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 โพสต์เมื่อ: 17/08/2007-19:58 GMT+7
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มาอัพเดทข้อมูลเรื่องโรคIMNV ครับ ตอนนี้ มีโรคใหม่ที่คล้ายๆกัน คือ PvNV และอาจจะแยกสองโรคนี้ออกจากกันได้โดย อาการ ดังลิ๊งค์ต่อไปนี้ครับ
http://www.iq2000kit.com/news12.htm
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ต่อไปเป็น ความรู้เพิ่มเติมเรื่องโรค IMNV
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Whitetail--Not To Be Confused with Whitespot
Diagnosing IMNV
The major clinical sign of IMNV (infectious myonecrosis virus, a double-stranded RNA totivirus) is the appearance of white, opaque areas in the tail muscle. As the disease progresses, shrimp become lethargic and 40-60 percent may die. Brazilian shrimp farmers lost an estimated $20 million to IMNV in 2003.
Researchers from the University of Arizona have published a paper that says: Diagnosis of IMNV infection has proven problematic because current methods rely on clinical and histological examinations. Diagnosis based on clinical signs is not reliable, as a number of factors, including hypoxia, crowding, or sudden changes in temperature or salinity can cause similar symptoms. Diagnosis by histological examination is not specific or sensitive.
In the paper, the researchers report the development of a new molecular diagnostic method based on in situ hybridization (ISH, routinely used for the diagnosis of other shrimp viruses) that is both highly specific and sensitive. They developed the method, tested its specificity and then employed it in laboratory bioassays.
The researchers used the method to test the susceptibility of three species of penaeid shrimp to IMNV in laboratory bioassays. Seven animals (mean weight 3 grams) of each species (Penaeus monodon, P. vannamei and P. stylirostris) were injected with 0.1 ml of purified IMNV inoculum from infected shrimp. Shrimp were then maintained in three aquaria on a pelleted ration for 28 days.
The major clinical sign of infection, the appearance of whitish lesions in the tail muscle, was seen first in the vannamei group, in which all of the injected shrimp had obvious lesions after six days. In the stylirostris group, the lesions developed slowly, with only three animals showing signs of infection after seven days. All of the shrimp had lesions after 13 days. No clinical signs of infection were observed in any of the individuals of the monodon group, but lesions could have been obscured by monodon's highly pigmented exoskeleton. On the 14th day after injection, one individual from each species was sacrificed for ISH analysis. They all tested positive for IMNV. In the vannamei group, there were two mortalities (days 13 and 21); no mortalities occurred in either the stylirostris or monodon groups during the bioassay period.
Histological analysis showed that the viral infection was evident only in the skeletal muscle and lymphoid organ. Samples of vannamei (from Belize) and monodon (from Australia) exhibiting muscle necrosis suspected to be caused by IMNV infection were found to be ISH negative. Thus, without the availability of the ISH test, diagnosis based on gross signs or histology could be erroneous.
Vannamei, the natural host of IMNV, appears to be most susceptible based on the onset of clinical signs and degree of mortality. IMNV is not particularly virulent compared to other shrimp viruses such as TSV (Taura), YHV (Yellowhead) and WSSV (whitespot). In the bioassay described here, no mortalities occurred until 13 days after exposure to IMNV. In similar bioassays with TSV, YHV and WSSV, significant mortality usually occurs within 1-3 days. The relatively long delay in mortalities from IMNV infections is possibly because skeletal muscle, the primary target tissue of IMNV infection, can withstand more damage than the other tissues before survival is threatened. Losses from IMNV infection, however, can be significant; over 40 percent mortality often occurs--late in the production cycle. In addition, reduction in market value of the survivors, which have necrotic tail muscles, adds to the economic loss.
Source: World Aquaculture (the quarterly magazine of the World Aquaculture Society, http://www.was.org). Editor-in-Chief, Robert Stickney. In situ hybridization demonstrates that Litopenaeus vannamei, L. stylirostris, and Penaeus monodon are susceptible to Infectious Myonecrosis Virus (IMNV). Kathy F.J. Tang, Carlos R. Pantoja, Rita M. Redman and Donald V. Lightner (Department of Veterinary Science and Microbiology, University of Arizona, Tucson, Arizona 85721 USA, fax 520-621-4899, email fengjyu@.arizona.edu). Volume 38, Number 1, Page 18, March 2007.
ที่มา
http://www.shrimpnews.com/FreeNewsBackIssues/FreeNewsApril200713.html
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สรุปว่า เจ้าโรค IMNV นี้ ดูจากอาการ จะบอกยากว่า เป็นโรคนี้หรือไม่ใช่ เพราะ กล้ามเนื้อขุ่นขาว สามารถเกิดขึ้นได้จาก การขาดออกซิเจน (ดังที่ผมได้เคยนำเสนอสาเหตุจากการที่กุ้งขาดออกซิเจนแล้วทำให้เกิดอาการกล้ามเนื้อขุ่นขาว ตามกระทู้นี้ครับ http://www.buildboard.com/viewtopic.php?topic=15549&forum=2202&id=176 ) การเปลี่ยนแปลงของอุณหภูมิ หรือ ความเค็มอย่างรวดเร็ว, การตรวจทางชิ้นเนื้อ (Histo) ก็ไม่จำเพาะเจาะจง แต่ที่อาจจะบอกได้ว่า เป็นโรคนี้ก็คือ กุ้งจะตายมากครับ ตายได้ถึง40-60%
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