Experimental Porcine Reproductive and Respiratory Syndrome Virus Infection in One-, Four-, and 10-Week-Old Pigs

Abstract

Abstract. One-, 4-, and lo-week-old pigs were exposed to porcine reproductive and respiratory syndrome virus (PRRSV) to determine the effect of age on clinical signs, hematologic alterations, the onset and duration of viremia, routes of virus shedding, antibody production, and microscopic lesions produced by PRRSV isolate ATCC VR-2332. The response to PRRSV infection was similar among age groups. Fever, usually prolonged, and a marked dyspnea with cutaneous erythema when restrained for sample collection were the most consistent clinical signs. Prolonged periocular edema was unique to the l-week-old pigs. The white blood cell count was decreased on day 4 postexposure (PE) due to decreases in neutrophils and lymphocytes. The virus was isolated from buffy coats at day 1 PE and was isolated from serum, buffy coat, or plasma at each sample collection period through the end of the trial (day 28 PE). Virus was most consistently isolated from lung, lymph node, spleen, and tonsil on day 7 PE and exclusively from lymph node, spleen, and tonsil on day 28 PE. Virus was infrequently isolated from urine and fecal and nasal swabs. Consistent microscopic changes in all age groups included interstitial pneumonia and lymph node hypertrophy and hyperplasia on days 7 and 28 PE, lymph node necrosis on day 7 PE, and subacute mononuclear myocarditis on day 28 PE. Findings presented here indicate that interstitial pneumonia, lymphoid necrosis, and mononuclear myocarditis are characteristic lesions of PRRSV isolate ATCC VR-2332 infection in 1-, 4-, and lo-week-old pigs.Porcine reproductive and respiratory syndrome (PRRS), a recently emerging disease of swine, causes pneumonia and late term abortion characterized by stillborn pigs, partially autolyzed fetuses, and weak live-born pigs. [8][9][10][11][14][15][16]18,24,25 In conventional pigs, this virus causes fever, marked dyspnea ("thumping"), flulike signs, and an increase in pneumonia from opportunistic bacteria. ll,14,l6,18 Clinical signs in PRRS virus (PRRSV)-infected gnotobiotic pigs are inappetence, fever, diarrhea, hyperpnea, dyspnea, and rough hair coats.9 Clinical signs of the disease are reported to be more severe in neonatal pigs. The disease is caused by a positive-strand enveloped RNA virus closely related to lactate dehydrogenase-elevating virus (LDEV), equine arteritis virus (EAV), and simian hemorrhagic fever virus (SHF) and will probably be classified in the family Arteriviridae. 4,17,20 To determine the effect of age on disease, l-, 4-, and 10-week-old pigs were intranasally exposed to PRRSV. Hematologic alterations, onset and duration of vireFrom the Departments of Veterinary Diagnostic Medicine (Rosmia, routes of virus shedding, antibody production, and gross and microscopic lesions were evaluated. Materials and methodsAnimals. Thirty-two pigs (16 4-wk-old pigs and 16 10-wk-old pigs) and 2 sows with litters (each litter containing 9 1-wk-old piglets) were obtained from a swine herd seronegative for PRRS. The source herd was also seronegative for antibodies to pseu...

Characterization of Emerging European-Like Porcine Reproductive and Respiratory Syndrome Virus Isolates in the United States

“…Infection was confirmed by a direct fluorescent antibody test on macrophages removed (scraped) from the well, air dried on glass slides, fixed in acetone, and reacted with monoclonal antibody (MAb) conjugate against the N protein (40). When possible, U.S. and European isolates of PRRSV were propagated on MARC-145 cells as previously described (3,28,57).…”

Persistence of Porcine Reproductive and Respiratory Syndrome Virus in Serum and Semen of Adult Boars

“…VI of PRRSV from tissues and serum was performed as previously described, 17 except MARC-145 cells 9 were used for propagation and 2% horse serum was utilized in the replacement media. If cytopathic effects (CPE) were observed, the presence of virus was confirmed by a direct fluorescent antibody technique using the SDOW17 monoclonal antibody.…”

Characterization of the carrier state in porcine reproductive and respiratory syndrome virus infection

“…VR-2332 was initially isolated in Minnesota, USA in association with a clinical outbreak of PRRS (Collins et al, 1992). Rossow et al (1994Rossow et al ( , 1995 has previously described the clinical course and lesions produced by infection with VR-2332 in young pigs. The virus was purchased from a commercial vendor (American Type Culture Collection, Manassas, VA, USA) and used after passage in MARC-145 cells, a highly permissive clone derived from the African monkey kidney cell line MA-104 (Kim et al, 1993 CO2 atmosphere, after which the cells were subjected to one freeze-thaw cycle (minus 80°…”