Porcine respiratory corona virus(PRCV) was first recognized
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
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
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