New, emerging, and reemerging infectious diseases

Prospects of Nanostructure Materials and Their Composites as Antimicrobial Agents

Nanostructured materials (NSMs) have increasingly been used as a substitute for antibiotics and additives in various products to impart microbicidal effect. In particular, use of silver nanoparticles (AgNPs) has garnered huge researchers' attention as potent bactericidal agent due to the inherent antimicrobial property of the silver metal. Moreover, other nanomaterials (carbon nanotubes, fullerenes, graphene, chitosan, etc.) have also been studied for their antimicrobial effects in order ensure their application in widespread domains. The present review exclusively emphasizes on materials that possess antimicrobial activity in nanoscale range and describes their various modes of antimicrobial action. It also entails broad classification of NSMs along with their application in various fields. For instance, use of AgNPs in consumer products, gold nanoparticles (AuNPs) in drug delivery. Likewise, use of zinc oxide nanoparticles (ZnO-NPs) and titanium dioxide nanoparticles (TiO₂-NPs) as additives in consumer merchandises and nanoscale chitosan (NCH) in medical products and wastewater treatment. Furthermore, this review briefly discusses the current scenario of antimicrobial nanostructured materials (aNSMs), limitations of current research and their future prospects. To put various perceptive insights on the recent advancements of such antimicrobials, an extended table is incorporated, which describes effect of NSMs of different dimensions on test microorganisms along with their potential widespread applications.

Potential for the replication of the betanodavirus redspotted grouper nervous necrosis virus in human cell lines

The determination of the host ranges of viruses is important because of the possible emergence of infectious agents, which may result from the zoonotic transmission of animal viruses to humans. The family Nodaviridae, whose members are non-enveloped, positive-stranded bipartite RNA viruses, is comprised of the genera Alphanodavirus and Betanodavirus, whose members predominantly infect insects and fish, respectively. The alphanodaviruses can also infect suckling mice and suckling hamsters, resulting in paralysis and death. Pigs near the site of isolation of the Nodamura virus (NoV), an alphanodavirus, have been reported to have high levels of NoV neutralizing antibody, suggesting that they may be part of the natural host range of this virus. Betanodaviruses are the causative agents of viral nervous necrosis, which occurs in several species of fish. However, little is known regarding the mechanism of infection of these viruses. Whether betanodaviruses can infect hosts other than fish remains unclear. In this study, we examined the possibility that a betanodavirus, redspotted grouper nervous necrosis virus (RGNNV), can infect human cell lines and showed that this virus can attach to the cells but cannot penetrate them, although human cells can support the replication of the betanodavirus when viral RNAs are transfected. The betanodavirus in its present form cannot infect human cells.

Cross-species transfer of viruses: implications for the use of viral vectors in biomedical research, gene therapy and as live-virus vaccines

All living organisms are continuously exposed to a plethora of viruses. In general, viruses tend to be restricted to the natural host species which they infect. From time to time viruses cross the host-range barrier expanding their host range. However, in very rare cases cross-species transfer is followed by the establishment and persistence of a virus in the new host species, which may result in disease. Recent examples of viruses that have crossed the species barrier from animal reservoirs to humans are hantavirus, haemorrhagic fever viruses, arboviruses, Nipah and Hendra viruses, avian influenza virus (AI), monkeypox virus, and the SARS-associated coronavirus (SARS-CoV). The opportunities for cross-species transfer of mammalian viruses have increased in recent years due to increased contact between humans and animal reservoirs. However, it is difficult to predict when such events will take place since the viral adaptation that is needed to accomplish this is multifactorial and stochastic. Against this background the intensified use of viruses and their genetically modified variants as viral gene transfer vectors for biomedical research, experimental gene therapy and for live-vector vaccines is a cause for concern. This review addresses a number of potential risk factors and their implications for activities with viral vectors from the perspective of cross-species transfer of viruses in nature, with emphasis on the occurrence of host-range mutants resulting from either cell culture or tropism engineering. The issues are raised with the intention to assist in risk assessments for activities with vector viruses.

Characterization of enzootic foci of Venezuelan equine encephalitis virus in western Venezuela

The distribution of the sylvatic subtype ID Venezuelan equine encephalitis (VEE) viruses in the lowland tropical forests of western Venezuela was investigated using remote sensing and geographic information system technologies. Landsat 5 Thematic Mapper satellite imagery was used to study the reflectance patterns of VEE endemic foci and to identify other locations with similar reflectance patterns. Enzootic VEE virus variants isolated during this study are the closest genetic relatives of the epizootic viruses that emerged in western Venezuela during 1992-1993. VEE virus surveillance was conducted by exposing sentinel hamsters to mosquito bites and trapping wild vertebrates in seven forests identified and located by means of the satellite image. We isolated VEE viruses from 48 of a total of 1,363 sentinel hamsters in two of the forests on six occasions, in both dry and wet seasons. None of the 12 small vertebrates captured in 8,190 trap-nights showed signs of previous VEE virus infection. The satellite image was classified into 13 validated classes of land use/vegetation using unsupervised and supervised techniques. Data derived from the image consisted of the raw digital values of near- and mid-infrared bands 4, 5, and 7, derived Tasseled Cap indices of wetness, greenness, and brightness, and the Normalized Difference Vegetation Index. Digitized maps provided ancillary data of elevation and soil geomorphology. Image enhancement was applied using Principal Component Analysis. A digital layer of roads together with georeferenced images was used to locate the study sites. A cluster analysis using the above data revealed two main groups of dense forests separated by spectral properties, altitude, and soil geomorphology. Virus was isolated more frequently from the forest type identified on flat flood plains of main rivers rather than the forest type found on the rolling hills of the study area. The spatial analysis suggests that mosquitoes carrying the enzootic viruses would reach 82-97% of the total land area by flying only 1-3 km from forests. We hypothesize that humans within that area are at risk of severe disease caused by enzootic ID VEE viruses. By contrast, equines could actually become naturally vaccinated, thus preventing the local emergence of epizootic IC VEE virus strains and protecting humans indirectly.

A single amino acid substitution in nonstructural protein 3A can mediate adaptation of foot-and-mouth disease virus to the guinea pig

The genetic changes selected during the adaptation of a clonal population of foot-and-mouth disease virus (FMDV) to the guinea pig have been analyzed. FMDV clone C-S8c1 was adapted to the guinea pig by serial passage in the animals until secondary lesions were observed. Analysis of the virus directly recovered from the lesions developed by the animals revealed the selection of variants with two amino acid substitutions in nonstructural proteins, I(248)-->T in 2C and Q(44)-->R in 3A. On further passages, an additional mutation, L(147)-->P, was selected in an important antigenic site located in the G-H loop of capsid protein VP1. The amino acid substitution Q(44)-->R in 3A, either alone or in combination with the replacement I(248)-->T in 2C, was sufficient to give FMDV the ability to produce lesions. This was shown by using infectious transcripts which generated chimeric viruses with the relevant amino acid substitutions. Clinical symptoms produced by the artificial chimeras were similar to those produced by the naturally adapted virus. These results obtained with FMDV imply that one or very few replacements in nonstructural viral proteins, which should be within reach of the mutant spectra of replicating viral quasispecies, may result in adaptation of a virus to a new animal host.

Emerging and re-emerging infectious diseases

Microbial pathogens discovered as aetiological agents of human disease over the last 25 years are reviewed. Strengthening of laboratory and public health surveillance is of paramount importance for early detection and management of emerging infectious diseases.

Human biliary glycoproteins function as receptors for interspecies transfer of mouse hepatitis virus

A variant Mouse Hepatitis virus (MHV), designated MHV-H2, was isolated by serial passage in mixed cultures of permissive DBT cells and nonpermissive Syrian Hamster Kidney (BHK) cells. MHV-H2 replicated efficiently in hamster, mouse, primate kidney (Vero, Cos 1, Cos 7), and human adenocarcinoma (HRT) cell lines but failed to replicate in porcine testicular (ST), feline kidney (CRFK), and canine kidney (MDCK) cells. To understand the molecular basis for coronavirus cross-species transfer into human cell lines, the replication of MHV-H2 was studied in hepatocellular carcinoma (HepG2) cells which expressed high levels of the human homologue of the normal murine receptor, biliary glycoprotein (Bgp). MHV-H2 replicated efficiently in human HepG2 cells, at low levels in breast carcinoma (MCF7) cells, and poorly, if at all, in human colon adenocarcinoma (LS 174T) cell lines which expressed high levels of carcinoembryonic antigen (CEA). These data suggested that MHV-H2 may utilize the human Bgp homologue as a receptor for entry into HepG2 cells. To further study MHV-H2 receptor utilization in human cell lines, blockade experiments were performed with a panel of different monoclonal or polyclonal antiserum directed against the human CEA genes. Pretreatment of HepG2 cells with a polyclonal antiserum directed against all CEA family members, or with a monoclonal antibody, Kat4c (cd66abde), directed against Bgp1, CGM6, CGM1a, NCA and CEA, significantly reduced virus replication and the capacity of MHV-H2 to infect HepG2 cells. Using another panel of monoclonals with more restricted cross reactivities among the human CEA's, Col-4 and Col-14, but not B6.2 B1.13, Col-1, Col-6 and Col-12 blocked MHV-H2 infection in HepG2 cells. These antibodies did not block sindbis virus (SB) replication in HepG2 cells, or block SB, MHV-A59 or MHV-H2 replication in DBT cells. Monoclonal antibodies Col-4, Col-14, and Kat4c (cd66abde) all reacted strongly with human Bgp and CEA, but displayed variable binding patterns with other CEA genes. Following expression of human Bgp in normally nonpermissive porcine testicular (ST) and feline kidney (CRFK) cells, the cells became susceptible to MHV-H2 infection. These data suggested that phylogenetic homologues of virus receptors represent natural conduits for virus xenotropism and cross-species transfer.

Emerging diseases--what veterinarians need to know

The recent increase in emerging diseases can be attributed to a number of factors, all of which relate to some form of alteration in the way etiologic agents move around. Some of these factors responsible for altered agent trafficking include actual transport to a susceptible population or new species, environmental disruption that facilitates exchange of microbes, and a husbandry change that promotes new ways for microbes to move around. Given the exponential growth of the human population and all the attendant implications, including the mobility of this population, the ecological disruption that is accompanying the overall increase, and the necessity of exploring new agricultural technologies to feed a burgeoning population, it is a certainty that altered agent trafficking will not only continue but will undoubtedly increase. Veterinarians should be aware of the role they will be expected to play in this field.

Episodic evolution mediates interspecies transfer of a murine coronavirus

Molecular mechanisms permitting the establishment and dissemination of a virus within a newly adopted host species are poorly understood. Mouse hepatitis virus (MHV) strains (MHV-A59, MHV-JHM, and MHV-A59/MHV-JHM) were passaged in mixed cultures containing progressively increasing concentrations of nonpermissive Syrian baby hamster kidney (BHK) cells and decreasing concentrations of permissive murine DBT cells. From MHV-A59/MHV-JHM mixed infection, variant viruses (MHV-H1 and MHV-H2) which replicated efficiently in BHK cells were isolated. Under identical treatment conditions, the parental MHV-A59 or MHV-JHM strains failed to produce infectious virus or transcribe detectable levels of viral RNA or protein. The MHV-H isolates were polytrophic, replicating efficiently in normally nonpermissive Syrian hamster smooth muscle (DDT-1), Chinese hamster ovary (CHO), human adenocarcinoma (HRT), primate kidney (Vero), and murine 17Cl-1 cell lines. Little if any virus replication was detected in feline kidney (CRFK) and porcine testicular (ST) cell lines. The variant virus, MHV-H2, transcribed seven mRNAs equivalent in relative abundance and size to those synthesized by the parental virus strains. MHV-H2 was an RNA recombinant virus containing a crossover site in the S glycoprotein gene. At the molecular level, episodic evolution and positive Darwinian natural selection were apparent within the MHV-H2 S and HE glycoprotein genes. These findings differ from the hypothesis that neutral changes are the predominant feature of molecular evolution and argue that changing ecologies actuate episodic evolution in the MHV spike glycoprotein genes that govern interspecies transfer and spread into alternative hosts.

A morbillivirus that caused fatal disease in horses and humans

A morbillivirus has been isolated and added to an increasing list of emerging viral diseases. This virus caused an outbreak of fatal respiratory disease in horses and humans. Genetic analyses show it to be only distantly related to the classic morbilliviruses rinderpest, measles, and canine distemper. When seen by electron microscopy, viruses had 10- and 18-nanometer surface projections that gave them a "double-fringed" appearance. The virus induced syncytia that developed in the endothelium of blood vessels, particularly the lungs.

Emerging infections: getting ahead of the curve

The early history of infectious diseases was characterized by sudden, unpredictable outbreaks, frequently of epidemic proportion. Scientific advances in the late 19th and early 20th centuries resulted in the prevention and control of many infectious diseases, particularly in industrialized nations. Despite these improvements in health, outbreaks of infectious disease continue to occur, and new infections emerge. Since 1987, the National Academy of Science's Institute of Medicine (IOM) has published three reports that have identified erosion of the public health infrastructure among the factors contributing to new and reemerging infectious diseases. In partnership with many public and private organizations in the United States and abroad, the Centers for Disease Control and Prevention (CDC) has developed a strategic plan that addresses the priorities set forth in the IOM reports and serves as a guide for CDC and its partners to combat emerging microbial threats to health. Laboratory-based surveillance, better communication networks, and improvements in the public health infrastructure are the cornerstones of the strategy. Emerging Infectious Diseases, a new periodical produced by CDC, will serve as a forum for exchange of information about incipient trends in infectious diseases, analysis of factors contributing to disease emergence, and development and implementation of prevention measures.