Marine Viruses 4.7 Marine Viruses and Shrimp Aquaculture 43
Part A | 4.7
ture [4.51]. The genome contains three long ORFs:
ORF1 (or left ORF), ORF2 (or mid ORF), and ORF3
(or right ORF). ORF1 encodes a putative nonstructural protein-2 (NS2) of 428 amino acids, the function
of which is not yet known. ORF2 encodes nonstructural protein-1 of 579 amino acids, which possesses the
most conserved region that includes replication initiator motifs, NTP-binding, and helicase domains. ORF3
encodes a polypeptide of 818 amino acids, which is
the major capsid protein (VP) [4.51]. The purified viral
proteins were detected as a major band at 57 kDa and
a minor band at 54 kDa due to posttranslational modification of the deduced 92-kDa polypeptide. However,
the function of the minor band is still unknown [4.51].
Hosts and Geographical Distribution of HPV
HPV was first reported in 1984 in the wild shrimp
species F. chinensis from Singapore [4.53]. HPV was
detected in South Korea in 1985 in F. chinensis [4.54]
and was subsequently observed in wild and farmed
shrimp species in many geographical locations, including Australia, China, Thailand, India, Madagascar,
Tanzania, New Caledonia, the Philippines, Indonesia,
Malaysia, Kenya, Kuwait, Israel, and South and North
America [4.43].
HPV infects epithelial cells of the hepatopancreas
and shows basophilic inclusions within enlarged nuclei of tubular epithelial cells. HPV infects a wide
range of shrimp species including wild and farmed
P. monodon, Penaeusesculentus, Penaeusjaponicus,
F. chinensis, Penaeussemisulcatus, Penaeusindicus,
Penaeuspenicillatus, Penaeusschmitti, L. vannamei,
and Penaeusstylirostris [4.43, 44].
HPV Genotypes
Viruses are obligate parasites that are normally present
in the environment in stable ecological associations
with one or more hosts [4.55]. Viruses should have efficient replication and transmission of infection in the
environment or host. The environment is constantly
changing because of individual differences in host genetics and the immune response of the host. These
environmental variables select for mutants or suitable
variant phenotypes through the inherent capacity for
evasive behavior [4.41].
The HPV genome has greater genetic diversity than
those of other shrimp viruses, such as IHHNV and
TSV. In total, eight HPV genomes are currently available in GenBank, and among these, complete genome
sequence data are available for only four isolates, including the Korean isolates [4.51, 56–58]. However,
incomplete or partial genome sequences are available
in GenBank for many isolates. The sequencing results
of different isolates suggest that HPV isolates from
different shrimp species and/or different geographical
regions are genetically different [4.59]. Of the three
ORFs of HPV, ORF3 (or right ORF), which encodes
the major capsid protein, shows greater variability than
the other ORFs. Based on the amino acid sequence
of the capsid protein gene, it has been divided into
three genotypes: genotype I from Korea, Tanzania, and
Madagascar; genotype II from Thailand and Indonesia;
and genotype III from Australia and New Caledonia.
The Korean strains HPVchin and FcDNV were isolated from the shrimp species F. chinensis, Australian
(PmergDNV) and New Caledonian isolates were from
the host P. merguiensis, and Thai isolate (PmDNV) was
from P. monodon.
4.7.5 Diagnostic Methods
for Shrimp Virus Diseases
Microscopy
Most diagnostic methods applied to shrimp have been
adopted from other fields of pathology and are slightly
different from those used in fish, veterinary, and human
pathology. Diagnostic methods for shrimp pathogens
include the traditional methods of morphological
pathology (direct light microscopy, histopathology, and
electron microscopy), traditional microbiology, and the
application of serological methods. Initially, diagnosis
of shrimp diseases was dependent on microscopic observations, and characterization viruses isolated from
infected tissues. Transmission electron microscopy
(TEM) was added to the diagnostic toolkit in the mid1970s and was used to discover the first Baculoviruspenaei in shrimp [4.60]. However, electron microscopic
methods are not in common use due to their limited sensitivity as well as the long preparation time, specialized
equipment, and highly trained personnel requirements.
Hematology and Clinical Chemistry
Hematology and clinical chemistry are principal diagnostic tools for human and veterinary medicine,
but they have also been applied to shrimp pathology
by examining the changes in hemolymph parameters
(hemocyte count, hemolymph clotting time, glucose,
nonprotein nitrogen, ammonia, alkaline phosphatase,
and total serum protein levels). However, with the exception of hemocyte count and hemolymph clotting
time, these tests have not yet been adopted for routine
diagnostic purposes [4.61].
Part A | 4.7
ture [4.51]. The genome contains three long ORFs:
ORF1 (or left ORF), ORF2 (or mid ORF), and ORF3
(or right ORF). ORF1 encodes a putative nonstructural protein-2 (NS2) of 428 amino acids, the function
of which is not yet known. ORF2 encodes nonstructural protein-1 of 579 amino acids, which possesses the
most conserved region that includes replication initiator motifs, NTP-binding, and helicase domains. ORF3
encodes a polypeptide of 818 amino acids, which is
the major capsid protein (VP) [4.51]. The purified viral
proteins were detected as a major band at 57 kDa and
a minor band at 54 kDa due to posttranslational modification of the deduced 92-kDa polypeptide. However,
the function of the minor band is still unknown [4.51].
Hosts and Geographical Distribution of HPV
HPV was first reported in 1984 in the wild shrimp
species F. chinensis from Singapore [4.53]. HPV was
detected in South Korea in 1985 in F. chinensis [4.54]
and was subsequently observed in wild and farmed
shrimp species in many geographical locations, including Australia, China, Thailand, India, Madagascar,
Tanzania, New Caledonia, the Philippines, Indonesia,
Malaysia, Kenya, Kuwait, Israel, and South and North
America [4.43].
HPV infects epithelial cells of the hepatopancreas
and shows basophilic inclusions within enlarged nuclei of tubular epithelial cells. HPV infects a wide
range of shrimp species including wild and farmed
P. monodon, Penaeusesculentus, Penaeusjaponicus,
F. chinensis, Penaeussemisulcatus, Penaeusindicus,
Penaeuspenicillatus, Penaeusschmitti, L. vannamei,
and Penaeusstylirostris [4.43, 44].
HPV Genotypes
Viruses are obligate parasites that are normally present
in the environment in stable ecological associations
with one or more hosts [4.55]. Viruses should have efficient replication and transmission of infection in the
environment or host. The environment is constantly
changing because of individual differences in host genetics and the immune response of the host. These
environmental variables select for mutants or suitable
variant phenotypes through the inherent capacity for
evasive behavior [4.41].
The HPV genome has greater genetic diversity than
those of other shrimp viruses, such as IHHNV and
TSV. In total, eight HPV genomes are currently available in GenBank, and among these, complete genome
sequence data are available for only four isolates, including the Korean isolates [4.51, 56–58]. However,
incomplete or partial genome sequences are available
in GenBank for many isolates. The sequencing results
of different isolates suggest that HPV isolates from
different shrimp species and/or different geographical
regions are genetically different [4.59]. Of the three
ORFs of HPV, ORF3 (or right ORF), which encodes
the major capsid protein, shows greater variability than
the other ORFs. Based on the amino acid sequence
of the capsid protein gene, it has been divided into
three genotypes: genotype I from Korea, Tanzania, and
Madagascar; genotype II from Thailand and Indonesia;
and genotype III from Australia and New Caledonia.
The Korean strains HPVchin and FcDNV were isolated from the shrimp species F. chinensis, Australian
(PmergDNV) and New Caledonian isolates were from
the host P. merguiensis, and Thai isolate (PmDNV) was
from P. monodon.
4.7.5 Diagnostic Methods
for Shrimp Virus Diseases
Microscopy
Most diagnostic methods applied to shrimp have been
adopted from other fields of pathology and are slightly
different from those used in fish, veterinary, and human
pathology. Diagnostic methods for shrimp pathogens
include the traditional methods of morphological
pathology (direct light microscopy, histopathology, and
electron microscopy), traditional microbiology, and the
application of serological methods. Initially, diagnosis
of shrimp diseases was dependent on microscopic observations, and characterization viruses isolated from
infected tissues. Transmission electron microscopy
(TEM) was added to the diagnostic toolkit in the mid1970s and was used to discover the first Baculoviruspenaei in shrimp [4.60]. However, electron microscopic
methods are not in common use due to their limited sensitivity as well as the long preparation time, specialized
equipment, and highly trained personnel requirements.
Hematology and Clinical Chemistry
Hematology and clinical chemistry are principal diagnostic tools for human and veterinary medicine,
but they have also been applied to shrimp pathology
by examining the changes in hemolymph parameters
(hemocyte count, hemolymph clotting time, glucose,
nonprotein nitrogen, ammonia, alkaline phosphatase,
and total serum protein levels). However, with the exception of hemocyte count and hemolymph clotting
time, these tests have not yet been adopted for routine
diagnostic purposes [4.61].