Respiratory syncytial virus infection in tropical and developing countries

Little is known about the epidemiology of respiratory syncytial virus (RSV) infection in tropical and developing countries; the data currently available have been reviewed. In most studies, RSV was found to be the predominant viral cause of acute lower respiratory tract infections (ALRI) in childhood, being responsible for 27-96% of hospitalised cases (mean 65%) in which a virus was found. RSV infection is seasonal in most countries; outbreaks occur most frequently in the cold season in areas with temperate and Mediterranean climates and in the wet season in tropical countries with seasonal rainfall. The situation on islands and in areas of the inner tropics with perennial high rainfall is less clear-cut. The age group mainly affected by RSV in developing countries is children under 6 months of age (mean 39% of hospital patients with RSV). RSV-ALRI is slightly more common in boys than in girls. Very little information is available about the mortality of children infected with RSV, the frequency of bacterial co-infection, or the incidence of further wheezing after RSV. Further studies on RSV should address these questions in more detail. RSV is an important pathogen ill young children in tropical and developing countries and a frequent cause of hospital admission. Prevention of RSV infection by vaccination would have a significant impact on the incidence of ALRI in children in developing countries.     

In vitro generation of human cytomegalovirus pp65 antigenemia, viremia, and leukoDNAemia

Immunocompromised patients with disseminated human cytomegalovirus (HCMV) infection have circulating PMN carrying HCMV pp65 (antigenemia), infectious virus (viremia), and viral DNA (leukoDNAemia). Because HCMV does not fully replicate in PMN, it is generally hypothesized that virions and viral materials are taken up by phagocytosis from fully permissive HCMV-infected endothelial cells. However, no experimental evidence has ever been provided for these PMN-endothelium interactions. PMN from 11 donors were cocultured with endothelial cells infected with an endothelium-adapted HCMV strain and with human fibroblasts infected with low-passaged clinical and laboratory-adapted HCMV strains. pp65-positive PMN were detected after coculture with both HCMV-infected endothelial and fibroblast cells, provided that wild and not laboratory-adapted strains were used. In addition, cocultured PMN carried infectious virus as demonstrated by virus isolation and presence of complete virus particles by electron microscopy. Moreover, high levels of viral DNA were consistently detected by quantitative PCR in cocultured PMN. Thus, we have generated in vitro the three most important viral parameters detected in patients with disseminated HCMV infection (antigenemia, viremia, and leukoDNAemia). The failure of laboratory-adapted HCMV strain to induce this phenomenon demonstrates that important modifications have occurred in attenuated viral strains affecting basic biological functions.     

Chlamydia trachomatis infections

Chlamydia trachomatis is the most common bacterial cause of sexually transmitted disease in the developed countries. The most important implications of genital chlamydia infections involve the reproductive health sequalae of upper genital tract infections in women: pelvic inflammatory disease, ectopic pregnancy, and infertility, infection by this organism is insidious, symptoms are absent or minor among most infected women and many man. This large group of asymptomatic and infectious persons sustains transmission within a community. This review discusses the epidemiology, of sexually transmitted chlamydial infections, the spectrum of clinical manifestations and their sequelae, the laboratory diagnosis of genital chlamydiasis, antibiotic treatment and prevention.     

Hepatitis C: Part II. Prevention counseling and medical evaluation

An estimated 3.9 million Americans are infected with hepatitis C virus (HCV), and most do not know that they are infected. This group includes persons who are at risk for HCV-associated chronic liver disease and who also serve as reservoirs for transmission of HCV to others. Because there is no vaccine to prevent HCV infection and immune globulin is not effective for postexposure prophylaxis, prevention of HCV infection is paramount. Patients who are at risk of exposure to HCV should be advised on steps they might take to minimize their risk of infection. Patients who are infected with HCV should be counseled on ways to prevent transmission of HCV to others and to avoid hepatotoxins. They should also be examined for liver disease and referred for treatment, if indicated.     

Approach to the diagnosis of pulmonary disease in patients infected with the human immunodeficiency virus

Patients infected with the human immunodeficiency virus are predisposed to develop a variety of common and uncommon infectious and neoplastic pulmonary diseases. Clinical information that can stratify the risk of occurrence of these pulmonary conditions includes: 1) CD4 cell count-the most important determinant; 2) concurrent antimicrobial therapy; 3) prior travel history; 4) known latent infections that may reactivate: and 5) underlying respiratory disease. Specific pulmonary diseases are discussed including: bacterial pneumonia, bronchitis, mycobacterial and fungal infections, pneumocystis carinii pneumonia, toxoplasmosis, cytomegalovirus, Kaposi sarcoma, lymphoma, and lung cancer. A differential diagnosis can be generated based on the chest radiographic pattern. Focal or multifocal areas of consolidation usually represent conventional bacterial pneumonia or, less commonly, tuberculosis. In severely immunocompromised patients, unusual diseases causing consolidation should be considered including: Rhodococcus infection, nocardiosis, cryptococcosis, aspergillosis, and lymphoma. Nodules can be present in tuberculosis, histoplasmosis, cryptococcosis, and Kaposi sarcoma. Interstitial opacities are common in pneumocystis carinii pneumonia, histoplasmosis, and cytomegalovirus pneumonia. Cavitation and cysts are features of pneumocystis carinii pneumonia, tuberculosis, aspergillosis, and lung cancer. Disease of the airways is increasingly recognized in those with acquired immunodeficiency syndrome. Lymphadenopathy is most common in mycobacterial infection, but can be a feature of fungal infection, lymphoma, Kaposi sarcoma, and lung cancer. The combined use of clinical information, knowledge of typical conditions associated with the human immunodeficiency syndrome, and radiographic patterns offers a useful approach to the diagnosis of pulmonary disease in the patient with the human immunodeficiency virus.     

Hepatitis C: Part I. Routine serologic testing and diagnosis

Hepatitis C, which is caused by the hepatitis C virus (HCV), is a major public health problem in the United States. HCV is most efficiently transmitted through large or repeated percutaneous exposures to blood. Most patients with acute HCV infection develop persistent infection, and 70 percent of patients develop chronic hepatitis. HCV-associated chronic liver disease results in 8,000 to 10,000 deaths per year, and the annual costs of acute and chronic hepatitis C exceed $600 million. An estimated 3.9 million Americans are currently infected with HCV, but most of these persons are asymptomatic and do not know they are infected. To identify them, primary health care professionals should obtain a history of high-risk practices associated with the transmission of HCV and other bloodborne pathogens from all patients. Routine testing is currently recommended only in patients who are most likely to be infected with HCV.     

A short region from the LEU2 gene of Saccharomyces cerevisiae functions as an ARS in the yeast Saccharomyces exiguus Yp74L-3

Human cytomegalovirus (HCMV) infection can result in neurological symptoms. In vitro replication of the HCMV was studied in primary cultures of microglial cells from the central nervous systems (CNS) of human embryos. The microglial cells were infected with various amounts of either the AD169 laboratory HCMV strain or a clinical HCMV isolate. A specific cytopathic effect occurred within 24 h and persisted for two months. Immunocytochemical tests for immediate early and late viral antigens done one and three days after the infection demonstrated that 60% to 80% of the microglial cells were infected and that 3% to 8% were the site of viral DNA replication. Kinetic studies showed accumulation of viral particles in the supernatant during the first two weeks after the infection. Prestimulation of the cells by PMA 24 h before the infection was associated with increased release of viral particles and with an increased percentage of cells expressing late viral antigens. The microglial cells of the human embryonic CNS are fully permissive targets for the HCMV. The in vitro HCMV model used in this study may prove useful for investigating the pathophysiology of HCMV encephalitis, in particular after mother-to-fetus transmission of the virus.     

Epidemiology of porcine reproductive and respiratory syndrome (PRRS): an overview

PRRS disease was first recognised in the USA in 1987 and in Europe in 1990 and since then the disease has spread widely throughout many pig-producing countries. After a severe epidemic phase, the infection has become endemic. The prevalence of infection is generally high in infected countries. However, in areas with a low density of pigs, infection may spread slowly and if infected animal movements are not significant, farm-to-farm spread can be controlled and prevalence of infection maintained at a low level. The PRRS virus (PRRSV) was completely unknown before 1986, and the question of its origin remains unanswered. The exact epidemiologic relationship between American and European strains of PRRSV is difficult to establish because different isolates appear to belong to two distinct sub-populations which are only distantly antigenically related. In the environment, virus survival is optimal when temperature is cold and when ultra-violet light exposure is low (little sunshine). These conditions are easily attained in winter and that may explain why virus spread increases during this period. Pigs of any age (including wild boars) are the only animals known to be naturally infected with PRRSV. Relatively close contact between pigs is the primary factor in virus transmission. Aerial transmission is a second mechanism of spread, particularly in winter and particularly over distances of less than 3 km. A third route of transmission is via semen. The role of fomites is not clearly documented, however since the virus is excreted in faeces and urine, slurry should be considered as a potential source of contamination. Within herds, the virus spreads rapidly with up to 85 to 95% of pigs in a herd becoming sero-positive within two to three months. Thereafter, virus activity persists for extended periods (several month to years). Nevertheless, some authors have reported spontaneous elimination of PRRSV from infected farms. For the future, there remain questions concerning the possible evolution of the disease (in terms of its sanitary and economic impacts), and the possible influence of vaccines on the epidemiological features of PRRS.     

Chronic viral hepatitis in childhood

In endemic areas infection with hepatitis B virus is a common cause of chronic liver disease in childhood. High levels of viral replication and mild ALT abnormalities are the rule in children infected perinatally and many of them are likely to maintain viral replication through their youth. Conversely about 90% of children infected later in life clear HBeAg and achieve sustained remission of liver disease before reaching adulthood. The eventual outcome of infection and disease in these patients remains unpredictable as reactivation of liver damage and viral replication may occur after several years of sustained remission. Cirrhosis is a rare and early complication of chronic HBV infection in children, and a risk factor for hepatocellular carcinoma. IFN therapy can accelerate HBV DNA clearance, improving the spontaneous anti-HBe seroconversion rate in Caucasian children by two to three times. Hepatitis delta is the most severe form of chronic viral hepatitis in childhood. Cirrhosis can be diagnosed in up to 26% of patients at presentation, and few cases respond to IFN therapy. Hepatitis C is relatively rare in children. Before the discovery of HCV, blood transfusions were the most common source of infection. Hepatitis C is usually a mild, asymptomatic disease in otherwise healthy children, but has a poor propensity to spontaneous remission over the years. For this reason, and based on the experience in adults, IFN treatment is now being evaluated.     

Obesity, salt intake, and renal perfusion in healthy humans

OBJECTIVE: To evaluate the pathogenicity of a recently discovered arthropod-transmitted bunyavirus (Toscana virus) on the CNS in children and to provide information on the epidemiologic and clinical aspects of Toscana virus infection. STUDY DESIGN: Case-series analysis of children hospitalized with clinical and cerebrospinal fluid examination compatible with a CNS disease of viral origin. METHODS: Cerebrospinal fluid, acute, and convalescent sera were investigated for conventional neurotropic viruses and for Toscana and tickborne encephalitis viruses. A clinical-epidemiologic analysis was carried out on confirmed Toscana virus cases to clarify the profile of Toscana virus infection in children. RESULTS: The study indicates that (1) Toscana virus has been endemic in the Siena province for at least 15 years; (2) the virus is responsible for at least 80% of acute viral infections of the CNS in children throughout the summertime; (3) the clinical signs and symptoms range from aseptic meningitis to meningoencephalitis; (4) infected children resided habitually or temporarily in rural or suburban areas of the Siena province, where ecological characteristics allow arthropods to be peridomestic in human settlements. CONCLUSIONS: Toscana virus is the most common viral agent involved in acute infections of CNS in children in central Italy.     

Human cytomegalovirus persistently infects aortic endothelial cells

Endothelial cells (EC) have been implicated as constituting an important cell type in the pathogenesis of human cytomegalovirus (HCMV). Microvascular and macrovascular EC exhibit different biochemical and functional properties depending on the organ of origin. Phenotypic differences between microvascular and macrovascular EC may alter the ability of these cells to support HCMV replication. In this study, we compared the replication of HCMV in primary macrovascular aortic EC (AEC) with that in brain microvascular EC (BMVEC). An examination of IE72, pp65, and gB viral antigen expression in BMVEC and AEC by immunoflourescence revealed similar frequencies of infected cells. Intracellular production of virus was 3 log units greater in BMVEC than in AEC, while equal quantities of extracellular virus were produced in both cell types. HCMV infection of BMVEC resulted in rapid cellular lysis, while the virus was nonlytic and continuously released from HCMV-infected AEC for the life span of the culture. An examination of infected cells by electron microscopy revealed the formation of abundant nucleocapsids in both AEC and BMVEC. However, significant amounts of mature viral particles were only detected in the cytoplasm of BMVEC. These observations indicate that levels of HCMV replication in EC obtained from different organs are distinct and suggest that persistently infected AEC may serve as a reservoir of virus.     

Brain cell type specificity and gliosis-induced activation of the human cytomegalovirus immediate-early promoter in transgenic mice

Human cytomegalovirus (HCMV) can cause debilitating, sometimes fatal, opportunistic infections in congenitally infected infants and in immunodeficient individuals such as patients with the acquired immunodeficiency syndrome (AIDS). Molecular mechanisms that determine cell type specificity of HCMV infection and latency are poorly understood. We recently described a transgenic mouse model for analysis of HCMV major immediate-early (IE) promoter regulation and showed that sites of IE promoter activity during murine embryogenesis correlate with known target tissues of congenital HCMV infection in human fetuses (Koedood et al., 1995). Among various permissive human tissues, the brain is a site where HCMV infections can be devastating. Here, we have used immunohistochemical double-labeling analysis to identify specific cell types with HCMV-IE promoter activity in brains of transgenic mice at several postnatal stages. IE promoter activity was restricted to some endothelial cells, ependymal cells, choroid plexus epithelia, and neurons at discrete locations in the forebrain, brainstem, and cerebellum. Endothelial cells and neurons with activity were proportionately more abundant in neonatal than in adult brains. Although the IE promoter was normally silent in most astrocytes, activity was strongly induced in reactive astrocytes in response to a neocortical stab lesion. The findings support a model, consistent with clinical literature on HCMV encephalitis, whereby tissue damage and gliosis caused by HCMV infection of endothelial and ependymal cells progressively renders adjacent permissive neurons and reactive astrocytes accessible to infection. This transgenic model system should facilitate identification of factors that regulate the HCMV IE promoter with regard to infection permissivity and reactivation from latency.     

New trends in the drug therapy of localized and disseminated Mycobacterium avium complex infection

Recent advances in the drug therapy of localized and disseminated infection with Mycobacterium avium complex (MAC) are reviewed. MAC infection is the most commonly reported bacterial infection in patients with AIDS, and the frequency of this infection in patients negative for the human immunodeficiency virus (HIV) is increasing. The main portals of entry for MAC are the gastrointestinal and respiratory tracts. Localized MAC infection is more common in HIV-negative than HIV-infected patients. The symptoms of disseminated MAC disease are those typical of advanced HIV disease. The most reliable diagnosis is provided by blood cultures; radiometric culturing techniques are favored. The overall treatment of MAC infection has improved greatly with the introduction of new agents during the past 15 years; survival time has been extended. Clarithromycin and azithromycin have proven effective against both localized and disseminated MAC infection. Clarithromycin is the cornerstone of therapy for disseminated infection. Ciprofloxacin has been successfully used to treat disseminated infection as part of a four-drug regimen including rifampin, ethambutol, and clofazimine. Rifabutin has substantial efficacy when combined with other agents. Liposomal aminoglycosides, such as amikacin, and interferon gamma have shown some initial promise. Rifabutin is currently recommended for the prevention of MAC disease in HIV-infected patients. Clarithromycin and azithromycin have also shown efficacy for prophylaxis, and fluoroquinolones may play a preventive role as well. New drug therapies are improving the outlook for persons infected with MAC.     

Reciprocal interactions between human cytomegalovirus and human T cell leukemia-lymphoma virus type I in monocyte-derived macrophages cultured in vitro

Infection of macrophages with human cytomegalovirus (HCMV) has been shown to be nonlytic and exclusively cell associated. Human T cell leukemia-lymphoma virus type I (HTLV-I) is capable of establishing productive infection in macrophages. We studied the interactions between HCMV and HTLV-I in monocyte-derived macrophages cultured in vitro. We found that coinfection of macrophages with HCMV and HTLV-I significantly enhanced HCMV replication, resulting in release of infectious HCMV from dually infected cells. On the other hand, HCMV inhibited HTLV-I replication in macrophages coinfected with both viruses. Reciprocal interactions between HCMV and HTLV-I were mediated by their trans-acting proteins. Results of transfection studies demonstrated that the tax gene product of HTLV-I alone was capable of upregulating HCMV production. In a transient gene expression assay the immediate-early 2 (IE2) protein of HCMV alone could inhibit HTLV-I replication, whereas the IE1 protein, which had no effect by itself, produced a synergistic inhibitory effect together with the IE2 protein. Results from this study suggest that in vivo double infection of macrophages with HCMV and HTLV-I may contribute to the dissemination of HCMV infection in patients suffering from HTLV-I-associated T cell leukemia-lymphoma.     

Cytomegaloviruses use multiple mechanisms to elude the host immune response

The study of the effects of cytomegaloviruses on the MHC class I-restricted antigen presentation pathway has yielded an embarrassment of riches. The human cytomegalovirus (HCMV) encodes at least five to six different glycoproteins, each interfering in a different way with elimination of the virus by the host immune system. Most likely, it is the concerted action of these glycoproteins that allows HCMV to escape from elimination by the host immune system during acute and perhaps also persistent infection. Prime targets of these CMV glycoproteins are MHC class I glycoproteins: the very molecules that signal the presence of a virally infected cell to the immune system. Recently, several novel links in the multi-step process of immune evasion by HCMV have been discovered.     

Human cytomegalovirus infection in a retinoblastoma cell line in vitro

BACKGROUND: The focus of these studies was to determine whether the Y79 human retinoblastoma cell line could function as a good in vitro model system for studying human cytomegalovirus (HCMV) infection. METHODS: Y79 cells were exposed to an HCMV mutant carrying a LacZ gene, and the resulting beta-galactosidase expression in infected cells was assessed by flow cytometry. The extent to which the three classes of viral gene products immediate early, early, and late proteins - were expressed was analyzed by immunohistochemical staining and Western blotting. Infected Y79 cells were also co-cultivated on human foreskin fibroblast (SF cell) cultures to recover virus. RESULTS: Infection of Y79 cells with the virus resulted in beta-galactosidase expression as detected by flow-cytometric analysis. Immunohistochemical staining revealed that a portion of Y79 cells expressed antigens reactive to monoclonal antibodies against immediate early, early, and late HCMV proteins. The 43-kDa early gene product was also detected by Western blotting. Infected Y79 cells co-cultivated on SF cell cultures yielded infectious foci, which turned blue following X-gal staining, demonstrating productive HCMV infection in the Y79 cells. CONCLUSION: These results demonstrate that while HCMV can productively infect Y79 cultures, it does so in a highly inefficient manner, leading these authors to conclude that this cell line does not provide a particularly good model system to study HCMV infection.     

T lymphocytes and their cytokines in human immunodeficiency virus (HIV) infection: implications for associated neoplasias

Infection with the human immunodeficiency virus (HIV) results in gradual immunosuppression due to the loss of CD4+ T cells. In the wake of immune system breakdown, infected individuals may acquire multiple opportunistic infections and develop certain malignancies which ultimately account for the vast majority of deaths in these persons. A limited number of malignancies are directly associated with HIV infection and suggest a common tie between these tumors. Inappropriate immune surveillance resulting in insufficient inhibition of virus replication and inadequate control of the growth of transformed cells may contribute to the development of malignancies in HIV-infected individuals. Alternatively, malignancies in HIV infection may be the consequence of immune dysregulation. Cellular immune responses mediated by antigen-specific cytotoxic T lymphocytes (CTL) are of particular importance for immunologic control of viral infections and substantial information has been gathered about theses cells in HIV infection. The goal of this review is therefore to summarize recent findings regarding the cellular immune response to HIV with a particular focus on cytokines released by HIV-specific CTL.     

Strain-specific neutralization of human cytomegalovirus isolates by human sera

Induction of an effective antibody response against human cytomegalovirus (HCMV) is an important defense mechanism since it is potentially capable of neutralizing infectious viruses. We have analyzed the extent of HCMV strain-specific neutralization capacity in human sera. Nine recent HCMV isolates and their corresponding sera were investigated in cross-neutralization assays. We observed differences, independent of the overall neutralization capacity, in the 50% neutralization titers of the sera against individual strains, differences that ranged from 8-fold to more than 60-fold. For one isolate, complete resistance to neutralization by two human sera was observed. The neutralization capacity of human sera was not influenced by the presence of various concentrations (up to 100-fold excess) of noninfectious envelope glycoproteins, an inherent contamination of virus preparations from recent HCMV isolates. This indicated that the decisive parameter for neutralization is the titer of the neutralizing antibodies and that neutralization is largely independent of the concentration of virus. Analysis with transplant patients revealed that during primary infection strain-specific and strain-common antibodies are produced asynchronously. Thus, our data demonstrate that the induction of strain-specific neutralizing antibodies is a common event during infection with HCMV and that it might have important implications for the course of the infection and the development of anti-HCMV vaccines.