This document summarizes a case of chorioretinitis in an 11-year-old Collie dog caused by the algal organism Prototheca. Histopathology of the dog's right eye revealed granulomatous chorioretinitis with intralesional algal organisms consistent with Prototheca. Prototheca are achlorophyllic algae that can cause disease in both animals and humans by infecting the eyes, central nervous system, bones, kidneys and other tissues when the host's immunity is compromised.

1. Case Number: 61
AN UNCOMMON CAUSE OF
CHORIORETINITIS IN A DOG
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1Stephanie Shrader, DVM
1Jennifer (Jey) Koehler, DVM, PhD, DACVP
2Elizabeth Whitley, DVM, PhD, DACVP
1Department of Pathobiology, Auburn University College of Veterinary Medicine
2Department of Veterinary Pathology, Iowa State College of Veterinary Medicine

2.  11-year-old, castrated male, Collie breed dog
 Presented to a local veterinary ophthalmology
specialist following a 2-3 week history of
blepharospasm and chemosis of the right eye
SIGNALMENT AND HISTORY
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3.  Iris markedly swollen, fundus not visualized
 Lack of menace response, negative dazzle reflex
 Menace response
 Ability to see (CN II) and blink (CN VII)
 Dazzle reflex
 Involuntary aversion to intense light
 CN II, CN VII, retina and the rostral colliculus
 IOP @ 30-mmHg (12 to 25-mmHg)
 Treatment
 Xalatan® (latanoprost)
 Cosopt® (dorzolamide hydrochloride-timolol maleate)
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OPHTHALMIC EXAMINATION

4. HISTOPATHOLOGY
500--μm
200x, H&E
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5. HISTOPATHOLOGY
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400x, H&E
20--μm

6. Permission granted only for viewing on SEVPAC website
400x, H&E
20--μm
HISTOPATHOLOGY

7. 400x, PAS
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Algal Morphology
 Round to ovoid,
thin walled
sporangia
 Collapsed
refractile PAS-
positive cell
walls
 10 to 15-um in
diameter
 Empty and
crescent-shaped
(black arrow)
 Rare basophilic
daughter
endospores
(yellow arrow)
20--μm
HISTOPATHOLOGY

8.  Anterior displacement and thinning of the iris
 Narrowing of the iridocorneal angle
 Atrophy of the ciliary body
 Collapse of the ciliary cleft
 Hemorrhage in the posterior chamber
 Posterior synechiae
ADDITIONAL FINDINGS
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9. Right globe: Granulomatous chorioretinitis,
diffuse, marked, chronic with retinal
detachment and intralesional algal
organisms (consistent with Prototheca spp.)
MORPHOLOGIC DIAGNOSIS
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10.  Achlorophyllic algae
 Mutant form of Chlorella (green algae)
 Ubiquitous inhabitants of detritus and
contaminants of various substrates [1, 2]
 Two most common isolates are Prototheca
wickerhamii and Prototheca zopfii
 Both can cause disease in animals and people [3]
 Various routes of infection
 Regarded as an opportunistic pathogen in people
 Host immunosuppression usually required
PROTOTHECA
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11. Disseminated forms most common
Tropism for the eye, central nervous system (CNS),
bone, kidneys and myocardium
Refractory colitis also reported [4, 5]
Occasional reports of ocular protothecosis
without systemic involvement
Serous discharge, hyperemic conjunctivae, aqueous
flare with slow pupillary light reflex (PLR) and an
absent menace response
Secondary retinal detachment and glaucoma [6]
PROTOTHECOSIS IN DOGS
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12. PROTOTHECOSIS IN OTHER ANIMALS
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http://info.fujita-hu.ac.jp/~tsutsumi/photo/photo179-1.htm
Cattle
• Usually associated with
chronic mastitis
• Often found at slaughter
• Disseminated disease
uncommon [7]
Cats
• Several reports involving
cutaneous lesions [8, 9]
• Disseminated disease rare
Goats
and
Sheep
• Cutaneous and nasal lesions
[10, 11]
People
• Cutaneous lesions
• Olecranon bursitis
• Disseminated disease [2]

13. 1. Huerre M, et al. Human protothecosis and environment. Bull Soc Pathol Exot,
1993. 86(5 Pt 2):484-488.
2. Lass-Florl C. and A. Mayr. Human Protothecosis. Clin. Microbiol. Rev., 2007.
20(2):230-242.
3. Leimann B, et al. Protothecosis. Med Mycol, 2004. 42(2):95.
4. Stenner VJ, et al. Protothecosis in 17 Australian dogs and a review of the
canine literature. Med Mycol, 2007. 45(3):249-266.
5. Riberiro MG, et al. Phenotypic and genotypic characterization of Prototheca
zopfii in a dog with enteric signs. Res Vet Sci, 2009. 87(3):479-481.
6. Schultze A, et al. Clinical, cytologic and histopathologic manifestations of
protothecosis in two dogs. Vet Ophthalmol, 1998. 1(4):239-243.
7. Taniyama H, et al. Disseminated Protothecosis Caused by Prototheca zopfii in
a Cow. Vet Pathol, 1994. 31:123-125.
8. Dillberger JE, et al. Protothecosis in two cats. JAVMA, 1998. 192(11):1557 -
1559.
9. Finnie JW, et al. Cutaneous protothecosis in a cat. Australian Veterinary
Journal, 1981. 57(6):307-308.
10. Macedo JTSA, et al. Cutaneous and Nasal Protothecosis in a Goat. Vet Pathol,
2008. 45:352-354.
11. Camboim EK, et al. Protothecosis by Prototheca wickerhamii in goats.
Mycoses, 2011. 54(4):e196-200.
REFERENCES
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14.  Elizabeth Whitley, DVM, PhD, DACVP
 Jey Koehler, DVM, PhD, DACVP
 Histopathology Laboratory Technicians
AND A SPECIAL THANKS TO…
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