Carp Pox

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Also known as: Fish Pox — Carp Herpesvirus — Epithelioma papillosum — Carp Epithelioma

Caused by: Cyprinid Herpesvirus 1 — CyHV-1

Introduction

Carp pox is a fairly common, relatively benign proliferative skin disease of cyprinids (carps and minnows). It is caused by a herpes virus.

It occurs most commonly in ornamental cyprinids and the common Carp in the UK.

Mortalities are very rare but the impact is mainly economic as the cutaneous growths reduce marketability of the fish.

Carp pox is present in most European countries, China, Japan, the USA, Russia, Israel, Korea and Malaysia.

Clinical Signs

Carp pox leads to the formation of benign, hyperplastic, papillomatous growths in the epithelium of carp.

The tumours are milky-white to grey, often described as resembling molten candlewax, and are raised 1-3mm above the skin on the head, fins and other body surfaces. The growths can gradually increase in size and end up covering large areas of the body surface before they eventually regress and disappear.

Adult fish usually show no other signs.

Juvenile fish can be adversely affected by Carp Pox and can suffer a high mortality, developing signs such as anorexia, intermittent immobility, exophthalmia, darkened skin and haemorrhages on the operculum and abdomen.

Lesions usually develop in low temperatures (winter/spring) and regress with high temperatures (summer) but the latent infection remains. This means that lesions can recur the following year.

Diagnosis

Diagnosis is usually made from external clinical signs.

Skin histology will reveal epidermal epithelial cell hyperplasia, and intracytoplasmic and intranuclear inclusions.

Electron microscopy examination may reveal herpes-like particles in the hyperplastic epithelial cells.

Virus isolation and identification can be attempted by inoculation of tissue cultures, serum neutralisation or in-situ hybridisation.

Treatment and Control

The only effective method of control is preventing the introduction of affected fish.

No particular treatment exists, but recovery can be accelerated by raising the temperature of the water to above 15°C, liming the ponds, or transferring the fish to ponds supplied with large amounts of clear, oxygenated water.

If the disease is uncomplicated, the lesions will eventually be replaced by unmarked epidermis. However, lesions can recur due to the pathogen's nature as a herpes virus, and the disease can reappear the following Spring.


Carp Pox Learning Resources
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Flashcards
Test your knowledge using flashcard type questions
Ornamental Fish Q&A 05


References

Hoole, D. (2001) Diseases of carp and other cyprinid fishes John Wiley and Sons

Plumb, J. (2010) Health Maintenance and Principal Microbial Diseases of Cultured Fishes John Wiley and Sons

Woo, P. (2006) Fish Diseases and Disorders: Protozoan and metazoan infections CABI

Noga, E. (2010) Fish Disease: Diagnosis and Treatment John Wiley and Sons




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