Abstract.A recent epizootic of swine infertility and respiratory syndrome (SIRS) in a Minnesota swine herd was investigated. Examination of a sow, neonatal piglets, and stillborn fetuses obtained during the epizootic from the affected herd revealed interstitial pneumonitis, lymphomononuclear encephalitis, and lymphomononuclear myocarditis in the piglets and focal vasculitis in the brain of the sow. Fetuses did not have microscopic lesions. No cause for the infertility and respiratory syndrome was determined. Therefore, attempts were made to experimentally reproduce the disease. Eleven 3-day-old gnotobiotic piglets exposed intranasally to tissue homogenates of piglets from the epizootic became inappetent and febrile by 2-4 days postexposure and had interstitial pneumonitis and encephalitis similar to that seen in the field outbreak. After 2 blind passages in gnotobiotic piglets, tissue homogenates were cultured on continuous cell line CL2621, and a cytopathic virus (ATCC VR-2332), provisionally named SIRS virus, was isolated. Gnotobiotic piglets exposed intranasally to the SIRS virus developed clinical signs and microscopic lesions that were the same as those in piglets exposed to the tissue homogenates, and the virus was reisolated from their lungs. This is the first isolate of SIRS virus in the United States that fulfills Koch's postulates in producing the respiratory form of the disease in gnotobiotic piglets and the first report of isolation and propagation of the virus on a continuous cell line (CL2621). The virus is designated as American Type Culture Collection VR-2332.

Two different cell populations, high- (MARC-145) and low-permissive cell clones (L-1) to porcine reproductive and respiratory syndrome (PRRS) virus, were derived from MA-104 cell line (parent cell: P) by cell cloning. Maximum virus yields in MARC-145, P, and L-1 cell clones were 10(8.5), 10(3.5), and 10(2.5) tissue culture infective dose 50 (TCID50)/0.1 ml, respectively. The MARC-145 cell clone supported replication of all 11 different porcine reproductive and respiratory syndrome virus isolates that were tested. These results indicated that the MARC-145 cells will be useful for PRRS virus replication.

Various conditions were evaluated and modified to improve the sensitivity of the serum neutralization (SN) test for detecting antibody in pigs infected with porcine reproductive and respiratory syndrome virus (PRRSV). Higher SN titers were consistently obtained by the addition of 20% fresh swine serum to the virus diluent and by the use of a permissive cell clone (MARC-145) derived from the MA-104 cell line. Test sera used to assess the SN test were obtained from 2 groups of 3-week-old pigs infected intranasally with PRRSV (MN-1b). Using the modified method, SN antibody was first detected 9-11 days postinoculation (PI), with a peak evident at 11-21 days PI. The antibody subsequently declined, and a second peak was observed between 41 and 45 days PI. The first antibody peak was not observed and the SN antibody was only detectable between 32 and 41 days PI when the test was done with 20% heated swine serum or without supplemental swine serum. The SN antibody during 2-3 weeks PI was found to be sensitive to 2-mercaptoethanol or anti-swine IgM treatment. The SN antibody titers were high when homologous PRRSV isolate was used in the test but were markedly low for heterologous PRRSV isolates. No difference in antibody titers was observed when homologous and heterologous PRRSV isolates were tested by indirect fluorescent antibody assay. These results indicate that the modified SN method is useful in detecting earlier and higher PRRSV antibody and that it can differentiate among PRRSV isolates.

Background-The 2015 Middle East respiratory syndrome (MERS) outbreak in the Republic of Korea (ROK) is an example of an infectious disease outbreak initiated by international travelers to a high-income country.Objective-To determine the economic impact of the MERS outbreak on the tourism and travelrelated service sectors, including accommodation, food and beverage, and transportation, in the ROK.Methods-We projected monthly numbers of non-citizen arrivals and indices of services for three travel-related service sectors during and after the MERS outbreak (June 2015-June 2016) using seasonal autoregressive integrated moving average models. Tourism losses were estimated by multiplying the monthly differences between projected and actual numbers of non-citizen arrivals by average tourism expenditure per capita. Estimated tourism losses were allocated to travel-related service sectors to understand the distribution of losses across service sectors.Results-The MERS outbreak was correlated with a reduction of 2.1 million non-citizen visitors corresponding with US $2.6 billion in tourism loss for the ROK. Estimated losses in the accommodation, food and beverage service, and transportation sectors associated with the decrease of non-citizen visitors were US $542 million, US $359 million, and US $106 million, respectively. The losses were demonstrated by lower than expected indices of services for the accommodation, and food and beverage service sectors in June and July 2015 and for the transportation sector in June 2015. Conclusions-The results support previous findings that public health emergencies due to traveler-associated outbreaks of infectious diseases can cause significant losses to the broader economies of affected countries.

Abstract. An indirect fluorescent antibody (IFA) test was developed and standardized to detect and quantitate antibody for swine infertility and respiratory syndrome (SIRS) virus in swine sera. Test results were evaluated using sera of pigs infected both experimentally and naturally with SIRS virus. The IFA test used swine alveolar macrophage (SAM) monolayers prepared in 96-well microplates and infected with SIRS virus. The monolayers were incubated with test sera, washed, and stained with fluorescein isothiocyanate-labeled rabbit anti-swine IgG. After another wash step, the monolayers were examined under a fluorescent microscope. A noninfected SAM control well was included for each sample. The antibody titers for each serum sample were recorded as the highest serum dilutions with specific cytoplasmic fluorescence but no fluorescence in the control wells. To evaluate the test, sera of 4 6-week-old pigs that had been infected with SIRS virus, 2 contact pigs, and 13 experimentally infected sows were used. In the experimentally infected pigs, antibody was first detected at 7 days postexposure (PE) and peaked (1:256-1,024) between 11 and 21 days PE. All 13 sow sera were negative at time of infection but were positive (1:64-> 1: 1,024) at 14-26 days PE. Seven hundred twenty sera collected from 25 different swine farms with or without a history of SIRS were also tested. Of 344 sera from 15 swine farms with a clinical history of SIRS, 257 (74.7%) sera had IFA titers ≥ 1:4, whereas 371 (98.7%) of 376 sera from herds with no history of SIRS were negative. The present results indicate that the IFA is a useful test for the detection and quantitation of SIRS virus antibody in swine sera.Swine infertility and respiratory syndrome (SIRS) virus has recently been recognized as an important pathogen in the United States because the virus causes severe reproductive failure in pregnant sows and high mortality due to respiratory disease in young pigs. [1][2][3]8 A similar syndrome has been reported in several European countries, 4-7 and the causative agent, Lelystad virtus, 6 was identified. Antibody to the Lelystad virus has been detected by an immunoperoxidase monolayer assay (IPMA), 6 whereas a serum neutralization (SN) test was described for the detection of antibody to SIRS virus.2 The purpose of the present study was to develop a simple indirect fluorescent antibody (IFA) method for detection and quantitation of SIRS virus antibody in swine sera. The method was evaluated using sera of pigs experimentally infected with SIRS virus. Test results of field serum samples collected from 25 different farms with or without a clinical history of SIRS are also described.SIRS MN-lb isolate at the fifth passage level was prepared in SAM cells, and virus aliquots of 10 4.5 immunofluorescence infective dose 50 (IFID 50 )/ml were stored at -70 C. Materials and methodsPreparation of test plates. The SAM cells, either freshly prepared or stored at -70 C, were diluted at a concentration of 2 x 10 6 cells/ml in RPMI-1640 medium supplemented w...

Limited information is available on the transmission and spread of influenza virus in pig populations with differing immune statuses. In this study we assessed differences in transmission patterns and quantified the spread of a triple reassortant H1N1 influenza virus in naïve and vaccinated pig populations by estimating the reproduction ratio (R) of infection (i.e. the number of secondary infections caused by an infectious individual) using a deterministic Susceptible-Infectious-Recovered (SIR) model, fitted on experimental data. One hundred and ten pigs were distributed in ten isolated rooms as follows: (i) non-vaccinated (NV), (ii) vaccinated with a heterologous vaccine (HE), and (iii) vaccinated with a homologous inactivated vaccine (HO). The study was run with multiple replicates and for each replicate, an infected non-vaccinated pig was placed with 10 contact pigs for two weeks and transmission of influenza evaluated daily by analyzing individual nasal swabs by RT-PCR. A statistically significant difference between R estimates was observed between vaccinated and non-vaccinated pigs (p < 0.05). A statistically significant reduction in transmission was observed in the vaccinated groups where R (95%CI) was 1 (0.39-2.09) and 0 for the HE and the HO groups respectively, compared to an Ro value of 10.66 (6.57-16.46) in NV pigs (p < 0.05). Transmission in the HE group was delayed and variable when compared to the NV group and transmission could not be detected in the HO group. Results from this study indicate that influenza vaccines can be used to decrease susceptibility to influenza infection and decrease influenza transmission.

Abstract. The American and European strains of porcine reproductive and respiratory syndrome (PRRS) virus were initially isolated in an established cell line (CL 2621) and porcine alveolar macrophages (PAM), respectively. Subsequent isolation of American strains of this virus in PAM has also been reported. To determine their relative sensitivity for virus isolation, both PAM and CL 2621 cells were inoculated with 98 tissue specimens and 73 serum samples from animals suspected of having PRRS. Four of the 98 tissue samples yielded virus in both cell types, whereas 7 samples were positive only in PAM and 4 samples only in CL 2621. Of the 73 serum samples tested, 18 were positive in PAM of which only 2 were positive in CL 2621. Additionally, 82 isolates obtained initially in CL 2621 were inoculated in PAM cells, and 18 strains isolated originally in PAM were inoculated in CL 2621. Of the 82 CL 2621 isolates, 25 could not be propagated on PAM. Of the 57 that replicated in PAM, as detected by a positive test on indirect fluorescent antibody test, only 28 produced cytopathic effects and 29 did not. Of the 18 PAM isolates, 5 did not grow on CL 2621. Although PAM were relatively more sensitive for virus isolation, their failure to support the growth of certain strains of PRRS virus indicates the existence of variants among PRRS virus strains, and both PAM and CL 2621 should be used for virus isolation from clinical samples. In addition, the sensitivity of these 2 cell types was compared for the detection of fluorescent antibodies to PRRS virus using 179 serum samples from PRRS-infected animals. The results were comparable in both cell systems.

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