SARS-CoV-2 host tropism: An in silico analysis of the main cellular factors

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The role in host selectivity of ACE2, Tmprss2 and GPR78 in SARS-CoV-2 was explored.

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Differences in the SARS-CoV-2 RBD binding mode with ACE2 of secondary hosts could be associated with host permissiveness.

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Nafamostat could be considered a good inhibitor of mammalian hosts TMPRSS2 proteins.

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In silico studies confirm that the spike protein could interact with GRP78 in studied mammalian hosts.

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TMPRSS2 and GRP78 do not seem to play a role in host selectivity.

Recent reports have shown that small and big felines could be infected by SARS-CoV-2, while other animals, like swines and mice, are apparently not susceptible to this infection. These findings raise the question of the role of cell factors associated with early stages of the viral infection in host selectivity. The cellular receptor for SARS-CoV-2 is the Angiotensin Converting Enzyme (ACE2). Transmembrane protease serine 2 (TMPRSS2) has been shown to prime the viral spike for its interaction with its receptor. GRP78 has also been proposed as a possible co-receptor. In this study, we used several bioinformatics approaches to bring clues in the interaction of ACE2, TMPRSS2, and GRP78 with SARS-CoV-2. We selected several mammalian hosts that could play a key role in viral spread by acting as secondary hosts (cats, dogs, pigs, mice, and ferrets) and evaluated their predicted permissiveness by in silico analysis. Results showed that ionic pairs (salt bridges, N–O pair, and long-range interactions) produced between ACE2 and the viral spike has an essential function in the host interaction. On the other hand, TMPRSS2 and GRP78 are proteins with high homology in all the evaluated hosts. Thus, these proteins do not seem to play a role in host selectivity, suggesting that other factors may play a role in the non-permissivity in some of these hosts. These proteins represent however interesting cell targets that could be explored in order to control the virus replication in humans and in the intermediary hosts.

Hepatitis E virus infection in Latin America: a review

Data reported during recent years reveal the complex picture of the epidemiology of hepatitis E virus (HEV) infection in Latin America. Whereas in countries like Argentina and Brazil is almost identical to the characteristic of most countries from North America and Europe, HEV in the Caribbean and Mexico involves the water-borne, non-zoonotic viral genotypes responsible for epidemics in Asia and Africa. Nevertheless, Latin America has been considered a highly endemic region for hepatitis E in the scientific literature, a generalization that ignores the above complexity. In addition, reports from isolated Amerindian communities, which display well known, important and very specific epidemiological features for hepatitis B and D virus infections are neither taken into account when considering the epidemiology of hepatitis E in the region. This review updates compilation of the available information for the HEV infection, both among humans and other mammals, in Latin America, discusses the strengths and the weaknesses of our current knowledge, and identifies future areas of research.

Infection with transfusion-transmitted virus (TTV) in humans and other primates in Venezuela

Tranfusion-transmitted virus (TTV), a single-stranded circular DNA virus that chronically infects humans and other animals, displays a high degree of genetic diversity and was originally thought to be associated with hepatitis. The prevalences of TTV infection among different populations of humans and non-human primates from Venezuela have now been evaluated, using serum samples and three different detection tests. All three tests were PCR-based, one involving a hemi-nested PCR and primers based on the N22 open-reading-frame-1 region (N22-PCR), another employing 55 cycles with primers from the more conserved untranslated region (UTR-PCR), and the other using a hemi-nested PCR with primers from the same region (HUTR-PCR). The overall prevalences of human infection appeared much higher with the HUTR-PCR (52%) than with the N22-PCR (13%) or the UTR-PCR (5%). When the products amplified by N22-PCR from 28 human isolates of TTV were sequenced, only two genotypes of the virus were detected. The non-human sera tested came from primates kept in a zoo in north-western Venezuela. TTV DNA was detected, by HUTR-PCR, in both of the chimpanzee sera tested but not in any of the sera from the 11 New-World primates or the other 12 Old-World primates that were investigated. The results, particularly those of the HUTR-PCR, indicate that TTV infection is common in Venezuela, especially in populations, such as many Amerindian groups, who live under poor sanitary conditions. Although TTV infection may be relatively rare among non-human primates from the New World, this will have to be investigated further, using many more samples collected throughout the Americas.

Inhibition of hepatitis B virus and human immunodeficiency virus (HIV-1) replication by Warscewiczia coccinea (Vahl) Kl. (Rubiaceae) ethanol extract

The primary objective of this study was to search for natural products capable of inhibiting hepatitis B virus (HBV) replication. The research design, methods and procedures included testing hydro-alcoholic extracts (n = 66) of 31 species from the Venezuelan Amazonian rain forest on the cell line HepG2 2.2.15, which constitutively produces HBV. The main outcomes and results were as follows: the species Euterpe precatoria, Jacaranda copaia, Jacaranda obtusifolia, Senna silvestris, Warscewiczia coccinea and Vochysia glaberrima exerted some degree of inhibition on HBV replication. The leaves of W. coccinea showed a significant antiviral activity: 80% inhibition with 100 µg mL⁻¹ of extract. This extract also exerted inhibition on covalently closed circular deoxyribonucleic acid (cccDNA) production and on HIV-1 replication in MT4 cells (more than 90% inhibition with 50 µg mL⁻¹ of extract). Initial fractionation using organic solvents of increasing polarity and water showed that the ethanol fraction was responsible for most of the antiviral inhibitory activities of both the viruses. It was concluded that Warscewiczia coccinea extract showed inhibition of HBV and HIV-1 replication. Bioassay-guided purification of this fraction may allow the isolation of an antiviral compound with inhibitory activity against both viruses.

Subgenotype diversity of hepatitis B virus American genotype F in Amerindians from Venezuela and the general population of Colombia

The objective of this study was the evaluation of the genetic diversity found in HBV circulating among Venezuelan Amerindians and the general population in Colombia. Phylogenetic analysis of the S region in 194 isolates showed that genotype F is highly predominant in Colombia and Venezuela. This might be related to the genetic background of the population. F3 is the main subgenotype which circulates in both countries. Phylogenetic analysis of 61 complete genome sequences of HBV American genotypes confirms the presence of two genotypes F and H, and 4 F subgenotypes. In Venezuela, subgenotypes F1, F2, and F3 circulate in East and West Amerindians, while only F3 was found among South Amerindians. Japreira community derived from Yucpa Amerindians around 150 years ago. However, several Japreira HBV sequences were forming a clade that can be classified as subgenotype 2b, differing from Yucpa sequences that belong mainly to subgenotype F3. The apparent absence of correlation between the phylogenetic groupings of HBV isolates with the ethnical origin in aboriginal populations might be suggesting a recent origin of HBV American subgenotypes, or a genetic drift effect.

Calicivirus infection in human immunodeficiency virus seropositive children and adults

BACKGROUND

The importance of enteric viral infections in HIV-related diarrhea is uncertain. Human caliciviruses have emerged as a leading cause of acute diarrhea worldwide.

OBJECTIVES

To evaluate the importance of calicivirus infections in HIV-related diarrhea. Study design 151 fecal samples collected from children and adults infected with HIV, with and without diarrhea, were examined. In addition, 89 fecal samples from non HIV-infected children and adults were also tested. Samples were analyzed by RT-PCR using primer sets specific to Norovirus genogroup I or genogroup II as well as primers designed to react with both Noroviruses and Sapovirus genus.

RESULTS

Viruses were detected with equal frequencies in stools from HIV infected and non-infected adults (12%). However, specimens from HIV infected children were more likely than those of HIV-negative children to have caliciviruses (51% versus 24%, P<0.05). Viral infections were not significantly associated with diarrhea neither in children nor in adults, regardless of HIV status. Viruses genetically related to the common Lordsdale virus (Norovirus genogroup II) and London/92 virus (Sapovirus) clusters were detected circulating among children.

CONCLUSIONS

These results suggest that caliciviruses may be an important opportunistic pathogen in children infected with HIV.

The seroprevalences of anti-hantavirus IgG antibodies among selected Venezuelan populations

In Venezuela, the isolation of hantaviruses from rodents and the detection, in 1999, of a clinically confirmed human case of hantavirus infection led to increased interest in these viruses. In an attempt to estimate the problem posed by such viruses in Venezuela, ELISA based on purified, recombinant, nucleoprotein were used to check 1380 human serum samples for the presence of IgG antibodies to hantavirus. The ELISA results, as confirmed by indirect immunofluorescence and Western-blot assays, indicated that 23 (1.7%) of the serum samples contained antibodies to hantaviruses. Seroprevalences were similar among all age-groups and for both genders and were no higher among rural populations with a relatively high risk of exposure to rodents than among the overall study population. Although the numbers of samples involved were small, the seroprevalence among the subjects who were residents of Carabobo state was much higher than the overall value (10.3% v. 1.7%; P < 0.01). Human infection with hantavirus appears uncommon but widely distributed in Venezuela.

Molecular epidemiology of hepatitis B virus in Afro-Venezuelan populations

Hepatitis B virus (HBV) infection among Venezuelan populations of African origin was analyzed. These populations exhibited lower HBV prevalence than the one found in the African continent. Sequence analysis of 6 isolates showed that 3 belonged to genotype F, while the 3 others were HBV genotype A. HBV genotype A was more common in the Afro-Venezuelan groups than in the general Venezuelan population. This might reflect the introduction of genotype A during the slavery period. The absence of the African genotype E among these isolates supports the hypothesis of a recent origin for this HBV genotype. HBV genotype F has already been introduced to these relatively isolated communities.

[Low impact of silent hepatitis B virus infection on the incidence of post-transfusion hepatitis in Venezuela]

OBJECTIVE

Silent infection by hepatitis B virus (HBV) occurs in the absence of serological markers for the virus. This type of occult infection is generally chronic, asymptomatic, and associated with low levels of viral replication. This study determined the presence of HBV DNA in the sera of blood donors who were negative for serological markers that were tested during screening, with the goal of evaluating the impact of silent HBV infection in posttransfusion hepatitis B in Venezuela.

METHODS

A total of 2,075 sera were tested in 53 serum pools of 25-50 donations (0.5-1.0 mL from each sample). The pools were subjected to ultracentrifugation prior to DNA extraction by the proteinase K, phenol/chloroform method.

RESULTS

No HBV DNA was found in any of the pools by nested polymerase chain reaction, using primers for highly conserved regions of the genes that code for the surface antigen and for the viral capsid. Aminotransferase levels were normal in 98% of 200 sera that were tested.

CONCLUSIONS

These results suggest that there is a low risk of acquiring posttransfusion hepatitis B in Venezuela.

Hepatitis delta virus genotypes I and III circulate associated with hepatitis B virus genotype F In Venezuela

The genotypes of hepatitis B (HBV) and delta (HDV) viruses circulating among Venezuelan Amerindian populations, where these viruses are endemic, were determined by sequencing of PCR amplified products from HBsAg positive sera. HDV genotype I (n = 7, 6 from West Amerindians), and III (n = 5, 4 from South Amerindians), were found. Only one HDV genotype I isolate was associated with HBV genotype D, 4 HDV genotype I and 2 HDV genotype III infected individuals were co-infected with HBV genotype F. The failure to detect the South American HDV genotype III in West Amerindians might be related to the outbreak of fulminant hepatitis with high mortality rate occurred between 1979 and 1982, probably affecting more the Amerindians infected with HDV genotype III. These results suggest the circulation of HDV genotype I among Amerindians, probably introduced through European immigrations, and that this HDV genotype is able to replicate in association with HBV genotype F.

Prevalence of infection with hepatitis C virus in Venezuela, as assessed with an immuno-assay based on synthetic peptides

Information on infection with hepatitis C virus (HCV) in South America is scarce. The seroprevalences of antibodies to HCV among urban, rural and Amerindian populations from Venezuela, and the genotypes of the HCV isolates recovered, were therefore determined. A total of 2592 sera were tested with an immuno-assay which was developed in-house and based on synthetic peptides. Each reactive sample was then re-tested, using other enzyme immuno-assays and a reverse-transcription, nested PCR, and any sample confirmed positive (in any test) was considered HCV-positive. Genotypes were determined by analysis of RFLP. Overall, 39 (1.5%) of the samples were found HCV positive. The results of the immuno-assays indicated that the seroprevalence of HCV markers among the Amerindians investigated (23/1082, or 2.1%) was significantly higher than that among the other subjects (16/1510, or 1.1%; P = 0.02). No such difference was observed in the numbers of subjects confirmed positive by PCR, however (6/1082 v. 10/1510), and some of the anti-HCV reactivity observed among Amerindians may have been the result of cross-reactivity with parasitic infections. The relative low prevalence of active HCV infection (16/2582, or 0.6%) and the HCV genotypes observed (mainly genotype 1) are in agreement with the results of previous studies indicating that HCV is not autochthonous to South America. However, it is clear that the virus may now be found even in isolated Amerindian populations. The in-house, synthetic-peptide-based immuno-assay seems to be a valuable tool for epidemiological studies.

Enteric virus infections and diarrhea in healthy and human immunodeficiency virus-infected children

Forty-three stool samples from 27 human immunodeficiency virus (HIV)-seropositive children and 38 samples from 38 HIV-negative children, collected during a 15-month period, were examined for enteric viruses. Diagnostic assays included enzyme immunoassays for rotavirus, adenovirus, and Norwalk virus; polyacrylamide gel electrophoresis for picobirnavirus and atypical rotavirus; and PCR for astrovirus and enterovirus. Specimens from HIV-positive children were more likely than those of HIV-negative children to have enterovirus (56 versus 21%; P < 0.0002) and astrovirus (12 versus 0%; P < 0.02), but not rotavirus (5 versus 8%; P > 0.5). No adenoviruses, picobirnaviruses, or Norwalk viruses were found. The rates of virus-associated diarrhea were similar among HIV-positive and HIV-negative children. Enteroviruses were excreted for up to 6 months in HIV-positive children; however, no evidence for prolonged excretion of poliovirus vaccine was observed. These results suggest that although infection with enterovirus and astrovirus may be frequent in HIV-infected children, enteric viruses are not associated with the diarrhea frequently suffered by these children.

Hepatitis B virus DNA in blood samples positive for antibodies to core antigen and negative for surface antigen

Anti-hepatitis B core antigen (HBcAg)-positive hepatitis B surface antigen (HBsAg)-negative plasma samples from blood donors were tested by nested PCR. DNA positivity was more significantly associated with high levels of anti-HBcAg than with low levels of anti-HBsAg antibodies. Analysis of a dilution of anti-HBcAg antibodies might result in a more rational exclusion of anti-HBcAg-positive HBsAg-negative samples, reducing the number of donations discarded and enabling more countries to incorporate anti-HBcAg testing.

Sequence heterogeneity within three different regions of the hepatitis G virus genome

Two sets of primers derived from the 5'-terminal region and the NS5 region of the hepatitis G virus (HGV) genome were used to amplify PCR fragments from serum specimens obtained from different parts of the world. All PCR fragments from the 5'-terminal region (5'-PCR, n = 56) and from the NS5 region (NS5-PCR, n = 85) were sequenced and compared to corresponding published HGV sequences. The range of nucleotide sequence similarity varied from 74 and 78% to 100% for 5'-PCR and NS5-PCR fragments, respectively. Additionally, five overlapping PCR fragments comprising an approximately 2.0-kb structural region of the HGV genome were sequenced from each of five sera obtained from three United States residents. These sequences were compared to 20 published sequences comprising the same region of the HGV genome. Nucleotide and deduced amino acid sequences obtained from different individuals were homologous from 82.9 to 93. 6% and from 90.4 to 99.0%, respectively. Sequences obtained from follow-up specimens were almost identical. Comparative analysis of deduced amino acid sequences of the HGV structural proteins and hepatitis C virus (HCV) structural proteins combined with an analysis of predicted secondary structures and hydrophobic profiles allowed prediction of processing sites within the HGV structural proteins. A phylogenetic sequence analysis performed on the 2.0-kb structural region supports the existence of three previously identified HGV genetic groups. However, phylogenetic analysis performed on only small DNA fragments yielded inconsistent genetic grouping and failed to confirm the existence of genetic groups. Thus, in contrast to HCV where almost any region can be used for genotyping, only large or carefully selected genome fragments can be used to identify consistent HGV genetic groups.

Restricted isotypic antibody reactivity to hepatitis C virus synthetic peptides in immunocompromised patients

An enzyme immunoassay based on three synthetic peptides from the core, NS4, and NS5 regions of hepatitis C virus allowed the detection of antibodies in 100% of immunocompetent infected patients and in 91% of immunocompromised patients (hemodialysis and hemophiliac patients). Immune impairment seemed to restrict the spectrum of antibody isotypes reacting to the core peptide.

Prevalence of enteric viruses in human immunodeficiency virus seropositive patients in Venezuela

The prevalence of enteric viruses associated with gastroenteritis was determined in 125 stool samples from patients infected with the human immunodeficiency virus (HIV), with or without diarrhea. Diagnostic assays included enzyme immunoassays for the identification of rotavirus, adenovirus, and Norwalk virus; polyacrylamide gel electrophoresis for atypical rotaviruses and picobirnaviruses and polymerase chain reaction for astrovirus. Enteric viruses were detected in 6.4% (8 of 125) of the stools collected: five (4.0%) samples positive for adenoviruses, and three (2.3%) samples positive for picobirnaviruses were detected. No rotavirus, astrovirus, or Norwalk virus were observed. Only one of the viruses identified (adenovirus) was found in a sample from a patient with diarrhea. Viruses were detected in 10% of the patients with AIDS, 14% of the symptomatic patients, and none of the asymptomatic persons. These results do not support a major role for enteric viruses in the diarrhea suffered by HIV-infected patients.

Turnover of hepatitis C virus genotypes in hemodialysis patients

Hepatitis C virus (HCV) genotypes were determined in hemodialysis patients with a high prevalence and incidence of infection. A change of HCV genotype was observed in 6/14 follow-up samples analyzed 13 and 21 months later. The appearance and disappearance of HCV genotypes may be due to either genotype-specific intermittent viremic status or viral interference.

Antigenic diversity of hepatitis B virus strains of genotype F in Amerindians and other population groups from Venezuela

The adw4 subtype of hepatitis B virus (HBV) belongs to a unique genomic group (genotype F) representing the original HBV strains from the New World. Data regarding the prevalence of this subtype among HBV carriers in South America are, however, scarce, and those concerning HBV genotype F are based on only a few samples from Latin America. In this study, serum samples were obtained from 141 hepatitis B surface antigen (HBsAg) carriers from Amerindians and urban populations from Venezuela. The HBsAg subtype was identified with monoclonal antibodies in 105 samples, and the HBV genotype was identified by reverse-phase hybridization with DNA fragments in 58 samples. The adw4 subtype was highly prevalent in the population studied (75%); among the Amerindians, the prevalence was 97%. The adw2 subtype was also present (10%), while other subtypes (ayw3 and ayw4) were only occasionally found. The HBV subtype was associated with the expected genotype in most cases (80%), and thus genotype F was highly prevalent. Sequencing of viral strains that gave genotypes unpredicted by the HBsAg subtyping confirmed seven of them as belonging to not previously described genotype-subtype associations: namely, adw2 and ayw4 within genotype F.

[Development of an enzyme assay for detection of hepatitis B virus core IGM antibodies]

Detection of IgM anti-core (anti-HBcAg) antibodies of Hepatitis B Virus (HBV) is an useful marker for hepatitis B virus (HBV) acute infection. The aim of this study was to perform an immunodiagnostic assay for the detection of IgM anti-HBcAg antibodies. Hepatitis B core antigen (HBcAg) was produced by a recombinant clone of Escherichia coli and used for the development of the immunoassay. An IgM capture enzyme immunoassay (EIA) was selected for the detection of IgM anti-HBcAg antibodies. A total of 110 human plasma or sera were tested by the capture EIA and a commercial assay. The capture EIA yielded 99% of sensitivity and 93% specificity, when compared with the commercial test. The capture EIA developed here is of interest for epidemiological studies, particularly for endemic regions in South America.

Norwalk virus infection in Venezuela

The presence of antibodies against Norwalk virus (NV) was studied in sera from different Venezuelan populations, using an enzyme immuno-assay (EIA) based on recombinant NV protein. Antibodies to NV were found in 47%-53% of urban subjects from Caracas, 83% of rural subjects from the west of the country, and 73%-93% of Amerindian subjects. The prevalences found in the rural and Amerindian groups were significantly higher than that in the urban group. Although about 50% of the children studied were seropositive for NV by the age of 5 years, only four (0.4%) of 1120 faecal samples from children with diarrhoea which were tested for the presence of NV antigen by sandwich EIA were found positive. An increase of at least 4-fold in the titre of anti-NV IgA was found in three (5%) of 61 pairs of sera taken during and 1 month after an acute episode of diarrhoea not due to rotavirus. NV was therefore not a predominant aetiological cause of gastro-enteritis in young children in Venezuela between 1993 and 1995, although it can be the cause of diarrhoea in infants.

Hepatitis G virus infection in Amerindians and other Venezuelan high-risk groups

Recently, a new virus related to flaviviruses, the hepatitis G virus (HGV), or GBV-C virus, was discovered as a putative blood-borne human pathogen. HGV RNA (NS5 region) was amplified by reverse transcription-nested PCR in the sera of 6 of 64 (9%) hemodialysis patients; 2 of 80 (2.5%) West Yukpa Amerindians, a population with a high rate of HBV infection but negative for HCV infection; and 1 patient with an acute episode of non-A, non-B, non-C hepatitis (NABCH). The patterns of single-strand conformation polymorphism of the amplified products were unique among different specimens and similar on follow-up for hemodialysis patients. All patients tested remained HGV RNA positive 1 and 2 years later, without major sequence variation, except for the NABCH patient, for whom a double infection and an apparent clearance of the original dominant variant was observed after 2 years. The sequences of the NS5 amplified products demonstrated 85 to 90% identity with other reported HGV sequences.

Reduced antibody reactivity to hepatitis C virus antigens in hemodialysis patients coinfected with hepatitis B virus

Antibody reactivities to hepatitis C virus (HCV) antigens and to synthetic peptides derived from different parts of the HCV genome (core, NS4, and NS5) were evaluated in HCV-infected hemodialysis patients. In the RIBA 3 assay, NS5 was significantly less recognizable by sera of hemodialysis patients compared to other HCV-infected subjects. Among hemodialysis patients, those coinfected with hepatitis B virus (HBV) (positive for hepatitis B surface antigen [HBsAg+]) showed a reduction in reactivity to C33 and C100. Sera of only 23% of the hemodialysis patients (37 of 161) reacted with more than three of eight peptides tested, significantly fewer than the 60% (12 of 20) of the sera of other HCV-infected patients tested (P = 0.001). This immunosuppression was also manifested by a reduced frequency of recognition of additional peptides on follow-up. An even more reduced reactivity was observed among the HBV-coinfected patients (HBsAg+). The low-responder hemodialysis patients were not infected with any particular genotype of HCV, and the same HCV genotypes observed in the whole group of hemodialysis patients (1a, 1b, 2a, and 3a) were found circulating in the low-responder group. Even in this low-responder population, the good performance of two peptides (peptide 716, corresponding to a portion of the core, and peptide 59, corresponding to a portion of NS4) corroborates the immunodominance of the conserved epitopes within these peptides.

Productive penetration of rotavirus in cultured cells induces coentry of the translation inhibitor alpha-sarcin

Internalization of rotavirus in MA104 cells was found to induce coentry of alpha-sarcin, a toxin that inhibits translation in cell-free systems and to which cells are normally impermeable. Entry of the toxin, measured by inhibition of protein synthesis at early times after infection, correlated with virus penetration leading to expression of infectivity, since toxin entry (1) was induced only by trypsin-treated triple-layered virions, to a degree dependent on the toxin and the virus concentration; (2) correlated with the degree of permissivity of different cell lines to rotavirus infection; (3) was inhibited to a similar extent as infectivity by treatment of cells with neuraminidase; and (4) was inhibited by pre- or postadsorption incubation of the virus with neutralizing monoclonal antibodies to VP7 and VP4 (VP8*). Neither the virus infectivity nor the toxin coentry was significantly affected by treatment of cells with bafilomycin A1, an inhibitor of the vacuolar proton ATPase, indicating that both events are independent of the endosomal acid pH. Virus-like particles (VLP), composed of rotavirus proteins 2/6/7/4, but not 2/6/7 or 2/6, were able to induce toxin entry as efficiently as virions. Use of genetically modified VLP in combination with the toxin coentry assay, which measures entry through a productive pathway, should allow identification of the regions of the outer capsid proteins essential for rotavirus penetration.

Determination of genotypes of hepatitis C virus in Venezuela by restriction fragment length polymorphism

Hepatitis C virus genotypes in Venezuela were analyzed by restriction fragment length polymorphism in the 5' noncoding region. The absence of BstUI digestion was found to be a useful marker for genotype 2 specimens. From 122 serum samples, 66, 20, and 2.5% were classified as genotypes 1, 2, and 3, respectively; 0.8% were classified as genotype 4; and 10% appeared to be mixed infections.

High incidence of hepatitis C virus infection in hemodialysis patients in units with high prevalence

The prevalence of hepatitis C virus (HCV) infection was evaluated in 227 hemodialysis patients from four units in Caracas, Venezuela, by using different second- and third-generation enzyme immunoassays (EIAs) and immunoblot assays. HCV antibodies were detected in 162 patients (71%) by the recombinant-based second-generation assays (Abbott and Ortho) and in 161 patients by the synthetic peptide-based EIA (UBI). Of the 162 HCV antibody-positive serum samples, 161 were confirmed to be positive by RIBA 3. HCV RNA was detected in 49 of 68 (72%) of the seropositive patients and in 5 of 21 (24%) of the seronegative ones. HCV RNA was not always correlated with an increase in alanine aminotransferase (ALT) levels. Among 20 patients positive for HCV RNA and for HCV antibodies (without any hepatitis B virus [HBV] marker), only 10 had elevated ALT levels. The possible interference of HBV for HCV replication was evaluated. No significant difference was found between the presence of HCV RNA and the presence of any HBV serological markers. The possible routes of transmission of HCV in hemodialysis patients are multiple, and some of them are still controversial. Of the HCV-positive patients, 30% received a blood transfusion, significantly more than the 15% found for the HCV-negative group. However, blood transfusions alone could not account for the high incidence observed in this group of patients (38% from 1994 to 1995). In conclusion, about one-quarter of the apparently non-HCV-infected patients were probably seroconverting, ALT may not be a useful indicator of HCV infection in hemodialysis patients, and nosocomial transmission of HCV may play a role in the spread of HCV in this group.

Characterization of the antibody reactivity to synthetic peptides from different parts of the hepatitis C virus genome

Infection by hepatitis C virus (HCV)*, the aetiologic agent responsible for the majority of non-A-non-B posttransfusion hepatitis, is detected by assaying for antibodies against structural and nonstructural recombinant proteins or synthetic peptides. The aim of this study was to characterize the antibody reactivity of selected sera against antigenic peptides spanning immunodominant regions of the core, NS4 and NS5 HCV proteins. Reactivity to synthetic peptides was determined by enzyme immunoassay (EIA) for 11 selected sera from blood donors (good responders), for 27 selected sera from hemodialysis patients (poor responders), all positive for HCV antibodies (tested by different second and third-generation assays), and for 7 negative sera. Some peptides from the core and the NS4 region were widely recognized by the tested sera. Sera not reactive with core, NS4, or NS5 region by some immunoblot assays exhibited reactivity against peptides from these proteins. Autoimmune reactivity associated with HCV infection was evaluated by using a synthetic peptide derived from the GOR peptide; 8/11 HCV-positive sera were found reactive against this peptide. No correlation was found between reactivity to any of the peptides tested and the presence of HCV RNA in the serum or with HCV genotype. The EIA reactivity of peptides from the core region suggested a multideterminant antigenic structure, where reactivity of each epitope may be differentially affected by neighboring amino acids depending on individual sera. This situation was particularly evidenced in selected sera from poor responder specimens where a more restricted antibody response to core peptides was observed. Reactivity of sera from HCV-infected patients with synthetic peptides from the core, NS4, and NS5 regions indicated the presence of multiple linear epitopes (particularly in the core region) that may be used in a mixture for immunodiagnosis; however, the length and exact position of the synthetic peptides must be chosen carefully.

[High prevalence of hepatitis B and C markers in an indigent community in Caracas, Venezuela]

Hepatitis B and C serological markers were evaluated in indigent patients living in a workhouse in Caracas, Venezuela. Three out of 146 specimens were reactive for HBsAg (2.1%) and 41 for anti-HBc (28%). Eight sera were reactive for antibodies against HCV, and 7 were confirmed by immunoblot assays (4.8%). Four out of these 7 HCV-positive sera were also HCV-RNA positive. The prevalence for viral hepatitis markers was significantly higher than that found in blood donor population in Caracas. The probable risk factors associated with this high prevalence of blood-borne viral hepatitis were: promiscuity, transfusion, drug addiction, alcoholism and history of reclusion. This high prevalence of hepatitis B and C compels the precaution for medical and paramedical staff attending this kind of patients.

A monoclonal inhibition enzyme immunoassay for detection of antibodies against hepatitis B core antigen: confirmation of an immunodominant epitope

Monoclonal antibodies (mAbs) were raised against hepatitis B virus core produced by a recombinant clone of Escherichia coli (rHBc). The three mAbs recognized rHBc by Western blot, suggesting that they reacted with non-conformational epitopes. Competition experiments between mAbs and human anti-HBc sera confirmed the existence of an immunodominant HBc epitope within the viral antigen. A monoclonal competition enzyme immunoassay using an IgM mAb conjugated to biotin and streptavidin-peroxidase as the detection system yielded 99% sensitivity and 100% specificity, when compared to other commercial assays.

[Usefulness of the PCR technique (polymerase chain reaction) in the follow-up of patients infected with hepatitis C virus. Preliminary communication]

In the study we show the usefulness of PCR (polymerase chain reaction) to follow patients with chronic hepatitis, infected with hepatitis C virus (HCV) of Centro Médico de Caracas. The study included 14 patients: 12 anti-HCV positive, 1 with chronic autoimmune hepatitis and 1 classified as non B-non C hepatitis. The patients were divided in 3 groups: Group 1 (5 pretreatment patients, anti-HCV+), 4 with increase in ALT and PCR positive, 1 with normal ALT and PCR negative. Group 2 (7 treated with recombinant interferon alpha 2b), 4 without normalization of ALT and PCR positive, 3 with normalization of ALT and PCR negative. Group 3 (control) 2 patients anti-HCV negative and PCR negative. Two posttreatment patients could be genotyped: one patient was infected with 1a and showed an early relapse with treatment and the other was infected with genotype 1b, which is reported to be more refractory to antiviral treatment.

CONCLUSIONS

the results show a 100% correlation between biochemical markers of HCV infected patients and the presence of viral RNA detected by PCR. the usefulness of determination of genotype to assess any prognostic value of this parameter in Venezuela is discussed.

Prevalence of antibodies against hepatitis E virus among urban and rural populations in Venezuela

Antibodies against hepatitis E virus (HEV) were detected in sera by a synthetic peptide-based enzyme immunoassay (EIA) from different populations in Venezuela. Antibodies against HEV were found in 1.6% (3/184) of urban pregnant woman (Caracas), in 3.9% (8/204) of rural populations (San Camilo, Edo Apure), and in 5.4% (12/223) of rural Amerindians (Padamo, Edo Amazonas). Positivity was confirmed by a neutralization EIA based on the use of competing soluble free peptides. The prevalence of antibodies in the Amerindian group was significantly higher than in urban pregnant women. No relation was found between age and HEV prevalence in rural populations. Three of 21 positive sera were also weakly positive by Western blot for IgM antibodies. This result, together with the low optical density values observed by EIA, suggested that the presence of antibodies in these sera reflects past infections. Based on these results, Venezuela does not seem to be highly endemic for hepatitis E. This is the first report of serological evidence of infection by HEV in South America.

Viral hepatitis serological markers among pregnant women in Caracas, Venezuela: implication for perinatal transmission of hepatitis B and C

Viral hepatitis serological markers were analyzed in two groups of pregnant women residing in Caracas from: 1) a maternity unit at the moment of delivery (106 sera, low income population), and 2) a private clinic during the third trimester of pregnancy (105 sera, medium-high economic class population). A higher percent positivity was observed in the maternity unit compared to the private clinic for hepatitis A virus (HAV) as measured by anti-HAV activity (96% vs 48%; p < 0.01%), for hepatitis B virus (HBV) as measured by anti-HBc activity (13% vs 2%; p < 0.01%), but not for HBV carriage, as measured by HBsAg (3.8% vs 0%; p = 0.06 %). These differences appear to correlate with the socio-economic level. All the HBsAg positive sera were HBeAg negative and negative for the presence of DNA by PCR, confirming the low rate of perinatal transmission observed in Venezuela. Two out of 106 sera (1.9%) were positive for HCV antibodies in the maternity unit and 0/105 in the private clinic, although these differences were non significant (N.S.). Two out of 106 sera (1.9%) were positive for HEV antibodies in the maternity unit and 1/80 (1.3%) in the private clinic (N.S.). The anti-HEV seropositivity probably reflects a past infection. The importance of testing these viral markers during pregnancy is discussed.

Characterization of mouse monoclonal antibodies against common and repeated epitopes of different developmental stages of Schistosoma mansoni

Eight IgM monoclonal antibodies (mAbs) obtained from a Schistosoma mansoni chronically infected mouse immunized twice with adult worms butanolic extract (BE) and soluble egg antigen (SEA) were characterized by immunochemical methods. An intense cross-reactivity between different developmental stages was observed by indirect immunofluorescence assay (IIFA) with five anti-SEA mAbs. These mAbs appeared to recognize glycosidic residues, as suggested by 1) the inhibition of their reactivity by periodate oxidation of SEA, 2) the multiple polypeptide recognition in radioimmunoprecipitation and immunoblot assays and 3) reactivity with KLH. Anti-SEA mAbs were able to mediate in vitro killing of schistosomula but they were not consistently able to mediate passive transfer immunity in vivo. Three of anti-SEA mAbs were suitable for the performance of a sandwich ELISA for antibody detection in S. mansoni infected patients, allowing an increase in the signal to noise ratio as compared to the direct ELISA SEA method. Three anti-BE mAbs showed a more stage restricted pattern of antigen recognition by IIFA. Only one out of three seemed to be directed against glycan residues, but the other mAbs showed a plural pattern of polypeptide recognition on BE immunoblot, suggesting that repeated epitopic motifs are also present in different proteins within the same parasite developmental stage.

Schistosoma mansoni: surface membrane isolation with lectin-coated beads

Lectins from Lens culinaris and Arachis hypogaea immobilized on polyacrylamide beads were used for selective isolation of glycosylated surface membrane domains of adult Schistosoma mansoni worms, and the method was compared with the membrane isolation procedure developed with polycationic (Affi-Gel) beads. The lentil lectin proved to be suitable for interaction with surface membrane components: an increment in the specific activities of tegumental phosphohydrolases was observed in the bound fraction with respect to that observed in a total worm homogenate. A characteristic polypeptide pattern on gel electrophoresis was also seen, more restricted than that obtained with the bound Affi-Gel fraction. Immobilized peanut lectin was not successful as a method for isolating membrane material from the tegument of adult worms. Solubilization and dissociation of the lentil lectin-bound enzyme markers was achieved after addition of detergent and competing sugars. Glycosylation of the solubilized enzymes was further confirmed by affinity chromatography with fresh lentil lectin-coated beads. These results, together with histochemical evidences, suggest that the active sites of some of these enzymes are located within or close to the cytoplasmic leaflet of the surface tegumental membranes, and allow us to propose a model for the double surface membrane complex where some proteins may be crossing the two bilayers.

A double sandwich monoclonal enzyme immunoassay for detection of hepatitis B surface antigen

An enzyme immunoassay for detection of hepatitis B surface antigen based on the use of 3 monoclonal antibodies (mAbs) was developed: an IgM as capture and 2 IgG1 for detection. The system biotin-streptavidin was compared with direct conjugation of mAbs to peroxidase and was preferred because of its higher signal to noise ratio. The possibility of simultaneous addition of human serum and biotin-mAb was discarded because of an evident prozone effect with some sera containing high HBsAg levels. The conjugation of biotin to IgG1 mAbs through a spacer arm (amidocaproyl) and the use of a highly sensitive substrate (tetramethylbenzIdine) improved the assay detection limit by about 10 times.

[Production and characterization of monoclonal antibodies directed against the hepatitis B surface antigen]

Hepatitis B virus surface antigen (HBsAg) found in a commercial vaccine was use as immunogen and antigen for the production and selection of murine monoclonal antibodies against this viral antigen. Antibody relative avidity was determined based on their capture capacity. Competition studies, and the differential recognition pattern of vaccine preparations showed that high avidity IgG1 antibodies were directed against two distinct antigenic regions. Among them, 6F4 was most suitable for the detection of HBsAg in a sandwich ELISA system, using an IgM antibody, 5E8, as capture. However, the combined use of 6F4 with another which does not recognize the same epitope did not improve the sensitivity of the assay. On the other hand, the combination of 6F4 with a lower avidity IgG1 antibody, 6G10, increased the universe of antigenic diversities recognized by this system. An enzyme immunoassay for detection of HBsAg is proposed, using 3 monoclonal antibodies: one IgM as capture and two IgG1 for detection.

Production of a mouse monoclonal antibody against the alkaline phosphatase of adult Schistosoma mansoni

This study describes the production and characterization of a monoclonal antibody (mAb) against the alkaline phosphatase of Schistosoma mansoni from splenocytes of chronically infected mice. Convenient selection of the mAb was achieved using the catalytic activity of the antigen in a developed enzyme-antigen immunoassay. The mAb was of the IgG1 subclass and it specifically recognized the alkaline phosphatase in adult worm sections by indirect immunofluorescence. Preincubation of the antibody with partially purified adult alkaline phosphatase did not result in inhibition of the enzyme activity and it did not mediate complement-dependent cytotoxicity against mechanically transformed schistosomula in vitro. The mAb was able to immunoprecipitate under reducing conditions a polypeptide of 65 kDa, similar in size to the monomeric subunit of the schistosome enzyme. The specificity of the mAb was assessed by competitive inhibition with antibodies of infected human sera in an immunoadsorption assay. Periodate treatment of the antigen resulted in altered electrophoretic mobility of alkaline phosphatase, which confirmed the presence of carbohydrate in the molecule, but this did not prevent binding by the mAb. Although the use of the mAb in capture assays for detection of circulating alkaline phosphatase in infected host sera was unsuccessful, the production of this antibody confirmed that the enzyme is exposed by adult worms to the host and that it is immunogenic; additionally, a monoclonal probe is available for further characterization of the structure and function of this important parasite surface molecule.

Antigenicity of adult Schistosoma mansoni alkaline phosphatase

Antibodies to the alkaline phosphatase (AP) of Schistosoma mansoni in infected human and mice sera were evaluated by a direct solid-phase AP immunoadsorption assay (APIA) and by Western blot and immunostaining. APIA consisted of (a) solid-phase capture of immunoglobulins from infected human or mice, (b) immunoadsorption of the enzyme antigen by the antibodies, and (c) detection of the enzymatic activity. By this procedure the appearance of the anti-AP response in mice was detected around 50 days post-infection; this response was not specific for an AP of a given schistosome strain and it was not induced by an autoimmunity phenomenon. Fourteen out of 15 sera from infected people tested by APIA showed a clear antibody response against this enzyme. Immunoblots in non-reducing conditions supported APIA results indicating that the parasite AP was specifically recognized by the antibodies present in infected human and mice sera. These results suggest the possible usefulness of the schistosome AP as a marker for S. mansoni infection.

Immunodiagnosis of Schistosomiasis mansoni with APIA (alkaline phosphatase immunoassay)

The previously shown antigenicity of Schistosoma mansoni (JL venezuelan strain) alkaline phosphatase (Mg2+, pH 9.5) allowed its use in an immunodiagnosis assay, that consisted in the immunoadsorption of the enzymatic activity. Protein-A coated polyvinyl plates were used as solid phase to capture IgG from sera of infected human patients. After buffered saline washings, the plates were incubated with an enzyme-rich fraction (a n-butanol aqueous extract of adult worm obtained from pairs). Immunoadsorbed alkaline phosphatase (AP) was revealed by adding rho-nitrophenyl phosphate. Anti-AP antibodies were detected in 93% of coproparasitologically proven S. mansoni-infected venezuelan patients but not in parasite-free control sera and sera from patients infected with parasitosis other than schistosomiasis. The APIA did not correlate with cure but the anti-AP antibody response was progressively reduced after treatment. The use of an AP substrate amplifying system allowed an improvement of the assay sensitivity without loss of specificity. The data suggest that the APIA could be used as a marker of infection by S. mansoni.

Antigenic enzymes of Schistosoma mansoni: possible use for immunodiagnosis

Different enzymes of Schistosoma mansoni are recognized by IgG antibodies present in the sera of infected human patients. The antigenicity of these enzymes suggests their possible use in immunodiagnostic assays that would take advantage of their activities.

A simplified methodology for purification of peanut (Arachis hypogaea) agglutinin

The agglutinin from peanut (Arachis hypogaea) was readily isolated by affinity chromatography on acid-treated Sepharose 6B. The recovered lectin (50 mg/100 g seeds) appeared as a single band of Mr 32,000 on gel electrophoresis and its specific haemagglutination titre on desialylated human A red blood cells was very high (2(15)).