Evaluation of the effects of animal age, concurrent bacterial infection, and pathogenicity of porcine reproductive and respiratory syndrome virus on virus concentration in pigs.
OBJECTIVE
To evaluate the influences of animal age, bacterial coinfection, and porcine reproductive and respiratory syndrome virus (PRRSV) isolate pathogenicity on virus concentration in pigs.


METHODS
Twenty-one 2-month-old pigs and eighteen 6-month-old pigs.


METHODS
Pigs were grouped according to age and infected with mildly virulent or virulent isolates of PRRSV. The role of concurrent bacterial infection was assessed by infecting selected pigs with Mycoplasma hyopneumoniae 21 days prior to inoculation with PRRSV. On alternating days, blood and swab specimens of nasal secretions and oropharyngeal secretions were collected. On day 21 after inoculation with PRRSV, selected tissues were harvested. Concentrations of PRRSV were determined by use of quantitative real-time PCR and expressed in units of TCID(50) per milliliter (sera and swab specimens) or TCID(50) per gram (tissue specimens).


RESULTS
Concentrations of virus were higher in blood and tonsils of pigs infected with virulent PRRSV. Pigs infected with virulent PRRSV and M hyopneumoniae had significantly higher concentrations of viral RNA in lymphoid and tonsillar tissue. Coinfection with M hyopneumoniae resulted in a higher viral load in oropharyngeal swab specimens and blood samples, independent of virulence of the PRRSV isolate. Two-month-old pigs had significantly higher viral loads in lymph nodes, lungs, and tracheal swab specimens than did 6-month-old pigs, independent of virulence of the PRRSV isolate.


CONCLUSIONS
Multiple factors affect PRRSV concentration in pigs, including pathogenicity of the PRRSV isolate, age, and concurrent infection with M hyopneumoniae.
Cho
Jenny G
JG
Swine Disease Eradication Center, College of Veterinary Medicine, University of Minnesota, Saint Paul, 55108, USA.
Dee
Scott A
SA
Deen
John
J
Guedes
Alonso
A
Trincado
Carlos
C
Fano
Eduardo
E
Jiang
Yin
Y
Faaberg
Kay
K
Collins
James E
JE
Murtaugh
Michael P
MP
Joo
Han Soo
HS
D000375:Aging / Q000502:physiology*; D000818:Animals; D045729:Pneumonia of Swine, Mycoplasmal; D019318:Porcine Reproductive and Respiratory Syndrome / Q000097:blood / Q000382:microbiology* / Q000821:virology*; D019316:Porcine respiratory and reproductive syndrome virus / Q000472:pathogenicity*; D013552:Swine / Q000382:microbiology / Q000502:physiology / Q000821:virology; D019562:Viral Load / Q000662:veterinary*; D014774:Virulence