BVDV Flashcards
What is etiological agent of BVDV and route of transmission?
The etiological agent is a RNA virus that is a pestivirus of the family flaviridae called Bovine Virus Diarrhea virus. The virus is highly mutable and can be classified according to genotype (BVDV type 1 causes classic disease; BVDV type 2 causes mucosal disease) and activity in cell culture (cytopathic that cause damage to cells; and non-cytopathic that do not damage the cells). The routes of transmission include direct ingestion or contact of mucosa or abraded skin with saliva, nasal secretions, urine, feces, milk, semen, and mucus discharge containing the virus. The disease can also transmitted transplacentally and venereally. Transmission through aerosol over short distances have been reported.
What are the clinical presentations of BVDV?
BVDV have clinical presentation that will vary according to pregnancy status of the cow, stage of the gestation, and if the infection is transient or persistent. If a open cow is transiently infected with BVDV the virus will compromise immune system ability to perform phagocytosis, will reduce antibody receptor, antimicrobiano activity and presence of cytokines such as TNF-alpha IFN-gamma, which will lead to thrombocytopenia, neutropenia, immunosuppression, acute diarrhea, and acute death. However, in most cases the immune system will contain the virus and eliminate the infection in two weeks. If a cows is transiently infected with BVDV type when she is pregnant in the first two months of gestation the expected outcome is early embryonic or fetal loss. If a cow is transiently infected with BVDV types when she is pregnant between 2 and 4 months of pregnancy before calf immune system develop the calf might become a persistent infected calf. If a cow is persistently infected with BVDV types when she is pregnant between 100 and 150 days of pregnancy (during organogenesis) congenital defects such as cerebelar hypoplasia, hydrocephalus, hydranencephaly, spinal cord hypoplasia, microcephaly, and poroencephaly and variety of ocular changes as cataracts, optic neuritis, retinal degeneration, and microphtalmia might be present. If a cow is transiently infected with BVDV when she is pregnant between after 6 months of pregnancy weak to normal calves might born or occasional abortion might occur. If a persistent infected cows is infected with non cytopathic virus a persistent infected calf will be born. If a persistent infected cows is infected with cytopathic virulent strain mucosal disease will occur leading to severe diarrhea, high fever, lesions on nose, mouth, and mucosa, emaciation, sudden death.
Which sample can be collected and what method can be used to diagnosis BVDV?
A routine method use for sample collection for BVDV is the collection of an ear notch sample that can be used for diagnosis through immunohistochemistry (IHC). The IHC is highly sensitive and specific test. In adult animals virus isolation (VI) in serum would the more accurate method, but is not practical for a herd because the long turn around. Another method called immunoperoxidase microliter plate (IPMA) that is adaptation of VI can be used to screen herds. Real-time PCR (RT-PCR) can be used with skin, blood, serum and milk samples to screen herds. RT-PCR is sensitive, but not specific therefore positive results need to be confirmed with VI. Enzyme-linked immunoabsorbent assay (ELISA) is used to test individual blood samples for BVDV antigen.
What is the methods to control a BVDV in a herd?
The disease can be controlled mostly through a strict vaccination program and identification and culling of persistent infected animals, which can be described as biocontainment. A comprehensive biosecurity program can help maintain BVDV controlled in a herd. A strict vaccination program that can be used include vaccination of calves with modified-live vaccine with BVDV type 1 and 2 starting at 3 months of age with boost given 6, and 12 months of age. Then vaccinate each 6 months for heifers and for lactating dairy cows two-months after calving and at time of dry-off. For beef cows that are nursing vaccinate before the next breeding season and the time of weaning calves. All calves born in farm should have a ear notch collected and send for IHC. Biosecurity components of controlling BVDV include testing all purchased animals and preferably quarantine before exposure to other animals; keep herd closed; use only semen from reputable sources certified free for the virus; maintain good fences.
