Changes

BVDV can be transmitted from infected to susceptible cattle in several ways. Firstly, direct contact with a virus-shedding animal can cause disease. Both acutely and persistently infected animals shed virus, but levels of shedding are much higher in persistently infected cattle and transmission is more efficient. Transmission to heifers and cows may also occur venereally or via artificial insemination as acutely and persistently unfected bulls sheed bovine viral diarrhoea virus in their semen²⁴. The testes is an immunoprivileged site, and the virus can persist in this location despite otherwise systemic clearance²⁵. Indirect spread is possible: BVDV has been shown to spread through the re-use of needles, nose tongs²⁶ and rectal gloves²⁷, and blood feeding flies also give transmission.

BVDV can be transmitted from infected to susceptible cattle in several ways. Firstly, direct contact with a virus-shedding animal can cause disease. Both acutely and persistently infected animals shed virus, but levels of shedding are much higher in persistently infected cattle and transmission is more efficient. Transmission to heifers and cows may also occur venereally or via artificial insemination as acutely and persistently unfected bulls sheed bovine viral diarrhoea virus in their semen²⁴. The testes is an immunoprivileged site, and the virus can persist in this location despite otherwise systemic clearance²⁵. Indirect spread is possible: BVDV has been shown to spread through the re-use of needles, nose tongs²⁶ and rectal gloves²⁷, and blood feeding flies also give transmission.

Cattle that are persistently infected with noncytopathic BVDV serve as a natural reservoir for virus. Persistent infection develops when noncytopathic BVDV is transmitted transplacentally during the first 4 mo of fetal development. The calf is born infected with virus, remains infected for life, and usually is immunotolerant to the resident noncytopathic virus. Transplacental infection that occurs later in gestation results in abortion, congenital malformations, or birth of normal calves that have antibody against BVDV. The prevalence of persistent infection varies among countries and between regions within a country. In some areas, the prevalence of persistent infection in calves may be as high as 1-2% of cattle <1 yr of age. On a given farm, persistently infected cattle are often found in cohorts of animals that are approximately the same age. Persistently infected cattle can shed large amounts of BVDV in their secretions and excretions and readily transmit virus to susceptible herdmates. Clinical disease and reproductive failure often are seen after healthy cattle come in contact with a persistently infected animal. Biting insects, fomites, semen, biologic products, and possibly wild ruminants also can spread BVDV.

*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

**Are infected with BVDV-1nc and NEVER BVDV-1c

**Are often antibody-negative (though they can show low levels of Ab to ''heterologous'' virus)

***Increased susceptibility to enteric and respiratory disease

*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.

==Pathogenesis==

==Pathogenesis==