Carlos Trincado

Studies on the carriage and transmission of porcine reproductive and respiratory syndrome virus by individual houseflies (Musca domestica)

The objectives of the study were to determine the site of porcine reproductive and respiratory syndrome virus (PRRSV) in individual houseflies, to assess whether an individual housefly could transmit PRRSV to a susceptible pig, and to compare the ability of PCR, virus isolation and a pig bioassay to detect PRRSV in houseflies. In the first experiment 26 houseflies were fed on a pig infected experimentally with PRRsv; 13 were processed as a whole fly homogenate, while an exterior surface wash and a gut homogenate were collected from the other 13. Infectious PRRSV was recovered from nine of the whole fly homogenates, 12 of the gut homogenates and one of the exterior surface washes. In the second experiment, two of 10 individual houseflies, which had fed on an infected pig, transmitted PRRSV to a susceptible pig in a controlled manual transmission protocol. In the third experiment, single flies or pools of 30 flies were immersed in different concentrations of a PRRSV inoculum, then tested by PcR, virus isolation and bioassay. The virus was detected at a concentration of 101 TCID5O/ml by PCR, 102 TCID5O/ml by the bioassay and 103 TCID50/ml by virus isolation.

Attempts to transmit porcine reproductive and respiratory syndrome virus by aerosols under controlled field conditions

An experimental infection with porcine reproductive and respiratory syndrome virus (PRRSV) was established in 150 five-month-old pigs housed in a fan-ventilated finishing facility, the infected barn. To determine whether air exhausted from the wall fans contained infectious PRRSV, a trailer containing 10 four-week-old PRRsv-naive sentinel pigs was placed 10 m from the building from day 3 after the 150 pigs were infected until day 10. To connect the two airspaces, one end of an opaque plastic tube, 15 m in length and 5 cm in diameter, was fastened to the wall fan of the infected barn, and the other end was placed inside the trailer. Air from the building was exhausted into the trailer 24 hours a day for seven consecutive days and PRRSV infection was monitored in the infected pigs and the sentinel pigs. Air samples were collected from the infected barn and the trailer. PRRSV infection was detected in the infected pigs three and seven days after they were infected, but not in the sentinel pigs. All the air samples were negative for PRRSV by PCR, virus isolation and a pig bioassay.

Evaluation of the role of mallard ducks as vectors of porcine reproductive and respiratory syndrome virus

To assess the transmission of porcine reproductive and respiratory syndrome virus (PRRSV) from pigs to mallard ducks, 10 adult (one-year-old) female mallard ducks were housed with pigs infected experimentally with PRRSV, and allowed to be in close contact with them for 21 days. To evaluate the transmission of PRRSV from mallard ducks to pigs, two adult ducks were inoculated orally with PRRSV (total dose 106.0 TCID50) and allowed to drink PRRsv-infected water; 24 hours later, two four-week-old PRRSv-naive sentinel pigs were housed in pens below the cages housing the ducks for 14 days. In both experiments, cloacal and faecal samples were collected three times a week from the ducks and tested by PcR, virus isolation and a pig bioassay. Blood samples from the pigs were tested by ELISA, PCR and virus isolation. Sera from the ducks were tested by serum neutralisation. The ducks were examined postmortem and selected tissues were tested by PcR, virus isolation, histopathology and pig bioassay. In both experiments all the cloacal swabs, faecal samples, tissues and sera from the ducks were negative by all the tests. The sera from the pigs in the first experiment were PCR positive at three, seven, 14 and 21 days after infection and ELISA positive at 14 and 21 days. Sera from the pigs in the second experiment were negative by all the tests. The virus was isolated from the oral inoculum and the drinking water provided for the ducks in the second experiment. Under the conditions of this study, it was not possible to demonstrate the transmission of PRRSV either from the pigs to the ducks or from the ducks to the pigs.

Effect of vaccination with a modified-live porcine reproductive and respiratory syndrome virus vaccine on dynamics of homologous viral infection in pigs

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.

Evaluation of an all-glass impinger for the detection of porcine reproductive and respiratory syndrome virus in natural and artificial aerosols

TCID50 (total dose) and 103 TCID50 (total dose). A negative control inoculum consisted of PRRSV-free MEM. The hand sprayer containing the suspension of virus was attached to one of the chamber’s inlet walls in order to introduce the aerosols inside the chamber (Fig 2). To collect aerosols from the chamber, the impinger was attached to the chamber’s air inlet on the opposite wall (Fig 3) and operated. Two replicates per virus concentration were conducted, using a 20-minute sampling period. At the end of each sampling period, a 10 ml aliquot of MEM was removed from the impinger and tested by TaqMan (Perkin-Elmer Applied Biosystems) PCR (Molitor and others 1997). The chambers and sprayers were cleaned and allowed to dry between replicates. Experiment 2 involved the use of experimentally infected pigs for the evaluation of naturally produced aerosols. Four three-week-old PRRSV-negative pigs were divided into two groups, an infected group (group A) and a control group (group B), each containing two pigs. During the study, the pigs were housed in veterinary isolation facilities at the University of Minnesota and cared for according to the University of Minnesota Institutional Animal Care and Use Committee guidelines. Upon arrival, the pigs were blood tested and evaluated by PCR and ELISA to ensure their PRRSVnaive status. To generate the aerosols, pigs in group A were infected intranasally with 5 ml of 102·4 TCID50 (total dose) of PRRSV isolate MN 30-100 (Bierk and others 2001). Pigs in the control group were sham inoculated with PRRSV-free cell culture fluid. On day 1 postinfection (pi), both pigs in each group were placed in one of the previously described aluminium chambers, which provided an area of 0·07 m2 per pig. Two chambers were used, one chamber per group. Air samples were collected while the pigs were inside the chamber. Following completion of the sampling period, the pigs were removed from the chamber and returned to their respecEvaluation of an all-glass impinger for the detection of porcine reproductive and respiratory syndrome virus in natural and artificial aerosols