Development of a recombinase-aided amplification method combined with lateral flow dipstick assay to detect Porcine circovirus type 2.

Background and Aim: Porcine circovirus type 2 (PCV2) is a pathogenic virus that suppresses the immune system of pigs, impacting their health and causing economic losses. Rapid diagnostic tools for early detection of PCV2 are critical to disease prevention and control. Several molecular techniques have been established for detecting PCV2 but costly equipment and time-consuming methods are unsuitable for field inspection. In this study, we developed a recombinase-aided amplification combined with lateral flow dipstick (RAA-LFD) assay to compare with polymerase chain reaction (PCR) and quantitative PCR (qPCR) in detecting PCV2 in suspected field samples. Materials and Methods: To amplify RAA products, 15 primer pairs were designed from the conserved region of the open reading frame (ORF) 1 gene based on multiple alignments of eight PCV2 genotypes. The most efficient primer pair and conditions for the RAA-LFD assay were tested and selected. Limit of detection, repeatability, and reproducibility were determined using the constructed plasmid. DNA was extracted from positive samples for specificity testing as well as from 100 field samples to compare the detection of the RAA-LFD assay with PCR and qPCR. Results: The F1/R1 primer pair was chosen and labeled with fluorescein isothiocyanate at the 5' end of the forward primer and with biotin at the 5' end of the reverse primer. The limit of detection of the RAA-LFD assay was 10 copies/µL at 38°C for 30 min. The RAA-LFD assay was repeatable and reproducible, with no cross-reaction with PCV3, Actinobacillus pleuropneumoniae, Porcine epidemic diarrhea virus, Classical swine fever virus, Porcine reproductive and respiratory syndrome virus - North America strain (PRRSV-US) and Porcine reproductive and respiratory syndrome virus - European strain (PRRSV-EU). Based on testing with 100 samples, the developed RAA showed 100% specificity and 90.56% and 85.71% sensitivity when compared to PCR and qPCR, respectively Cohen's kappa coefficients showed a good agreement with the established techniques. Conclusion: The RAA-LFD assay targeting the ORF1 gene was highly sensitive, specific, quick, and simple to perform in the field.

Effectiveness of gilt acclimatization - improvement procedures in a farm with recurrent outbreaks of porcine epidemic diarrhea.

Background and Aim: Porcine epidemic diarrhea (PED) is a severe infectious disease that causes very high mortality in newborn piglets up to 2-3 weeks age. The main cause of repeated outbreaks of PED in infected farms is the continuing circulation of the PED virus (PEDV). Improper gilt management, including inappropriate gut feedback, commingling, and inadequate immunization, causes a prolonged virus circulation in breeding herds. Moreover, insufficient transfer of passive immunity through the colostrum to newborn piglets can also increase infection risk. Therefore, a gilt management program that controls infection should focus on infection monitoring and acclimatization. We investigated the source of recurrent PEDV outbreaks and examined how the effect of immunization methods, specifically using gut feedback mechanism and vaccination, can reduce PEDV circulation and improve immune responses in replacement gilts. Materials and Methods: The study site was a segregated commercial production farm with endemic PEDV. The acclimatization methods included gut feedback and vaccination. This longitudinal study evaluated two strategies of gilt acclimatization against PEDV: Program 1 (routine farm management) and Program 2 (early feedback program and all-in-all-out system). Levels of PED RNA in fecal samples were measured using quantitative reverse transcription-polymerase chain reaction, and the PEDV S gene was sequenced. Porcine epidemic diarrhea-specific immune responses were assessed using enzyme-linked immunosorbent assay and the serum neutralization test. Results: Porcine epidemic diarrhea outbreaks occurred in the farrowing, nursery, and finishing units and farrowed litters 5-10 days old were symptomatic of PED. Phylogenetic analyses of the S gene showed PEDV sequence divergence between PEDV field strains and vaccine strain, which may contribute to periodic outbreaks and continued persistence of PEDV in the farm. After gut feedback and acclimatization, replacement gilts from Program 1 continued to shed PEDV before being introduced to sow herds, while those from Program 2 did not shed PEDV before being introduced to sow herds. However, the components of the immune response against PEDV in serum samples, including specific immunoglobulin (Ig)G, specific IgA, and neutralizing antibodies were lower in gilts of Program 2 than those in Program 1. Conclusion: We speculate that implementing the appropriate gilt acclimatization program can control PEDV circulation in farm. However, the acclimatization methods in Program 2 did not induce a strong and adequate immune response in replacement gilts. Therefore, maternal immunity levels and the degree of protection against PEDV require further study.

PCV3 in Thailand: Molecular epidemiology and relationship with PCV2.

Porcine circovirus type 3 has been circulating throughout the world and since their first report, various clinical signs and disease developments have been documented. The virus is similar to the closely related PCV2 and is associated with several clinical signs called porcine circovirus-associated diseases (PCVAD). PCV2 or PCV3 is occasionally reported with clinical signs such as PDNS, respiratory signs and reproductive failure. Retrospective research conducted in Thailand revealed that both PCV2 and PCV3 have been circulation for decades. However, awareness about PCV3 infection has just arisen in recent years because of the similarities observed in disease circulation and clinical signs that have led to concerns. This study was conducted to find the relationship between the quantity of PCV2 and PCV3 in Thai pigs displaying the clinical signs related to PCVAD. A total of 479 serum samples with different production phases and clinical signs were sent to Kamphaeng Saen Veterinary Diagnostic Center (KVDC) for qPCR to detect the presence of PCV2 or PCV3. There was no relationship between the PCV3 and PCVAD-related clinical signs. Also, the relationship between PCV2 and PCV3 with no clinical signs suggested that both viruses might come from the same reservoir or have been circulating in Thailand for a long time, leading to common incidents in finding. The viral load of PCV2 was significantly different among the pig groups with and without clinical signs. The capsid sequence analysis of PCV3 revealed that 22 capsid sequences obtained from this study were found as clusters within PCV3a with a minor variation. Additional control measures are further needed to reduce the findings of the viruses. A future study with a control experiment may be needed to clarify the pathogenesis of PCV3.

Correlation between antibody response against porcine epidemic diarrhea virus in sows and their offspring under field conditions.

BACKGROUND AND AIM: Thai pig farmers have suffered huge financial losses from porcine epidemic diarrhea (PED) since 2007. PED, caused by the PED virus (PEDV), leads to severe diarrhea, vomiting, and subsequent dehydration in suckling piglets. Lactogenic immunity derived from colostrum and milk is very important because immunoglobulins (Ig) cannot cross the placenta in pregnant sows. The aim of this study was to investigate the immunological correlation of the sample-to-positive (S/P) ratios of IgA and IgG against PEDV between colostrum, sow serum, and their piglet serum. MATERIALS AND METHODS: A total of 43 sows were divided into three groups according to the experience of PEDV infection: Negative sow group (n=7) and treatment group (n=36, sows previously infected with PEDV). The treatment group was subdivided into two groups: Sows immunized with live-attenuated PEDV vaccine (n=15) and sows immunized with feedback (n=21) at 3 weeks before farrowing. The 7-day-old piglets (n=425) were obtained from negative sows (n=89), vaccinated sows (n=150), and feedback sows (n=275). Colostrum, sow serum, and their piglet serum were collected and analyzed for S/P ratios of their IgA and IgG levels against PEDV using an enzyme-linked immunosorbent assay. RESULTS: The piglets from sows immunized with live-attenuated PEDV vaccine had a higher S/P ratio of IgG against PEDV (p<0.001), whereas the piglets from the feedback group had a higher S/P ratio of IgA against PEDV (p<0.001) compared with piglets from the negative sows. In addition, the S/P ratios of PEDV-specific IgA and IgG between sow serum and colostrum showed a positive correlation (Pearson's coefficient r=0.61 and 0.75, respectively). Both S/P ratios of PEDV-specific IgA and IgG in sow serum and colostrum had a positive correlation to those in piglet serum. CONCLUSION: Overall, this study suggested that pregnant sows immunized with the live-attenuated vaccine against PEDV and feedback may provide maternal immunity against PEDV to their offspring.

Mycotoxin profiles of animal feeds in the central part of Thailand: 2015-2020.

BACKGROUND AND AIM: Mycotoxin contamination in animal feeds is of considerable concern because it can affect animal health systems. As a result of contamination in the food chain, humans can indirectly come into contact with mycotoxins. The present study aimed to present mycotoxin contamination patterns in animal feeds from 2015 to 2020 and elucidate associations between the type of feed and the type of ingredient. MATERIALS AND METHODS: Data were summarized from the records of the Kamphaeng Saen Veterinary Diagnosis Center from 2015 to 2020, which comprised the analyses of aflatoxin (AFL), zearalenone (ZEA), T-2 toxin (T-2), fumonisin (FUM), and deoxynivalenol (DON) contamination in feed ingredients, complete feeds, and unclassified feeds. Descriptive statistics, Chi-squared tests, and Fisher's exact tests were used for data analysis. RESULTS: ZEA was prevalent in animal feeds. The prevalence of each mycotoxin was constant from 2015 to 2020. Approximately 20-30% of samples were positive for AFL and FUM. The highest contamination was ZEA, which was found in 50% of the samples, and the occurrence of T-2 and DON was <10%. AFL significantly contaminated complete feeds more than feed ingredients. Feed ingredients were related to mycotoxin contaminations. The highest levels of AFL, FUM, and DON contamination occurred in 2017. The data in this year consisted mostly of soybean, corn, and rice bran. CONCLUSION: The number of positive samples of all five mycotoxins was constant from 2015 to 2020, but the occurrence of ZEA was the highest. Mycotoxins in feedstuffs are significantly related to the type of feed and the type of ingredient.

Genotypic and phenotypic situation of antimicrobial drug resistance of Escherichia coli in water and manure between biogas and non-biogas swine farms in central Thailand.

Currently, Thai livestock is rapidly expanding, especially the production of ruminants, chicken, and swine. The improper use of antibiotics will probably lead to an antimicrobial resistance problem. It has long been suspected that wastewater released from swine farms is a crucial aspect of the spread of antimicrobial resistance to the environment. Biogas systems are wastewater treatment systems commonly used on swine farms; however, little is known about the roles they play in the occurrence and transmission of resistant bacteria between biogas and non-biogas systems. This study collected pooled water, wastewater, and feces samples from five biogas farms and three non-biogas farms in Central Thailand. The samples were isolated to hemolytic E. coli (HEC) and non-hemolytic E. coli (NHEC) to test the drug resistance by using VITEK® 2 Compact (BioMérieux, USA) and detect resistant genes by using the polymerase chain reaction (PCR) technique to correlate the determined phenotypic and genotypic patterns. The results demonstrated that enumeration levels of E. coli ranged from 20.1 to 70.4 (MPN/100 ml), 105 to 107 (cfu/ml), and 105 to 109 (cfu/g), while they were 0-148.7 (MPN/100 ml), 105 to 107 (cfu/ml) and 105 to 109 (cfu/g) for water, wastewater and manure from biogas and non-biogas swine farms, respectively. The amount of E. coli in the sow feces samples was higher than the samples of nursery piglets on biogas farms at a 0.05 significant level (p < 0.05). The antimicrobial resistance indicated the relevant resistance characteristics of E. coli: the highest antimicrobial resistance was for ampicillin (AMP), followed by amoxicillin (AMX), tetracyclines (TET), chloramphenicol (C), and piperacillin (PIP), respectively. Multidrug resistance (MDR) of E. coli was 15 drugs: AMP-AMX-AMC-PIP-CEX-CEV-CPD-XNL-GM-IMP-SXT-C-TE (11.9%) and AMP-AMX-AMC-PIP-CEX-CEV-CPD-XNL-GM-IMP-SXT-C-ENR-MBR-TE (18.55%), which were the most commonly found in biogas and non-biogas swine farms, respectively. The blaTEM, tetA, sul2, and sul3 were dominantly resistant genes isolated from the water from both types of farm; while, blaTEM, aadA1, tetA, dfrA12, sul2, sul3, and cmlA were isolated from feces. The amount of E. coli in the final effluent from biogas swine farms was higher than the non-biogas swine farms; however, it was not significantly different at (p > 0.05). Furthermore, the findings of study found that genotypic characteristic of HEC showed similarity 100%. Thus, it was concluded that the levels of E. coli were accelerated in biogas wastewater treatment systems, and isolated E. coli demonstrated multidrug resistance. Even though E. coli was found in different locations, it showed relevant resistance characteristics. Therefore, regular monitoring of antimicrobial resistance on livestock farms is necessary for efficient management and drug uses on farms.

Cell-mediated immune response and protective efficacy of porcine reproductive and respiratory syndrome virus modified-live vaccines against co-challenge with PRRSV-1 and PRRSV-2.

Cell-mediated immunity (CMI), IL-10, and the protective efficacy of modified-live porcine reproductive and respiratory syndrome virus (PRRSV) vaccines (MLV) against co-challenge with PRRSV-1 and PRRSV-2 (HP-PRRSV) were investigated. Seventy, PRRSV-free, 3-week old, pigs were allocated into 7 groups. Six groups were intramuscularly vaccinated with MLV, including Porcilis (PRRSV-1 MLV, MSD Animal Health, The Netherlands), Amervac (PRRSV-1 MLV, Laboratorios Hipra, Spain), Fostera (PRRSV-2 MLV, Zoetis, USA), Ingelvac PRRS MLV and Ingelvac PRRS ATP (PRRSV-2, Boehringer Ingelheim, USA), and Prime Pac PRRS (PRRSV-2 MLV, MSD Animal Health, The Netherlands). Unvaccinated pigs were left as control. Lymphocyte proliferative response, IL-10 and IFN-γ production were determined. At 35 days post-vaccination (DPV), all pigs were inoculated intranasally with 2 ml of each PRRSV-1 (105.4 TCID50/ml) and PRRSV-2 (105.2 TCID50/ml, HP-PRRSV). Following challenge, sera were quantitatively assayed for PRRSV RNA. Pigs were necropsied at 7 days post-challenge. Viremia, macro- and microscopic lung lesion together with PRRSV antigen presence were evaluated in lung tissues. The results demonstrated that, regardless of vaccine genotype, CMI induced by all MLVs was relatively slow. Increased production of IL-10 in all vaccinated groups was observed at 7 and 14 DPV. Pigs in Amervac, Ingelvac MLV and Ingelvac ATP groups had significantly higher levels of IL-10 compared to Porcilis, Fostera and Prime Pac groups at 7 and 14 DPV. Following challenge, regardless to vaccine genotype, vaccinated pigs had significantly lower lung lesion scores and PRRSV antigens than those in the control group. Both PRRSV-1 and PRRSV-2 RNA were significantly reduced. Prime Pac pigs had lowest PRRSV-1 and PRRSV-2 RNA in serum, and micro- and macroscopic lung lesion scores (p < 0.05) compared to other vaccinated groups. In conclusion, PRRSV MLVs, regardless of vaccine genotype, can reduce viremia and lung lesions following co-challenge with PRRSV-1 and PRRSV-2 (HP-PRRSV). The main difference between PRRSV MLV is the production of IL-10 following vaccination.

The retrospective identification and molecular epidemiology of porcine circovirus type 3 (PCV3) in swine in Thailand from 2006 to 2017.

Porcine circovirus type 3 (PCV3) has recently been detected in pigs worldwide, with similar clinical manifestations to porcine circovirus-associated disease (PCVAD) from porcine circovirus type 2 (PCV2) infection. Here, we report the identification and molecular epidemiology of PCV3 in swine in Thailand from clinical samples retrieved from 2006 to 2017. The epidemiological data revealed co-infection with PCV2, PRRSV, and PCV2/PRRSV was common in our samples. Circulating PCV3 from this study shared a high similarity of nucleotide and deduced amino acid sequences of the partial capsid gene (96.7%-100% and 96.7%-100% respectively), indicated the genetic stability of PCV3 in Thailand. Phylogenetic analysis based on the capsid gene revealed scatter clustering with current PCV3 having no relation to the geographical origin of the virus strains. In this retrospective study, results have demonstrated that PCV3 has spread extensively within Thai swine from as early as 2006 and may also be involved in PRDC and PCVAD.

Oral fluid samples used for PRRSV acclimatization program and sow performance monitoring in endemic PRRS-positive farms.

An effective gilt acclimatization program is one of the most important management strategies for controlling porcine reproductive and respiratory syndrome virus (PRRSV) infection. Recently, oral fluid samples have been used as alternative diagnostic samples for various swine diseases. This study utilized oral fluids for PRRSV monitoring during the gilt acclimatization period in PRRSV endemic farms. The study was performed in two selected commercial breeding herds (farm A and farm B). PRRSV RNA and PRRSV-specific antibodies were monitored using oral fluid and serum samples. Sow performance parameters related to PRRSV infection were recorded and assessed. After PRRSV exposure during acclimatization, viral RNA was demonstrated in oral fluids from 1 to 10 weeks post-exposure (WPE). PRRSV RNA was detected in serum at 1 and 4 WPE in farm A and at 1, 4, 8, and 12 WPE in farm B. Prolonged viremia of gilts from farm B was possibly due to re-infection (within the herd) and later, reproductive problems were found in the breeding herd. The correlation of PRRSV RNA concentration in oral fluids and serum was evident. The S/P ratio values of PRRSV antibodies in oral fluid samples were higher and had similar patterns of antibody responses to the serum samples. The results suggest that the use of oral fluid samples for PRRSV monitoring during gilt acclimatization in endemic farms is effective, convenient, practical, and economical and would be most beneficial when used with other parameters.

Genetic diversity of porcine circovirus type 2 (PCV2) in Thailand during 2009-2015.

Porcine circovirus type 2 (PCV2), the essential cause of porcine circovirus associated disease (PCVAD), has evolved rapidly and it has been reported worldwide. However, genetic information of PCV2 in Thailand has not been available since 2011. Herein, we studied occurrence and genetic diversity of PCV2 in Thailand and their relationships to the global PCV2 based on ORF2 sequences. The results showed that 306 samples (44.09%) from 56 farms (80%) were PCV2 positive by PCR. Phylogenetic trees constructed by both neighbor-joining and Bayesian Inference yielded similar topology of the ORF2 sequences. Thai PCV2 comprise four clusters: PCV2a (5.5%), PCV2b (29.41%), intermediate clade 1 (IM1) PCV2b (11.03%) and PCV2d (54.41%). Genetic shift of PCV2 in Thailand has occurred similarly to the global situation. The shift from PCV2b to PCV2d was clearly observed during 2013-2014. The viruses with genetically similar to the first reported PCV2 in 2004 have still circulated in Thailand. The first Thai PCV2b and PCV2d were closely related to the neighboring countries. The haplotype network analysis revealed the relationship of PCV2 in Thailand and other countries. These results indicate that genetic diversity of PCV2 in Thailand is caused by genetic drift of the local strains and intermittent introduction of new strains or genotypes from other countries. Genetic evolution of PCV2 in Thailand is similar to that occurs globally.

Humoral immune responses and viral shedding following vaccination with modified live porcine reproductive and respiratory syndrome virus vaccines.

The antibody response and pattern of shedding of vaccine virus following vaccination with modified live genotype I or II porcine reproductive and respiratory syndrome virus (PRRSV) vaccines (MLVs) were investigated. Ninety PRRSV-free pigs were divided randomly seven, groups including the NEG, EU1, EU2, US1, US2, US3 and US4 groups. The NEG group was unvaccinated. The EU1, EU2, US1, US2, US3 and US4 groups were vaccinated with the following MLVs: AMERVAC® PRRS, Porcillis® PRRS, Fostera™ PRRS, Ingelvac® PRRS MLV, Ingelvac® PRRS ATP, and PrimePac™ PRRS+ , respectively. Sera were quantitatively assayed for viral RNA using qPCR. Antibody responses were measured using Idexx ELISA and serum neutralization (SN). Shedding of vaccine virus was investigated using sentinel pigs and by detection of viral RNA in tonsil scrapings. Antibody responses were detected by ELISA at 7-14 days post-vaccination (DPV) and persisted at high titers until 84 DPV in all MLV groups. The SN titers were delayed and isolate-specific. SN titers were higher for the homologous virus than for heterologous viruses. Age-matched sentinel pigs introduced into the EU2, US2 and US3 groups at 60 DPV seroconverted. In contrast, sentinel pigs introduced at 84 DPV remained negative in all of the MLV groups. Vaccine viral RNA was detected in tonsil scrapings from the EU2, US2 and US3 groups at 84-90 DPV. No viral RNA was detected beyond 70 DPV in the EU1, US1 and US4 groups. In conclusion, all MLV genotypes induced rapid antibody responses, which were measured using ELISA. The development of SN antibodies was delayed and isolate-specific. However, the shedding pattern was variable and depended on the by virus isolate used to manufacture the vaccine.

Comparative study of heavy metal and pathogenic bacterial contamination in sludge and manure in biogas and non-biogas swine farms.

The objective of this study is to determine and compare the heavy metal (Zn, Cu, Cd, Pb) and bacterial (E. coli, coliform and Salmonella spp.) contamination between swine farms utilizing biogas and non-biogas systems in the central part of Thailand. Results showed that average levels of E. coli, coliform, BOD, COD, Zn, Cu and Pb in sludge from the post-biogas pond were higher than the standard limits. Moreover, the levels of E. coli, coliform, Cd and Pb were also higher than the standard limits for dry manure. The levels of E. coli, coliform and BOD on biogas farms were lower than on non-biogas farms. Following isolation of Salmonella spp., it was found that Salmonella serovars Rissen was the most abundant at 18.46% (12/65), followed by Anatum 12.31% (8/65), and Kedougou 9.23% (6/65). The pathogenic strains of Salmonella serovars Paratyphi B var. java and Typhimurium were present in equal amounts at 4.62% (3/65) in samples from all swine farms. This study revealed that significant reduction in E. coli and coliform levels in sludge from covered lagoon biogas systems on swine farms. The presence of Salmonella as well as Cd and Pb, in significant amount in dry manure, suggests that there is a high probability of environmental contamination if it is used for agricultural purposes. Thus, careful waste and manure disposal from swine farms and the regular monitoring of wastewater is strongly recommended to ensure the safety of humans, other animals and the environment.

Genetic characterization of porcine circovirus type 2 in piglets from PMWS-affected and -negative farms in Thailand.

Porcine circovirus type 2 (PCV2) is the major swine pathogen associated with Porcine circovirus associated disease (PCVAD) including post-weaning multisystemic wasting syndrome (PMWS). Currently, there are 4 subtypes of PCV2 (PCV2a, b, c and d) and some epidemiological evidences demonstrated that virulence of PCV2 may relate to its subtypes. Recently, PMWS was observed more frequently in swine farms in Thailand; however, the information regarding to PCV2 subtype involved was limited. Therefore, this study was aimed to determine the association between occurrence of PMWS and PCV2 subtypes as well as genetically characterize PCV2 in Thailand. PCV2 DNA was isolated from faecal swabs and whole blood of piglets from PMWS-affected and -negative farms. The full length ORF2 sequences were compared using multiple alignment. The results showed that PCV2 DNA was detected more frequently in PMWS-affected farms. The nucleotide identities of the ORF2 from 9 PCV2 isolates representing each PMWS-affected farm and one from the negative farm ranged from 92.4 to 99.5% suggesting that there is some genetic variation of PCV2 in Thai swine. The 10 PCV2 isolates were classified into 2 clusters, in which the 7 isolates from PMWS-positive farms were in PCV2b cluster 1 A/B. The remaining isolates were separated in the new subtype called PCV2e. The results suggest the presence of new PCV2 subtypes in addition to PCV2a and PCV2b in Asian swine population. However, correlation between subtypes and virulence of PCV2 infection is not conclusive due to limited number of the PCV2 sequences from PMWS negative farms.

Chinese-like strain of porcine epidemic diarrhea virus, Thailand.

Since late 2007, several outbreaks of porcine epidemic diarrhea virus (PEDV) infection have emerged in Thailand. Phylogenetic analysis places all Thai PEDV isolates during the outbreaks in the same clade as the Chinese strain JS-2004-2. This new genotype PEDV is prevailing and currently causing sporadic outbreaks in Thailand.

Occurrence of swine influenza virus infection in swine with porcine respiratory disease complex.

We studied the occurrence of swine influenza virus (SIV) infection in piglets with respiratory symptoms resembling porcine respiratory disease complex (PRDC). A total of 106 samples including nasal swab and lung suspension from sick piglets were collected from 30 farms of medium size in the central and eastern parts of Thailand from August 2006 to February 2007. Samples were inoculated onto Mardin-Darby Canine Kidney (MDCK) cells and SIV infection was confirmed by immunofluorescent assay (IFA) and reverse transcriptase polymerase chain reaction (RT-PCR) specific for M gene. Of 106 samples, 3 pigs from 3 different farms were found to be SIV positive on all assays. The positive samples were further identified by RT-PCR as H3N2 subtype using specific primers for hemagglutinin (HA) and neuraminidase (NA) genes. SIV infection was found in 2.8% of swine suffering from respiratory distress suggesting SIV may not be the major pathogen for PRDC in the central and eastern Thailand. SIV was present in 3 of 30 farms (10%) indicating the prevalence of SIV in these regions is considerable. Since pigs are vulnerable to infection from both human and avian influenza viruses and interspecies transmission between humans and swine occurs sporadically, it is essential to continue surveillance and monitoring of SIV infection in the swine population.