Disease is one of the industry’s most limiting factors
Top three disease challenges in shrimp
Disease constrains growth
*
hite spot syndrome virus — W the top viral agent.
†
cute hepatopancreatic necrosis A disease — caused by pathogenic isolates of Vibrio parahaemolyticus (and other species) bearing a Pir toxin releasing plasmid — the top bacterium.
‡
Enterocytozoon hepatopenaei — a fungal microsporidian causing hepatopancreatic microsporidiosis — top parasite.
The graph below shows the percentage year-on-year change in the growth of Asian and global shrimp production. Episodes of disease have been a key factor in shaping growth.
TSV, WSSV, YHV
IHHNV
60
WSSV*
AHPND†
White spot syndrome virus (WSSV) is a large DNA virus that only infects crustaceans; it is an OIE (the World Organisation for Animal Health) listed notifiable disease.
A pathogenic isolate of Vibrio parahaemolyticus, a rod-shaped bacterium, that carries a plasmid encoding two toxins that results in AHPND. This disease is commonly called ‘early mortality syndrome’ or ‘EMS’ by farmers. Infection resulting in AHPND is also an OIE listed disease.
Signs/symptoms: In culture systems, the shrimp may not show any distinctive signs but may be lethargic, stop feeding or begin aggregating at the edge of ponds. Clinical signs can include the presence of white calcium deposits up to 3 mm in diameters which can link to form larger plates, shrimp can appear dark with a red/pink colour to the body and appendages, may have heavily fouled gills and external shell, and, heavily infected shrimp may have a white midgut. Losses: Infections can result in a typical 40% loss of stock over the first two years of infection on site; historically, this is the most significant pathogen impacting on commercial crustacean production.
AHPND/EHP
50
40
30
20
Signs/symptoms: Infection results in significant shrinkage of the hepatopancreas and the shrimp frequently have soft shells and guts with discontinuous contents or no content. Early signs of an infection include slow growth, a shrunken, pale hepatopancreas. Losses: Infections can result in entire loss within 30 days. Infection resulting in AHPND is currently the number one bacterial pathogen problem within the global shrimp industry.
EHP‡ EHP infects the hepatopancreas of shrimp which can result in severe growth retardation, morbidity and, in heavy chronic infections, mortality. Signs/symptoms: Although shrimp continue to feed, there is arrested growth; a drop in food conversion ratios (FCR) may provide the first indication of a potential EHP infection.
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0
-10 1970
1975
1980
IHHNV = Infectious Hypodermal and Haematopoietic Necrosis Virus TSV = Taura Syndrome Virus WSSV = White Spot Syndrome Virus
1985
1990
1995
2000
2005
AHPND = Acute Hepatopancreatic Necrosis Disease previously known as Early Mortality Syndrome (EMS) EHP = Enterocytozoon hepatopenaei YHV = Yellow-head Virus
2005
2010 World
Losses: While mortality rates may be low, the farmer’s decision to prematurely harvest may be based on farm production economics.
2015 Asia
Source: Shinn et al. (2018) Asian Fisheries Science, S31, 210-255. Image: WSSV infection in shrimp carapace.
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