BOVINE VIRUS DIARRHEA (BVD)
Bruce R. Hoar, School of Veterinary Medicine, Department of Medicine and
Epidemiology, University of California, Davis
Bovine virus diarrhea (BVD) is a complicated dia to discuss as it can result in a wide variety of dia problems from very mild to very vere. BVD can be one of the most devastating dias cattle encounter and one of the hardest to get rid of when it attacks a herd. The virus that cau BVD have been grouped into two genotypes, Type I and Type II. The dia syndrome caud by the two genotypes is basically the same, however dia caud by Type II infection is often more vere. The various dia syndromes noted in cattle infected with BVD virus are mainly attributed to the age of the animal when it became infected and to certain characteristics of the virus involved. Dias caud by BVD infection高中英语学习方法
Fetal BVD infections (infection of the unborn calf): The result of a fetal infection with the BVD virus is usually determined by the age of the fetus at the time of
infection. The virus is capable of passing from an infected cow to the unborn fetus which is particularly vulnerable to the BVD virus during the first 6 months of
pregnancy. Death of the fetus is common if the infection occurs during the first
120 days of pregnancy and the cow will lo the pregnancy. However, if the fetus survives an early infection, it will be born without a detectable antibody titer and
be persistently infected (PI) with the BVD virus. During the first 120 days of
gestation, the fetus has an underdeveloped immune system and does not recognize the BVD virus as foreign. The fetus does not mount an immune respon against
the virus, remains infected, and does not have a detectable anti-BVD titer. It is not uncommon for the surviving fetus to be malformed; blindness, skeletal
abnormalities and under-developed brains are common defects noted in such
calves. A BVD PI calf may appear normal, be weak at birth, grow poorly, be
susceptible to respiratory dias, and die before they can be weaned. They may also grow normally, reach breeding age, and produce more persistently BVD infected calves (The virus is pasd from generation to generation). PI carriers
can only be created by infection with BVD virus during the first 110-120 days of pregnancy. The animals shed billions of virus particles every day in their urine, feces, and saliva, and are a source of infection for other animals in the herd. If the fetus becomes infected after 120 days of pregnancy, there may be an abortion but usually, becau this aged fetus has a more developed immune system and can垂钓中心
elicit an immune respon against the BVD virus, a healthy calf is born that has a good level of BVD antibody titer.
Subclinical BVD infections: Most animals that become infected with BVD never show signs of dia caud by the virus; however infection can lower the
animal’s resistance to other infections, which could result in illness. For example, in feedlot calves, BVD infection may go unnoticed, but the lungs become
susceptible to infection with bacteria such as Mannheimia haemolytica
(previously called Pasteurella haemolytica) and other agents that cau “shipping fever”. Some people believe that BVD is one of the most significant dia
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organisms involved with respiratory dia of cattle.
Severe acute BVD infections: This dia syndrome is usually (but not always) associated with Type II BVD virus infection. The affected animals will exhibit
high fevers (107-110 F), occasional diarrhea, respiratory dia, and they will not eat. Peracute BVD can affect cattle of all ages and often results in death of the
animal within 48 hours of dia ont regardless of age.
Acute BVD infections: The classic, acute form of BVD is characterized by a
fever of 104-106 F, discharge from the no and eyes, erosions of the muzzle and in the mouth, and diarrhea that may contain mucus and blood. Diarrhea is usually prent in every herd that has an outbreak of acute BVD, but diarrhea is not
prent in every animal that has acute BVD. The percentage of the herd exhibiting clinical dia and dying can vary extremely; however, if "condary infections"
are controlled, most animals survive the acute dia. This syndrome usually
occurs in cattle 6 to 24 months of age.
Acute Mucosal dia: An animal persistently infected with BVD virus is not
able to mount any defen against becoming subquently infected with a
different BVD virus. When a BVD infection is superimpod on a PI animal,
mucosal dia usually results. Acute mucosal dia is characterized by fever, profu, watery diarrhea, erosions of the mouth, lack of appetite, discharge from
the eyes and no, and occasionally lameness. Secondary infections, such as
pneumonia and mastitis, are common. Cattle with acute mucosal dia usually
die within 3 to 10 days.
Chronic Mucosal dia: Some cattle that develop mucosal dia do not die
as soon as expected but rather become chronically infected. Cattle with chronic
mucosal dia are poor doers, and may have persistently loo stools or
intermittent diarrhea, chronic bloat, decread appetite, weight loss, erosions
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between the claws, or non-healing skin lesions. Discharge from the eyes and no, bald spots due to loss of hair, and long-term lameness are also common. Cattle
with chronic mucosal dia rarely survive beyond 18 months and ultimately die. Treatment and Prevention of BVD infections
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There is no effective treatment for infection with BVD, but most cas are subclinical and lf-limiting. Antibiotics, fluid and supportive therapy may be indicated to control condary infections. Offering highly palatable feed could tempt sick animals to eat needed nutrients. Vaccination of susceptible cattle has been the principal approach to the prevention and control of BVD. However, preventing the introduction of BVD into your herd and identifying and eliminating PI animals from your herd are important steps to take to control the dia.
Vaccinate calves: Calves should be vaccinated twice with a modified live virus (MLV) vaccine before leaving the herd of origin. Ideally, BVD vaccinations should be completed in the calves at least 30 days prior to weaning, but whatever program you initiate needs to fit with your management system. Check with your veterinarian for specific recommendations for your herd.
Vaccinate the cow herd: It is difficult to provide blanket recommendations for vaccinating the cow herd, but some general guidelines can be given. Unvaccinated heifers and cows should be properly vaccinated before breeding to ensure protection for the fetus. All bulls should be properly vaccinated before putting them out with the cows or heifers and new additions should be properly vaccinated before adding them to the herd. Modified live virus vaccines can be safely ud in open cows (there are new MLV
vaccines safe for pregnant cows if the cows have been previously vaccinated with certain products) and provide long-lasting protection. Killed vaccines are safe for all cattle, but usually don’t provide as strong an immune respon and may need more frequent booster vaccinations. Again, check with your veterinarian for specific recommendations.
Prevent introduction of BVD into your herd: BVD virus is shed from cattle in the feces and in cretions from the no and mouth. BVD is also readily transmitted by aerosol droplets and direct contact. Avoiding contact with other cattle is therefore an important step to take to prevent infection from entering your herd. “Good fences make good neighbors”. It is especially important to keep pregnant cows less than 120 days pregnant parated from other cattle. New introductions into your herd need to be tested for PI status.
Eliminate PI animals from your herd: Until recently, testing cattle for PI
infection was prohibitively expensive but now there are tools available making it feasible to test for and eliminate the “typhoid Mary” animals from the herd. There are two types of test available, one using a skin sample and one using a blood sample:
Immunohistochemistry – for this test, a small notch of skin is taken from the edge of the ear, easily done using a pig ear-notching tool. The triangular piece of skin removed
should be ¼ to ½ inches per side. Depending on the laboratory the sample will be nt to, the removed skin is placed either in a vial containing formalin or an individual plastic bag. All samples must be clearly labeled with the animals’ identification number. PCR – this test requires that a blood sample in a “purple top” tube be taken and
submitted. Again, all samples must be clearly labeled with the individual animal ID. Samples can be nt to a number of different laboratories; three are listed below. Be sure to contact the lab and talk to your veterinarian before taking and nding samples – if you take the wrong samples, all your work may be wasted. Be aware that it is possible to have “fal positive” results – some animals may test positive when they are not truly
persistently infected, and may need to be re-tested. Your veterinarian can help interpret the results of the testing. (Thank you to Dr. John Maas for the following information)
1. Tulare branch of the California Animal Health & Food Safety Laboratory (CAHFS)
(559)
688-7543
CAHFS-Tulare Phone
18830 Road 112 Fax (559) 686-4231
Tulare, CA 93274
Sample description: Ear notch (triangle notch ¼ to ½ inch per side) in zip lock bag (or whirl pack bag). Refrigerated—not frozen. Ship overnight (not for Saturday arrival). Technique: Immunohistochemistry.
Cost: $16.50 per 1-5 samples, i.e. $33.00 for ten (10) samples and $33.00 for 6 samples. Additional one time accession fee is also charged.
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2. University of Nebraska, Lincoln, NE爱国英雄事迹
(402)
472-1434
Phone
Center
Diagnostic
Veterinary
Nebraska Fax
472-3094
(402)
University
of
Fair Street and East Campus Loop
P. O. Box 82646
Lincoln, NE 68501-2646
Sample description: Ear notch (triangle notch ¼ to ½ inch per side) in neutral-buffered formalin. Leak proof tubes are mandatory for containers. Do not hold skin samples in formalin for more than 7 days prior to submission.
Technique: Immunohistochemistry.
Cost: Accession fee: $7.00 per each shipment (submission). First sample: $12.00. Two (2) to 6 samples: $20.00, multiples of 6: $20.00/six samples.
3. Davis branch of CAHFS.
752-7578
CAHFS-Davis
(530)
Phone
University of California, Davis Fax (530) 752-6253
West Health Sciences Drive
Davis, CA
Sample description: whole blood, refrigerated (not frozen). Ship in leak proof containers on ice bags (gel bags).
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Technique: PCR.
Cost: $22.70 for the first sample, $5.65 per each sample after the first. Additional one time accession fee is also charged.
