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Gray patch disease

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Synonym(s): Herpes of green turtles

Introduction

  • Cause: Herpes virus.
  • Signs: pustular lesions on neck and flippers of young turtles; gray patches on epidermis of older turtles.
  • Diagnosis: histopathology, PCR.
  • Treatment: none.
  • Prognosis: variable but some mortality.

Presenting signs

  • Pustular lesions on skin of neck and flippers of young turtles aged 2-6 weeks.
  • Large areas of grey patches on epidermis of turtles aged 8-15 weeks.

Acute presentation

  • Lesions as above or death.

Geographic incidence

  • Predominantly in areas where green turtles are captive farmed (Grand Cayman).

Age predisposition

  • 2-6 weeks of age 20% mortality but do not show gray patch lesions.
  • 8-15 weeks of age develop gray patch lesions.

Breed/Species predisposition

  • Green sea turtles (Chelonia mydas).

Cost considerations

  • Cost is borne by commercial turtle farming enterprise.
  • Decreased profits due to loss of stock.

Pathogenesis

Etiology

Predisposing factors

General

  • Age.
  • Water temperature.
  • Stocking density.
  • Stress.
  • Water quality.

Specific

  • 20% mortality with Herpes virus in 2-6 week old green sea turtles.
  • Grey patch disease and mortality in 8-15 week old green sea turtles.
  • Warm temperatures lead to increased mortality especially temperatures around 30°C/86°F.
  • High stocking density results in stress and wounds from fighting which can result in inoculation of the virus in the skin leading to clinical disease.
  • Stress caused by high stocking density and high water temperatures lead to increased levels of infection.
  • Poor water quality, eg uneaten food and poor filtration, concentrates viral particles and harbors bacteria which give rise to secondary bacterial infections.

Pathophysiology

  • Direct contact between turtles.
  • Contact with vectors.
  • Contact with virus in sediments.
  • Contact with virus suspended in sea water.
  • In trials the virus was introduced in 100% of cases where skin was inoculated with the virus.
  • 0% of controls developed lesions.

Timecourse

  • 2-6 week old turtles die of Herpes in very short time (20% mortality).
  • 8-15 week old turtles - mortality less than 20%.
  • Mortality is higher when water temperatures are higher, eg 30°C/86°F.
  • Mortality is lower when water temperature is lower, eg winter months.
  • Herpes viruses have been shown to survive in sea water for up to 120 h.

Epidemiology

  • Higher incidence in more densely populated ponds.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed Papers

  • Recent references from PubMed and VetMedResource.
  • Arena P C, Warwick C & Steedman C (2014) Welfare and enviromental implications of farmed sea turtles. J Agric Environ Ethics 27, 309-330 SpringerLink (pdf download).
  • Curry S S, Brown D R, Gaskin J M et al (2000) Persistent infectivity of a disease-associated herpesvirus in green turtles after exposure to seawater. J Wild Dis 36 (4), 792-797 PubMed.
  • Haines H (1987) A Herpesvirus Disease of Green Sea Turtles in Aquaculture. MFR Paper 1294. Marine Fisheries Review. 40 (3), 33-37 NOAA (pdf download).
  • Haines H & Kleese W C (1977) Effect of water temperature on a herpesvirus infection of sea turtles. Infect Immunol 15 (3), 756-759 PubMed.
  • Rebell G, Rywlin A & Haines H (1975) A Herpesvirus-type agent associated with skin lesions of green sea turtles in aquaculture. Am J Vet Res 36 (8), 1221-1224 PubMed.

Other sources of information

  • Marschang R E (2009) EAZWV Transmissible Disease Fact Sheet No. 26. Grey Patch Disease. EAZWV (pdf download).
  • Godley B J (2002) Cayman Turtle farm: Consultancy report to DEFRA September 15. pp 23.
  • Haines H G, Rywlin A & Rebell G (1974) A Herpesvirus Disease of Farmed Green Turtles (Chelonia mydas). In: Proc World Mariculture. pp 183-195 WileyOnline.