Difference between revisions of "Bovine Virus Diarrhoea"

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#REDIRECT[[Bovine Viral Diarrhoea Virus]]
 
 
{{toplink
 
|linkpage =Viruses
 
|linktext =VIRUSES
 
|sublink1=Flaviviridae
 
|subtext1=FLAVIVIRIDAE
 
|pagetype =Bugs
 
}}
 
<br>
 
 
 
 
 
 
 
====Antigenicity====
 
*RNA virus closely related to [[Classical Swine Fever]] and [[Border Disease Virus]]
 
*2 Serological Types
 
**BVDV-1 is traditional, existing as two biotypes
 
***BVDV-1nc: noncytopathogenic
 
***BVDV-1c: cytopathogenic
 
**BVDV-2 is an emerging hemorrhagic virus
 
 
 
====Hosts====
 
*Cattle
 
 
 
====Pathogenesis====
 
[[Image:BVD-MD.gif|right|thumb|125px|<small><center>Small erosions of MDV/BVDV - vesicles are microscopic (Courtesy of Alun Williams (RVC))</center></small>]]
 
[[Image:Bvd2.gif|right|thumb|125px|<small><center>Coalescing lesions of BVDV (Courtesy of Alun Williams (RVC))</center></small>]]
 
'''BVDV-1c'''
 
*Infects cattle regardless of age
 
*Usually mild: diarrhoea with recovery in 10 dyas
 
*Immunosuppression can lead to secondary infection
 
'''BVDV-2nc'''
 
*Transient '''thrombocytopenia''' and '''leukopenia'''  over 2 weeks
 
*Hemorrhages
 
*Secondary infection
 
*Death
 
'''BVDV-1nc'''
 
*'''Transplacental''' infection of naive heifers
 
*Outcome depends on age of fetus at contraction
 
**0-110 days: '''abortion''' or '''persistently infected (PI)''' calves born
 
**110-220 days: congenital damage with noticeable '''CNS''' and '''musculoskeletal''' lesions
 
**220 days to term: '''active immunity''' developed
 
'''Mucosal Disease'''
 
*Mucosal disease is caused by a '''superinfection''' of PI animals with a second homologous cytopathic biotype (eg BVDV-1nc followed by BVDV-1c)
 
*Infection typically occurs between '''6-18 months of age''' but is variable
 
*Superinfection will quickly '''spread horizontally''' among PI animals
 
*Invariable '''fatal'''
 
*Characterized by [[Cavity & Gingiva - Pathology#Bovine Viral Diarrhoea / Mucosal Disease|'''oral]] and enteric erosions''', particularly overlying Peyer's patches, and ulceration of the feet
 
*Animals can show anorexia, depression and/or diarrhoea for 2-5 days before death
 
*Vaccination can lead to '''iatrogenic''' infection in undiagnosed PI calves
 
 
 
====Epidemiology====
 
*A major concern is that it can be confused with [[Foot and Mouth Disease (FMDV)|FMD]] (especially as it often occurs with clinical signs of salivation and depression)
 
*Virus is widespread: 60-70% exposure by 4 years of age
 
**Often may sweep through a whole colony of young stock causing profuse diarrhoea (perhaps febrile) for a few days and then recover
 
**Due to primary exposure to cytopathic strain of virus
 
*PI cows:
 
**100% vertical transmission to offspring
 
**Are infected with BVDV-1nc and NEVER BVDV-1c
 
**Are often antibody-negative (though they can show low levels of Ab to ''heterologous'' virus)
 
**Show a wide range of clinical signs:
 
***Severe congenital damage (ataxia)
 
***Poor body condition
 
***Increased susceptibility to enteric and respiratory disease
 
**Act as the herd '''reservoir''' of BVDV
 
**Can ONLY be identified by blood testing
 
*Transfer via '''semen''', '''direct contact''' with acutely infected animals, or vertical from dam to offspring
 
*Transfer can be iatrogenic: repeated use of needles and gloves, etc.
 
 
 
====Diagnosis====
 
*Traditional test: virus isolation followed by serology on infected cells
 
*'''ELISA''' for virus '''antigen''' in animals with persistent viremia (will show up 3-8 days post-infection)
 
*PI calves often appear virus negative as a result of receiving neutralizing Ab in colostrum: can be countered by RT-PCR
 
*'''Paired serum samples''' from cows with acute BVDV
 
*'''Herd sampling''' by ELISA for antibody on bulk milk
 
 
 
====Control====
 
*No known treatment to reverse persistent infection or to cure mucosal disease
 
*BUT, without exposure to BVDV, the whole herd is at risk as there is no developed immunity
 
*'''Vaccination of dams''' before pregnancy will prevent PI calves being born
 
**'''Beta-propiolactone inactivated''' vaccine
 
**Combine with screening for antigen and removal of PI animals
 

Latest revision as of 15:59, 25 May 2010