Infection of growing swine with porcine reproductive and respiratory syndrome virus and Mycoplasma hyopneumoniae--effects on growth,serum metabolites,and insulin-like growth factor-I

This study evaluated the influence of concomitant infections with porcine reproductive and respiratory syndrome virus (PRRSV) and Mycoplasma hyopneumoniae on growth performance, serum metabolite concentrations, and serum insulin-like growth factor-I (IGF-I) in growing pigs. Twenty-two barrows (10 weeks of age) were treated with either an intranasal administration of PRRSV and an intratracheal infusion of M. hyopneumoniae (treatment; n = 8) or a sham inoculation with medium (sham; n = 8), or were not treated (control; n = 6). The sham pigs were matched by body weight and pair-wise fed with treatment pigs. Pigs were weighed on the day of inoculation (day 0) and at 4 weeks postinoculation (day 28). Blood samples were collected prior to inoculation and at weekly intervals for 4 weeks. Pigs in the treatment group exhibited clinical signs consistent with PRRSV infection and M. hyopneumoniae pneumonia. Diagnostic procedures confirmed that treatment pigs were inoculated with PRRSV and M. hyopneumoniae and that sham and control pigs remained free of both pathogens. Average daily gain and feed conversion did not differ among the 3 groups. The IGF-I levels differed (P < 0.05) between control and treatment pigs, even after feed intake returned to similar levels among groups. At day 7, IGF-I concentrations were greater in sham pigs compared with treatment pigs, despite similar feed intake. Sham inoculation and decreased feed intake in sham pigs did not alter serum IGF-I concentrations. Evidently, IGF-I status of pigs affected with disease is influenced by nutritional and nonnutritional factors during the disease process.     

Experimental reinfection with homologous porcine reproductive and respiratory syndrome virus in SPF pigs

The present examination was conducted to determine if the pigs infected with one strain of porcine reproductive and respiratory syndrome virus (PRRSV) would be protected against a subsequent homologous virus challenge. Sixteen 4-week-old SPF pigs were assigned to 2 experimental groups A and B. The pigs in group A were inoculated with 10(6.5) TCID50 of PRRSV by intranasal route. On 77 days post-inoculation (PI), pigs in groups A and B were similarly inoculated with same virus. After the secondary inoculation, the pigs in group A didn't show any clinical sign including pyrexia and reduction of white blood cell (WBC) number. Viremia was detected only on 3 days PI with low virus titer and any virus was not recovered from serum and tissues at the time of necropsy on 14 or 28 days PI. In contrast, pigs in group B showed pyrexia for 14 days and reduction of WBC number on 3 days PI. Viremia was detected between 3 and 28 days PI, and virus was isolated from several tissues of all pigs. These results indicate that previous exposure to PRRSV can prevent development of clinical signs and reduce virus proliferation in pigs after subsequent infection with the homologous PRRSV.     

Vitamin E supplementation does not mitigate the acute morbidity effects of porcine reproductive and respiratory syndrome virus in nursery pigs

The objective of this study was to determine whether feeding a vitamin E-rich diet would benefit nursery pigs infected with porcine reproductive and respiratory syndrome virus (PRRSV). Sixty-four pigs were subjected to one of four treatment combinations (2 x 2 factorial) of dietary vitamin E (adequate or excess) and PRRSV (medium or inoculation with VR-2385 isolate P-129). Pigs were fed experimental diets during a 3-wk period before inoculation as well as during a 12-d period after inoculation. Growth performance was determined throughout the study, and lipid peroxidation in liver, glutathione peroxidase (GPX) activity in serum, circulating white blood cells, and serum interleukin-1beta (IL-1beta) and interferon-gamma (IFN-gamma) were determined in samples collected from pigs killed 4 or 12 d after inoculation. Infection by PRRSV (P < 0.001) induced a marked decrease in both ADFI and ADG, but neither the main effect of diet nor the diet x PRRSV interaction was significant. Neither diet nor PRRSV affected feed efficiency. At 12 d after inoculation, lipid peroxidation in liver and GPX activity in serum were lower in pigs fed excess vitamin E than in those fed adequate vitamin E (P < 0.01), suggesting that the diet high in vitamin E bolstered the antioxidant status of the pigs. However, PRRSV did not affect lipid peroxidation in liver or serum GPX activity, and the diet x PRRSV interaction was not significant. White blood cell counts were decreased and IFN-gamma, and IL-1beta were increased (P < 0.05) 4 and 12 d after inoculation in PRRSV-infected pigs, but neither diet nor the diet x PRRSV interaction was significant. Collectively, these results indicate that increasing antioxidant defenses by feeding high levels of vitamin E did not ameliorate the effects of PRRSV on decreased growth, leukopenia, and increased serum IL-1beta and IFN-gamma. Thus, feeding nursery pigs a diet high in vitamin E may not be useful for mitigating the acute morbidity effects of PRRSV infection.     

猪繁殖与呼吸综合征免疫防制新途径的研究进展

猪繁殖与呼吸综合征(porcine reproductive and respiratory syndrome,PRRS)是一种主要表现为母猪繁殖障碍与仔猪呼吸道症状的传染病。近年来,猪繁殖与呼吸综合征病毒(porcine reproductive and respiratory syndrome virus,PRRSV)变异株不断出现,免疫逃避及持续性感染使得猪群发病率或复发率均相继增高,给养猪业带来了巨大的损失。目前所采用的胃肠道途径接种活疫苗或灭活疫苗的方法无法诱导对猪群的全面保护作用。为减少养猪业的经济损失,亟需研制新防制方法和新疫苗接种途径。作者主要从黏膜免疫的免疫部位、呼吸道保护性黏膜免疫反应诱导、黏膜免疫途径、佐剂的选择及病毒的免疫抑制反应等方面简要论述了有效防制PRRSV的黏膜免疫方法的研究进展,为进一步了解黏膜免疫抵御PRRSV突变株感染及黏膜疫苗研制等方面提供有用的信息。     

Interleukin-12 (IL-12) ameliorates the effects of porcine respiratory and reproductive syndrome virus (PRRSV) infection

Porcine respiratory and reproductive syndrome virus (PRRSV) disease, one of the most economically significant viral diseases in the swine industry, is characterized by miscarriages, premature farrowing, stillborn pigs, and respiratory disease associated with death and chronic poor performance of nursing and weaned pigs. Interleukin-12 (IL-12) is a key component in driving the development of cell-mediated immunity as well as stimulating interferon-gamma (IFN-gamma) production from T cells and natural killer cells. Although some studies have investigated the use of IL-12 as a vaccine adjuvant in swine, little is known about its effectiveness as a treatment against viral diseases in swine. The present study investigated whether recombinant porcine IL-12 (rpIL-12) enhances the immune response and thereby diminishes the effects of PRRSV infection in young pigs. Interestingly, in vitro experiments demonstrated that rpIL-12 is capable of inducing swine pulmonary alveolar macrophages (PAMs), the target cells of PRRSV, to produce IFN-gamma in a dose and time dependent manner. In addition, in vitro studies also revealed that rpIL-12 treatment was capable of significantly reducing PRRSV viral titers in PAMs. In vivo administration of rpIL-12 significantly decreased PRRSV titers in the lungs and blood of infected animals. Furthermore, treatment with rpIL-12 prevented significant growth retardation in PRRSV-infected animals. Finally, in response to viral antigen recall challenge, PAMs isolated from rpIL-12-treated/PRRSV-infected animals produced greater amounts of IFN-gamma and lesser amounts of interleukin-10 than PAMs isolated from non-rpIL-12-treated/PRRSV-infected animals. Taken together our data indicate that treatment with rpIL-12 may provide an effective approach to control or ameliorate PRRSV-induced disease in swine.     

Infection with Porcine reproductive and respiratory syndrome virus stimulates an early gamma interferon response in the serum of pigs

The early release of cytokines by cells involved in innate immunity is an important host response to intracellular pathogens. Gamma interferon (IFN-gamma) is an important cytokine produced during the early stages of an infection by macrophages, natural killer (NK) cells, and other cell types, and it is also a central cytokine mediator for the induction of cellular or Th1 immunity. To better understand innate and adaptive immune responses after infection with Porcine reproductive and respiratory syndrome virus (PRRSV), we investigated serum IFN-gamma concentrations and the duration of viremia. For 2 strains of atypical PRRSV, IFN-gamma was detectable in swine serum soon after infection and lasted for approximately 3 wk. Serum concentrations of IFN-gamma peaked at about 10 d after inoculation and returned to approximately baseline levels by day 22. However, individual pigs manifested short, sporadic increases in the serum concentration of IFN-gamma from 18 to 50 d after inoculation. Prior vaccination blocked the serum IFN-gamma response associated with homologous virus challenge and altered the kinetics of the response after heterologous challenge. Two other respiratory viruses of pigs, Porcine respiratory coronavirus and Swine influenza virus, do not appear to induce serum IFN-gamma. The early production of IFN-gamma in PRRSV-infected pigs might result from activation of NK cells, a response that is more characteristic of immune pathways stimulated by intracellular bacterial and protozoan infections.     

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.     

Eradication of porcine reproductive and respiratory syndrome virus by serum inoculation of na?ve gilts

The acclimatization program included exposure to serum and recovery. A continuous flow unit (nursery to finishing) from the same farm was selected as a potential source of porcine reproductive and respiratory syndrome virus (PRRSV). Negative gilts were inoculated 5 d after arrival by intramuscular injection of serum from selected animals. There was a significant reduction in seroprevalence in the sow herd 1 y after implementation of the gilt inoculation program (P < 0.05). At that time, all of the tested nursery pigs were negative for PRRSV. The fully segregated finisher population had a significant reduction in the frequency of PRRSV positive animals (P < 0.05) by enzyme-linked immunosorbent assay (ELISA), with all animals testing negative by the end of the study. However a persistent seroconversion was observed in the partially segregated finisher pigs (P > 0.05). In conclusion, the gilt serum inoculation program achieved sow herd stabilization, as defined by the production of negative weaned pigs and this resulted in the eradication of PRRSV in the fully segregated flow.     

猪链球菌2型仔猪感染动物模型的建立及免疫保护试验

采用猪繁殖与呼吸综合征(PRRS)弱毒与猪链球菌2型协同感染仔猪的方式,建立动物感染模型,结果协同感染组试验仔猪均死亡,PRRS弱毒、猪链球菌攻毒组及空白对照组仔猪均存活.结果表明,PRRS弱毒可增强猪链球菌2型对猪的易感性.将建立的动物感染模型用于猪链球菌灭活苗(马链球菌兽疫亚种 猪链球菌2型)的效力检验,结果灭活苗可以保护PRRSV与链球菌的协同感染.     

Effects of intranasal inoculation with Bordetella bronchiseptica, porcine reproductive and respiratory syndrome virus, or a combination of both organisms on subsequent infection with Pasteurella multocida in pigs

OBJECTIVE: To determine effects of intranasal inoculation with porcine reproductive and respiratory syndrome virus (PRRSV) or Bordetella bronchiseptica on challenge with nontoxigenic Pasteurella multocida in pigs. ANIMALS: Seventy 3-week-old pigs. PROCEDURE: In experiment 1, pigs were not inoculated (n= 10) or were inoculated with PRRSV (10), P. multocida (10), or PRRSV followed by challenge with P. multocida (10). In experiment 2, pigs were not inoculated (n = 10) or were inoculated with B. bronchiseptica (10) or PRRSV and B. bronchiseptica (10); all pigs were challenged with P. multocida. Five pigs from each group were necropsied 14 and 21 days after initial inoculations. RESULTS: Pasteurella multocida was not isolated from tissue specimens of pigs challenged with P. multocida alone or after inoculation with PRRSV. However, in pigs challenged after inoculation with B. bronchiseptica, P. multocida was isolated from specimens of the nasal cavity and tonsil of the soft palate. Number of bacteria isolated increased in pigs challenged after coinoculation with PRRSV and B. bronchiseptica, and all 3 agents were isolated from pneumonic lesions in these pigs. CONCLUSIONS AND CLINICAL RELEVANCE: Infection of pigs with B. bronchiseptica but not PRRSV prior to challenge with P. multocida resulted in colonization of the upper respiratory tract and tonsil of the soft palate with P. multocida. Coinfection with PRRSV and B. bronchiseptica predisposed pigs to infection of the upper respiratory tract and lung with P. multocida. Porcine reproductive and respiratory syndrome virus and B. bronchiseptica may interact to adversely affect respiratory tract defense mechanisms, leaving pigs especially vulnerable to infection with secondary agents such as P. multocida.     

Immunohistochemical detection of porcine reproductive and respiratory syndrome virus using colloidal gold.

Two cytopathic agents were isolated on porcine alveolar macrophages following inoculation with homogenates of lung tissues from pigs showing respiratory problems. These isolates were identified as porcine reproductive and respiratory syndrome (PRRS) virus isolates by indirect immunofluorescence using a PRRS virus (PRRSV) specific monoclonal antibody (MAb) and were designated as LHVA-92-1 and LHVA-92-2. Immunogold electron microscopy using a porcine PRRS positive serum pool and protein A-gold resulted in an intense labelling of aggregates of viral particles. Dark specific cytoplasmic staining of porcine alveolar macrophages infected with both virus isolates could be observed by immunogold silver staining (IGSS) using the specific MAb. This method proved effective in detecting PRRSV antigens in several ethanol-fixed tissues of piglets intranasally inoculated with the supernatants of macrophages infected with each isolate. Immunogold silver staining was also successfully used for the detection of PRRSV antigens on sections of formalin-fixed paraffin-embedded lung tissues and on frozen sections of lungs. The present results indicate that colloidal gold may be useful for the identification and immunohistochemical detection of PRRSV in tissues.     

Influence of ampicillin, ceftiofur, attenuated live PRRSV vaccine, and reduced dose Streptococcus suis exposure on disease associated with PRRSV and S. suis coinfection

The objective of this research was to evaluate the efficacy of two antimicrobials (ampicillin and ceftiofur), a modified-live porcine reproductive and respiratory syndrome virus (PRRSV) vaccine, and low dose exposure to Streptococcus suis on disease associated with PRRSV/S. suis coinfection. Fifty-six, crossbred, PRRSV-free pigs were weaned at 10-12 days of age and randomly assigned to five treatment groups. All pigs were inoculated with 2ml of 10(6.4) TCID50/ml of high virulence PRRSV isolate VR-2385 intranasally at 29-31 days of age (day 0 of the study) followed 7 days later by intranasal inoculation with 2ml of 10(8.9)colony forming units(CFU)/ml S. suis type 2 isolate ISU VDL #40634/94. Pigs in group 1 (n=10) served as untreated infected positive controls. Pigs in group 2 (n=12) were treated with 5.0 mg/kg ceftiofur hydrochloride intramuscularly (IM) on days 8, 11, and 14. Pigs in group 3 (n=11) were treated with 11 mg/kg ampicillin IM on days 8-10. Pigs in group 4 (n=12) were vaccinated 14 days prior to PRRSV challenge with a commercial modified-live PRRSV vaccine. Pigs in group 5 (n=11) were exposed to a 1:100 dilution of the S. suis challenge inoculum 19 days prior to S. suis challenge. Mortality was 80, 25, 82, 83, and 36% in groups 1-5, respectively. The reduced dose S. suis exposure had some residual virulence, evidenced by S. suis induced meningitis in two pigs after exposure. Treatment with ceftiofur hydrochloride and reduced dose exposure to S. suis were the only treatments which significantly (P<0.05) reduced mortality associated with PRRSV/S. suis coinfection, significantly (P<0.05) reduced recovery of S. suis from tissues at necropsy, and significantly (P<0.05) reduced the severity of gross lung lesions.     

Development and characterization of stable cell lines constitutively expressing the porcine reproductive and respiratory syndrome virus nucleocapsid protein

Despite global efforts to control porcine reproductive and respiratory syndrome virus (PRRSV) infection, the virus continues to cause economic problems in the swine industry worldwide. In this study, we attempted to generate and characterize a panel of stable BHK cell lines that constitutively express the nucleocapsid (N) protein of type 1 or type 2 PRRSV. The established BHK cell lines were found to react well with N-specific antibodies as well as the hyperimmune serum of pigs raised against each genotype of PRRSV. Taken together, the data implicate a potential usefulness for the newly generated stable cell lines as a diagnostic reagent for PRRSV serology.     

抗独特型抗体对猪繁殖与呼吸综合征病毒感染的免疫作用

用PRRSV感染SPF猪，血清检测结果显示，机体不仅产生抗PRRSV抗原的各种抗体(Ab1)，而且产生针对这些抗体的抗独特型抗体(Ab2)。根据各种蛋白质的等电点不同，应用IEF技术分离纯化出PRRSV感染猪血清中的不同IgG。分别以纯化的抗PRRSV—GP5蛋白、抗PRRSV-M蛋白的Ab2免疫SPF猪各5头，7d后经鼻腔感染PRRSV，定期采集血样进行病毒分离或鉴定试验。抗PRRSV-GP5蛋白的Ab2免疫的猪，其血样自感染后3～7d均检出PRRSV；3头猪在感染后14～63d未检出PRRSV；2头猪在感染后14～35d检出PRRSV，从42～56d转为阴性，其中1头猪在63d时检出PRRSV。抗PRRSV—M蛋白的Ab2免疫的猪，其血样自感染后3～7d均检出PRRSV；2头猪在感染后14～63d未检出PRRSV；3头猪在感染后14～35d检出PRRSV，从42～56d转为阴性，其中1头猪在63d时检出PRRSV。抗PRRSV—GP5和抗PRRSV—M蛋白的Ab2免疫作用显著，可作为PRRSV-GP5和PRRSV—M蛋白的替代抗原产生具有中和效应的抗体，保护机体免受PRRSV的感染。     

Epidemiologic assessment of porcine circovirus type 2 coinfection with other pathogens in swine

OBJECTIVE: To identify important pathogens and characterize their serologic and pathologic effects in porcine circovirus type 2 (PCV2)-infected pigs in relation to pig age and type of swine production system. DESIGN: Cross-sectional study. ANIMALS: 583 conventionally reared pigs. PROCEDURES: 3- (n = 157), 9- (149), 16- (152), and 24-week-old (125) pigs from 41 different 1-, 2-, and 3-site production systems (5 pigs/age group/farm) were euthanized and necropsied. Pigs with and without PCV2 infection were identified (via PCR assay); infection with and serologic responses to other pathogens and pathologic changes in various tissues (including lungs) were assessed. Logistic regression models were constructed for effects overall and within each age group and type of production system. RESULTS: Compared with PCV2-negative pigs, PCV2-positive pigs were more likely to have swine influenza virus (SIV) type A and Mycoplasma hyopneumoniae infections and sample-to-positive (S:P) ratios for SIV H1N1 from 0.50 to 0.99; also, PCV2-positive pigs had higher serum anti-porcine reproductive and respiratory syndrome virus (PRRSV) antibody titers and more severe lung tissue damage. Infection with SIV (but lower SIV H1N1 S:P ratio) was more likely in 3-week-old PCV2-positive pigs and evidence of systemic disease was greater in 16-week-old PCV2-positive pigs than in their PCV2-negative counterparts. By site type, associations of coinfections and disease effects between PCV2-positive and -negative pigs were greatest in 3-site production systems. CONCLUSIONS AND CLINICAL RELEVANCE: In PCV2-positive pigs, coinfections with SIV, M. hyopneumoniae, and PRRSV are important, having the greatest effect in the early to late nursery phase and in 3-site production systems.     

Identification and characterization of auto-anti-idiotypic antibodies specific for antibodies against porcine reproductive and respiratory syndrome virus envelope glycoprotein (GP5)

Auto-anti-idiotypic antibodies (Aab-2s) were detected from pigs experimentally infected with porcine reproductive and respiratory syndrome virus (PRRSV). The Aab-2s were specific against the idiotypic antibodies (Ab-1s) to the envelope glycoprotein GP5 of PRRSV and were detected from serum samples collected between 21 and 98 days post-infection (DPI). Serological characterization indicated that the Aab-2s recognized the idiotype located within or near the antigen-combining sites of the anti-GP5 antibodies, which was shared by both mouse MAb anti-GP5 and swine polyclonal antibodies. The fact that the Aab-2 inhibited the anti-GP5 antibodies from binding to PRRSV and that they were detected at different time periods in pigs that cleared the infection prior to 98 DPI versus pigs in which virus was detected at 98 DPI suggests that Aab-2 antibodies may play a role in immunity to PRRSV infection.     

Effects of intranasal inoculation of porcine reproductive and respiratory syndrome virus, Bordetella bronchiseptica, or a combination of both organisms in pigs

OBJECTIVE: To examine effects of co-infection with porcine reproductive and respiratory syndrome virus (PRRSV) and Bordetella bronchiseptica in pigs. ANIMALS: Forty 3-week-old pigs. Procedure-30 pigs (10 pigs/group) were inoculated with PRRSV, B bronchiseptica, or both. Ten noninoculated pigs were control animals. RESULTS: Clinical signs, febrile response, and decreased weight gain were most severe in the group inoculated with both organisms. The PRRSV was isolated from all pigs in both groups inoculated with virus. All pigs in both groups that received PRRSV had gross and microscopic lesions consistent with interstitial pneumonia. Bordetella bronchiseptica was cultured from all pigs in both groups inoculated with that bacterium. Colonization of anatomic sites by B bronchiseptica was comparable between both groups. Pigs in the group that received only B bronchiseptica lacked gross or microscopic lung lesions, and B bronchiseptica was not isolated from lung tissue. In the group inoculated with B bronchiseptica and PRRSV, 3 of 5 pigs 10 days after inoculation and 5 of 5 pigs 21 days after inoculation had gross and microscopic lesions consistent with bacterial bronchopneumonia, and B bronchiseptica was isolated from the lungs of 7 of those 10 pigs. CONCLUSIONS AND CLINICAL RELEVANCE: Clinical disease was exacerbated in co-infected pigs, including an increased febrile response, decreased weight gain, and B bronchiseptica-induced pneumonia. Bordetella bronchiseptica and PRRSV may circulate in a herd and cause subclinical infections. Therefore, co-infection with these organisms may cause clinical respiratory tract disease and leave pigs more susceptible to subsequent infection with opportunistic bacteria.