Metastatic protothecal retinitis in a dog. Electron microscopic observations

Species- and strain-specific differences in the phagocytosis of Prototheca: insights from live-cell imaging

The genus Prototheca is an extremely unusual group of achlorophyllic, obligately heterotrophic algae. Six species have been identified as pathogens of vertebrates, including cattle and humans. In cattle, P. bovis is the main infectious pathogen and is associated with bovine mastitis. In contrast, human infections typically involve P. wickerhamii and are associated with a spectrum of varying clinical presentations. Prototheca spp. enter the host from the environment and are therefore likely to be initially recognized by cells of the innate immune system. However, little is known about the nature of the interaction between Prototheca spp. and host phagocytes. In the present study, we adopt a live-cell imaging approach to investigate these interactions over time. Using environmental and clinical strains, we show that P. bovis cells are readily internalized and processed by macrophages, whereas these immune cells struggle to internalize P. wickerhamii. Serum opsonization of P. wickerhamii only marginally improves phagocytosis, suggesting that this species (but not P. bovis) may have evolved mechanisms to evade phagocytosis. Furthermore, we show that inhibition of the kinases Syk or PI3K, which are both critical for innate immune signaling, drastically reduces the uptake of P. bovis. Finally, we show that genetic ablation of MyD88, a signaling adaptor critical for Toll-like receptor signaling, has little impact on uptake but significantly prolongs phagosome maturation once P. bovis is internalized. Together, our data suggest that these two pathogenic Prototheca spp. have very different host-pathogen interactions which have potential therapeutic implications for the treatment of human and animal disease.

An Intractable Case of Prototheca Keratitis and Chronic Endophthalmitis in Stevens-Johnson Syndrome With Boston Type 1 Keratoprosthesis

PURPOSE

To report a case of recalcitrant Prototheca spp. keratitis and endophthalmitis in a patient with Stevens-Johnson syndrome (SJS) and Boston type 1 keratoprosthesis (B1 KPro).

METHODS

Case report.

RESULTS

A 67-year-old female with a history of SJS with chronic severe ocular surface disease in her monocular left eye underwent placement of a B1 KPro. Her course was subsequently complicated by persistent Prototheca spp. keratitis and endophthalmitis requiring ongoing treatment with triazole and polyene antifungal agents and multiple surgical revisions of her keratoprosthesis.

CONCLUSIONS

Protothecosis is an algal infection that is rarely pathologic in humans, but when present can be difficult to manage. We present the second known case of persistent chronic Prototheca spp. keratitis and endophthalmitis in a patient with long-standing SJS and B1 KPro.

Prototheca wickerhamii infection of a corneal graft

Algae are generally noninfectious agents in mammals, with few known pathogenic algae. Prototheca is an achlorophylic nonphotosynthetic algae, globally ubiquitous, and readily isolated from rivers, lakes, ponds, and soil. Although canine and bovine protothecosis have been reported more widely, infections in humans are rare, particularly in patients with an intact immune system. The majority of protothecal infections in humans is associated with Prototheca wickerhamii. We report an unusual case of P. wickerhamii infection in an immunocompetent corneal transplant patient.

Protothecosis in 17 Australian dogs and a review of the canine literature

Systemic protothecosis was diagnosed in 17 Australian dogs between 1988 and 2005. There was a preponderance of young-adult (median 4 years), medium- to large-breed dogs. Females (12/17 cases) and Boxer dogs (7 cases, including 6 purebreds and one Boxer cross) were over-represented. Sixteen of 17 dogs died, with a median survival of four months. A disproportionate number of cases were from coastal Queensland. In most patients, first signs were referable to colitis (11/17 cases), which varied in severity, and was often present for many months before other symptoms developed. Subsequent to dissemination, signs were mostly ocular (12 cases) and/or neurologic (8 cases). Two dogs had signs due to bony lesions. Once dissemination was evident, death or euthanasia transpired quickly. Prototheca organisms had a tropism for the eye, central nervous system (CNS), bone, kidneys and myocardium, tissues with a good blood supply. Microscopic examination and culture of urine (5 cases), cerebrospinal fluid (CSF;1 case), rectal scrapings (4 cases), aspirates or biopsies of eyes (5 cases) and histology of colonic biopsies (6 cases) as well as skin and lymph nodes (2 cases) helped secure a diagnosis. Of the cases where culture was successful, P wickerhamii was isolated from two patients, while P zopfii was isolated from five. P zopfii infections had a more aggressive course. Treatment was not attempted in most cases. Combination therapy with amphotericin B and itraconazole proved effective in two cases, although in one of these treatment should have been for a longer duration. One surviving dog is currently still receiving itraconazole. Protothecosis should be considered in all dogs with refractory colitis, especially in female Boxers.

Cutaneous protothecosis: report of five cases

Prototheca, a genus of achlorophyllic algae, is a rare cause of opportunistic infection in humans. About 80 human cases, mostly cutaneous infection caused by P. wickerhamii, have been reported world-wide. We describe the clinicopathological findings and treatments of five cases diagnosed in our department during the period 1991-97. The patients, including four elderly farmers, presented with pyoderma-like lesions or infiltrating papules and plaques on the extensor side of the extremities or face. All patients were immunocompromised, mostly due to systemic or topical steroids. The diagnosis was made in each case by finding typical endospores with morula-like structures in skin biopsy specimens. P. wickerhamii was isolated in four cases in which pretreatment culture of skin tissue was done. Except for one patient who died of asthma, the infection was cured after 2-7 weeks of amphotericin B, ketoconazole, itraconazole or fluconazole. Our cases illustrate that cutaneous protothecosis commonly manifested non-tender, pyoderma-like or infiltrating lesions and should be considered in the differential diagnosis of deep fungal or mycobacterial infection. This rare infection seemed more frequent in our region, possibly due in part to common steroid abuse among old people in Taiwan and there was a large population of elderly farmers in our area.

Clinical, cytologic and histopathologic manifestations of protothecosis in two dogs

Two cases of sudden onset of blindness associated with ocular protothecosis in dogs are reported. Both were adult, spayed female, mixed-breed dogs that lacked the usual clinical signs of systemic infection with Prototheca species. Physical abnormalities at the time of presentation were limited to the affected eyes which had serous discharge, hyperemic conjunctiva, and aqueous flare. The pupillary light reflexes were slow, and the menace reflexes were absent. Both dogs had glaucoma. Results of complete blood counts and serologic titres for antibodies to Blastomyces dermatitidis and Histoplasma capsulatum were within reference intervals. Protothecosis was diagnosed by cytologic analysis of vitreous humor and was confirmed at necropsy. These two cases were unusual because of their presenting signs and prolonged course of disease progression.

Canine protothecosis

Canine protothecosis remains a difficult condition to manage. The paucity of clinical cases hinders the development of successful treatment strategies. The clinical signs associated with the disease are nonspecific, and the course is so insidious that, by the time a definitive diagnosis is reached, the organism has often disseminated throughout the body. At this point, the condition is beyond treatment, and death occurs owing to failure of any number of organ systems, including the gastrointestinal, cardiovascular, renal, and central nervous systems. It is of some encouragement that the few patients that have undergone aggressive early treatment have survived longer than patients presenting late in the disease course. Nevertheless, the outlook for any dog with protothecosis is grave, and it remains to be determined whether early diagnosis can truly provide a better long-term prognosis. By including protothecosis as a consideration for dogs initially brought in with a history of chronic diarrhea or acute blindness and with a subsequent finding of exudative retinal separation, early diagnosis is possible. This recognition potentially affords the opportunity for an immune status work-up and intervention with increasingly better treatment options.