台灣養殖草蝦感染四種蝦病毒之流行狀況：過去和目前

Abstract

目前已知的蝦病毒約有20種之多(Lightner, 1999)，其中草蝦桿狀病毒(Penaeus monodon baculovirus, MBV)在1980年中期、黃頭病毒(Yellow head virus, YHV)和白點病毒(White spot syndrome virus, WSSV) 在1990年初期、桃拉病毒(Taura syndrome virus, TSV) 在1990年末期都分別造成台灣養殖蝦大量死亡。1987年蝦病爆發迄今已19年，台灣養殖草蝦病毒感染的嚴重性是否隨著時間有所改變是本調查的目的。 參考國際疫病組織(OIE)水族動物診斷手冊2003版病毒標準篩選法，針對1994、1995年兩地點四批冷凍儲存的40個草蝦樣本、1995年的一批福馬林固定石蠟包埋草蝦及2004、2005年三地點收集的七批117個活草蝦樣本，利用巢式聚合酵素鏈反應(nest PCR)檢測上述四種病毒。 結果顯示，草蝦的MBV帶原率除自1994、1995年的86%顯著降2004、2005年的42%，草蝦感染MBV的嚴重性亦顯著下降。1994、1995年草蝦的WSSV、YHV、TSV帶原率分別為47%、67%、2%，而2004、2005年的帶原率則分別為41%、82%、1%，以上三種病毒的帶原率及感染的嚴重性十年前後並無顯著差異。此外，病毒共感染同一隻草蝦的情形普遍。1994、1995年有83%的草蝦同時感染兩種以上的病毒，其中，以36%的草蝦同時感染MBV、WSSV及YHV三種病毒、38%的草蝦同時感染MBV及YHV兩種病毒為最；2004、2005年亦有50%的草蝦同時感染兩種以上的病毒，並以24%的草蝦同時感染WSSV及YHV為最。 本調查除了是首次針對台灣養殖草蝦同時進行MBV、WSSV、YHV及TSV此四種重要蝦類病毒的檢測外，亦是利用福馬林固定石蠟包埋草蝦進行蝦類病毒調查的首例，並發現目前台灣養殖草蝦疑似以第三型黃頭病毒為帶原率最高的病毒，也是首次報告台灣養殖草蝦有同時帶原MBV、WSSV及YHV三種病毒的現象。此外，根據調查的結果，可分別將YHV及TSV此兩種RNA病毒存於台灣的時間往前推至1994及1995年。

There are 20 Penaeid shrimp viruses described at present. Some of them caused huge mortalities of cultured shrimp locally such as MBV in mid 1980’s, YHV and WSSV in early 1990’s and TSV in late1990’s. Shrimp viral diseases in Taiwan catch our attention since the prevalence changed during the two sampling time. Based on the Manual of Diagnostic Tests for Aquatic Animals (OIE, 2003), we screened 40 frozen samples collected during 1994-1995, one batch of formalin-fixed and paraffin-embedded (FFPE) samples gathered in 1995 and 117 live samples from 2004-2005. 86% of shrimp had MBV in 1994-1995 and remarkably reducing to 42% in 2004-2005. Between the collection period, the variation is not remarkable either in the prevalence of shrimp that had WSSV, YHV and TSV or in infecting intensity of these three viruses except MBV. Multiple infections were common wherein more than 83% of samples carried at least 2 viruses simultaneously in 1994-1995 and 50% in 2004-2005. 36% of shrimp had multiple infections caused by MBV, YHV and WSSV, and 38% had MBV and YHV in 1994-1995. 24% of the shrimp samples had simultaneous infection caused by WSSV and YHV in 2004-2005. Conclusively, this is the first time that simultaneous and multiple infection caused by four shrimp viruses(MBV, WSSV, YHV and TSV) was investigated in hatchery-reared tiger shrimp in Taiwan. The investigation is also the first to use FFPE shrimps to detect the viruses. The third genotype of YHV should be the most serious virus in tiger shrimp cultured in Taiwan. This is also the first report that Taiwan hatchery-reared tiger shrimp carried MBV, WSSV and YHV simultaneously. Acoording to our investigation, YHV should have been existing in Taiwan since 1994 and TSV in 1995 which is earlier than previous reports.