Changes

====Mucosal Disease====

====Mucosal Disease====

 

Mucosal disease  is an invariably fatal condition of 6-18 month-old cattle⁴³. Disease follows a course of several days to weeks, and intially presents as pyrexia, depression and weakness. Anorexia leads to emaciation, and animals suffer profuse, watery, foul-smelling and sometimes bloody diarrhoea. Dehydration ensues. As suggested by the name, lesions are localised to mucosal surfaces. These include the oral mucosa, tongue, external nares,nasal cavities and conjunctiva³⁴, where large lesions  cause excessive salivation, lacrimation, and oculo-nasal discharge.  The coronet and interdigital surface are also affected, causing the animal to become disinclined to walk and eventually recumbent.  Figure 1.5 shows examples of tongue and small intestine lesions.

Mucosal disease  is an invariably fatal condition of 6-18 month-old cattle⁴⁴. Disease follows a course of several days to weeks, and intially presents as pyrexia, depression and weakness. Anorexia leads to emaciation, and animals suffer profuse, watery, foul-smelling and sometimes bloody diarrhoea. Dehydration ensues. As suggested by the name, lesions are localised to mucosal surfaces. These include the oral mucosa, tongue, external nares,nasal cavities and conjunctiva³⁴, where large lesions  cause excessive salivation, lacrimation, and oculo-nasal discharge.  The coronet and interdigital surface are also affected, causing the animal to become disinclined to walk and eventually recumbent.  Figure 1.5 shows examples of tongue and small intestine lesions.

MD occurs when animals persistently infected with noncytopathic BVDV are superinfected with an antigenically similar cytopathic strain. Cytopathic virus arises from the persistent noncytopathic virus by mutation (see 1.1.4), and may then be transmitted to cause MD in animals PI with the same noncytopathic strain. Immunotolerance induced by the noncytopathic strain prevents superinfecting virus being recognised by the immune system; the biotypes are “homologous” to the immunotolerance (Brownlie, 1990). “Heterologous” superinfection with a non-related cytopathic biotype causes an antibody response and mucosal disease does not usually occur.

MD occurs when animals persistently infected with noncytopathic BVDV are superinfected with an antigenically similar cytopathic strain. Cytopathic virus arises from the persistent noncytopathic virus by mutation (see 1.1.4), and may then be transmitted to cause MD in animals PI with the same noncytopathic strain. Immunotolerance induced by the noncytopathic strain prevents superinfecting virus being recognised by the immune system; the biotypes are “homologous” to the immunotolerance (Brownlie, 1990). “Heterologous” superinfection with a non-related cytopathic biotype causes an antibody response and mucosal disease does not usually occur.