Enhancement of systemic virus-specific T lymphocyte responses in pigs supplemented with algae-derived ß-glucan.

Algae-derived ß-glucan has been widely used as a feed additive in the swine industry. The supplementation of ß-glucan aims to improve growth performance and modulate the immunity of pigs. However, the potential effects of supplementing ß-glucan from algae on immune responses in pigs-specifically antigen-specific immunity-must be determined. In this study, the effects of algae-derived ß-glucan supplementation on growth performance, virus neutralising antibody and virus-specific T lymphocytes responses were investigated in pigs. Piglets (n=112 per treatment) were assigned to three treatments including non-supplemented group (control), ß-glucan 100 g/ton supplemented group (BG100), and ß-glucan 200 g/ton supplemented group (BG200). In this study, production performance of pigs was not found to be different between the experimental groups. Pigs supplemented with ß-glucan exhibited high levels of classical swine fever virus (CSFV)-specific producing T lymphocytes and neutralising antibody titer, compared to the control group. Interestingly, supplementation of ß-glucan significantly enhanced porcine reproductive and respiratory syndrome virus (PRRSV)-specific interferon-gamma (IFN-γ) producing T lymphocytes, including CD4+, CD8+, and CD4+CD8+ T lymphocyte subpopulations. Moreover, PRRS modified live vaccine (MLV) viremia was reduced in earlier for ß-glucan-supplemented pigs compared to the control group. The findings indicate that the algae-derived ß-glucan possesses biological potential as an immunomodulatory substance to enhance antiviral immunity, which may contribute to disease resistance in pigs.

First molecular detection of porcine circovirus type 4 (PCV4) in Malaysia.

Porcine circovirus type 4 (PCV4) is the newest member in the porcine circovirus family, first reported in 2020. To date, the presence of PCV4 has only been reported in China, South Korea and most recently in Thailand. Detection of PCV4 have been reported in various production stages of pigs from piglets, finishers to sows; associated with a myriad of clinical manifestations including porcine dermatitis and nephropathy syndrome (PDNS), postweaning multisystemic wasting syndrome (PMWS), respiratory, enteric and neurological diseases. While successful virus isolation and culture has yet to be reported, pathogenicity of PCV4 has been demonstrated through infectious clone studies. The objective of this study is to investigate the presence of PCV4 in Malaysian porcine population to update the epidemiology of porcine circoviruses in Malaysia. A total of 49 samples from commercial intensive pig farms, abattoir and wild boar population were subjected to conventional polymerase chain reaction assay to detect PCV4 capsid (cap) genome. Resulting cap nucleotide sequences were analyzed for maximum likelihood phylogeny relationship. Results revealed that PCV4 is present in Peninsular Malaysia at a molecular prevalence of 4.08% (2 / 49 samples). Both PCV4 positive samples originated from clinically healthy finishers. Malaysian PCV4 strains were classified as genotype PCV4b, and were found to be phylogenetically distinct from the China, South Korea and Thailand strains. With this latest update of the novel PCV4 in Malaysia, it is clear that more attention needs to be given to the investigation of novel porcine circoviruses (PCV) and management of PCV diseases.

Anti-Müllerian hormone levels in serum and testes of male dogs: relations with neuter status and bilateral abdominal cryptorchidism.

Anti-Müllerian hormone (AMH) analysis has contributed to new information in the reproductive endocrinology of domestic animals, due to clinically available diagnostic tools. An accurate and rapid diagnostic method to distinguish between neutered and bilateral abdominal cryptorchid dogs is needed in veterinary practice. Therefore, this study uses an enzyme-linked immunosorbent assay to evaluate the clinical relevance of AMH analysis in peripheral blood as a diagnostic tool for dogs with suspected bilateral abdominal cryptorchidism. The possible alteration of the AMH localization in testicular tissue caused by this pathologic condition was also investigated using immunohistochemistry. Male dogs were divided into three groups of healthy intact (n = 14), healthy castrated (n = 14), and bilateral abdominal cryptorchid (n = 14) dogs. The results demonstrated a higher level of serum AMH in the cryptorchid group compared to the intact group (P < 0.01), while serum AMH levels of all castrated dogs were below the limit of detection (<0.05 ng/mL). Moreover, the percentage of positive AMH immunostaining of the intact group was less than that of the cryptorchid group (P < 0.01). A significantly positive correlation was found between serum AMH concentration and localization in testicular tissues (r = 0.93, P < 0.01). Our findings suggest that AMH levels in the peripheral blood could be used as an alternative and rapid screening method for detecting dogs with abdominal cryptorchidism.

First molecular detection of porcine circovirus type 4 (PCV4) in Malaysia

@#Porcine circovirus type 4 (PCV4) is the newest member in the porcine circovirus family, first reported in 2020. To date, the presence of PCV4 has only been reported in China, South Korea and most recently in Thailand. Detection of PCV4 have been reported in various production stages of pigs from piglets, finishers to sows; associated with a myriad of clinical manifestations including porcine dermatitis and nephropathy syndrome (PDNS), postweaning multisystemic wasting syndrome (PMWS), respiratory, enteric and neurological diseases. While successful virus isolation and culture has yet to be reported, pathogenicity of PCV4 has been demonstrated through infectious clone studies. The objective of this study is to investigate the presence of PCV4 in Malaysian porcine population to update the epidemiology of porcine circoviruses in Malaysia. A total of 49 samples from commercial intensive pig farms, abattoir and wild boar population were subjected to conventional polymerase chain reaction assay to detect PCV4 capsid (cap) genome. Resulting cap nucleotide sequences were analyzed for maximum likelihood phylogeny relationship. Results revealed that PCV4 is present in Peninsular Malaysia at a molecular prevalence of 4.08% (2 / 49 samples). Both PCV4 positive samples originated from clinically healthy finishers. Malaysian PCV4 strains were classified as genotype PCV4b, and were found to be phylogenetically distinct from the China, South Korea and Thailand strains. With this latest update of the novel PCV4 in Malaysia, it is clear that more attention needs to be given to the investigation of novel porcine circoviruses (PCV) and management of PCV diseases.

One world--one health: the threat of emerging swine diseases. An Asian perspective.

Owing to the expanding globalization, the trans-boundary spread of an epizootic can easily result from uncontrolled animal movements and human traffic. Foot and mouth disease (FMD) is a major trans-boundary disease in most Asian countries. Its sporadic re-emergence suggests that collaborative FMD control strategies should be uniformly implemented in endemic countries to ensure the overall national herd vaccination coverage, biocontainment when outbreaks occur, and strict biosecurity control of animal movement between countries. Sustained commitments from governments, cooperative diplomatic relationships, and public awareness campaigns are critical to FMD control, to ensure collaboration among veterinarians, traders and farmers throughout Southeast Asia (SEA). Recently, highly pathogenic porcine reproductive and respiratory syndrome (HP-PRRS) and porcine epidemic diarrhoea (PED) spread from China to Southeast Asian countries, causing major economic losses. Foot and mouth disease, HP-PRRS, and PED currently remain endemic and may continue to sporadically re-emerge, owing to inadequate public health management and/or biosecurity failures. Therefore, the risk factors must be identified to better understand the epidemiology of these diseases in an effort to develop effective control measures. International coordination through the establishment of a collaborative network supported by the World Organization for Animal Health (OIE) and the Food and Agriculture Organization (FAO) should be implemented to prevent trans-boundary transmission among countries. This review discusses trans-boundary swine diseases of particular importance to SEA, including FMD, HP-PRRS and PED, with a primary focus on major factors contributing to the spread of these diseases and important control measures, reflecting the impact of globalization on disease control and surveillance.

Factors critical for successful vaccination against classical swine fever in endemic areas.

Classical swine fever (CSF) or hog cholera, caused by the classical swine fever virus (CSFV), is one of the most important viral diseases that cause serious economic loss to the swine industry worldwide. During the past 5 years, several techniques for measuring porcine cell-mediated immunity (CMI) were applied, in conjunction with other conventional techniques, to study factors that influence the induction of CSFV-specific immunity. Information, obtained from a series of experiments, demonstrated cell-mediated immune responses in providing protective immunity against CSF infection. Although it has been confirmed that commercially available modified live CSF vaccines are able to induce complete protection in vaccinated pigs, several factors including maternal immunity, the age of primary vaccination, vaccination protocol and complications caused by other pathogens, can greatly affect the effectiveness of CSF vaccines in the field.

Negative impact of porcine reproductive and respiratory syndrome virus infection on the efficacy of classical swine fever vaccine.

Recent findings suggest that porcine reproductive and respiratory syndrome virus (PRRSV) possesses immunomodulatory properties. To investigate the effect of PRRSV infection on classical swine fever (CSF) vaccine efficacy, 17-day-old pigs were divided into five groups. The experimental group was infected with a Thai PRRSV (US genotype) a week before CSF vaccination and challenged with a virulent CSF virus (CSFV) 3 weeks following vaccination. The control groups received no PRRSV infection, no CSF vaccination, no CSF challenge, or in combination were included. The results demonstrated that PRRSV infection significantly inhibited host immune response that resulted in vaccination failure in the subsequent CSFV exposure. Following CSF challenge, the PRRSV-infected, vaccinated pigs exhibited clinical, virological and pathological features resembled to those of the non-vaccinated groups. The findings indicated that CSF immunization during an acute phase of PRRSV infection could result in vaccination failure.

Genetics and geographical variation of porcine reproductive and respiratory syndrome virus (PRRSV) in Thailand.

The Thai isolates of porcine reproductive and respiratory syndrome virus (PRRSV) were obtained from the Chulalongkorn University-Veterinary Diagnostic Laboratory (CU-VDL). Virus isolation was confirmed by immunoperoxidase monolayer assay (IPMA) using SDOW-17. The virus genotype was determined using nested multiplex RT-PCR (nm RT-PCR) of ORF 1b. The nm RT-PCR was able to detect at least 10TCID50/ml of PRRSV. Of 137 Thai isolates, 66.42% belonged to the European (EU) genotype and 33.58% to the North American (US) genotype. ORF5 products of the eight US strains (00CS1, 01NP1, 01UD6, 02CB13, 02KK1, 02PB1, 02SP2 and 02SP3) and the six EU strains (01CB1, 01RB1, 02BR1, 02CB12, 02SB2 and 03RB1) were sequenced for genetic variation analysis. The US strains of the Thai isolates are clustered within the same group and are more closely related to the IAF-EXP91 from Canada (89-90% nucleotide identity), whereas the EU strains were very similar to the EU prototype, Lelystad virus (87-97.5% nucleotide identity). The ORF5 nucleotide identities within the US genotype tested in this study compared to the US prototype, VR-2332 varied from 83.7 to 85.2%, whereas 83.5-85.5% amino acid identities were found. Based on the phylogenetic tree, each pair of the Thai isolates (01NP1 and 02KK1, 00CS1 and 01UD6, and 01CB1 and 01RB1) was identical despite they were collected from different provinces. Therefore, there was no geographic influence on the spreading of PRRSV in Thailand. Interestingly, 02CB12 (EU genotype) shared over 99% similarity of the ORF5 nucleotide sequence and 98.6% of amino acid identity with the European vaccine, Porcillis (AF378819). However, modified live virus vaccines for PRRSV have not yet been used in the swine population in Thailand. The results suggested that both US and EU genotypes exist in Thailand, genetic variation does occur in both genotypes, and the sources of the viruses appear to be from Canada and Northern Europe, respectively. In addition, the spreading of PRRSV in Thailand might be due to introducing infected replacement pigs or infected semen into the farm.

Differential production of proinflammatory cytokines: in vitro PRRSV and Mycoplasma hyopneumoniae co-infection model.

An in vitro culture system was developed to investigate the induction of proinflammatory cytokines by Mycoplasma hyopneumoniae and porcine reproductive and respiratory syndrome virus (PRRSV). M. hyopneumoniae infected porcine tracheal ring explants were co-cultured with PRRSV infected pulmonary alveolar macrophages (PAMs) for 24h to assess the cytokine production of each pathogen alone and the interaction between the two pathogens in vitro. Semiquantitative RT-PCR was used to measure interleukin (IL) 1alpha, IL1beta, IL6, IL8, IL10, IL12 and tumor necrosis factor (TNF) alpha mRNA in PAMs. Commercial ELISAs were used to measure soluble IL1beta, IL8, IL10 and TNF in the culture supernatant. In the dual infected group, mRNA expression of IL1alpha, IL1beta, IL8 and TNF was increased. Both the M. hyopneumoniae- and PRRSV-infected only groups tended to have increased expression of IL1alpha, IL1beta and IL8 mRNA, although no statistical difference was observed. Increased levels of IL1beta, IL8 and IL10 were present in the supernatant of the dual infected group as measured by ELISA. No increase in soluble TNF was observed in any of the groups. IL8 levels appeared high in all groups independent of infection status. The cause of the elevated IL8 was unknown, however, it may have been a non-specific response by the cells to tissue damage during the harvesting of the tracheal rings. Correlation between mRNA expression and the soluble cytokine levels were similar in the dual infected groups with the exception of IL10 and TNF. Levels of mRNA and soluble protein levels in the single pathogen infected groups were not as consistent. The increased production of proinflammatory cytokines IL1alpha, IL1beta, IL8 and TNF in the group infected with both M. hyopneumoniae and PRRSV suggests that cytokine induced inflammation may play an important role in the severe, chronic pneumonia induced by the concurrent infection of the two pathogens.

Efficacy of antimicrobial treatments and vaccination regimens for control of porcine reproductive and respiratory syndrome virus and Streptococcus suis coinfection of nursery pigs.

Seventy-six, crossbred, porcine reproductive and respiratory syndrome virus (PRRSV)-free pigs were weaned at 12 days of age and randomly assigned to seven groups of 10 to 11 pigs each. Pigs in group 1 served as unchallenged controls. Pigs in groups 2 to 7 were challenged intranasally with 2 ml of high-virulence PRRSV isolate VR-2385 (10(4.47) 50% tissue culture infective doses per 2 ml) on day 0 of the study (30 days of age). Seven days after PRRSV challenge, pigs in groups 2 to 7 were challenged intranasally with 2 ml of Streptococcus suis serotype 2 (10(8.30) CFU/2 ml). Group 2 pigs served as untreated positive controls. Antimicrobial treatments included daily intramuscular injection with 66,000 IU of procaine penicillin G per kg of body weight on days 8 to 10 (group 3), drinking water medication with 23.1 mg of tiamulin per kg during days 8 to 10 (group 4), and daily intramuscular injection of 5.0 mg of ceftiofur hydrochloride per kg on days 8 to 10 (group 5). Vaccination regimens included two intramuscular doses of an autogenous killed S. suis vaccine (group 6) prior to S. suis challenge or a single 2-ml intramuscular dose of an attenuated live PRRSV vaccine (group 7) 2 weeks prior to PRRSV challenge. Mortality was 0, 63, 45, 54, 9, 40, and 81% in groups 1 to 7, respectively. Ceftiofur treatment was the only regimen that significantly (P < 0. 05) reduced mortality associated with PRRSV and S. suis coinfection. The other treatments and vaccinations were less effective. We conclude that ceftiofur administered by injection for three consecutive days following S. suis challenge was the most effective regimen for minimizing disease associated with PRRSV and S. suis coinfection.

Pathogenesis of porcine reproductive and respiratory syndrome virus-induced increase in susceptibility to Streptococcus suis infection.

Eighty 3-week-old crossbred pigs were randomly assigned to six groups (13-14 pigs/group). Group 1 pigs served as uninoculated controls, group 2 pigs were inoculated intranasally (i.n.) with Streptococcus suis serotype 2, group 3 pigs were inoculated i.n. with a modified live porcine reproductive and respiratory syndrome virus (PRRSV) vaccine, group 4 pigs were inoculated i.n. with the same vaccine and with S. suis, group 5 pigs were inoculated i.n. with VR-2385 (a high-virulence strain of PRRSV), and group 6 pigs were inoculated i.n. with VR-2385 and S. suis. Pigs exposed to both PRRSV and S. suis were inoculated with PRRSV 7 days prior to S. suis inoculation. The pigs were 26 days old when inoculated with S. suis. Respiratory disease was significantly more severe in groups 5 and 6. Mortality rate was the highest in group 6 (87.5%). This rate was significantly higher than that observed in all other groups except group 4 (37.5%). The mortality rate in group 2, inoculated with S. suis alone, was 14.3%. No pigs from groups 1, 3, or 5 died prior to the scheduled necropsies at 10 and 28 days postinoculation with PRRSV (DPI). To study the effect of PRRSV and/or S. suis on pulmonary clearance by pulmonary intravascular macrophages, six pigs from each group were intravenously infused with 3% copper phthalocyanine tetrasulfonic acid in saline prior to necropsy at 10 DPI. Mean copper levels in the lungs of pigs in groups 2, 5, and 6 were significantly lower than those in control pigs. The mean percentage of lung tissue grossly affected by pneumonia at 10 DPI was 0%, 1%, 0%, 3%, 64%, and 62% for groups 1-6, respectively. Both gross and microscopic interstitial pneumonia lesions were significantly more severe in the VR2385-inoculated groups (5 and 6). PRRSV was isolated from bronchoalveolar lavage fluid collected at necropsy from 100% of the pigs in groups 5 and 6, 71.4% of pigs in group 4, 38.5% of pigs in group 3, and none of the pigs in groups 1 or 2. Streptococcus suis serotype 2 was cultured from the internal tissues of 7.7%, 28.6%, and 78.6% of the pigs in groups 2, 4, and 6, respectively. Streptococcus suis serotype 2 was isolated from whole blood at necropsy from 7.7%, 35.7%, and 78.6% of pigs in groups 2, 4, and 6, respectively. Significantly more pigs in group 6 had S. suis isolated from whole blood and internal tissues. In summary, both high-virulence PRRSV and S. suis decreased copper clearance, and the incidence of isolation of S. suis and PRRSV was higher in dually inoculated pigs. PRRSV-induced suppression of pulmonary intravascular macrophage function may in part explain PRRSV-associated increased susceptibility to S. suis infection.

The role of pulmonary intravascular macrophages in porcine reproductive and respiratory syndrome virus infection.

The objective of this article is to summarize the current state of knowledge of the complex interaction of porcine reproductive and respiratory syndrome virus (PRRSV) and porcine pulmonary intravascular macrophages (PIMs). PIMs play an important role in pulmonary surveillance, and in the past few years we have investigated their role in PRRSV infection. PRRSV antigens and nucleic acids have been demonstrated in PIMs both in vitro and in vivo. Examination of cultured PIMs infected with PRRSV revealed the accumulation of viral particles in the smooth-walled vesicles. PRRSV-infected PIMs in vitro yielded a virus titer similar to pulmonary alveolar macrophages. PRRSV infection induces either apoptosis or cell lysis of PIMs. The in vitro bactericidal activity of PRRSV-infected PIMs is significantly decreased. Phagocytic activity of PIMs, as measured by pulmonary copper clearance, is significantly decreased in PRRSV-infected pigs. This evidence supports the hypothesis that PRRSV-induced damage to PIMs results in increased susceptibility to bacteremic diseases. Recent studies with PRRSV and Streptococcus suis coinfection confirmed that PRRSV predisposes pigs to S. suis infection and bacteremia. These results could explain the increase in bacterial respiratory diseases and septicemias observed in PRRSV-infected pigs.

Mycoplasma hyopneumoniae potentiation of porcine reproductive and respiratory syndrome virus-induced pneumonia.

An experimental model that demonstrates a mycoplasma species acting to potentiate a viral pneumonia was developed. Mycoplasma hyopneumoniae, which produces a chronic, lymphohistiocytic bronchopneumonia in pigs, was found to potentiate the severity and the duration of a virus-induced pneumonia in pigs. Pigs were inoculated with M. hyopneumoniae 21 days prior to, simultaneously with, or 10 days after inoculation with porcine reproductive and respiratory syndrome virus (PRRSV), which induces an acute interstitial pneumonia in pigs. PRRSV-induced clinical respiratory disease and macroscopic and microscopic pneumonic lesions were more severe and persistent in M. hyopneumoniae-infected pigs. At 28 or 38 days after PRRSV inoculation, M. hyopneumoniae-infected pigs still exhibited lesions typical of PRRSV-induced pneumonia, whereas the lungs of pigs which had received only PRRSV were essentially normal. On the basis of macroscopic lung lesions, it appears that PRRSV infection did not influence the severity of M. hyopneumoniae infection, although microscopic lesions typical of M. hyopneumoniae were more severe in PRRSV-infected pigs. These results indicate that M. hyopneumoniae infection potentiates PRRSV-induced disease and lesions. Most importantly, M. hyopneumoniae-infected pigs with minimal to nondetectable mycoplasmal pneumonia lesions manifested significantly increased PRRSV-induced pneumonia lesions compared to pigs infected with PRRSV only. This discovery is important with respect to the control of respiratory disease in pigs and has implications in elucidating the potential contribution of mycoplasmas in the pathogenesis of viral infections of other species, including humans.

Influence of pig age on virus titer and bactericidal activity of porcine reproductive and respiratory syndrome virus (PRRSV)-infected pulmonary intravascular macrophages (PIMs).

Twelve pigs (six 4-week-old and six 4-month-old cross-bred, specific pathogen free pigs) were used as donors for both pulmonary intravascular macrophages (PIMs) and pulmonary alveolar macrophages (PAMs). The PIMs and PAMs were infected in vitro with low (ISU-55) or high (VR-2385) virulence strains of PRRSV at 1 multiplicity of infection (m.o.i.) for comparisons of virus titers at 48 h post infection (PI). PIMs were as permissive as PAMs to infection with both PRRSV isolates yielding similar progeny titers (10(4.81) vs. 10(5.22) TCID50/ml, respectively). Both ISU-55 and VR-2385 were able to infect PIMs and no significant difference in virus replication as measured by virus titers between isolates was found (10(5.33) vs. 10(4.69) TCID50/ml, respectively). PIMs from 4-weak-old pigs yielded a higher virus titer following PRRSV infection than PIMs from 4-month-old pigs (10(5.43) vs. 10(4.59) TCID50/ml, respectively; p < 0.02). VR-2385-infected PIMs had significantly decreased bactericidal (Staphylococcus aureus) activity compared with uninfected PIMS at 48 h PI (p < 0.05). There was no difference in bactericidal activity between ISU-55 (low virulence)-infected PIMs and VR-2385 (high virulence)-infected PIMs. Both ISU-55 and VR-2385 infection significantly decreased the production of superoxide anion (SOA) at 24 and 48 h PI (p < 0.01). In conclusion, (1) PRRSV had a detrimental effect on bactericidal activity and SOA production of PIMs, (2) PIMs from younger pigs were more permissive to PRRSV infection, and (3) the selected PRRSV strains, which differ in their abilities to induce pneumonia in vivo were not different when tested in vitro by measuring virus titer and bactericidal functions.

Effects of low (modified-live virus vaccine) and high (VR-2385)-virulence strains of porcine reproductive and respiratory syndrome virus on pulmonary clearance of copper particles in pigs.

Seventy-five 3-week-old, crossbred pigs from a herd free of porcine reproductive and respiratory syndrome virus (PRSSV) were randomly assigned to three groups: uninfected controls, pigs inoculated intranasally with RespPRRS/Repro modified-live virus vaccine (RespPRRS), and pigs inoculated intranasally with a high-virulence strain of PRRSV (VR-2385). Pigs were intravenously infused with 3% copper phthalocyanine tetrasulfonic acid (0.2 ml/kg) in normal saline 30 minutes before necropsy, which was performed 3, 7, 10, 14, or 28 days postinoculation (DPI) with PRRSV. There were no differences in serum copper concentration in samples collected at 0, 15, or 30 minutes after infusion. Copper concentrations in the lungs of VR-2385-inoculated pigs were significantly lower than levels in the lungs of control and RespPRRS-inoculated pigs at 7, 10, and 14 DPI (P < 0.05). The greatest difference between the groups was observed at 10 DPI. Liver and spleen copper concentrations were slightly, but not significantly, higher in both PRRSV-infected groups. The percentage of lung affected by grossly visible pneumonia ranged from 0 to 5.6% in the RespPRRS-inoculated group and from 15.2 to 46.4% in the VR-2385-inoculated group, with lesions peaking at 7 and 10 DPI, respectively. PRRSV antigen was demonstrated in both pulmonary alveolar macrophages (PAMs) and pulmonary intravascular macrophages (PIMs) by immunohistochemical methods. Copper particles were demonstrated in the PIMs by light microscopy. PRRSV was isolated from bronchoalveolar lavage fluid of VR-2385-infected pigs from 3 to 28 DPI and from RespPRRS-inoculated pigs from 7 to 28 DPI. No PRRSV, PRRSV antibodies, or PRRSV-induced pneumonia was detected in the control group. These results suggest that 1) PRRSV has a detrimental effect on the uptake of copper particles by PIMs, 2) the severity of PRRSV-induced damage to PIMs differs among strains, and 3) demonstration of PRRSV-induced decreased pulmonary clearance supports the hypothesis that PRRSV infection may make pigs more susceptible to bacterial septicemia.

Effect of porcine reproductive and respiratory syndrome virus (PRRSV) (isolate ATCC VR-2385) infection on bactericidal activity of porcine pulmonary intravascular macrophages (PIMs): in vitro comparisons with pulmonary alveolar macrophages (PAMs).

Porcine pulmonary intravascular macrophages (PIMs) were recovered by in situ pulmonary vascular perfusion with 0.025% collagenase in saline from six 8-week old, crossbred pigs. Pulmonary alveolar macrophages (PAMs) were recovered by bronchoalveolar lavage from the same pigs for comparisons in each assay. The macrophages were exposed to PRRSV (ATCC VR-2385) in vitro for 24 h and infection was confirmed by an indirect immunofluorescence test or transmission electron microscopy. Viral particles tended to accumulate in the vesicles of the Golgi apparatus or endoplasmic reticulum. Bactericidal function assays were performed on the recovered macrophages to determine the effects of the virus on macrophage functions. In vitro PRRSV infection reduced the bactericidal ability of PIMs from 68.3% to 56.4% (P < 0.09), and PAMs from 69.3% to 61.0% (P > 0.1) at 24 h post-infection. The mean percentage of bacteria killed by macrophages after PRRSV infection was not significantly different among the treatment groups or between the treatment groups and non-infected controls based on colorimetric MTT bactericidal (Staphylococcus aureus) assay. PRRSV did not affect the ability of PIMs or PAMs to internalize opsonized 125I-iododeoxyuridine-labeled S. aureus (P > 0.05). PRRSV infection significantly decreased the production of superoxide anion (P < 0.01) by 67.0% in PIMs and by 69.4% in PAMs. PRRSV reduced the myeloperoxidase-H2O2-halide product (P < 0.01) by 36.5% for PIMs and by 48.1% for PAMs. The results suggest: (1) PIMs should be considered as an important replication site of PRRSV; (2) PRRSV may have a detrimental effect on both PIMs and PAMs; (3) loss of bactericidal function in PIMs may facilitate hematogenous bacterial infections.