Cutaneous Disease as Sole Clinical Manifestation of Protothecosis in a Boxer Dog

Cutaneous protothecosis in a dog successfully treated with oral itraconazole in pulse dosing

BACKGROUND

Protothecosis is a rare infectious disease caused by unicellular, achlorophyllous, microalgae of the genus Prototheca, ubiquitously distributed in nature. The algae are emerging pathogens, whose incidence is increasing in both human and animal populations and serious systemic infections related to this pathogen have been increasingly described in humans in recent years. After mastitis in dairy cows, canine protothecosis is the second most prevalent form of the protothecal disease in animals. Here, we report the first case of chronic cutaneous protothecosis due to P. wickerhamii in a dog in Brazil, successfully treated with a long-term therapy with itraconazole in pulse.

CASE PRESENTATION

Upon clinical examination, exudative nasolabial plaque, ulcered, and painful lesions in central and digital pads and lymphadenitis were observed in a 2-year-old mixed-breed dog, with a 4-month history of cutaneous lesions and contact with sewage water. Histopathological examination revealed intense inflammatory reaction, with numerous spherical to oval, encapsulated structures stained with Periodic Acid Schiff, compatible with Prototheca morphology. Tissue culture on Sabouraud agar revealed yeast-like, greyish-white colonies after 48 h of incubation. The isolate was subjected to mass spectrometry profiling and PCR-sequencing of the mitochondrial cytochrome b (CYTB) gene marker, leading to identification of the pathogen as P. wickerhamii. The dog was initially treated with oral itraconazole at a dosage of 10 mg/kg once daily. After six months, the lesions resolved completely, yet recurred shortly after cessation of therapy. The dog was then treated with terbinafine at a dose of 30 mg/kg, once daily for 3 months, with no success. The resolution of clinical signs, with no recurrence over a 36-months follow-up period, was achieved after 3 months of treatment with itraconazole (20 mg/kg) in pulse intermittently on two consecutive days a week.

CONCLUSIONS

This report highlights the refractoriness of skin infections by Prototheca wickerhamii with therapies proposed in the literature and suggests a new treatment option with oral itraconazole in pulse dosing for long-term disease control successfully performed in a dog with skin lesions.

Protothecosis and Toxoplasma gondii co-infection in a dog from Nova Scotia, Canada

A 2-year-old, neutered male mixed-breed dog from Nova Scotia, Canada was evaluated for panuveitis, polyuria, polydipsia, and hind limb ataxia. Toxoplasmosis was diagnosed ante-mortem based on markedly increased Toxoplasma gondii titers. The post-mortem examination confirmed systemic toxoplasmosis and demonstrated disseminated protothecosis. This article documents the first reported case of canine protothecosis in Atlantic Canada. Key clinical message: This case report demonstrates that protothecosis should be a clinical consideration for dogs in Canada. Co-infection with other organisms may occur, which may mask clinical signs and potentially delay diagnosis.

Molecular characterization of Prototheca in 11 symptomatic dogs

Protothecosis is an uncommon disease caused by algae of the genus Prototheca. In dogs, the infection is usually first localized to the colon but has the propensity to later disseminate hematogenously to many other organs, with marked tropism for the eyes and central nervous system. Diagnosis is established by culture and/or evidence of Prototheca organisms in cytologic or histologic preparations. Species characterization, however, requires molecular investigations. Our laboratory set up a real-time PCR targeting portion D1/D2 of the 28S rRNA for identification of Prototheca species from both positive cultures (of rectal swabs and urine) and formalin-fixed, paraffin-embedded tissue. Prototheca bovis, P. ciferrii, and P. wickerhamii were characterized in 11 dogs with systemic or cutaneous protothecosis. Prototheca identifications were phylogenetically consistent with the new taxonomy proposed for this genus based on the mitochondrial cytochrome b gene. As a pilot study, we screened feces and rectal scrapes from 200 asymptomatic dogs, using 2 cohorts of stray and owned animals, to determine the prevalence of intestinal carriage of Prototheca spp. The Prototheca-negative results from both cohorts of healthy dogs suggest that predisposing factors related to the host probably contribute more to the acquisition of clinical disease than exposure to contaminated environments.

Protothecosis in Dogs and Cats-New Research Directions

Protothecosis refers to disease of humans and animals caused by infection with fungus-like, colourless microalgae of the genus Prototheca. Although protothecosis remains an uncommon infection, increasing numbers of human and animal cases are being diagnosed worldwide. This review summarises major new findings in basic science (sequencing analyses of sterol 14α-demethylase (CYP51/ERG11) genes and organelle genomes of Prototheca wickerhamii) to elucidate taxonomic features of this pathogen. Furthermore, this review updates and summarises the clinical features, diagnosis and treatment of protothecosis in dogs and cats. This content of this review is based on information presented at the medical phycology symposium held in the 20th Congress of the International Society for Human and Animal Mycology ( https://www.isham.org/ ).

A Case of Prototheca zopfii Genotype 1 Infection in a Dog (Canis lupus familiaris)

Protothecosis is a rare disease caused by environmental algae of the genus Prototheca. These are saprophytic, non-photosynthetic, aerobic, colorless algae that belong to the Chlorellaceae family. Seven different species have been described. Prototheca zopfii genotype 2 and P. wickerhamii are most commonly involved in pathogenic infections in humans and animals. The objective of this work is to describe, for the first time, a case of protothecosis caused by P. zopfii genotype 1 in a dog. The dog, a 4-year-old mix bred male, was presented to a veterinary clinic in Montevideo, Uruguay, with multiple skin nodules, one of which was excised by surgical biopsy. The sample was examined histologically and processed by PCR, DNA sequencing, and restriction fragments length polymorphisms for the detection and genotyping of P. zopfii. In addition, transmission electron microscopy and scanning electron microscopy were performed. Histology showed severe ulcerative granulomatous dermatitis and panniculitis with myriads of pleomorphic algae. Algal cells were 4-17 µm in size, with an amphophilic, 2-4-µm-thick wall frequently surrounded by a clear halo, contained flocculant material and a deeply basophilic nucleus, and internal septae with daughter cells (endospores) consistent with endosporulation. Ultrastructurally, algal cells/endospores at different stages of development were found within parasitophorous vacuoles in macrophages. Prototheca zopfii genotype 1 was identified by molecular testing, confirming the etiologic diagnosis of protothecosis.

Evidence of a Prototheca Zopfii Genotype 2 Disseminated Infection in a Dog with Cutaneous Lesions

Protothecosis is a disease caused by saprophyte aerobic unicellular algae belonging to the genus Prototheca. In dogs, it mainly occurs as a disseminated form, with initial clinical manifestations often referable to the gastrointestinal tract, followed by typical ocular and neurological signs. So far, Prototheca zopfii genotype 2 infection has been reported in severe forms of disseminated protothecosis, while in dogs has never been associated with cutaneous forms. In this study, we describe a case of Prototheca zopfii genotype 2 infection in a dog characterized by nodular and ulcerative dermatitis and with evidence of dissemination. In December 2015, a 5-year-old unneutered male English Setter dog was presented with a 4-month history of footpads ulcerations and multifocal nodular lesions (3-5 cm diameter) on both front limbs. Cytological examination of the aspirated fluid collected from all nodules revealed the presence of sporangic forms compatible with Prototheca spp. organisms. Suspected Prototheca spp. colonies were isolated from the aspirated fluid and identified as Prototheca zopfii genotype 2 by molecular methods. Few days after the visit, the patient developed serious neurological and ocular signs, and the owners elected humane euthanasia. To the authors' knowledge, this case could represent the first report of a disseminated Prototheca zopfii genotype 2 infection associated with cutaneous lesions in a dog. This study underlines the importance of considering Prototheca zopfii genotype 2 infection in the differential etiological diagnosis of nodular and ulcerative dermatitis in dogs.