博士 / 國立臺灣大學 / 動物學研究所 / 88 / Investigation of the host range of WSSV with the highly sensitive and specific tool of WSSV diagnostic PCR revealed that WSSV could be detected in cultured shrimp (Penaeus monodon, Marsupenaeus japonicus, Fenneropenaeus penicillatus, Metapenaeus ensis, P. semisulcatus, Litopenaeus vannamei) and crab (Scylla serrata). It also confirmed that WSSV exists in wild-caught shrimp (P. monodon, M. japonicus, F. penicillatus, M. ensis, P. semisulcatus) and crabs (Portunus sanguinolentus, Portunus pelagicus, Charybdis feriatus, Charybdis natator, Calappa philarigus, Scylla serrata, Helice tridens). Detection of WSSV in non-cultured arthropods collected from WSSV-affected shrimp farms revealed that copepods, the pest crab Helice tridens, small pest Palaemonidae prawn and the larvae of an Ephydridae insect were reservoir hosts of WSSV. Additionally, the cysts and nauplii of some Artemia were also found to be WSSV PCR positive. The results of this investigation together with other reports, show that WSSV has a very broad host range that extends across 2 classes, 3 subclass, 2 orders , 14 families, 29 genara and 49 species in the phylum Arthropoda.
At least in P. monodon, WSSV diagnostic PCR was almost always able to distinguish between uninfected, pre-patent (also referred to as latent, persistent or asymptomatic carrier state), transition and patent states of WSSV infection. Shrimp at the persistent state of infection are only two-step PCR positive and they may or may not display any clinical signs of white spot syndrome. Shrimp at the transition stage are 1-step PCR positive, and may have tiny spots in their exoskeleton but they do not show any terminal clinical signs; at this stage the shrimp still swim normally and are generally active. Although a latent infection might persist for months, the transition stage might last for only a few hours, and it is inevitably followed by the patent stage of infection, by which time shrimp will have white spots in their exoskeleton. In the patent stage, shrimp display terminal clinical signs, are 1-step PCR positive, and are certain to die within days if not hours.
Shortly after stocking 27 Penaeus monodon culture ponds with postlarvae (~PL 10) at medium density (30-40 shrimp/m2), single-step nested WSSV PCR was used to measure initial WSSV infection rates. More than 70% of the ponds stocked with WSSV-negative shrimp (n=7) were harvested successfully, whereas in the ponds (n=8) where detection rates were higher than 50%, mass mortality occurred during the growth period, and none of these ponds were harvested successfully. When brooders were divided into three groups (group A, WSSV-positive before spawning; group B, WSSV-positive just after spawning; and group C, WSSV-negative after spawning), WSSV was detected in 75%, 43.5% and 14.3% of the nauplii from the respective groups. WSSV prevalence was high (50%) in most of the nauplii from group A brooders. Stocking of batches of nauplii with WSSV-positive detection rates higher than 50% led to low survival rates in the culture ponds. On the other hand, when there was no outbreak of WSS, the performance of WSSV-positive nauplii with low (50%) detection rates were similar to the WSSV-negative nauplii.
In conclusion, WSSV diagnostic PCR is not only useful for screening carriers in shrimp larvae, parental spawners and invertebrate populations that share the same habitat, it also gives an accurate and reliable picture of the WSSV status of a population and allows the progress of a WSSV infection to be monitored. WSSV diagnostic PCR thus facilitates several affective strategies that prevent or reduce the occurrence of WSS in cultured shrimp.
| Identifer | oai:union.ndltd.org:TW/088NTU00312008 |
| Date | January 2000 |
| Creators | Shao-En Peng, 彭紹恩 |
| Contributors | Guang-Hsiung Kou, Chu-Fang Lo, 郭光雄, 羅竹芳 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 82 |
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