Diagnostic virology using electron microscopic techniques

Circulation of Coronavirus Images: Helping Social Distancing?

As soon as the SARS-Cov2 disease was recognized by experts to potentially cause a serious pandemic, a three dimensional diagrammatic image of the virus, colored in strong red, conquered public media globally. This study confronts this iconic virus image with a historic image analysis of 33,000 biomedical articles on coronaviruses published between 1968-2020 and interviews with some of their authors. Only a small fraction of scientific virus publications entail images of the complete virus. Red as an alarm color is not used at all by scientists who don't aim for a non-scientific public. Circulation in this case concerns the movement of iconic images from a scientific context into a general public. On the basis of hps-studies on scientific diagrams and especially on color use in scientific diagrams to convey specific messages in public, the paper discusses the role of the claim of public corona-virus diagram as "scientific." It points at relevant differences between most frequent scientific corona-virus images and the diagrammatic image used in public. Both author- and readerships (in science and public) follow contrasting aims and values. Thus, the images meet non-expert readers for whom the images entail very different - and potentially unintended - meanings then to virus experts.

Viral Infection at the Blood-Brain Barrier in Multiple Sclerosis: – An Ultrastructural Study of Tissues from a Uk Regional Brain Bank

Although viral infections are often invoked as environmental factors in the aetiology and pathogenesis of multiple sclerosis (MS) it is only recently that a specific, indirect, cytokine-mediated mechanism for triggering of relapses during viral infections has been demonstrated. It is not yet clear however whether this indirect mechanism can account for all reported viral associations with the aetiopathogenesis of MS. A direct causal role of central nervous system (CNS) viral infection in MS has largely been discounted following repeated failures to demonstrate virus within the oligodendrocyte-myelin unit In the light of increasing evidence of blood-brain barrier (BBB) dysfunction in MS and to further explore the issue of possible viral involvement in MS, an ultrastructural search for viruses was undertaken in the CNS microvasculature, in autopsy and biopsy tissue from human CNS primary demyelinating diseases, including MS (20 cases), idiopathic monophasic CNS demyelinating disease (Mdemy, four cases) and metabolic or immunopathological demyelinating disease (two cases). For comparison, tissues from CNS viral disease in which demyelination is a major feature (nine cases) were examined in the same way. Control CNS tissues (nine cases) from a range of other neurological and non-neurological diseases were also examined. Outside the MS and Mdemy groups, morphological evidence of virus associations with the BBB were found only in the acute and subacute viral encephalitides (three cases subacute sclerosing panencephalitis, one case of Herpes encephalitis) and in one case of disseminated Cytomegalovirus infection. In a small proportion of MS and Mdemy cases, particles resembling either adenovirus (one case of MS) or paramyxovirus (one case of MS, one case of Mdemy) were found in the vicinity of microvessels. In each case a different cell type or extracellular compartment was involved and an exact correlation between the virus particles and the demyelinating lesions could not be demonstrated. Furthermore, corroborative clinical or laboratory evidence of current CNS infection in these primary demyelinating disease cases was available only from the single positive Mdemy case and not from the two cases of MS. This and other previously published evidence from MS (which implicated a Coronavirus) and other diseases highlights the potential vulnerability to viral infection of cells associated with the BBB. Furthermore it is concluded that the detection rate of such infections in pathological tissue could underestimate their true frequency. A possible role of transient virus-BBB interactions in triggering focal inflammation, BBB breakdown and demyelination in some cases of MS and parainfectious demyelinating disease cannot be discounted.

Rapid Viral Diagnosis of Orthopoxviruses by Electron Microscopy: Optional or a Must?

Diagnostic electron microscopy (DEM) was an essential component of viral diagnosis until the development of highly sensitive nucleic acid amplification techniques (NAT). The simple negative staining technique of DEM was applied widely to smallpox diagnosis until the world-wide eradication of the human-specific pathogen in 1980. Since then, the threat of smallpox re-emerging through laboratory escape, molecular manipulation, synthetic biology or bioterrorism has not totally disappeared and would be a major problem in an unvaccinated population. Other animal poxviruses may also emerge as human pathogens. With its rapid results (only a few minutes after arrival of the specimen), no requirement for specific reagents and its "open view", DEM remains an important component of virus diagnosis, particularly because it can easily and reliably distinguish smallpox virus or any other member of the orthopoxvirus (OPV) genus from parapoxviruses (PPV) and the far more common and less serious herpesviruses (herpes simplex and varicella zoster). Preparation, enrichment, examination, internal standards and suitable organisations are discussed to make clear its continuing value as a diagnostic technique.

High quality RNA isolation from Aedes aegypti midguts using laser microdissection microscopy

Background

Laser microdissection microscopy (LMM) has potential as a research tool because it allows precise excision of target tissues or cells from a complex biological specimen, and facilitates tissue-specific sample preparation. However, this method has not been used in mosquito vectors to date. To this end, we have developed an LMM method to isolate midgut RNA using Aedes aegypti.

Results

Total RNA was isolated from Ae. aegypti midguts that were either fresh-frozen or fixed with histological fixatives. Generally, fresh-frozen tissue sections are a common source of quality LMM-derived RNA; however, our aim was to develop an LMM protocol that could inactivate pathogenic viruses by fixation, while simultaneously preserving RNA from arbovirus-infected mosquitoes. Three groups (10 - 15 mosquitoes per group) of female Ae. aegypti at 24 or 48-hours post-blood meal were intrathoracically injected with one of seven common fixatives (Bouin's, Carnoy's, Formoy's, Cal-Rite, 4% formalin, 10% neutral buffered formalin, or zinc formalin) to evaluate their effect on RNA quality. Total RNA was isolated from the fixed abdomens using a Trizol^® method. The results indicated that RNA from Carnoy's and Bouin's fixative samples was comparable to that of fresh frozen midguts (control) in duplicate experiments. When Carnoy's and Bouin's were used to fix the midguts for the LMM procedure, however, Carnoy's-fixed RNA clearly showed much less degradation than Bouin's-fixed RNA. In addition, a sample of 5 randomly chosen transcripts were amplified more efficiently using the Carnoy's treated LMM RNA than Bouin's-fixed RNA in quantitative real-time PCR (qRT-PCR) assays, suggesting there were more intact target mRNAs in the Carnoy's fixed RNA. The yields of total RNA ranged from 0.3 to 19.0 ng per ~3.0 × 10⁶ μm² in the LMM procedure.

Conclusions

Carnoy's fixative was found to be highly compatible with LMM, producing high quality RNA from Ae. aegypti midguts while inactivating viral pathogens. Our findings suggest that LMM in conjunction with Carnoy's fixation can be applied to studies in Ae. aegypti infected with arboviruses without compromising biosafety and RNA quality. This LMM method should be applicable to other mosquito vector studies.

Flow cytometric analysis of bacteria- and virus-like particles in lake sediments

Flow cytometry (FCM) was successfully used to analyze freshwater bacteria and viruses in lake sediments after relatively simple sample treatment and optimization of dilution/fixation/staining procedures. Biological particles from Lakes Geneva and Bourget were first separated from the sediments by using both Sodium Pyrophosphate (0.01 M final concentration) and Polyoxyethylene-Sorbitan Monooleate (10% final concentration) and sonicating for 3 min in a water bath. The best results (based on FCM signature and the highest virus and bacterial yields from the sediments) were obtained by formaldehyde fixation carried out within less than one hour (2% final concentration, vs. no fixation or using glutaraldehyde at different concentrations), SYBR-Green II staining (x1/20,000 stock solution concentration, vs. use of SYBR-Gold and SYBR-Green I dyes at different concentrations). There was a considerable loss of particles after only a few days of storage at either 4 or -22 degrees C. For FCM analysis, the samples were diluted in Tris-EDTA buffer (pH 8) and heated for 10 min at 75 degrees C after incubating for 5 min in the dark. The bacterial and viral counts paralleled those obtained using epifluorescence microscopy (EFM), but EFM always gave lower counts than FCM. Analysis of the distribution of the viruses in the water column and in the sediments of Lakes Bourget revealed a marked gradient, with larger quantities in the top layer of the sediment than in the water above it. These results are discussed, as well as the possible novel application of flow cytometry in the study of aquatic viral ecology.

Detection and identification of viruses by electron microscopy

Electron microscopy can aid in the rapid diagnosis of viral diseases, as it can be performed in a matter of hours, but on a routine basis it should be used in conjunction with other techniques. Initially, the specimen source and patient symptoms should be ascertained, as these will lend suggestions of possible agents while eliminating others; however, this information should not be allowed to prejudice observation in such a way as to cause oversight of an unlikely pathogen. Second, selection of the method of preparation should be based on sample consistency; extraction, debris clarification, concentration, tissue culture amplification, or embedment may be necessary. Finally, false-positive results must be avoided by differentiating viruses from cell organelles or debris, mycoplasmal or bacterial contamination, and bacteriophages.

Diagnostic electron microscopy is still a timely and rewarding method

BACKGROUND

Parallel to its technical development starting in the 1930s, electron microscopy (EM) became an important tool in basic and clinical virology. First utilized in the rapid diagnosis of smallpox, it developed to a diagnostic routine in the early 1960s using the negative staining technique. EM was applied to infected cell-cultures and also to 'dirty' specimens including urine, feces, vesicle fluid, liquor. With the implementation of molecular biological and genetic techniques, the use of diagnostic EM decreased.

OBJECTIVES

(1) To give a perspective on future indications and possible uses by discussing the past and the present of diagnostic EM, (2) To describe the system of External Quality Assessment on EM virus diagnosis (EQA-EMV) established in 1994 by our laboratory and its achievements.

STUDY DESIGN

EQA-EMV is run to evaluate, to confirm and to improve the quality of diagnostic EM. Two different types of specimen are sent out: (1) prepared grids to assess and train the diagnostic skills of the participants, (2) stabilized virus particle suspensions to assess preparation efficiency.

RESULTS

Diagnostic EM differs from other diagnostic tests in its rapidity and its undirected 'open view'. To emphasize these advantages, the indications for diagnostic EM are discussed, fundamental for a continuing future adaptation. Besides appropriate techniques, quality control measures are required to achieve and keep high diagnostic standards. The results from 6 years of EQA-EMV are presented.

CONCLUSIONS

In the history of diagnostic EM in virology, a change in use has been seen. Starting in the 1990s and coincident with the broad introduction of 'modern' diagnostic techniques, the number of EM diagnostic labs has decreased considerably--in spite of the obvious advantages of this technique. To guarantee the continuing performance of diagnostic EM in the future. EQA runs have to be performed as with other techniques in the diagnostic armament. The growing number of participants and participating countries indicates an interest in as well as a need for this program.

Identification of focal viral infections by confocal microscopy for subsequent ultrastructural analysis

A correlative microscopy method for the ultrastructural analysis of focal viral tissue infections is presented. Using a confocal scanning laser microscope, foci of infection are identified in tissue sections prior to embedment; a variety of techniques can be employed for viral detection, including staining with standard histochemical reagents and fluorescently labeled antibodies. Areas of infection identified using confocal microscopy are excised from the tissue sections, embedded, and examined by transmission electron microscopy. Applications of this technique in both diagnostic and basic research settings are described.

Three-dimensional ultrastructural study of molluscum contagiosum in the skin using scanning-electron microscopy

The three-dimensional ultrastructure of molluscum contagiosum virus (MCV) in human skin was visualized using scanning-electron microscopy with the osmium-dimethyl sulphoxide-osmium method. There were spherical, ellipsoidal, brick-shaped, miniature and incomplete forms of MCV. In all the forms the surface had densely distributed small protrusions and all had the same ultrastructure. All the forms had one or two long cord-like substances that appeared to be linked together, but became short, vestigial or absent on the surface of the mature virus. The cord-like substances were connected to the core of the MCV. In the matrix between the viruses, the cord-like substances formed an intricate fine network.

Detection of rubella virus in amniotic fluid by electron microscopy

We report in this paper the observation of rubella virus by electron microscopy in an amniotic fluid sample, collected from a pregnant woman with rubella infection. Virological investigations by inoculation of cell cultures with amniotic fluid and fetal blood remained negative, due probably to the presence of neutralizing antibodies in the samples. Electron microscopy is a rapid but weakly sensitive method to detect viruses in clinical specimens. However, this unusual observation would indicate that in some cases electron microscopy could be a useful technique to evidence a fetal rubella infection.

Development and evaluation of monoclonal antibody-based immune electron microscopy for diagnosis of adenovirus types 40 and 41

Immune electron microscopy based on monoclonal antibodies was developed and evaluated for diagnosis of adenovirus type 40 and adenovirus type 41 directly from clinical specimens. One adenovirus type 40 monoclonal (5-8) and one adenovirus type 41 monoclonal (5-15) were found to react to high titre with homotypic but not heterotypic antigen. These monoclonals were tested on a coded batch of 20 stools which contained adenovirus type 40 or adenovirus type 41. The results showed that 5/6 adenovirus type 40 and 13/14 adenovirus type 41 strains were correctly serotyped but one strain of each type failed to react with either serum. A wide variation in the numbers of virions bound to positive grids was observed. A further coded batch of 27 specimens, a mixture of subgenus F (i.e. type 40 or 41) or non-subgenus F adenoviruses, was then tested. There was complete serotype concordance with reference results for 16/19 subgenus F strains and all 8 non-subgenus F adenoviruses gave negative results. However, three subgenus F adenoviruses also gave negative results. In conclusion, monoclonal antibody-based immune electron microscopy accurately distinguished adenovirus type 40 from adenovirus type 41 and both viruses from other adenovirus serotypes in clinical specimens and will therefore be useful in the diagnosis of adenovirus gastroenteritis, but some strains may be missed, presumably because of antigenic variation in surface epitopes.

Evaluation of a commercial monoclonal antibody-based enzyme immunoassay for detection of adenovirus types 40 and 41 in stool specimens

A commercial monoclonal antibody-based enzyme immunoassay (Adenoscreen; Mercia Diagnostics Ltd., Guildford, United Kingdom) for the detection of adenovirus types 40 and 41 in stool specimens was evaluated. Two assay modes were tested. In the first, 177 stool samples were screened for the presence of adenovirus type 40 or 41 (assay mode 1). Virus was detected in 79 of 82 specimens positive for adenovirus type 40 or 41 by a polyclonal antibody-based immune electron microscope test, giving a sensitivity of 96.3%. The enzyme immunoassay was negative in 91 of 95 stool samples which contained either other adenovirus serotypes or other viruses or were virus negative. The specificity was thus 95.8%. The positive and negative predictive values of this assay against immune electron microscopy were 95.2 and 96.8%, respectively, and the diagnostic accuracy was 96.0%. Viruses from the three false-negative enzyme immunoassay stool samples were verified as adenovirus type 40 or 41 by restriction enzyme analysis, monoclonal antibody-based immune electron microscopy, or both. Two of the three false-negative stool samples were subsequently concentrated by ultracentrifugation, and one of the two stool samples was then positive by enzyme immunoassay. The third false-negative virus was typed as adenovirus type 41 in the second (serotyping) enzyme immunoassay mode. The four enzyme immunoassay false-positive stool samples all contained other adenovirus serotypes (two were type 2, and two were type 5), but no cross-reactivity was seen with other strains of these serotypes and the results probably reflected simultaneous excretion of adenovirus type 40 or 41 with other adenovirus serotypes. In the second assay mode viruses from 15 stool samples were serotyped. The results by enzyme immunoassay (4 were type 40 and 11 were type 41) correlated completely with previous results from restriction endonuclease analyses. The commercial enzyme immunoassay system showed excellent sensitivity and specificity for the detection of adenovirus types 40 and 41 in stool specimens and will make an important contribution to the accurate diagnosis of adenovirus gastroenteritis.

One-year prospective cross-sectional study to assess the importance of group F adenovirus infections in children under 2 years admitted to hospital

A 1-year prospective cross-sectional study of 363 children under 2 years of age admitted to hospital was undertaken to assess the importance of group F adenovirus infections. Faeces obtained within 48 hours of admission from 97 patients with and 266 patients without diarrhoea were screened by electron microscopy. Viruses were identified by morphological criteria, and all adenoviruses seen were retested by immune electron microscopy to identify group F serotypes. Group F adenoviruses (4 infections) were second in frequency to rotaviruses (16 infections), and both viruses were significantly associated with diarrhoea (P = 0.005 and 0.00001 respectively, chi-squared test). All four group F infections occurred in children with diarrhoeal disease aged between 1 and 6 months and were numerically as important as rotavirus (three infections) in this group. Rotavirus infections occurred significantly more frequently in the 7-24-month age group with diarrhoea (11 v.0 infections, P = 0.001, chi-squared test). Nosocomial infection occurred with group F adenovirus as well as rotavirus. The finding that group F adenoviruses occur as frequently as rotaviruses in diarrhoeal disease that results in hospital admission in children between 1 and 6 months of age could have important implications for preventative strategies.

Comparison of dot-blot DNA hybridisation and immediate early nuclear antigen production in cell culture for the rapid detection of human cytomegalovirus in urine

The sensitivity and specificity of four modes of two assays, immediate early nuclear antigen detection in cell culture (IENAD) at 24 and 48 h post-infection (p.i.) by immunofluorescence using a murine monoclonal antibody, and dot-blot DNA hybridisation with overnight or prolonged autoradiography using the 32P-labelled HindIII J fragment of human cytomegalovirus (HCMV) DNA as probe, were compared for the rapid detection of HCMV in urine. The sensitivity of IENAD was enhanced by low-speed centrifugation at the time of inoculation. DNA hybridisation with overnight autoradiography was significantly less sensitive than IENAD at 24 h p.i. (P less than 0.001), and even with prolonged autoradiography the hybridisation assay was slower and significantly less sensitive than IENAD at 48 h p.i. (P less than 0.02). The specificity of the two assays was virtually 100%. The sensitivity of DNA hybridisation was thus clearly inferior to that of IENAD.

Laboratory Diagnosis of Viral Diseases

Tests for the specific diagnosis of a viral infection in an animal are of two general types: (1) those that demonstrate the presence of the virus and (2) those that demonstrate the presence of specific viral antibody. The provision, by a single laboratory, of a comprehensive service for the diagnosis of viral infections of domestic animals is a formidable undertaking. There are about 200 individual viral species in some 20 different viral families that infect the eight major domestic animal species. If antigenic types within an individual viral species are considered and the number of animal species is broadened to include turkey, duck, and zoo and laboratory animals, then the number of individual viruses exceeds 1000. It is, therefore, not surprising that few single laboratories could have available the necessary specific reagents, skills, and experience for the diagnosis of such a large number of infections.

Direct demonstration of the human parvovirus in erythroid progenitor cells infected in vitro

The human parvovirus (HPV), the cause of transient aplastic crisis of hereditary hemolytic anemia, has been shown to be cytotoxic for erythroid progenitor cells and its presence in these cells demonstrated by morphologic techniques. A relatively pure population of progenitors, isolated by removal of immature erythroid bursts from primary culture, was the target of the virus infection. Infected cells failed to proliferate in secondary culture. Using a monoclonal antibody to HPV, specific fluorescence was demonstrated in a minority of cells 24-48 h after infection with virus. Infected cells examined by electron microscopy showed marked toxic ultrastructural alterations and parvovirus-like particles in crystalline arrays in the nucleus.

A simplified microwell pseudoreplica for the detection of viruses by electron microscopy and immunoelectron microscopy

Simplified procedures for immunoelectron microscopy (IEM) and electron microscopy (EM) are described. The procedures employ the principle of agar filtration and pseudoreplication. The modification consisted of the use of microwells for storage of gels with or without antiserum (for IEM or EM, respectively) and an array of containers in which pseudoreplication and negative staining were performed. The containers were prepared from 5 ml syringes from which the needle holding parts were cut. This device enabled simultaneous and rapid handling of specimens. With Sindbis virus as a model, our microwell pseudoreplica IEM (MW-PR-IEM) was compared to six other IEM techniques and was found to be the most rapid and sensitive technique. With the MW-PR-IEM technique, the specific minimal detection limit (detection of clumps) was 1.5 x 10(7) virus particles per ml, and the non-specific detection limit (detection of single virions) was 1.8 x 10(6) virus particles per ml.

Immunosorbent electron microscopy for detection of viruses

This chapter discusses the newer modifications of immunosorbent electron microscopy (ISEM) methods in both plant and animal virology. ISEM methods presented in the chapter include all the techniques where the “solid phase principle” is essential in a way similar to other solid phase immunoassays. These methods include (1) the antibody-coated grid technique (AB-CGT); (2) the protein A-coated grid technique (PA-CGT); (3) the protein A-coated bacteria technique (PA-CBT); and (4) the antigen-coated grid technique (AG-CGT). In all ISEM methods, one of the components of the system is adsorbed to a solid phase. In AG-CGT, PA-CGT, and AB-CGT, one of the reagents is adsorbed to an electron microscopic grid, while in PA-CBT protein A is naturally present on the surface of a bacterium that serves as a solid support. In ISEM methods, the viruses can be statistically evaluated and numerically expressed as number of virions per unit of area, and can, therefore, be statistically evaluated. Thus, these methods optimize the results of a test by quantifying the effects of the quality of the supporting grid, the time of adsorption, the pH, the presence of salts, and the type of staining. The ISEM also permits a detailed study of antigenic variations in the same genus of virus, and thus would visually pinpoint the type or strain differences.