Bovine Viral Diarrhea Virus

Genus: Pestivirus

Family: Flaviviridae

virusintro
BVDV immunoabsorbed to micro-carrier
Heinrich Pette Institue of Experimental Virology
www.hpi-hamburg.de

Viral Characteristics

 

 Bovine Viral Diarrhea (BVD) and Mucosal Disease (MD) are two diseases caused by the Bovine Viral Diarrhea Virus (BVDV), a member of the Pestivirus genus of the family Flaviviridae. To date, three species of pestiviruses are recognized: BVDV, Hog Cholera Virus, and Border Disease Virus (Coetzer and Tustin, 2004).

 

Morphology

 

Bovine Viral Diarrhea Virus is a single stranded RNA virus with positive polarity. Virions are spherical particles that measure approximately 50nm in diameter and are encapsulated by a tightly adherent envelope containing glycolipids (Coetzer and Tustin, 2004). Due to the lipid rich envelope surrounding each virion, the virus is susceptible to many common disinfectants.  Structural proteins of the virus are encoded by the first third of the viral genome, whereas non-structural proteins are encoded by the last two thirds. The E2 structural protein, one of numerous surface glycoproteins, is the major target of virus-neutralizing antibodies (Coetzer and Tustin, 2004).   

virion

www.expasy.org

Bovine Viral Diarrhea Virus exists as one of two biotypes that are identified in the laboratory: Non-cytopathic isolates and Cytopathic isolates. 

Non-Cytopathic Biotypes

 

Non-cytopathic biotypes represent the majority of BVDV isolates collected from the field and do not affect the integrity of cultured cells (Murphy et al, 1999).  It is important to note that non-cytopathic viruses are still pathogenic however they cannot cause overt pathological changes in affected cells.  This is important diagnostically because infected cells may appear normal. Non-cytopathic biotypes are the most important economincally because they are capable of crossing the placenta and producing persistently infected (PI) calves (Deregt and Loewen, 1995). The immune system of PI calves is unable to recognize the virus as foreign and thus will not mount an immune response, allowing for continual shedding of the virus without clinical signs of infection. Non-cytopathic isolates in PI animals are capable of mutation to cytopathic forms that cause severe mucosal disease (Deregt and Loewen, 1999).

Cytopathic Biotypes

cytopath
 

Cytopathic isolates are most often collected from animals with mucosal disease and will alter the integrity (or cause death) of cultured cells. Cultured cells may appear vacuolated (see photo).  The viral protein NS3 is considered its molecular marker (Coetzer and Tustin, 2004).  Unlike non-cytopathic isolates, it cannot cross the placenta to cause PI calves.  However, cytopathic isolates may mutate from non-ctytopathic isolates and cause mucosal disease in PI calves. 

Genotypes

 

In addition, two genotypes of BVDV  (BVDV1 and BVDV2) are identified, within which non-cytopathic and cytopathic isolates exist. Recent studies show that genotype 2 isolates are more virulent than genotype 1 (Deregt and Loewen, 1995).  Severe disease is most often caused by non-cytopathic BVDV-2 and is therefore used for the manufacture of most commercial vaccines.


           

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