Protists as opportunistic pathogens: public health impact in the 1990s and beyond

Protist organisms (protozoa and fungi) have become increasingly prominent as opportunistic pathogens among persons infected with human immunodeficiency virus (HIV) and among organ transplant recipients--two immunocompromised populations that have increased dramatically in the past two decades. Pneumocystis carinii pneumonia continues to be the most common serious opportunistic infection (OI) among HIV-infected persons in the United States, occurring frequently among persons not previously receiving medical care. Toxoplasmosis, cryptococcosis, cryptosporidiosis, and isosporiasis occur frequently in HIV-infected persons in the developing world. Candidiasis and aspergillosis are common OIs in organ transplant recipients. As these populations of immunosuppressed patients continue to expand worldwide new OIs caused by protist pathogens are likely to emerge.     

Generalized immune response to Pneumocystis carinii infection in the lung.

We studied inflammatory cells retrieved by bronchoalveolar lavage (BAL) from immunocompromised patients with or without Pneumocystis carinii pneumonia (PCP). Twenty-four patients with PCP, and 20 patients without PCP underwent lavages of both an uninvolved lobe and the lobe involved in pulmonary infection. Patients without P. carinii, had a significant increase (p less than 0.02) in the percentages of neutrophils (22 +/- 7.1%, mean +/- SEM) and lymphocytes (16 +/- 3.8%) in the involved lobe compared to those in the uninvolved area (neutrophils: 9 +/- 4.8%; lymphocytes: 10 +/- 2.4%). Patients with PCP, had no differences between the % neutrophils or % lymphocytes in the involved vs. uninvolved lobes. Patients with PCP had more (p less than 0.01) P. carinii in the upper lobe (23 +/- 4.6 P. carinii clusters/500 cells) than the middle lobe (11 +/- 3.6). In PCP, despite regional infections, there was a diffuse inflammatory response.     

Clinical presentation and significance of emerging opportunistic infections

In recent years the clinical face of the Acquired Immune Deficiency Syndrome has changed significantly as a consequence of use of prophylaxis against Pneumocystis carinii pneumonia and combination antiretroviral therapy. In this context several opportunistic pathogens have emerged as causes of clinically important disease. Many of these infective agents have previously been defined by specific geographical locations. Their clinical presentation frequently mimics other (non) opportunistic infections with which they may co-exist. The diagnosis is frequently delayed as the diagnostic possibility may not be in the clinician's differential diagnosis. Invasive procedures are frequently required in order to secure a diagnosis. Despite treatment, prognosis is often poor. Clinicians should be aware of these opportunistic pathogens in order that a timely diagnosis may be made and appropriate therapy given.     

Length of survival of patients with acquired immune deficiency syndrome in the United Kingdom.

An analysis of the lengths of survival of patients with the acquired immune deficiency syndrome presenting with different opportunistic diseases was performed using epidemiological data routinely collected at the PHLS Communicable Disease Surveillance Centre. The overall crude case fatality rate was 55.4% (93/168). The median survival times were: 21.2 months for Kaposi''s sarcoma, 12.5 months for Pneumocystis carinii pneumonia, and 13.3 months for other opportunistic infections. The shortest median survival time (6.6 months) was found for those with both Kaposi''s sarcoma and P carinii pneumonia. There were significant differences between durations of survival of patients with Kaposi''s sarcoma and those with all other diseases, which indicated impaired cellular immunity apart from opportunistic infections. This analysis shows that those with Kaposi''s sarcoma alone have the most favourable prognosis.     

Temozolomide-related infections: review of the literature

Temozolomide (TMZ) is an alkylating, antineoplastic agent which is being used to treat cases of refractory anaplastic astrocytoma, newly-diagnosed glioblastoma multiforme and metastatic melanoma. TMZ causes lymphopenia and T-cell dysfunction in most of the patients. Related to this toxicity several opportunistic infections have been reported in the literature, but were not well characterized. To further investigate this topic, relevant English language studies were identified through Medline. There were 36 previously reported cases of infection related to TMZ. The median age of the cases was 55 years (range 33-73). The most frequently experienced infections were mucocutaneous candidiasis (n=11; 28.2%), herpes zoster (n=5; 12.8%), herpes simplex virus (n=4; 10.2%), cytomegalovirus (CMV) (n=5; 12.8%), pneumocystis carinii pneumonia (PCP) (n=3; 7.6%), hepatitis B virus (HBV) (n=2; 5.1%) and others (n=9; 23%). Mortality rates were 28.5% (n=4/14) in patients with reported outcome. In this survey, about one third of the TMZ-related severe infections resulted in death. Patients treated with TMZ are at increased risk for opportunistic viral and bacterial infection. Therefore, close monitoring of patients receiving TMZ for opportunistic infections should be carried out.     

Antibodies to the infective agents of opportunistic infections in blood of patients with hemoblastosis complicated with pneumonia

The examination of 112 hematological patients with diagnosed acute and chronic leucosis, lymphoma, myeloma, anemia, melanoma and other diseases revealed not a single subject among these examinees in whom no markers of opportunistic infections were detected. Low titers of antibodies to Pneumocystis carinii, cytomegalovirus (CMV), Epstein-Barr virus (EBV) were noted in 42%, 46.4% and 40.2% of examinees, respectively. Markers of acute diseases, such as class IgM, IgG antibodies in high titers, as well as P.carinii, CMV, EBV antigens, were detected in 37.5%, 30.4% and 22.3% of patients of a hematological hospital. In the group of comparison (donors) these figures were, respectively, 15.3%, 2.4% and 6.9%. The signs of monoinfection were detected in 11.6% (pneumocystosis), in 10.7% (CMV infection) and in 14.3% (EBV infection), while the markers of two infections, EBV infection and pneumocystosis, were detected in 9.8%, EBV and CMV infections in 11.6%, pneumocystosis and CMV infection in 14.3%; mixed contamination with all three infective agents was detected in 12.5% of the patients.     

Herpes simplex virus type 1 dysregulates anti‐fungal defenses preventing monocyte activation and downregulating toll‐like receptor‐2

We investigated the interplay occurring between pathogens in the course of dual infections, using an in vitro model in which the THP‐1 monocytic cell line is first infected with HSV‐1 and then exposed to Ca or Cn. These three pathogens share some pathogenic features: they cause opportunistic infections, target macrophages and are neurotropic. Here, we show that HSV‐1‐infected THP‐1 cells exhibited augmented phagocytosis against the two opportunistic fungi but reduced capability to counteract fungal infection: the better ingestion by monocytes was followed by facilitated fungal survival and replication. Reduced IL‐12 production was also observed. Cytofluorimetric analysis showed that HSV‐1‐infected monocytes exhibit: (i) downregulated TLR‐2 and TLR‐4, critical structures in fungal recognition; (ii) reduced expression of CD38 and CD69, known to be important markers of monocyte activation; and (iii) enhanced expression of apoptosis and necrosis markers, in the absence of altered cell proliferation. Overall, these findings imply that HSV‐1 infection prevents monocyte activation, thus leading to a significant dysfunction of the monocyte‐mediated anti‐Candida response; HSV‐1 induced apoptosis and necrosis of monocytes further contribute to this impairment.     

The Impact of Opportunistic Infections on Clinical Outcome and Healthcare Resource Uses for Adult T Cell Leukaemia

We examined the impact of opportunistic infections on in-hospital mortality, hospital length of stay (LOS), and the total cost (TC) among adult T-cell leukaemia (ATL) patients. In this retrospective cohort study, we identified 3712 patients with ATL using national hospital administrative data. Analysed opportunistic infections included Aspergillus spp., Candida spp., cytomegalovirus (CMV), herpes simplex virus (HSV), pneumocystis pneumonia (PCP), tuberculosis, varicella zoster virus (VZV), Cryptococcus spp., nontuberculous mycobacteria, and Strongyloides spp. Multilevel logistic regression analysis for in-hospital mortality and a multilevel linear regression analysis for LOS and TC were employed to determine the impact of opportunistic infections on clinical outcomes and healthcare resources. We found ATL patients infected with CMV had significantly higher in-hospital mortality (adjusted odds ratio (AOR) 2.29 [1.50–3.49] p < 0.001), longer LOS (coefficient (B): 0.13 [0.06–0.20] p < 0.001) and higher TC (B: 0.25 [0.17–0.32] p < 0.001) than those without CMV. Those with CAN and PCP were associated with a lower in-hospital mortality rate (AOR 0.72 [0.53–0.98] p = 0.035 and 0.54[0.41–0.73] p < 0.001, respectively) than their infections. VZV was associated with longer LOS (B: 0.13 [0.06–0.19] p < 0.001), while aspergillosis, HSV, or VZV infections were associated with higher TC (B: 0.16 [0.07–0.24] p < 0.001, 0.12 [0.02–0.23] p = 0.025, and 0.17 [0.10–0.24] p < 0.001, respectively). Our findings reveal that CMV infection is a major determinant of poor prognosis in patients affected by ATL.     

Cytomegalovirus and Herpes Simplex Virus Effect on the Prognosis of Mechanically Ventilated Patients Suspected to Have Ventilator-Associated Pneumonia

Objective

Cytomegalovirus (CMV) and herpes simplex virus (HSV) are common viruses that can affect critically ill patients who are not immunocompromised. The aim of this study was to determine whether the identification of CMV and/or HSV in mechanically ventilated critically ill patients suspected of having pneumonia was associated with an increased mortality.

Design

Prospective epidemiological study.

Setting

Medical intensive care unit of a tertiary medical center.

Patients

Ninety-three patients with suspected pneumonia.

Interventions

Patients with suspected pneumonia had bronchoalveolar lavage and blood samples taken to confirm the diagnosis. Antigenemia was used to detect CMV in the blood. Bronchoalveolar lavage samples were submitted to testing using quantitative real-time Polymerase Chain Reaction.

Measurements and Main Results

We identified 22 patients with a CMV infection, 26 patients with an HSV infection and 45 patients without CMV or HSV infection (control group). Mortality at day 60 was higher in patients with a CMV infection than in patients from the control group (55% vs. 20%, P<0.01). Mortality at day 60 was not significantly increased in the group with HSV infection. Duration of ICU stay and ICU mortality were significantly higher in patients with CMV infections when compared to patients from the control group, whereas ventilator free days were significantly lower in patients with CMV infections when compared to patients from the control group.

Conclusions

In critically ill patients, a CMV infection is associated with an increased mortality. Further interventional studies are needed to evaluate whether treatment could improve the prognosis.     

Bronchoalveolar lavage fluid cytology in patients with Pneumocystis carinii pneumonia

OBJECTIVE: To evaluate bronchoalveolar lavage (BAL) cytology and organism burden in patients with Pneumocystis carinii pneumonia (PCP) who were infected with the human immunodeficiency virus (HIV) and in those with other immunodeficiencies. STUDY DESIGN: BAL fluid samples from patients with PCP were selected (HIV-infected patients, n = 15; patients with other immunodeficiencies, n = 11). May-Grünwald-Giemsa-stained cytocentrifuge preparations were evaluated. Foamy alveolar casts (FACs) and P carinii clusters were counted. RESULTS: The numbers of FACs and P carinii clusters in BAL fluid samples of HIV-infected patients were significantly higher as compared to those in samples from patients with other immunodeficiencies. Striking cytologic findings observed in half the samples from both patient groups included the presence of foamy alveolar macrophages, activated lymphocytes, plasma cells and reactive type II pneumocytes. Furthermore, a peculiar cell type, "nonidentified cell" (NIC), was observed almost exclusively in BAL fluid samples from HIV-infected patients. CONCLUSION: BAL fluid samples from HIV-infected patients with PCP displayed higher organism burdens as compared to those from patients with other immunodeficiencies. Moreover, cytologic findings suggestive of noninfectious lung conditions were common in BAL fluid samples obtained from patients with PCP. Further study is required to elucidate the identity of the NIC cell type.     

Phenotypic analysis of bronchoalveolar lavage lymphocytes from acquired immunodeficiency patients with and without Pneumocystis carinii pneumonia.

A study was performed to reveal possible differences in lymphocyte subpopulations from bronchoalveolar lavage (BAL) of acquired immunodeficiency patients with and without Pneumocystis carinii pneumonia. Forty-one consecutive human immunodeficiency virus-seropositive patients were studied. Pneumocystis carinii infection was detected in the BAL fluid from 18 patients. The BAL lymphocyte subpopulations were determined by surface marker analysis with the immunoperoxidase slide assay. No significant differences in the percentage of CD4+ and CD8+ lymphocytes were found between the two groups. The percentage of CD57+ natural killer (NK) cells was significantly higher in the Pneumocystis carinii-negative group than in the -positive group. Since NK cells protect from microbial infections, it is conceivable that the loss of CD57+ NK cells may be one of the phenomena leading to the immunodeficiency state that underlies the pulmonary complications characteristic of the acquired immunodeficiency syndrome.     

Some Opportunistic Parasitic Infections in AIDS: Candidiasis, Pneumocystosis, Cryptosporidiosis, Toxoplasmosis

Almost 80% of patients with AIDS die from infections other than human immunodeficiency virus (HIV). These infections usually occur late in the course of disease when CD4(+) T-cell count has fallen below 200 permm(3) cells per milliliter. Most of these infections are caused by organisms that do not normally afflict healthy individuals and are thus considered to be opportunistic. In this article, Lloyd Kasper and Dominique Buzoni-Gatel review the host-parasite interaction for four important pathogens: Candida albicans and Pneumocystis carinii (usually non-invasive pathogens), Cryptosporidium parvum (invades the cells but remains localized in the gut) and Toxoplasma gondii (penetrates through the gut to cause systemic infection). These organisms, which generally cause limited or even insignificant clinical evidence of infection in the normal host, were chosen because of their high prevalence in AIDS patients and because they exhibit different invasive abilities. The reason why individuals with AIDS are susceptible to this particular group of pathogens is uncertain.     

T cell costimulatory molecule function determines susceptibility to infection with Pneumocystis carinii in mice

Loss of T cell number and function during HIV infection or secondary to pharmacologic immunosuppression renders individuals susceptible to opportunistic infections, including Pneumocystis carinii pneumonia. Because costimulatory receptors are critical for optimal T cell function, we hypothesized that these proteins would regulate susceptibility to opportunistic infections. We found that despite normal T cell numbers, mice deficient in the costimulatory molecules CD2 and CD28 spontaneously developed P. carinii pneumonia. In experiments using intratracheal injection of P. carinii organisms to induce infection, the loss of CD28 alone was sufficient to render mice susceptible to acute infection; however, the organism was eventually cleared. Examination of inflammatory responses to P. carinii revealed that mice deficient in both CD2 and CD28 accumulated CD8(+) T cells in their lungs in response to infection and demonstrated markedly reduced specific Ab titers. Analysis of cytokine profiles suggested that regulation of IL-10 and IL-15 may be important elements of the response to this pathogen. Thus, costimulatory molecule function is critical in determining the initial susceptibility to infection with P. carinii. Analysis of immunologic responses in these mice may provide important insights into the defects that render individuals susceptible to opportunistic infection, and provide opportunities for novel immunologically based therapies.     

Oral Valganciclovir as a Preemptive Treatment for Cytomegalovirus (CMV) Infection in CMV-Seropositive Liver Transplant Recipients

Objectives

Cytomegalovirus (CMV) infections in liver transplant recipients are common and result in significant morbidity and mortality. Intravenous ganciclovir or oral valganciclovir are the standard treatment for CMV infection. The present study investigates the efficacy of oral valganciclovir in CMV infection as a preemptive treatment after liver transplantation.

Methods

Between 2012 and 2013, 161 patients underwent liver transplantation at Samsung Medical Center. All patients received tacrolimus, steroids, and mycophenolate mofetil. Patients with CMV infection were administered oral valganciclovir (VGCV) 900mg/day daily or intravenous ganciclovir (GCV) 5mg/kg twice daily as preemptive treatment. Stable liver transplant recipients received VGCV.

Results

Eighty-three patients (51.6%) received antiviral therapy as a preemptive treatment because of CMV infection. The model for end-stage liver disease (MELD) score and the proportions of Child-Pugh class C, hepatorenal syndrome, and deceased donor liver transplantation in the CMV infection group were higher than in the no CMV infection group. Sixty-one patients received GCV and 22 patients received VGCV. The MELD scores in the GCV group were higher than in the VGCV group, but there were no statistical differences in the pretransplant variables between the two groups. AST, ALT, and total bilirubin levels in the GCV group were higher than in the VGCV group when CMV infection occurred. The incidences of recurrent CMV infection in the GCV and VGCV groups were 14.8% and 4.5%, respectively (P=0.277).

Conclusion

Oral valganciclovir is feasible as a preemptive treatment for CMV infection in liver transplant recipients with stable graft function.     

The effect of human immunodeficiency virus infection on the distribution and outcome of pneumonia in intensive care units.

To determine the frequency and distribution of pneumonia in an intensive care unit (ICU), we retrospectively examined the records of 1,854 consecutive ICU admissions between January 1987 and April 1990. A total of 266 patients met criteria for pneumonia (unilateral or bilateral infiltrate by chest roentgenogram, plus 2 of the following: leukocyte count > 10 x 10(9) per liter, temperature > 38.5 degrees C, or culture of blood or sputum positive for pathogens). Pneumocystis carinii pneumonia in patients infected with the human immunodeficiency virus was the most frequent cause (28%) precipitating an ICU admission in this series of patients. Streptococcus pneumoniae (13%), Staphylococcus aureus (8%), Haemophilus influenzae (4%), and viruses (4%) were also commonly observed. Overall mortality was 20%. An APACHE II score of greater than 24, the need for intubation, and the presence of P carinii were predictive of increased mortality. Age, sex, and length of stay did not predict final results. Patients with P carinii pneumonia who required intubation had an overall mortality of 54%, which was higher than patients without P carinii pneumonia who required intubation (P < .05). Our experience shows the changing spectrum of pneumonia in ICUs. In contrast to reports of a decade ago in which S pneumoniae and Pseudomonas aeruginosa are cited as most common, P carinii is now most prevalent in our ICU. Although our findings reflect the increasing incidence of human immunodeficiency virus infection in San Francisco, California, they may also be pertinent to other areas in the United States where the incidence of this infection continues to increase.     

Pneumocystis carinii enhances soluble mannose receptor production by macrophages

Phagocytosis of extracellular organisms in the alveolar spaces of the lungs represents the first-line of host defense against pulmonary pathogens. Disruption of this process is likely to interfere with the generation of appropriate specific immune responses, and lead to a delayed or inefficient clearance of the pathogen. Pneumocystis carinii, an opportunistic pathogen in immunodeficient individuals, is cleared from the lung by alveolar macrophages. In the absence of specific anti-Pneumocystis antibodies, phagocytosis is dependent on the non-opsonic macrophage mannose receptor (MR). Recent studies have demonstrated that alveolar macrophage MR activity is downregulated in individuals infected with HIV, and that functional MR is shed from the macrophage cell surface. Here we report that P. carinii enhances the formation of soluble MR by macrophages in vitro. Soluble MR was detected in cell-free alveolar fluid from humans infected with HIV and/or P. carinii, but not in alveolar fluid from healthy controls. Soluble MR was found in association with extracellular clumps of P. carinii in the lungs of mice with P. carinii pneumonia, and was associated with P. carinii organisms purified from these mice. When purified P. carinii organisms were incubated with soluble MR-containing supernatants, they were phagocytosed less readily by alveolar macrophages than were control organisms. Our results suggest that P. carinii organisms enhance the shedding of MR from the surface of alveolar macrophages, and that the resultant soluble MR binds to intra-alveolar organisms, thereby interfering with their non-opsonic uptake via the macrophage cell surface MR.     

Leukotriene B4 protects latently infected mice against murine cytomegalovirus reactivation following allogeneic transplantation

Human CMV is often associated with transplant rejection and opportunistic infections such as pneumonia in immunosuppressed patients. Current anti-CMV therapies, although effective, show relatively high toxicity, which seriously limits their long-term use. In this study, we provide evidence that leukotriene B(4) (LTB(4)) plays an important role in the fight against murine CMV (MCMV) infection in vivo. Intravenous administration of 50 and 500 ng/kg/day of LTB(4) to mice infected with a lethal dose of MCMV significantly increases their survival (50 and 70%, respectively), compared with the placebo-treated group (10% of survival). In mice infected with a sublethal dose of MCMV and treated daily with 50 ng/kg/day of LTB(4), the salivary gland viral loads were found to be reduced by 66% compared with the control group. Furthermore, using an allogeneic bone marrow transplantation mouse model, the frequency of MCMV reactivation from latently infected mice was much lower (38%) in LTB(4) (500 ng/kg)-treated mice than in the placebo-treated group (78%). Finally, in experiments using 5-lipoxygenase-deficient mice, MCMV viral loads in salivary glands were found to be higher in animals unable to produce leukotrienes than in the control groups, supporting a role of endogenous 5-lipoxygenase products, possibly LTB(4), in host defense against CMV infection.     

Fiberoptic Bronchoscopy in Diagnosis of Opportunistic Lung Infections: Assessment of Sputa,Washings, Brushings and Biopsy Specimens

Fiberoptic bronchoscopy (washings, brushings and biopsies) was done in 25 cases of proven opportunistic pulmonary infections in compromised hosts. Diagnostic yields of bronchoscopic procedures and expectorated sputum were compared. Sputum examination gave the lowest yield (14 percent). Bronchial washings and brushings were diagnostic in 30 percent and 38 percent of patients, respectively. On transbronchial biopsy of the lung (TBB) pathogens were identified in 75 percent of patients with Pneumocystis carinii infection and 67 percent of patients with other opportunistic infections. The overall TBB yield of 73 percent was superior (P<0.05) to that of either washings or brushings. The yield from combining washings and brushings was greater than from either procedure alone, but combination with TBB did not result in any significant improvement. TBB is recommended as a useful diagnostic procedure in patients with suspected opportunistic pulmonary infections. Morbidity was minimal with this procedure, and the need for thoracotomy was reduced when it was used.     

Pathogens in children with severe combined immune deficiency disease or AIDS.

We evaluated the frequency and severity of illnesses caused by various microbial pathogens in 15 children with severe combined immune deficiency disease (SCID) and 8 with acquired immune deficiency syndrome (AIDS). There were 35 viral, 23 bacterial, 19 mycotic and 13 parasitic infections. Nineteen of the 23 patients died of infection; Pneumocystis carinii pneumonia, giant-cell pneumonia due to paramyxoviruses and various disseminated viral infections were responsible for most deaths in both groups. The emerging role of paramyxoviruses was illustrated by the fact that they were responsible for giant-cell pneumonia in seven patients. Viral enteric infections were frequent in both groups. The variety of infectious microorganisms and the severity of resulting illnesses in the patients with AIDS were similar to those in the patients with SCID.