Faecal Occult Blood Test

Case of the Month (Tim Cushing October 2015)

Prototheca infection in a dog

A dog presented to the rDVM with a history of vomiting, diarrhoea and haematochezia.  Examination also revealed retinal detachment.

Fig 1. Lower magnification view of colonic mucosa showing mild to moderate lymphoplasmacytic and histiocytic colitis with surface ulceration and intramucosal algal organisms (arrows). 200x magnification

Fig 2. High magnification of the mucosa showing the presence of algae, including a cyst exhibiting characteristic endosporulation (arrow). 400 magnification


Fig 3. PAS stain highlighting the algae within the mucosa. 400x magnification.

Final Diagnosis

Moderate lymphoplasmacytic and eosinophilic colitis with mild to moderate, multifocal mucosal fibrosis and intra-mucosal algae


Algal infection in dogs is an uncommon to rare occurrence and is often associated with Chlorella spp or Prototheca spp, a non-chloroplast containing variant of Chlorella. These organisms are ubiquitous in the environment and have been identified on all continents other than Antarctica. Attempts at recreating disease have met with varied success, suggesting these are opportunistic pathogens that require some degree of immune suppression/tissue defect to allow for infection.  Most veterinary infections are cutaneous, reflecting secondary infection of open wounds or implantation of the organisms into the skin.  In dogs, more disseminated infection can be seen and often involve the intestine and eyes.  Ingestion of the organisms from the environment and presumed opportunistic infection of the intestinal tract (colon, predominantly) occur.  The organisms invade mucosal blood vessels and spread systemically.  The observed retinal detachment in this dog is likely related to spread of the organisms to the eye; however as histologic examination was not pursued this assumption cannot be verified.  Definitive differentiation of these organisms is often difficult by histology alone.  Histochemical or immunohistochemical stains, PCR, culture and/or electron microscopy can be used to help differentiate.  The PAS stain used to highlight the organisms reveals smooth capsular staining without the presence of distinct starch granules.  This would have me favour Prototheca infection in this animal. 

Previous Monthly Cases

Hypertensive Retinopathy January 2010
FIP in a cat - uncommon presentation February 2010
Phaeohyphomycosis    March 2010 
Scleral Rupture April 2010
Canine and feline epulides May 2010
Erythema multiforme in a labrador retreiver June 2010
Keloidal fibrosarcoma in a labrador retreiver July 2010
Cutaneous epitheliotropic lymphoma  August 2010 
Benign cutaneous histiocytoma  September 2010 
Iridociliary adenoma October 2010
Proliferative thrombovascular necrosis of the pinnae November 2010
Signet-ring cell carcinoma in the stomach of a dog December 2010
Cutaneous infiltrative lipoma in a labrador January 2011

Tonsillar squamous cell carcinoma February 2011
Canine orbital meningioma March 2011
"Lung-digit" syndrome in a cat April 2011
Hepatic amyloidosis in a cat May 2011
Haemophagocytic histiocytic sarcoma June 2011
Alternaria spp. infection in an immunocompromised dog July 2011
Ocular manifestation of lymphoma in a cat  August 2011
Kerion dermatophytosis in a Cocker spaniel September 2011
Subcuticular coenurus in a rabbit  October 2011
Optic nerve glioma in a dog November 2011
Malignant transformation of a viral papilloma in a dog  December 2011
Uveodermatological syndrome in an Akita
January 2012
Cutaneous angiostomatosis in a dog  February 2012
Transitional cell carcinoma in a dog  March 2012
Corneal inclusion cysts in a dog   April 2012
Extraskeletal osteosarcoma in a dog  May 2012
Subungual melanoma in a dog  June 2012
Retrobulbar grass seed in a dog   July 2012
Lungworm infection associated with hypercalcaemia in a dog  August 2012
Conjunctival melanoma in a dog  September 2012
Pneumocystis infection in a Cavalier King Charles Spaniel  October 2012
Fungal keratitis and secondary endophthalmitis in a horse November 2012
Myeloid leukaemia with lymph node invasion in a dog    December 2012
Cutaneous toxoplasmosis in a cat   January 2013
Glomerulonephritis in a dog  February 2013
Splenic mast cell tumour in a cat  March 2013
Laryngeal rhabdomyoma in a dog  April 2013
Mycobacterial infection in an eye May 2013
Key Gaskell syndrome in a cat June 2013
Intraosseous epidermoid cyst in the toe of a dog July 2013
Septic Lens Implantation Syndrome August 2013
Fungal Keratitis in a dog September 2013
Fatal Cowpox Infection in a Cat
October 2013
Lingual granular cell tumour in a dog November 2013
Leydig cell tumour in a dog December 2013
Urticarial allergic reaction in a dog January 2014
Conjunctival foreign body in a dog  February 2014
An enlarged sublumbar lymph node in a hypercalcaemic dog  March 2014
Perineural invasion of a carcinoma in a dog  April 2014
Intestinal pseudo-obstruction in a dog  May 2014
Sebaceous adenitis in a dog  June 2014
Ovarian teratoma  July 2014
Cutaneous cowpox virus infection in a cat  August 2014
Acute renal falure in a cat  September 2014
Azothioprine toxicity in a dog  October 2014
Neoplastic pleural effusion in a dog November 2014
Squamous cell carcinoma in the orbit of a dog December 2014
Feline lungworm January 2015
Cutaneous haemangiosarcoma in an elderly dog February 2015
Ductal plate malformation  March 2015
Hodkin's-like lymphoma in a cat  April 2015
Interstitial (Leydig) cell tumour in a cat May 2015
Sialocoele in a dog June 2015
Bilateral ovotestes in a dog July 2015
Myelofibrosis in a dog with non-regenerative anaemia August 2015
Demodex mites in a dog September 2015

CytoPath Ltd | PO Box 24 | Ledbury | Herefordshire | HR8 2YD |
tel: 01531 63 00 63 | fax: 01531 63 46 83 | email: customer.enquiries@cytopath.co.uk | web: www.cytopath.co.uk

2009 Cytopath Limited / / all rights reserved / / design and development by mightyweb.co.uk

Faecal Occult Blood Test