocompromised can develop disseminated disease, which is often fatal.

• 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 and has been reported following injection of a sclerosing agent for varicose vein treatment.³
• 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.

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.

Clinical

History

The classic history is that of trauma (eg, abrasion, cut) to the skin and subsequent exposure to contaminated water. In severely immunocompromised individuals, cutaneous lesions can be widespread and the algae can be present in the blood.

• Patients typically present with an isolated plaque or nodule, with or without ulceration and/or pustules. However, large eczematous plaques or ulcers have also been reported. Erythema and pain may occur.
• Patients with protothecosis bursitis present with painful swelling of the elbow; mild erythema; and, occasionally, drainage.

Physical

The skin is the most common site of infection, followed by the periarticular bursae (typically causing olecranon bursitis).

• Patients typically have an ill-defined plaque or nodule that may have a verrucous surface. Large eczematous plaques; pustular lesions; and atrophic, herpetiform, hypopigmented, and cutaneous ulceration have also been reported.
• Bullous lesions may occur with subsequent rupture, drainage, and crusting.
• Lesions with the appearance of apple jelly have been reported.
• The extremities are the most common sites of involvement.
• In patients who are immunocompetent, the lesions may be more subtle, with papules or plaques with mild erythema that have been stable for long periods.
• Patients with olecranon bursitis have swelling; mild erythema; and, occasionally, drainage in the vicinity of the elbow.
• In cases of meningeal involvement, patients may have meningeal signs of headache, nuchal rigidity, and photophobia.

Causes

Infection is usually caused by Prototheca wickerhamii. Less commonly, infection occurs with Prototheca 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 transplantation⁴ ; autoimmune disease; graft versus host disease; as a result of chemotherapy or radiation therapy,⁵ AIDS,^6,7 diabetes mellitus, chronic renal failure, or Cushing disease).

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