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  • Author or Editor: Scott A. Dee x
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in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine effects of vaccination protocols with modified-live porcine reproductive and respiratory syndrome virus (PRRSV) vaccine on persistence and transmission of virus in pigs infected with a homologous isolate and determine clinical and virologic responses following heterologous viral challenge.

Animals—Four hundred forty 6- to 8-week-old PRRSV-naïve pigs.

Procedures—Pigs were allocated into 5 groups. Groups A to D were inoculated with wild-type PRRSV VR2332. Group A (positive control pigs) received PRRSV only. Groups B, C, and D received modified-live PRRSV vaccine (1, 2, or 3 doses). Group E served as a negative control group. To evaluate viral transmission, sentinel pigs were introduced into each group at intervals from 37 to 67, 67 to 97, and 97 to 127 days postinoculation (DPI). To evaluate persistence, pigs were euthanized at 37, 67, 97, or 127 DPI. To assess clinical and virologic response after challenge, selected pigs from each group were inoculated at 98 DPI with a heterologous isolate (PRRSV MN-184).

Results—Mass vaccination significantly reduced the number of persistently infected pigs at 127 DPI. Vaccination did not eliminate wild-type PRRSV; administration of 2 or 3 doses of modified-live virus vaccine reduced viral shedding after 97 DPI. Previous exposure to wild-type and vaccine virus reduced clinical signs and enhanced growth following heterologous challenge but did not prevent infection.

Conclusions and Clinical Relevance—Findings suggest that therapeutic vaccination may help to reduce economic losses of PRRSV caused by infection; further studies to define the role of modified-live virus vaccines in control-eradication programs are needed.

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in American Journal of Veterinary Research

Abstract

Objective—To determine whether flies can acquire porcine reproductive and respiratory syndrome virus (PRRSV) and disperse the virus throughout a designated area.

Animals—60 four-month-old pigs.

Procedure—On day 0, 28 of 60 pigs were inoculated with PRRSV MN 30-100 (index variant). On the same day, 100,000 pupae of ochre-eyed houseflies and 100,000 pupae of red-eyed (wild-type) houseflies were placed in the swine facility for a release-recapture study. Flies were recaptured at 2 locations within the swine facility, 6 locations immediately outside the facility, and 30 locations 0.4, 0.8, 1.3, 1.7, 1.9, and 2.3 km from the facility. Traps were emptied on days 2, 7, 8, 10, and 14. Samples derived from flies were tested by use of a polymerase chain reaction assay, virus DNA was sequenced, and viruses were tested for infectivity by means of a swine bioassay.

Results—PRRSV RNA homologous to the index PRRSV was detected in trapped flies collected inside and immediately outside the facility and from 9 of 48 samples collected at 0.4 km, 8 of 24 samples collected at 0.8 km, 5 of 24 samples collected at 1.3 km, and 3 of 84 samples collected at > 1.7 km from the facility. Two samples collected at 0.8 km contained genetically diverse variants of PRRSV. Swine bioassays revealed the virus in flies was infectious.

Conclusions and Clinical Relevance—Flies appeared to become contaminated with PRRSV from infected pigs and transported the virus ≥ 1.7 km. Flyborn transmission may explain how PRRSV is seasonally transported between farms. (Am J Vet Res 2004;65:1284–1292)

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in American Journal of Veterinary Research

Abstract

Objective—To evaluate retention of porcine reproductive and respiratory syndrome virus (PRRSV) in houseflies for various time frames and temperatures.

Sample Population—Fifteen 2-week-old pigs, two 10-week-old pigs, and laboratory-cultivated houseflies.

Procedure—In an initial experiment, houseflies were exposed to PRRSV; housed at 15°, 20°, 25°, and 30°C; and tested at various time points. In a second experiment to determine dynamics of virus retention, houseflies were exposed to PRRSV and housed under controlled field conditions for 48 hours. Changes in the percentage of PRRSV-positive flies and virus load per fly were assessed over time, and detection of infective virus at 48 hours after exposure was measured. Finally, in a third experiment, virus loads were measured in houseflies allowed to feed on blood, oropharyngeal washings, and nasal washings obtained from experimentally infected pigs.

Results—In experiment 1, PRRSV retention in houseflies was proportional to temperature. In the second experiment, the percentage of PRRSV-positive houseflies and virus load per fly decreased over time; however, infective PRRSV was found in houseflies 48 hours after exposure. In experiment 3, PRRSV was detected in houseflies allowed to feed on all 3 porcine body fluids.

Conclusions and Clinical Relevance—For the conditions of this study, houseflies did not support PRRSV replication. Therefore, retention of PRRSV in houseflies appears to be a function of initial virus load after ingestion and environmental temperature. These factors may impact the risk of insect-borne spread of PRRSV among farms. (Am J Vet Res 2005;66:1517–1525)

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in American Journal of Veterinary Research

Abstract

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.

Animals—Twenty-one 2-month-old pigs and eighteen 6-month-old pigs.

Procedure—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 TCID50 per milliliter (sera and swab specimens) or TCID50 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 and Clinical Relevance—Multiple factors affect PRRSV concentration in pigs, including pathogenicity of the PRRSV isolate, age, and concurrent infection with M hyopneumoniae.

Full access
in American Journal of Veterinary Research