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

Circulation of a novel pattern of infections by enteric adenovirus serotype 41 among children below 5 years of age in Kolkata, India

Human adenovirus of strains subgenus F (AdV F) are the most common strains detected in acute gastroenteritis cases in developing countries. Subgenus F is represented by AdV serotype 40 (AdV-40) and AdV-41. Most of the reports have described the predominance of AdV-41 in acute gastroenteritis cases. To gain insight into the epidemiology and genetic variation of AdV-41 strains, we analyzed 1,053 stool specimens from children with diarrhea. Among them, 42 (4.0%) and 56 (5.3%) were positive for enteric adenovirus 40/41 by enzyme-linked immunosorbent assay (ELISA) and PCR, respectively. For 1,305 asymptomatic children, 9 (0.7%) and 22 (1.7%) samples were positive for enteric adenovirus 40/40 by ELISA and PCR, respectively. The age distribution revealed a higher frequency (90%) in children <24 months of age. AdV F infection was observed at a low frequency throughout the year, with an increased incidence occurring during February and March. Sequence analysis of one to three hypervariable regions (HVRs) of the hexon genes of 16 representative AdV-41 strains in this study confirmed circulation of a unique strain with genomic type cluster 1 (GTC1)/GTC2. However, sequence analysis of the fiber genes of these strains confirmed 15 amino acid deletions from the 15th repeat motif of the shaft region. The existence of two GTCs reflects the accumulation of amino acid mutations in the HVR of the hexon gene. The novel AdV-41 strain might follow the same infection pattern as AdV-40. There is no significant variation in the sequences of hexon and fiber genes among strains from symptomatic and asymptomatic children. Our data confirm the circulation of an AdV-41 strain with a novel pattern in Kolkata, India, among children below 5 years of age.

Infection kinetics of human adenovirus serotype 41 in HEK 293 cells

The purpose of this work was to acquire an overview of the infectious cycle of HAdV-41 in permissive HEK 293 cells and compare it to that observed with the prototype of the genus, Human adenovirus C HAdV-2. HEK 293 cells were infected with each virus separately and were harvested every 12 h for seven days. Infection kinetics were analysed using confocal and electronic microscopy. The results show that, when properly cultivated, HAdV-41 was not fastidious. It had a longer multiplication cycle, which resulted in the release of complete viral particles and viral stocks reached high titres. After 60 h of infection, the export of viral proteins from the infected cell to the extracellular milieu was observed, with a pattern similar to that previously described for HAdV-2 penton-base trafficking after 30 h of infection. HAdV-41 had a non-lytic cycle and the infection spread from the first infected cell to its neighbours. The release process of the viral particles is unknown. The results observed for HAdV-41 infection in HEK 293 cells show how different this virus is from the prototype HAdV-2 and provides information for the development of this vector for use in gene therapy.

Comparison of primer sets for detection of fecal and ocular adenovirus infection using the polymerase chain reaction

Adenoviruses of subgenus F (types 40 and 41) cause infantile gastroenteritis and adenoviruses principally of types 1-7 are found in feces during respiratory or generalized infections. Adenoviruses (mostly types 3, 4, 8, 19, or 37) are also linked with follicular or epidemic conjunctivitis. The diagnostic efficiency of the polymerase chain reaction (PCR) for adenoviruses was assessed using genus-reactive primers H1 and H2 or JCH1 and JCH2 or subgenus F-specific primers F1a and F2a. With diarrheal stool specimens containing subgenus F adenoviruses, F1a/F2a PCR achieved at least as high a positivity rate (75/76 [99%]) as electron microscopy (72/76 [95%]) and was more sensitive than polyclonal antibody-based immune electron microscopy (IEM) for subgenus identification (75/76 [99%] vs. 66/76 [87%], P = 0.008). Twenty-three subgenus F strains untypeable by monoclonal antibody-based IEM were typed as 40 (n = 4) or 41 (n = 19) by Hha I digestion of the PCR product. The genus-reactive primer pairs provided DNA amplification assays of generally equal efficiency on conjunctival swab specimens though possible nucleic acid degradation in DNA extracts during storage could have meant that JCH1/JCH2 PCR was truly the more sensitive. The use of either genus-reactive primer set on fecal specimens cannot be recommended because, although the positivity rates with subgenus F PCR positive specimens were high (70/75 [93%] for H1 and H2, 14/15 [93%] for JCH1 and JCH2), the detection rates were disappointing with similar specimens yielding nonsubgenus F adenoviruses.

Detection and typing of subgroup F adenoviruses using the polymerase chain reaction

A DNA amplification test was developed for the sensitive detection of the diarrhoea-associated subgroup F adenoviruses in clinical specimens. The test was made highly specific for serotypes 40 and 41 by using a region of the genome (the long-fiber gene) which is not significantly homologous to other human adenoviruses, but which is highly conserved between Ad40 and Ad41. A positive subgroup F adenovirus diagnosis was characterized by the presence of an amplification product of 152 base pairs, which could be digested into products of predictable length by restriction enzymes XbaI and SpeI. The viruses were typed as either Ad40 or Ad41 by digestion of the amplification product with a restriction enzyme which digested only Ad40 DNA. The specificity of the test was assessed using DNA from other adenoviruses, from human and simian cells, and from bacteria commonly found in the human intestine. There was a strong correlation between results of typing obtained with PCR and restriction enzyme typing of Ad40 and Ad41, and also positivity using subgroup F specific probes in dot blot hybridizations.

Comparison of detection methods for adenovirus from enteric clinical specimens

Fecal samples submitted for virus examination over July 1990 to June 1991 from children < 3 years of age were examined by electron microscopy (EM), virus culture (VC), and enzyme immunoassay [EIA, group-reactive and adenovirus (Ad) 40/41 specific; Cambridge BioScience] to compare the detection rate of adenovirus from pediatric fecal specimens. Ad isolates of serotypes 1-7 grown in HEp-2 or primary rhesus monkey kidney cells were identified by neutralization. Graham 293 cell cultures were used only when specimens were found to be positive for Ad by EM, type-specific Ad40/41 EIA, and for isolates not identified by neutralization. Ads grown in 293 cells were identified by DNA restriction endonuclease analysis. Of the 1187 specimens examined, 105 (9%) were found to be positive for Ad. VC detected 93, while 12 additional positives were detected by EM or EIA. The relative sensitivity of VC, EIA, and EM for the 105 specimens was 89% (93), 45% (47), and 35% (37), respectively. Among the 105 positive specimens, enteric Ad, nonenteric Ad, and untypeable Ad were 28% (29), 65% (68), and 7% (8), respectively. Of 37 EM positives, 62% (23) were enteric Ad; 27% (10) were nonenteric including serotypes 2, 3, 4, 5, 12, and 31, with 4, 1, 1, 2, 1, and 1 isolates of each type positive, respectively; and 11% (4) were detectable only by EM. Five isolates were identified as variant of Ad 2(3), Ad 3(1) and Ad 31(1). Over a 1-year period, a single Ad41 variant strain was the most frequently detected enteric Ad in Winnipeg, Manitoba, Canada.(ABSTRACT TRUNCATED AT 250 WORDS)

Computer network for a diagnostic virology laboratory

A data base for a large diagnostic virology laboratory is described. The system uses a network of personal computers. It allows the entry, long-term storage, and subsequent retrieval of specimen and patient records (comprising personal identifiers and specimen and result information), and hard-copy results reporting. Sited entirely within the laboratory, the network is not connected to a modem. Within the laboratory there is restricted access to human immunodeficiency virus test results to guarantee patient confidentiality. Retention of a hard-copy of specimen request cards ensures the availability of the original clinical information. The data base is copied on a second file server to facilitate searches, and daily streaming onto magnetic tape provides system protection in the event of hard disc failure. Matching of old and new patient records is done by surname, date of birth, and sex, and therefore duplicate records accumulate when patient names are misspelt on specimen request forms. The system requires further development to speed searches of the data base and to achieve automatic generation of laboratory worksheets. Future goals are the replacement of hard-copy records of clinical information and hard-copy reporting with on-line access to hospital data bases and on-line requesting by and reporting to the clinician.

Infectious diarrhoea. Viruses

Increased knowledge has been gained into the aetiology and pathogenesis of viral gastroenteritis during the past two decades. There are now thought to be four major subclassifications of gastroenteritis-causing viruses; these include rotavirus, enteric adenovirus, calicivirus, including Norwalk and Norwalk-like viruses, and astrovirus. The association of these agents with gastroenteritis has been made by their electron microscopic detection in stool and intestinal biopsy specimens from affected patients, the inability to detect the viruses after recovery from disease, and the subsequent development of immunoglobulin responses after infection; in some instances disease transmission was achieved in human volunteers. The association of these viral agents with gastroenteritis has facilitated the study of classification, epidemiology, immunity, diagnostic tests, methods of treatment and, most importantly, disease prevention strategies such as vaccine development for rotavirus. This chapter highlights the major features of these agents, with special attention being given to the pertinent molecular biology as well as current and future prospects for vaccination. Enteric viral infections of the gastrointestinal tract in patients with AIDS are also discussed.

Detection, typing, and subtyping of enteric adenoviruses 40 and 41 from fecal samples and observation of changing incidences of infections with these types and subtypes

Monoclonal antibody (MAb) preparations specific for the enteric adenoviruses of subgenus F (AdF) were generated and evaluated as typing reagents in virus neutralization tests and enzyme-linked immunosorbent assays (ELISAs). A panel of 11 genome types of adenovirus 40 (Ad40), 24 genome types of Ad41, and 47 adenovirus prototype strains was used to determine the specificities of the MAbs in the two assays. In this way two MAbs, MAb 40-1 (anti-Ad40) and MAb 41-1 (anti-Ad41) were selected. These two MAbs showed strict type specificity in both assays. A third MAb reacted in an ELISA with all 47 human adenovirus types. With two other MAbs, three antigenic subtypes of Ad41 could be distinguished by their reactivities in virus neutralization tests and ELISAs. On the basis of the five selected MAbs, a sensitive ELISA system was developed for the direct detection and simultaneous typing and subtyping of Ad40 and Ad41 present in stool specimens. The five MAbs were also used to study the epidemiology of infections with Ad40 and Ad41 in The Netherlands in the period 1981 through 1989. It was shown that there were no significant fluctuations in the annual incidence of the cluster of enteric adenoviruses as a whole. This cluster should therefore be considered to belong to the "endemic" rather than the "epidemic" adenoviruses. The relative incidence of Ad40 infections compared with that of Ad41 infections changed considerably during the period studied; the proportion of Ad41 infections rose from about 30% in 1981 to about 95% in 1986, after which it stabilized at 90 to 95%. The proportion of one of the subtypes of Ad41 (Ad41 subtype M3) increased from about 40 to 80% in the same period.

Comparative epidemiology of rotavirus, subgenus F (types 40 and 41) adenovirus and astrovirus gastroenteritis in children

We report a 5 year prospective study of episodes of rotavirus, subgenus F adenovirus, and astrovirus gastroenteritis diagnosed by electron or immune electron microscopy in a single regional virology laboratory. Of 1426 total infections, the numbers in each category were 1117 (78.3%), 254 (17.8%), and 20 (7.9%), respectively. Using restriction endonuclease analysis or immune electron microscopy, all but 20 of the subgenus F adenovirus strains were classified as type 40 (n = 50) or type 41 (n = 184). Rotavirus and astrovirus infections were more prevalent in winter than summer, whereas subgenus F (either type 40 and 41) adenoviruses showed no seasonal variation in prevalence. The ratio of type 40 to all typable subgenus F adenoviruses declined between 1984 and 1986 and then increased again. Adenoviruses were relatively more important as causes of viral gastroenteritis in infants aged less than 6 months than in toddlers aged 12 months or more, but even in young infants more rotavirus than adenovirus infections were diagnosed. Our data confirmed the epidemiological differences between rotavirus, subgenus F adenovirus and rotavirus gastroenteritis and documented the shared epidemiological characteristics of type 40 or 41 adenovirus infections.

Negative staining in the detection of viruses in clinical specimens

Viruses have unique morphology and are therefore good candidates for negative staining. Negative staining with phosphotungstic acid (PTA) or uranyl acetate has facilitated the detection of many viruses in clinical specimens. Enhancement procedures have included the use of centrifugation and agar diffusion for concentrating virus particles, the use of solid phase capture reagents to trap virus particles and the use of secondary antibodies and electron dense markers to help visualize them. Techniques currently in use and employing negative staining include direct EM, immune electron microscopy (IEM), solid phase immune electron microscopy (SPIEM), colloidal gold-labeled protein A (PAG), solid phase IEM employing a second decorator antibody (SPIEMDAT), and solid phase IEM using colloided gold-labeled secondary antibodies (SPEIMDAGT). IEM methods assist with the detection of small viruses or viruses present in low numbers while PAG offers increased sensitivity over direct EM and IEM. In our experience the serum-in-agar (SIA) method is the most sensitive of the PAG IEM techniques for detection of rotavirus particles in clinical specimens. SPIEMDAT enhances the detection of small viruses which are often missed by other techniques due to background staining in specimens. SPEIMDAGT employing colloidal gold-labeled secondary antibody has increased sensitivity and offers the advantage of detecting viral antigen when whole virus particles are not visible. IEM techniques have recently been used for typing viruses using either monospecific antisera or monoclonal antibodies and colloidal gold-labeled secondary antibody.

Laboratory identification of adenoviruses associated with gastroenteritis in Canada from 1983 to 1986

A retrospective analysis of adenovirus serotypes associated with gastroenteritis involved the examination of 143 stool specimens collected between 1983 and 1986 from symptomatic patients whose stools were positive for adenovirus by electron microscopy. The virus isolates obtained from 140 of the specimens were typed according to the SmaI cleavage pattern of the viral DNA and by neutralization with specific antisera. The predominant types were adenovirus type 31 (Ad31) (18%), Ad40 (16.9%), and Ad41 (38%), which together accounted for more than 70% of the isolates. The remaining virus isolates were typed as Ad1, 2, 3, 5, 7, and 12. DNA restriction analysis proved to be better than serum neutralization for identification of the enteric adenovirus serotypes in stool specimens. HindIII cleavage identified four Ad41 variants, none of which had a HindIII restriction pattern identical to that of the prototype strain Tak. Over the time period of the study, the incidence of Ad40 showed an overall decrease accompanied by an increased incidence of Ad41, while the incidence of Ad31 was relatively stable.

Time-resolved fluoroimmunoassay for enteric adenoviruses using the europium chelator 4,7-bis(chlorosulfophenyl)-1,10-phenanthroline-2,9-dicarboxylic acid

A time-resolved fluoroimmunoassay (TR FIA) was developed for the direct detection of adenovirus types 40 (Ad40) and 41 (Ad41) in stool specimens by using a monoclonal antibody (5D8/2C2) which recognizes both Ad40 and Ad41 but does not cross-react with other adenovirus serotypes. In this assay, the detector antibody is biotinylated directly rather than labeled with europium, and the fluorescent signal is generated on a solid phase in the presence of excess europium (Eu3+). The strength of the signal is dependent on the amount of a Eu3+ chelator [4,7-bis(chlorosulfophenyl)-1,10-phenanthroline-2,9-dicarboxylic acid (BCPDA)]-streptavidin complex bound by the biotinylated detector antibody (5D8/2C2). In a pilot study with 41 specimens, this TR FIA demonstrated a maximum sensitivity and specificity of 88% compared with SmaI restriction analysis of adenovirus isolates from the same specimens. TR FIA using the europium chelator BCPDA represents a feasible approach for the direct identification of specific adenovirus serotypes in stool specimens.