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Response to Questions and Concerns about BVDV
October 2005 – On March, 24, 2005 ARF held a special meeting to discuss the response to Bovine Viral Diarrhea Virus (BVDV). Two veterinary virologists were invited to participate. Dr. Donald Mattson of Oregon State University and Dr. Edward Dubovi, Cornell University shared their knowledge of testing and control of the spread of BVDV. The abbreviated minutes of this special BVDV meeting are available on the ARF website--alpacaresearchfoundation.org. Drs. Mattson and Dubovi are continuing to serve as consultants to ARF in the area of BVDV concerns.
Frequently Asked Questions About Bovine Viral Diarrhea Virus (BVDV):
1. Will vaccination of my alpacas protect my herd from BVDV infection? --No. Based on studies in cattle, we have to assume that vaccination of the dam does not prevent the birth of persistently infected (PI) crias, who will continue to spread the infection for their entire lives.
2. Can a cria that is persistently infected with BVDV in utero develop antibodies later in life and fight its own infection? -- No. A cria that was exposed to a particular strain of BVDV in utero during the time when it did not recognize the virus as foreign (first trimester in cattle) will never develop antibodies to that strain even when it becomes immunocompetent, although it may develop antibodies to other strains.
3. Will antibodies in the dam's milk be effective against the virus in the persistently infected cria? -- No. Colostral antibodies will not cure the PI cria.
4. If my cria appears healthy can I be sure it is not persistently infected with BVDV? -- No. While most PI crias appear sick, some do not show any clinical signs of disease and may in fact grow to be adults that continue to shed the virus.
5. How can I determine if my herd is virus free? --Consult with your veterinarian and develop a plan that best suits your herd's needs. Testing methods can be found on the ARF website www.alpacaresearchfoundation.org under BVDV census. In the next few months you may be asked to participate in an ARF funded research study that will offer you free and confidential testing for BVDV. The study will help us to determine the prevalence of BVDV in North American alpaca herds. Please plan to participate whether or not you have had your herd tested previously.
6. What should I do if one of my alpacas is found to be persistently infected with BVDV? --All PI animals must be euthanized to prevent further spread of the virus.
On May 1, 2005 ARF sent out an RFP to all Colleges of Veterinary medicine in the United States and Canada to determine the prevalence of BVDV in North American alpaca herds. Four proposals were received on Sept 1st. They are currently under review with funding to start on Nov 1st. If you receive a request for samples from your alpacas to test for prevalence of BVDV in your herd, it is very important that you respond. The larger the response, the faster we can determine the significance of a BVDV problem and set up appropriate measures to control it.
ARF is also keeping a census of confirmed cases of BVDV on the ARF website. Cases are identified by region according to the AOBA Farm and Ranch guide. If you or your designee wish to report a confirmed case of BVDV, the information will be kept strictly confidential. Contact Alan (Abe) Rosenbloom--aar@pinehurst.net for additional information.
For Immediate Release
DIAGNOSTIC TESTS AND PROCEDURES FOR ALPACAS
PERSISTENTLY INFECTED WITH BOVINE VIRAL DIARRHEA VIRUS
By Patricia Craven, PhD
October 2005 -- An alpaca that was persistently infected (PI) with bovine viral diarrhea virus (BVDV) has been recognized recently in Canada. Some cases have been diagnosed in the USA and there is much concern among alpaca producers as to the proper methods and procedures used to identify this condition. Since this is a relative new challenge for the camelid industry, diagnosticians, and veterinarians who serve this industry do not have a great deal of experience dealing with this problem. Accordingly, we must use the information gathered from cattle in establishing criteria for making a diagnosis.
Tests used for detecting BVDV
Virus isolation (VI) is the gold standard for detecting BVDV. Serum, white blood cells (WBCs), and tissue from infected animals taken at necropsy can all be used for VI. While feces from an animal with diarrhea may appear to be a good sample, there are a number of reasons why this material is not satisfactory. After a sample is received and processed, it is inoculated into cell cultures and virus allowed to replicate. Other procedures are used to detect presence of virus. This test is very sensitive for identifying virus-infected animals if samples are taken properly.
Polymerase chain reaction (PCR) is also a commonly used test for diagnosing BVDV. The same types of samples as listed for VI can be submitted for this test. However, the sample is tested directly without first replicating the virus in cell cultures. The PCR test reacts with a specific segment of the viral genetic material. Since it is so sensitive, it is more prone to giving a false-positive reaction. However, diagnostic laboratories go to great lengths to control this problem; very rarely is a false diagnosis made. It is a very rapid test with results available within a day after the sample is processed.
The enzyme-linked immunosorbent assay (ELISA) test is used by some diagnostic laboratories; the test identifies antigens of the virus. Similar samples as listed for VI are used with the ELISA test. In addition, this test can be used to detect virus from skin biopsies. It is a moderately sensitive test and results can be obtained in a rapid fashion.
The immunohistochemical (IHC) staining test is used extensively in identifying viral antigens in infected cells. As virus replicates in the animal and gains access to the blood, (a characteristic of PI animals), it infects a number of cell types including cells in the skin and hair follicles. When a sample is subjected to IHC staining and viewed with a microscope, virus-infected cells can be identified. This test is used extensively in identifying PI cattle. However, a low percentage of animals undergoing an acute infection with BVDV (and are not PI) may give positive test results for a variable period of time after the acute infection is over. One form of the IHC test is called the immunoperoxidase test or IPX.
Procedures for detecting PI animal using the above-listed tests
A blood sample is taken and placed in a tube with an anticoagulant. In the laboratory, white blood cells (WBCs) or serum are separated and examined for presence of virus. Tests used for this procedure include VI, PCR or ELISA. This initial procedure will detect virus from acutely infected as well as PI animals. A second sample must be submitted 3 to 4 weeks later. An acutely infected animal will test negative on the second sample while a PI animal will remain positive. This is the traditional method for identifying PI animals.
A skin biopsy is taken, placed in formalin, and sent to the laboratory where it is subjected to IHC staining. If virus-infected cells are observed and the animal shows typical disease signs of being PI, many veterinarians will make a diagnosis on this basis. This is often the practice when dealing with bovines. However, to verify that the animal was not just acutely infected and viral antigens lingered in skin cells, a second confirmatory test should be submitted. A confirmatory test consists of submitting a blood sample (serum or WBCs) 3 to 4 weeks later and testing for virus by VI, PCR, or ELISA.
There is a third procedure that has been used to identify PI bovines. It consists of a skin biopsy that is refrigerated, sent to the laboratory and subjected to ELISA testing. This procedure just demonstrates presence of virus in the sample so a second confirmatory test, as listed for IHC, should be taken 3 to 4 weeks later. Continued presence of virus confirms a PI diagnosis.
Comments and Recommendations
Diagnosis of a PI alpaca is an important issue. It has far-reaching implications in that the animal readily sheds virus to other members of the herd where it can induce a variety of disease conditions. Of special concern is the pregnant animal that becomes infected and passes the PI condition to its fetus. It should be noted that a fetus is vulnerable to becoming PI only during a certain phase of its development. Generally, this period starts when the embryo implants onto the uterus and continues to just a little over the end of the first trimester. An animal can not develop the PI condition at any other time.
The Veterinary Diagnostic Laboratory at Oregon State University has recently tested a PI alpaca using the IHC skin testing protocol. The veterinarian submitted skin from both an ear notch (a common practice with bovines) and a region of the skin ventral and laterally from the rectum (perineal area). Both samples were strongly positive. With the understanding that alpaca owners will not want to take notches from the ear of their animals, this serves to verify that skin samples may be taken in locations other than the ear. A sample taken from the perineal area would not disfigure the animal.
We must address the issue of PI animals openly and aggressively. This problem may or may not be a major issue with camelids. If it is a problem, the more aggressively we diagnose cases the less impact it will have. It is hoped that detecting a PI animal and controlling spread of the virus will not blemish the reputation of any specific producer. In fact, it should serve to identify those individuals who are progressive leaders in health issues related to their animals.
To learn more about the Alpaca Research Foundation and to review ARF’s funded studies; please visit our website at www.alpacaresearchfoundation.org.
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The Alpaca Research Foundation is a non-profit corporation for charitable, educational and scientific purposes. The Board of Directors is comprised of a select group of camelid veterinarians, research scientists and medical professionals. Their job is to establish research goals and critically evaluate research proposals from qualified research scientists.
The mission of the Alpaca Research Foundation is to encourage and support scientific research which benefits the North American alpaca industry, primarily in the areas of alpaca health and husbandry, genetics and fiber. For more information, visit our website at www.alpacaresearchfoundation.org.
The ARF Board of Directors extends a note of thanks to ARI, AOBA and all the alpaca owners and breeders who have demonstrated how much they really care for these wonderful creatures that have given us so much, by donating generously to the Alpaca Research Foundation.
The Alpaca Research Foundation provides this news release to be used by AOBA Affiliates only. This information may be reproduced in affiliate newsletters to provide further education to your members. All other organizations or publications must receive permission by the ARF Board to reproduce any or all parts of this news release. We thank you for your cooperation.
If you have any questions, please contact the following ARF Development Committee members via email:
ARF News Release: Naomi E. Flam, Astral-Light Alpacas, LLC; naomiflam@comcast.net or
Kerry Anderson, A Star Alpacas; kka119@aol.com.
ARF Research Questions & Information: Patricia Craven, Ph.D., Cherry Ridge Alpacas; alpacas@ptd.net
ARF Donations & Sponsorships: Patrick Long, DVM, (541) 752-3786; lama _dr@msn.com
Scheduling an ARF presentation at your ranch: Peter Canning, Summit Suri Alpacas; summitsuris@kc.rr.com
To join the ARF Development Committee: Kerry Anderson, A Star Alpacas; kka119@aol.com.
Alpaca Research Foundation Board Of Directors
President: Patricia Craven, Ph.D.; Cherry Ridge Alpacas, Creekside, PA
Vice-President: Randy Larson, DVM; Kalmar Kolors Alpacas, Alpha, IL
Secretary: Roxanna Smolowitz, DVM; Coonamessett Farm, E. Falmouth, MA
Treasurer: Patrick Long, DVM; Eastgate Veterinary Clinic, Corvallis, OR
Director: Karen Baum, DVM; Little Doc’s Veterinary Care, Huddleston, VA
Director: Allan Dewald, MD; Alpacas of Canyon Ridge, Rapid City, SD
Director: Alan (Abe) Rosenbloom, MD; Black Tulip Farms, Siler City, NC
Written by Patricia Craven, PhD
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