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Porcine respiratory corona virus(PRCV) was first recognized in Belgium in 1984, when routine     serological     surveys     from slaughterhouses identified high liters to transmissible      gastroenteritis      (TGE). Retrospective studies of source farms did not indicate occurrence of enteric disease.   In Indiana, PRCV was most recently identified in May of 1995.

PRCV is a mutant of TGE corona virus. PRCV and TGE virus share antigenic sites, but TGE has additional antigenic sites which PRCV does not have because of a deletionalmutation. There are multiple strains of PRCV which have varied pathogenicity.

The various strains of PRCV have different affinities for the respiratory system tissue. In many cases, the damage does not result in clinical disease and the most virulent strains generally only result in mild clinical disease.

Grossly, PRCV pneumonia resembles other viral pneumonias. Generally, the cranial and middle lung lobes are affected and appear molded reddish-purple to tan. The pneumonia may become more severe if complicated by secondary bacterial infection.

Microscopically,   acute  infections  are characterized by necrosis of bronchial and bronchiolar epithelial cells. The healing stage is characterized by squamousmetaplasia of the epithelium. PRCV has been shown to infect epithelial cells lining the nasal cavity, trachea, bronchi, bronchioles, and terminal bronchioles.

PRCV usually infects nursery age pigs, immediately after they are weaned.   The infection is spread through aerosol or direct contact with nasal secretions from an infected animal in which virus is present for two weeks following infection.

Diagnosis of PRCV is a challenge. Because both PRCV and TGE share many antigenic sites, routine serology does not distinguish between the two. Suspicion of PRCV may be based on serological evidence in the absence of enteric disease.   At the PurdueADDL, a presumptive diagnosis of PRCV is made by positive FA for corouavirus in lung tissues, coupled with a negative FA on intestine and no evidence of diarrhea in the herd.   Virus isolation can be attempted from swabs of nasal mucosa. Use of monoclonal antibodies may distinguish between PRCV and TGE, but these are not commercially available at this time.

- Jennifer May, Class of 1996

- edited by Win. VanAlstine



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