Epidemiology of rotavirus and cholera in children aged less than five years in rural Bangladesh

Despite the known presence of rotavirus-associated diarrhoea in Bangladesh, its prevalence, including records of hospitalization in rural health facilities, is largely unknown. In a systematic surveillance undertaken in two government-run rural health facilities, 457 children, aged less than five years, having acute watery diarrhoea, were studied between August 2005 and July 2007 to determine the prevalence of rotavirus. Due to limited financial support, the surveillance of rotavirus was included as an addendum to an ongoing study for cholera in the same area. Rotavirus infection was detected in 114 (25%) and Vibrio cholerae in 63 (14%) children. Neither rotavirus nor V cholerae was detected in 280 (61%) samples; these were termed 'non-rotavirus and non-cholera' diarrhoea. Both rotavirus and cholera were detected in all groups of patients (<5 years). The highest proportion (41%; 47/114) of rotavirus was in the age-group of 6-11 months. In children aged less than 18 months, the proportion (67%; 76/114) of rotavirus was significantly (p < 0.001) higher than that of cholera (16%; 10/63). By contrast, the proportion (84%; 53/63) of cholera was significantly (p < 0.001) higher than that of rotavirus (33%; 38/114) in the age-group of 18-59 months. During the study period, 528 children were hospitalized for various illnesses. Thirty-eight percent (202/528) of the hospitalizations were due to acute watery diarrhoea, and 62% were due to non-diarrhoeal illnesses. Rotavirus accounted for 34% of hospitalizations due to diarrhoea. Severe dehydration was detected in 16% (74/457) of the children. The proportion (51%; 32/63) of severe dehydration among V cholerae-infected children was significantly higher (p < 0.001) compared to the proportion (16%; 18/114) of rotavirus-infected children. The study revealed that 12-14% of the hospitalizations in rural Bangladesh in this age-group were due to rotavirus infection, which has not been previously documented.

Diagnostic limitations to accurate diagnosis of cholera

The treatment regimen for diarrhea depends greatly on correct diagnosis of its etiology. Recent diarrhea outbreaks in Bangladesh showed Vibrio cholerae to be the predominant cause, although more than 40% of the suspected cases failed to show cholera etiology by conventional culture methods (CMs). In the present study, suspected cholera stools collected from every 50th patient during an acute diarrheal outbreak were analyzed extensively using different microbiological and molecular tools to determine their etiology. Of 135 stools tested, 86 (64%) produced V. cholerae O1 by CMs, while 119 (88%) tested positive for V. cholerae O1 by rapid cholera dipstick (DS) assay; all but three samples positive for V. cholerae O1 by CMs were also positive for V. cholerae O1 by DS assay. Of 49 stools that lacked CM-based cholera etiology despite most being positive for V. cholerae O1 by DS assay, 25 (51%) had coccoid V. cholerae O1 cells as confirmed by direct fluorescent antibody (DFA) assay, 36 (73%) amplified primers for the genes wbe O1 and ctxA by multiplex-PCR (M-PCR), and 31 (63%) showed El Tor-specific lytic phage on plaque assay (PA). Each of these methods allowed the cholera etiology to be confirmed for 97% of the stool samples. The results suggest that suspected cholera stools that fail to show etiology by CMs during acute diarrhea outbreaks may be due to the inactivation of V. cholerae by in vivo vibriolytic action of the phage and/or nonculturability induced as a host response.

Causes for hospitalizations at upazila health complexes in Bangladesh

Morbidity and mortality data are important for planning and implementing healthcare strategies of a country. To understand the major causes for hospitalizations in rural Bangladesh, demographic and clinical data were collected from the hospital-records of five government-run rural health facilities (upazila health complexes) situated at different geographical regions of the country from January 1997 to December 2001. During this period, 75,598 hospital admissions in total were recorded, of which 54% were for male, and 46% were for female. Of all the admissions, diarrhoeal disease was the leading cause for hospitalization (25.1%), followed by injuries (17.7%), respiratory tract diseases (12.6%), diseases of the gastrointestinal tract (10.5%), obstetric and gynaecological causes (8.5%), and febrile illnesses (6.7%). A considerable proportion (8.3%) of the hospitalized patients remained undiagnosed. Despite the limitations of hospital-based data, this paper gives a reasonable insight of the important causes for hospitalizations in upazila health complexes that may guide the policy-makers in strengthening and prioritizing the healthcare needs at the upazila level in Bangladesh.

Isolation of a bacteriophage specific for CS7-expressing strains of enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is the most common bacterial cause of childhood diarrhoea in Bangladesh. Among the virulence factors of ETEC, toxins and colonization factors (CFs) play a major role in pathogenesis. Unlike Vibrio cholerae, the relationship between ETEC and ETEC-specific phages is poorly understood and the possible role of ETEC phages in the evolution of ETEC strains in the environment is yet to be established. This study was designed specifically to isolate phages that are specific for ETEC virulence factors. Among the 49 phages isolated from 12 different surface water samples, 13 were tested against 211 ETEC strains collected from clinical and environmental sources. One phage, designated IMM-001, showed a significant specificity towards CS7 CF as it attacked all the CS7-expressing ETEC. Electron microscopic analyses showed that the isolated phage possessed an isomeric hexagonal head and a long filamentous tail. An antibody blocking method and phage neutralization assay confirmed that CS7 pilus is required for the phage infection process, indicating the role of CS7 fimbrial protein as a potential receptor for IMM-001. In summary, this study showed the presence of a lytic phage in environmental water that is specific for the CS7 CF of ETEC.

Comparison of enterotoxigenicEscherichia coliisolated from surface water and diarrhoeal stool samples in Bangladesh

Enterotoxigenic Escherichia coli (ETEC) is a common cause of bacterial infection leading to acute watery diarrhea in infants and young children. Although the prevalence of ETEC is high in Bangladesh and infections can be spread through food and contaminated water, limited information is available about ETEC in the surface water. We carried out studies to isolate ETEC from surface water samples from ponds, rivers, and a lake from a site close to field areas known to have a high incidence of diarrhea in Dhaka, Bangladesh, and Matlab, Bangladesh. ETEC strains isolated from the water sources were compared with ETEC strains isolated from patients with diarrhea at two hospitals in these areas. ETEC were isolated from 30% (45 of 150) of the samples from the surface water sources and 19% (518 of 2700) of the clinical specimens. One hundred ETEC strains isolated from patients with similar phenotypes as the environmental strains were compared for phenotypic and genotypic properties. The most common O serogroups on ETEC were O6, O25, O78, O115, and O126 in both types of strains. Pulsed-field gel electrophoresis analyses of the ETEC strains showed that multiple clones of ETEC were present within each colonization factor type and that some clones detected in the environment were also isolated from the stools of patients. The strains showed multiple and similar antibiotic resistance patterns. This study shows that ETEC is prevalent in surface water sources in Bangladesh suggesting a possible reason for the endemicity of this pathogen in Bangladesh.Key words: enterotoxigenic Escherichia coli (ETEC), surface water samples, colonization factors, pulsed-field gel electrophoresis, toxin types.

Comparison of the antibody in lymphocyte supernatant (ALS) and ELISPOT assays for detection of mucosal immune responses to antigens of enterotoxigenic Escherichia coli in challenged and vaccinated volunteers

In the present study we compared the ELISPOT and antibody in lymphocyte supernatants (ALS) assays as surrogate measures of mucosal immunity. In separate studies, 20 inpatient volunteers received oral doses of 6 x 10(8) or 4 x 10(9)cfu of ETEC strain E24377A (LT+, ST+, CS1+, CS3+) and 20 subjects received 1 (n = 9) or 2 (n = 11) oral doses of the attenuated ETEC vaccine, PTL-003 expressing CFA/II (CS1+ and CS3+) (2 x 10(9)cfu/dose). Peripheral blood mononuclear cells (PBMCs) from all subjects were assayed for anti-colonization factor or toxin-specific IgA antibody responses using the ALS and ELISPOT procedures. ALS responses were measured using a standard ELISA, as well as by time-resolved fluorescence (TRF). Following challenge with E24377A, significant anti-CS3, CS1 and LT ALS responses were detected in the lymphocyte supernatants of 75-95% of the subjects. A similar proportion (75%) of subjects mounted an ALS response to CFA/II antigen after vaccination with the PTL-003 vaccine. Inter-assay comparisons between ALS and ELISPOT methods also revealed a high degree of correlation in both immunization groups. ALS sensitivity versus the ELISPOT assay for LT, CS3 and CS1-specific responses following challenge were 95%, 94% and 78%, respectively and 83% for the ALS response to CFA/II antigen after vaccination with PTL-003. Correlation coefficients for the LT and CS3 antigens were 0.94 (p<0.001) and 0.82 (p<0.001), respectively after challenge and 0.78 (p<0.001) after vaccination. The association between ALS and ELISPOT for the CS1 antigen was however, significant only when ALS supernatants were tested by TRF (r = 0.91, p<0.001). These results demonstrate the value and flexibility of the ALS assay as an alternative to ELISPOT for the measurement of mucosal immune responses to ETEC antigens, particularly when the complexities of ELISPOT may make it impractical to perform.

Role of cyanobacteria in the persistence of Vibrio cholerae O139 in saline microcosms

Recently, a new strain of cholera, Vibrio cholerae O139, has emerged as an epidemic strain, but there is little information about its environmental reservoir. The present investigation was aimed to determine the role of cyanobacteria in the persistence of V. cholerae O139 in microcosms. An environmental isolate of V. cholerae O139 and three cyanobacteria (Anabaena sp., Nostoc sp., and Hapalosiphon sp.) were used in this study. Survival of culturable V. cholerae O139 in microcosms was monitored using taurocholate-tellurite gelatin agar medium. Viable but nonculturable V. cholerae O139 were detected using a fluorescent antibody technique. Vibrio cholerae O139 could be isolated for up to 12 days in a culturable form in association with cyanobacteria but could not be isolated in the culturable form after 2 days from control water without cyanobacteria. The viable but nonculturable V. cholerae O139 could be detected in association with cyanobacteria for up to 15 months. These results, therefore, suggest that cyanobacteria can act as a long-term reservoir of V. cholerae O139 in an aquatic environment.

Molecular epidemiology of Shigella flexneri in a diarrhoea-endemic area of Lima, Peru

A year-long community-based study of diarrhoeal diseases was conducted in Canto Grande, a periurban community in Lima, Peru. In 109 (34%) houses out of 323 that were visited, at least one individual was detected with shigellosis. The frequency of the 161 shigella isolates obtained was as follows: 117 S. flexneri (73%), 21 S. boydii (13%), 15 S. dysenteriae (9%), and 8 S. sonnei (5%). Using a non-radioactive ipaH gene probe as a molecular epidemiological tool, a total of 41 S. flexneri strains were shown to be distributed in 25 intra-family comparisons by pairs (icp). Further subdivision, based on a comparison of the serotype, plasmid profile, antibiotic resistances and ipaH hybridization patterns indicated that Group I, with 11 icp (44%), had strains that were identical. Group II with 8 icp (32%), had strains that were different and Group III with 6 icp (24%), had strains with the same serotype and identical ipaH profiles but with differences in other markers. This data indicates that a diversity of shigella clones circulated in this community resulting from both clonal spread and horizontal transfer of genetic elements. Furthermore, ipaH profiling of isolates can be used not only to differentiate between closely related shigella strains but also with other parameters, help to understand the dynamics of the generation of new clones of pathogenic bacteria.

Wastewater-grown duckweed may be safely used as fish feed

Duckweed has been used for the treatment of wastewater and as fish feed. A comparative study was carried out to determine (i) the efficacy of duckweed in treating hospital-based wastewater and (ii) the level of the microbial contamination of fish fed on wastewater-grown duckweed. There were two groups of ponds where fish farming was done. In one group of ponds (control ponds), duckweed that was grown using artificial fertilizer was used as fish feed; in another group (study ponds), wastewater-grown duckweed was used as fish feed. The faecal contamination of water, duckweed, and fish from study and control ponds were monitored by faecal coliform estimation. The presence of enteric pathogens among handlers, water, duckweed, and fish samples was also examined. It was observed that the faecal coliform counts of raw wastewater were 4.7 Log10CFU/mL, which was reduced to <1 Log10CFU/mL after treating with duckweed. There was no significant difference (P > 0.05) in faecal coliform counts in water collected from duckweed ponds and fish ponds of study and control areas. The wastewater-grown duckweed did not pose any health hazard to the handlers. These results demonstrated that the wastewater-treated duckweed may be safely used as fish feed.Key words: wastewater, duckweed, fish feed, contamination, safety.

Identifying environmental risk factors for endemic cholera: a raster GIS approach

The bacteria that cause cholera are known to be normal inhabitants of surface water, however, the environmental risk factors for different biotypes of cholera are not well understood. This study identifies environmental risk factors for cholera in an endemic area of Bangladesh using a geographic information systems (GIS) approach. The study data were collected from a longitudinal health and demographic surveillance system and the data were integrated within a geographic information system database of the research area. Two study periods were chosen because they had different dominant biotypes of the disease. From 1992 to 1996 El Tor cholera was dominant and from 1983 to 1987 classical cholera was dominant. The study found the same three risk factors for the two biotypes of cholera including proximity to surface water, high population density, and poor educational level. The GIS database was used to measure the risk factors and spatial filtering techniques were employed. These robust spatial methods are offered as an example for future epidemiological research efforts that define environmental risk factors for infectious diseases.

The spatial epidemiology of cholera in an endemic area of Bangladesh

This paper defines high-risk areas of cholera based on environmental risk factors of the disease in an endemic area of Bangladesh. The risk factors include proximity to surface water, high population density, and low educational status, which were identified in an earlier study by the authors. Cholera data were analyzed by spatially referenced extended household units for two time periods, 1983-1987 and 1992-1996. These periods were chosen because they had different dominant cholera agents. From 1983-1987 classical cholera was dominant and from 1992-1996 El Tor was dominant. By defining high-risk areas based on risk factors, this study builds a spatial risk model for cholera. The model is then evaluated based on the locations of observed cholera cases. The study also identifies the determinants of death due to cholera for the two different time periods dominated by the different cholera agents. The modeled risk areas that were based on the risk factors were found to correspond with actual distributions of cholera morbidity and mortality. The high-risk areas of the dominant cholera agents are relatively stable over time. However, from 1983-1987 El Tor cholera, which was not the dominant agent during that period, was not associated with high-risk areas, suggesting that the El Tor habitat may have changed over time. The case fatality rate for cholera was related to proximity to a diarrhea treatment hospital in the study area.

Involvement of the hap gene (mucinase) in the survival of Vibrio cholerae O1 in association with the blue-green alga, Anabaena sp

Mucinase is a soluble haemagglutinin protease, which may be important for the survival of Vibrio cholerae in association with mucilaginous blue-green algae (cyanobacteria). A comparative survival study was carried out with an Anabaena sp. and a wild-type V. cholerae O1 strain hap+ gene (haemagglutinin-protease), together with its isogenic mutant hap (hap-deleted gene). A simple spread plate technique was followed to count culturable V. cholerae O1 on taurocholate tellurite gelatin agar plate. The fluorescent antibody technique of Kogure et al. (1979) was used for the microscopical viable count of V. cholerae O1. Polymerase chain reaction (PCR) and Southern blot hybridization were carried out to detect a lower number of viable but nonculturable (VBNC) V. cholerae O1 from the laboratory-based experiments. The wild and mutant V. cholerae O1 strains survived in culturable form for 22 and 10 days. respectively, in association with the Anabaena sp., with the difference being statistically significant (P < 0.01). The fluorescent antibody technique, PCR, and hybridization results also showed that the wild strain survived better in the VBNC state than did the mutant VBNC strain in association with an Anabaena sp. These results indicate that the enzyme mucinase may play an important role in the association and long-term survival of V. cholerae O1 with a mucilaginous blue-green alga, Anabaena sp.

Are the environmental niches of Vibrio cholerae O139 different from those of Vibrio cholerae O1 El Tor?

BACKGROUND

Vibrio cholerae are known to be normal inhabitants of surface water. However, the environmental niches of the different strains of cholera are not well known, and therefore, populations at risk for cholera outbreaks cannot be clearly identified.

METHODS

This study identifies environmental risk factors for cholera caused by V. cholerae O1 El Tor and O139 and environmental niches of the two strains present in Matlab, a cholera endemic area of Bangladesh. The study year was 1993, the year that the O139 strain first appeared in the study area. Patients who had either strain of cholera identified in a laboratory were included in the study. A geographic information system was used to map the household locations of the patients, to describe the human sanitary environment and population density, and to address potential anthropogenic and environmental risk factors of the disease. Spatial point pattern and exploratory spatial data analysis techniques were used to define the environmental niches of the two cholera strains.

RESULTS

The study suggests the niches of O1 El Tor and O139 strains of V. cholerae appear to be similar, based on common environmental risk factors.

CONCLUSIONS

The results of this study support a theory that O1 El Tor could possibly be replaced by the newer O139 strain in the future.

Emergence of multidrug-resistant Salmonella Gloucester and Salmonella typhimurium in Bangladesh

Infections due to non-typhoid Salmonella, resistant to antibiotics, have recently emerged as an important health problem worldwide. Antibiotic resistance was studied by the disc-diffusion method among 3,876 (2.78%) non-typhoid Salmonella isolates cultured from 139,279 faecal samples in a diarrhoea treatment centre in Dhaka, Bangladesh, during 1989-1996. Of 499 salmonellae isolated in 1989, serogroup C (1.12%) was the most common, followed by Salmonella Typhi (0.72%) and serogroup B (0.71%). Isolation rate of serogroup B increased significantly to 2.18% (p < 0.01) in 1992 compared to 0.56% in 1991, 2.86% in 1995, and 2.48% in 1996. Serotyping of 194 serogroup B isolates revealed Salmonella Typhimurium (52%) and Salmonella Gloucester (45%) as predominant serotypes. Resistance to ampicillin (A), chloramphenicol (C), and trimethoprim-sulphamethoxazole (Sxt) (R type-ACSxt) increased to 89-100% during 1992-1996 from 20-28% during 1989-1991 (p < 0.01) among S. Typhimurium and S. Gloucester isolates. In 1993, 8-10% of the strains of both the serotypes, resistant to ampicillin, chloramphenicol, and trimethoprim-sulphamethoxazole, acquired resistance to ceftriaxone (Cr) (R type-ACSxtCr), which increased to 85-92% in 1996 (p < 0.01). All were susceptible to ciprofloxacin. A 157-kb conjugative plasmid transferred R type-ACSxt from both the serotypes to Escherichia coli K-12. The findings of the study suggest the emergence of multidrug-resistant S. Gloucester and S. Typhimurium for the first time as a significant health problem in Bangladesh, and surveillance is essential to monitor the resistant non-typhoid Salmonella and identify its sources and modes of transmission.

Survival of Shigella dysenteriae type 1 on fomites

Studies have shown that various objects, such as utensils, toys, and clothes, can serve as vehicles for transmission of Shigella spp. Shigellae can become viable but non-culturable (VBNC) when exposed to various environmental conditions as shown in earlier studies. The present study was carried out to detect VBNC Shigella dysenteriae type 1 on various fomites by direct viable counting, polymerase chain reaction (PCR), and fluorescent antibody methods. S. dysenteriae type 1 was inoculated onto cloth, wood, plastic, aluminum, and glass objects. Results showed that 1.5-4.0 hours after inoculation, S. dysenteriae type 1 became non-culturable, and after five days, non-culturable but viable S. dysenteriae type 1 could be detected by both PCR and fluorescent antibody techniques. Fomites can be considered an important potential route of transmission of VBNC S. dysenteriae type 1 and a significant factor in the epidemiology of shigellosis.

The efficacy of bismuth subsalicylate in the treatment of acute diarrhoea and the prevention of persistent diarrhoea

A controlled, randomized, double-blind study in Bangladeshi children (ages 4-36 mo) with acute diarrhoea was undertaken to determine whether bismuth subsalicylate (BSS) would prevent the development of persistent diarrhoea (PD) in young children. The children were randomized to two groups: 226 were given liquid oral BSS, (as Pepto-Bismol), 100 mg/kg/d for 5 d; 225 were given placebo of identical appearance. On admission to the study, the two groups were comparable both clinically and microbiologically. Rotavirus was found in 56% of all the children, and enterotoxigenic E. coli in 31% of a subsample studied. Children treated with BSS had less severe and less prolonged illness than those treated with placebo (p = 0.057). There was, however, no difference in the development of PD between the two groups (8% and 11%). Unexpectedly, patients treated with BSS gained significantly more weight (2.3%) than those treated with placebo (0.5%; p < 0.001) during the course of the study. No toxicity of BSS was detected.

CONCLUSION

Treatment with BSS had a modest therapeutic effect on acute diarrhoea, as has been previously demonstrated, but with no suggestion of a therapeutic effect on the prevention of persistent diarrhoea in this group of patients.

Genotypes associated with virulence in environmental isolates of Vibrio cholerae

Vibrio cholerae is an autochthonous inhabitant of riverine and estuarine environments and also is a facultative pathogen for humans. Genotyping can be useful in assessing the risk of contracting cholera, intestinal, or extraintestinal infections via drinking water and/or seafood. In this study, environmental isolates of V. cholerae were examined for the presence of ctxA, hlyA, ompU, stn/sto, tcpA, tcpI, toxR, and zot genes, using multiplex PCR. Based on tcpA and hlyA gene comparisons, the strains could be grouped into Classical and El Tor biotypes. The toxR, hlyA, and ompU genes were present in 100, 98.6, and 87.0% of the V. cholerae isolates, respectively. The CTX genetic element and toxin-coregulated pilus El Tor (tcpA ET) gene were present in all toxigenic V. cholerae O1 and V. cholerae O139 strains examined in this study. Three of four nontoxigenic V. cholerae O1 strains contained tcpA ET. Interestingly, among the isolates of V. cholerae non-O1/non-O139, two had tcpA Classical, nine contained tcpA El Tor, three showed homology with both biotype genes, and four carried the ctxA gene. The stn/sto genes were present in 28.2% of the non-O1/non-O139 strains, in 10.5% of the toxigenic V. cholerae O1, and in 14.3% of the O139 serogroups. Except for stn/sto genes, all of the other genes studied occurred with high frequency in toxigenic V. cholerae O1 and O139 strains. Based on results of this study, surveillance of non-O1/non-O139 V. cholerae in the aquatic environment, combined with genotype monitoring using ctxA, stn/sto, and tcpA ET genes, could be valuable in human health risk assessment.

Amebiasis and mucosal IgA antibody against the Entamoeba histolytica adherence lectin in Bangladeshi children

Amebiasis is the third leading parasitic cause of death worldwide, and it is not known whether immunity is acquired from a previous infection. An investigation was done to determine whether protection from intestinal infection correlated with mucosal or systemic antibody responses to the Entamoeba histolytica GalNAc adherence lectin. E. histolytica colonization was present in 0% (0/64) of children with and 13.4% (33/246) of children without stool IgA anti-GalNAc lectin antibodies (P= .001). Children with stool IgA lectin-specific antibodies at the beginning of the study had 64% fewer new E. histolytica infections by 5 months (3/42 IgA(+) vs. 47/227 IgA(-); P= .03). A stool antilectin IgA response was detected near the time of resolution of infection in 67% (12/18) of closely monitored new infections. It was concluded that a mucosal IgA antilectin antibody response is associated with immune protection against E. histolytica colonization. The demonstration of naturally acquired immunity offers hope for a vaccine to prevent amebiasis.

Enterotoxin-specific immunoglobulin E responses in humans after infection or vaccination with diarrhea-causing enteropathogens

Cholera toxin (CT)-specific antibody responses of the immunoglobulin E (IgE) isotype in the sera of adult patients suffering from infection with either Vibrio cholerae O1, V. cholerae O139, or enterotoxigenic Escherichia coli (ETEC) were analyzed and compared with those in the sera of volunteers immunized with a bivalent B subunit O1/O139 whole-cell cholera vaccine. A significant IgE response to CT was observed in 90% of the patients with V. cholerae O1 infection (18 of 20; P = <0.001) and 95% of the patients with V. cholerae O139 infection (19 of 20; P = <0.001). Similarly, the majority of the patients with ETEC diarrhea (83%; 13 of 15) showed a positive IgE response to CT. Eight of 10 North American volunteers (80%) orally challenged with V. cholerae O1 showed CT-specific IgE responses (P = 0.004). In contrast, Swedish volunteers immunized with the oral cholera vaccine showed no IgE responses to CT (P value not significant). During the study period, total IgE levels in the sera of the diarrheal patients, the North American volunteers, and the Swedish cholera vaccinees alike remained unchanged. However, the total IgE levels in the sera of patients and healthy Bangladeshi controls were on average 89-fold higher than those in the sera of the healthy Swedish volunteers and 34-fold higher than those in the sera of the North American volunteers.

The O139 serogroup of Vibrio cholerae comprises diverse clones of epidemic and nonepidemic strains derived from multiple V. cholerae O1 or non-O1 progenitors

Sixty-four representative strains of Vibrio cholerae O139 were analyzed, to re-examine the origin of this serogroup. Ribotyping differentiated the strains into 3 HindIII and 7 BglI ribotypes. One HindIII and 5 BglI ribotypes were shared by all toxigenic O139 strains. Of 6 nontoxigenic O139 strains, 3 shared ribotypes with the toxigenic strains, carried genes encoding toxin coregulated pilus, and were susceptible to the cholera toxin-converting bacteriophage CTXPhi. The remaining 3 strains belonged to 2 different ribotypes distinct from toxigenic O139 strains and were resistant to CTXPhi and JA-1, an O139-specific lytic bacteriophage. Polymerase chain reaction amplicons corresponding to the gmhD gene carried by these 3 strains also differed from those of the toxigenic O139 strains but were identical to those of 15 environmental non-O1-non-O139 strains. Thus, the O139 antigen is present in different lineages, and this serogroup appears to comprise epidemic and nonepidemic strains derived separately from different progenitors.

Prevalence of enterotoxin genes in Aeromonas spp. isolated from children with diarrhea, healthy controls, and the environment

Aeromonads are causative agents of a number of human infections. Even though aeromonads have been isolated from patients suffering from diarrhea, their etiological role in gastroenteritis is unclear. In spite of a number of virulence factors produced by Aeromonas species, their association with diarrhea has not been clearly linked. Recently, we have characterized a heat-labile cytotonic enterotoxin (Alt), a heat-stable cytotonic enterotoxin (Ast), and a cytotoxic enterotoxin (Act) from a diarrheal isolate of Aeromonas hydrophila. Alt and Ast are novel enterotoxins which are not related to cholera toxin; Act is aerolysin related and has hemolytic, cytotoxic, and enterotoxic activities. We studied the distribution of the alt, ast, and act enterotoxin genes in 115 of 125 aeromonads isolated from 1, 735 children with diarrhea, in all 27 aeromonads isolated from 830 control children (P = 7 x 10(-4) for comparison of rates of isolation of aeromonads from cases versus those from controls), and in 120 randomly selected aeromonads from different components of surface water in Bangladesh. Aeromonas isolates which were positive only for the presence of the alt gene had similar distributions in the three sources; the number of isolates positive only for the presence of the ast gene was significantly higher for the environmental samples than for samples from diarrheal children; and isolates positive only for the presence of the act gene were not found in any of the three sources. Importantly, the number of isolates positive for both the alt and ast genes was significantly higher for diarrheal children than for control children and the environment. Thus, this is the first study to indicate that the products of both the alt and ast genes may synergistically act to induce severe diarrhea. In 26 patients, Aeromonas spp. were isolated as the sole enteropathogen. Analysis of clinical data from 11 of these patients suggested that isolates positive for both the alt and ast genes were associated with watery diarrhea but that isolates positive only for the alt gene were associated with loose stools. Most of the isolates from the three sources could be classified into seven phenospecies and eight hybridization groups. For the first time, Aeromonas eucrenophila was isolated from two children, one with diarrhea and another without diarrhea.

Safety and immunogenicity of an oral, inactivated enterotoxigenic Escherichia coli plus cholera toxin B subunit vaccine in Bangladeshi adults and children

We have compared the B cell responses evoked in Bangladeshi, adults (n=11, median age 25 years) and children (n=21, median age 4.5 years), 7 days after intake of each of two doses of an oral, inactivated enterotoxigenic Escherichia coli (ETEC) vaccine composed of formalin-killed ETEC strains expressing the colonization factors, CFA/I, CFA/II and CFA/IV together with 1 mg of recombinant cholera toxin B-subunit (rCTB). The vaccine was well tolerated and only gave rise to negligible side effects. Peak antibody-secreting cell (ASC) response of the IgA isotype were seen 7 days after the first dose of the vaccine. The ASC responses to the different colonization factors (CFs) increased from a 29- to 46-fold (responder frequency 90-100%) in the adults and 13- to 24-fold (responder frequency 67-90%) in the children. The IgA-ASC response to rCTB also peaked after the first dose in the adults (426-fold, responder frequency 100%) and the children (46-fold, responder frequency 95%). Increased IgA antibody levels against CFA/I as well as IgA and IgG antibody levels to rCTB were seen in plasma after immunisation. About 86% of the children and 80% of the adults responded with faecal antibodies to rCTB, whereas about 67% of both groups responded to CFA/I. These results show that a single dose of the ETEC vaccine may elicit significant mucosal immune responses in both children and adults residing in an ETEC-endemic country such as Bangladesh.

New insights on the emergence of cholera in Latin America during 1991: the Peruvian experience

After a century of absence, in late January 1991, Vibrio cholerae invaded the Western Hemisphere by way of Peru. Although a number of theories have been proposed, it is still not understood how that invasion took place. We reviewed the clinical records of persons attending hospital emergency departments in the major coastal cities of Peru from September through January of 1989/1990 and 1990/1991. We identified seven adults suffering from severe, watery diarrhea compatible with a clinical diagnosis of cholera during the four months preceding the cholera outbreak, but none during the previous year. The patients were scattered among five coastal cities along a 1,000 km coastline. We postulate that cholera vibrios, autochthonous to the aquatic environment, were present in multiple coastal locations, and resulted from environmental conditions that existed during an El Nino phenomenon. Once introduced into the coastal communities in concentrations large enough for human infection to occur, cholera spread by the well-known means of contaminated water and food.

Genomic diversity among Vibrio cholerae O139 strains isolated in Bangladesh and India between 1992 and 1998

In order to assess the extent of genomic diversity among Vibrio cholerae O139 strains, restriction fragment length polymorphisms in two genetic loci, rrn and ctx, were studied. Analysis of 144 strains isolated from different regions of Bangladesh and India between 1992 and 1998 revealed the presence of at least six distinct ribotypes (B-I through B-VI) of which three were new ribotypes, and one of these was represented by a nontoxigenic O139 strain. Strains of ribotypes B-I through B-V shared 11 different CTX genotypes (A through K). Antimicrobial resistance patterns of the strains varied independently of their ribotypes and CTX genotypes. Results of this study suggest that V. cholerae O139 is undergoing rapid genetic changes leading to the origination of new variants, and temporal changes in antimicrobial resistance patterns may be contributing to the selection of different variants.

Prevalence of toxin types and colonization factors in enterotoxigenic Escherichia coli isolated during a 2-year period from diarrheal patients in Bangladesh

The prevalence of toxin types and colonization factors (CFs) of enterotoxigenic Escherichia coli (ETEC) was prospectively studied with fresh samples (n = 4,662) obtained from a 2% routine surveillance of diarrheal stool samples over 2 years, from September 1996 to August 1998. Stool samples were tested by enzyme-linked immunoassay techniques and with specific monoclonal antibodies for the toxins and CFs. The prevalence of ETEC was 14% (n = 662), with over 70% of the strains isolated from children 0 to 5 years of age, of whom 93% were in the 0- to 3-year-old age range. Of the total ETEC isolates, 49.4% were positive for the heat-stable toxin (ST), 25.4% were positive for the heat-labile toxin (LT) only, and 25.2% were positive for both LT and ST. The rate of ETEC isolation peaked in the hot summer months of May to September and decreased in winter. About 56% of the samples were positive for 1 or more of the 12 CFs that were screened for. The coli surface antigens CS4, CS5, and/or CS6 of the colonization factor antigen (CFA)/IV complex were most prevalent (incidence, 31%), followed by CFA/I (23.5%) and coli surface antigens CS1, CS2, and CS3 of CFA/II (21%). In addition, other CFs detected in decreasing order were CS7 (8%), CS14 (PCFO166) (7%), CS12 (PCFO159) (4%), CS17 (3%), and CS8 (CFA/III) (2.7%). The ST- or LT- and ST-positive ETEC isolates expressed the CFs known to be the most prevalent (i.e., CFA/I, CFA/II, and CFA/IV), while the strains positive for LT only did not. Among children who were infected with ETEC as the single pathogen, a trend of relatively more severe disease in children infected with ST-positive (P < 0.001) or LT- and ST-positive (P < 0.001) ETEC isolates compared to the severity of the disease in children infected with LT only-positive ETEC isolates was seen. This study supports the fact that ETEC is still a major cause of childhood diarrhea in Bangladesh, especially in children up to 3 years of age, and that measures to prevent such infections are needed in developing countries.

Intestinal immune responses in patients infected with enterotoxigenic Escherichia coli and in vaccinees

Immune responses against enterotoxigenic Escherichia coli (ETEC) were examined in Bangladeshi adults with naturally acquired disease and compared to responses in age-matched Bangladeshi volunteers who had been orally immunized with a vaccine consisting of inactivated ETEC bacteria expressing different colonization factor antigens (CFs) and the B subunit of cholera toxin. B-cell responses in duodenal biopsy samples, feces, intestinal washings, and blood were determined. Because most of the patients included in the study were infected with ETEC expressing CS5, immune responses to this CF were studied most extensively. Vaccinees and patients had comparable B-cell responses against this antigen in the duodenum: the median numbers of antibody-secreting cells (ASC) were 3,300 immunoglobulin A (IgA) ASC/10(7) mononuclear cells (MNC) in the patient group (n = 8) and 1,200 IgA ASC/10(7) MNC in the vaccinees (n = 13) (not a significant difference). Similarly, no statistically significant differences were seen in the levels of duodenal B cells directed against enterotoxin among vaccinees and patients. A comparison of the capacities of the various methods used to assess mucosal immune responses revealed a correlation between numbers of circulating B cells and antibody levels in saponin extracts of duodenal biopsy samples (r = 0.58; n = 13; P = 0.04) after vaccination. However, no correlation was seen between blood IgA ASC and duodenal IgA ASC after two doses of vaccine. Still, a correlation between numbers of CF-specific B cells in blood sampled from patients early during infection and numbers of duodenal B cells collected 1 week later was apparent (r = 0.70; n = 10; P = 0.03).

Case-control study of enteropathogens associated with childhood diarrhea in Dhaka, Bangladesh

The International Centre for Diarrhoeal Disease Research, Bangladesh, is a major center for research into diarrheal diseases. The center treats more than 100,000 patients a year. To obtain useful information representative of all patients, a surveillance system in which a 4% systematic sample of all patients is studied in detail, including etiological agents of diarrhea, was installed in October 1979. The first paper on etiology for the surveillance patients was published in 1982, which identified a potential enteric pathogen in 66% of patients. In subsequent years, several new agents of diarrhea have been identified. To assess the importance of a broader spectrum of diarrheal agents including the ones identified relatively recently, we studied 814 children with diarrhea. The children were up to 5 years of age and were part of the surveillance system. They were matched with an equal number of community controls without diarrhea. The study was conducted from February 1993 to June 1994. A potential enteric pathogen was isolated from 74.8% of diarrheal children and 43.9% of control children (P = 0.0001). Even though the first study was not a case-control study, it identified rotavirus, Campylobacter jejuni, enterotoxigenic Escherichia coli, Shigella spp. , and Vibrio cholerae O1 as major pathogens. The present study identified these pathogens as being significantly associated with diarrhea. In addition, the study also identified six additional agents, including enteropathogenic E. coli, Aeromonas spp., V. cholerae O139, enterotoxigenic Bacteroides fragilis, Clostridium difficile, and Cryptosporidium parvum, as being significantly associated with diarrhea. Plesiomonas shigelloides, Salmonella spp., diffusely adherent E. coli, enteroaggregative E. coli, Entamoeba histolytica, and Giardia lamblia were not significantly associated with diarrhea. Enteroinvasive E. coli, enterohemorrhagic E. coli, and Cyclospora cayetanensis were not detected in any of the children. The major burden of diseases due to most pathogens occurred in the first year of life. As in the previous study, seasonal patterns were seen for diarrhea associated with rotavirus, V. cholerae, and enterotoxigenic E. coli, and infections with multiple pathogens were common. With a few exceptions, these findings are in agreement with those from other developing countries. This knowledge of a broader spectrum of etiological agents of diarrhea in the surveillance patients will help us plan studies into various aspects of diarrheal diseases in this population.

Molecular characterization of a new ribotype of Vibrio cholerae O139 Bengal associated with an outbreak of cholera in Bangladesh

Vibrio cholerae O139 Bengal initially appeared in the southern coastal region of Bangladesh and spread northward, causing explosive epidemics during 1992 and 1993. The resurgence of V. cholerae O139 during 1995 after its transient displacement by a new clone of El Tor vibrios demonstrated rapid changes in the epidemiology of cholera in Bangladesh. A recent outbreak of cholera in two north-central districts of Bangladesh caused by V. cholerae O139 led us to analyze strains collected from the outbreak and compare them with V. cholerae O139 strains isolated from other regions of Bangladesh and neighboring India to investigate their origins. Analysis of restriction fragment length polymorphisms in genes for conserved rRNA (ribotype) revealed that the recently isolated V. cholerae O139 strains belonged to a new ribotype which was distinct from previously described ribotypes of toxigenic V. cholerae O139. All strains carried the genes for toxin-coregulated pili (tcpA and tcpI) and accessory colonization factor (acfB), the regulatory gene toxR, and multiple copies of the lysogenic phage genome encoding cholera toxin (CTXPhi) and belonged to a previously described ctxA genotype. Comparative analysis of the rfb gene cluster by PCR revealed the absence of a large region of the O1-specific rfb operon downstream of the rfaD gene and the presence of an O139-specific genomic region in all O139 strains. Southern hybridization analysis of the O139-specific genomic region also produced identical restriction patterns in strains belonging to the new ribotype and those of previously described ribotypes. These results suggested that the new ribotype of Bengal vibrios possibly originated from an existing strain of V. cholerae O139 by genetic changes in the rRNA operons. In contrast to previously isolated O139 strains which mostly had resistance to trimethoprim, sulfamethoxazole, and streptomycin encoded by a transposon (SXT element), 68.6% of the toxigenic strains analyzed in the present study, including all strains belonging to the new ribotype, were susceptible to these antibiotics. Molecular analysis of the SXT element revealed possible deletion of a 3.6-kb region of the SXT element in strains which were susceptible to the antibiotics. Thus, V. cholerae O139 strains in Bangladesh are also undergoing considerable reassortments in genetic elements encoding antimicrobial resistance.

Effects of environmental factors on child survival in Bangladesh: a case control study

The need for further studies on relationships between deaths and environmental variables has been reported in the literature. This case-control study was, therefore, carried out to find out the associations between several social and environmental variables and deaths of children due to infectious diseases such as those leading to diarrhoea, acute respiratory infection, measles and other diseases. Six hundred and twenty-five deaths (cases) and an equal number of matched living children (controls) aged 1-59 months, were studied in rural Matlab. An analysis of crude and adjusted odds ratio showed differential associations. Sources of drinking water, amount of stored water, conditions of latrines, number of persons sleeping with the child and the type of cooking site were statistically significantly associated with deaths due to infectious diseases after controlling for breast feeding, immunization, and the family size. Significant associations were also observed between: (i) the sources of drinking water and deaths due to ARI, and (ii) conditions of latrines and deaths due to diarrhoeal diseases, after controlling for the confounding variables. Several other environmental factors also showed associations with these various death groups, but they were not statistically significant. The size of the samples in death groups (small) and the prevalence of more or less homogeneous environmental health conditions probably diminished the magnitude of the effects. The results of the study reconfirm the importance of environmental health intervention in child survival, irrespective of breast-feeding, immunization, and selected social variables.

Antimicrobial resistance and serotype distribution of Streptococcus pneumoniae strains causing childhood infections in Bangladesh, 1993 to 1997

Three hundred sixty-two Streptococcus pneumoniae strains were isolated from children under 5 years of age at Dhaka Shishu (Children) Hospital from 1993 to 1997. The strains were isolated from blood (n = 105), CSF (n = 164), ear swab (n = 61), eye swab (n = 20), and pus (n = 12). Of the 362 isolates, 42 (11.6%) showed intermediate resistance (MIC, <0.1 microgram/ml) and only 4 (1.1%) showed complete resistance (MIC, >2.0 microgram/ml) to penicillin. Penicillin resistance exhibited a strong relationship with serotype 14; 47.8% of the penicillin-resistant strains belonged to this type. A remarkably high (64.1%) resistance to co-trimoxazole was observed, along with a significant increase during the time period studied; there was no relationship to capsular type. By way of contrast, penicillin resistance did not show any significant change during the study period. Resistance to chloramphenicol (2.2%) and erythromycin (1.1%) was rare. The high resistance to co-trimoxazole and its increasing trend demand elucidation of the clinical impact of pneumonia treatment by this antimicrobial and reconsideration of the World Health Organization recommendation for co-trimoxazole administration to children with community-acquired pneumonia at the health care worker level in Bangladesh.

Association of Vibrio cholerae O1 with the cyanobacterium, Anabaena sp., elucidated by polymerase chain reaction and transmission electron microscopy

It has been hypothesized that Vibrio cholerae is an autochthonous flora of the estuarine and brackish water environment. Zooplankton and phytoplankton have been considered as possible reservoirs. The present study was carried out in microcosms to confirm the role of a cyanobacterium, Anabaena sp., as a reservoir of V. cholerae O1 using culture, polymerase chain reaction (PCR) and immunoelectron microscopy. Survival of culturable V. cholerae in microcosms was monitored by using tellurite taurocholate gelatin agar. Culturable V. cholerae were detected for up to 1 h in association with Anabaena sp. from a microcosm. However, viable but nonculturable (VBNC) V. cholerae O1 were detected for up to 25 months using PCR and immunoelectron microscopy. Results also showed that VBNC V. cholerae can multiply and maintain their progeny in the mucilaginous sheath of Anabaena sp. This is the first time that PCR and immunoelectron microscopy have been used to detect nonculturable V. cholerae in association with Anabaena sp. This study further clarifies the role of Anabaena sp. as a possible reservoir of cholera.

Increasing frequency of mecillinam-resistant shigella isolates in urban Dhaka and rural Matlab, Bangladesh: a 6 year observation

A total of 14,915 shigella isolates obtained in 1991-1996 from patients attending the Dhaka (urban) and Matlab (rural) treatment centres of the International Centre for Diarrhoeal Disease Research, Bangladesh were examined for susceptibility to ampicillin, co-trimoxazole, nalidixic acid, mecillinam and ciprofloxacin by a disc diffusion method. There were no ciprofloxacin-resistant shigella isolates. The prevalence of resistance to ampicillin, co-trimoxazole and nalldixic acid varied between isolates. It increased to similar degrees in isolates from both Matlab and Dhaka. However, resistance to mecillinam was more prevalent among isolates from Matlab than from Dhaka. The increase in mecillinam-resistant shigellae in the community may have grave implications for the empirical treatment of shigellosis in Bangladesh and other developing countries.

Validation of a volunteer model of cholera with frozen bacteria as the challenge

To evaluate a standardized inoculum of Vibrio cholerae for volunteer challenge studies, 40 healthy adult volunteers were challenged at three different institutions with a standard inoculum prepared directly from vials of frozen, virulent, El Tor Inaba V. cholerae N16961, with no further incubation. Groups of 5 volunteers, with each group including 2 volunteers with blood group O, were given a dose of 10(5) CFU, and 34 of the 40 volunteers developed diarrhea (mean incubation time, 28 h). Transient fevers occurred in 15 (37.5%) of the volunteers. V. cholerae was excreted by 36 of 40 volunteers. Five additional volunteers received 10(4) CFU, and four developed diarrhea but with a lower average purging rate than required for the model. Of the 40 volunteers, 37 developed rises in their vibriocidal and antitoxin titers similar to those in previous groups challenged with freshly harvested bacteria. We conclude that challenge with frozen bacteria results in a reproducible illness similar to that induced by freshly harvested bacteria. Use of this model should minimize differences in attack rates or severity when groups are challenged at different times and in different institutions.

Maternal measles antibody decay in rural Bangladeshi infants--implications for vaccination schedules

Considerable numbers of measles cases occur below the target age for vaccination in the Indian sub-continent. The immunogenicity of measles vaccine in infancy is dependent on the rate of decay in maternal antibody since this antibody interferes with vaccine induced seroconversion. This study investigated maternal antibody decay in a rural population in Bangladesh and evaluated possible risk factors for early decay. Measles antibodies were assessed using both ELISA and Plaque Reduction Neutralization (PRN) test in 330 infant-mother pairs in a cross-sectional survey. PRN was more sensitive method than ELISA for determining antibody levels. Antibody levels decreased rapidly in infants with increasing age. By the age of 5 months, 67% (28/42) infants had practically no protective antibody left (30 mIU ml-1 or below). Only 12% infants at 5 months of age, and 5% at 8 months, had levels greater than 120 mIU ml-1--stated to 'protect' children. Multiple regression showed that maternal age was the only variable associated with the level of antibody (maternal weight, height and MUAC were not associated), decreasing by 1.06 mIU ml-1 for each year of age (P = 0.002). Infant's antibody concentration decreased with age by an average 2 mIU mL-1 for every month of life (P < 0.0001), and was determined by the maternal antibody concentration (P < 0.0001) (child's length, weight, MUAC, mother's gestational age and parity were not associated). The relatively rapid antibody decay suggests that the target age for measles vaccination might be reduced. Further, as the cohort of vaccinated mothers enters reproductive age in Bangladesh, a more rapid decay of antibody may be expected in future generations of Bangladeshi children. The information presented here suggests that a formal trial of standard measles vaccine at younger ages is justified in this population as it could confer considerable benefit in reducing infant measles.

Induction of fimbriated Vibrio cholerae O139

Several fimbriated phases of Vibrio cholerae O139 strains were selectively induced and compared immunologically and biochemically with those of V. cholerae O1. Fimbrial antigens were detected on the surfaces of vibrio cells colonizing the epithelial cells of a rabbit small intestine. Convalescent-phase sera from six individuals infected with V. cholerae O139 revealed the development of antibody against the fimbrillin. These findings suggest that the fimbriae of V. cholerae O1 and O139 are expressed in vivo during infection and that consideration must be given to the use of fimbrial antigens as components of vaccines against cholera.

Malnutrition, cell-mediated immune deficiency and acute upper respiratory infections in rural Bangladeshi children

A community-based longitudinal study conducted in rural Bangladesh investigated the association between nutritional status, cell-mediated immune status and acute upper respiratory infections (URI). A total of 696 children aged 0-59 months was followed prospectively for 1 y yielding 183,865 child-days' observation. Trained field workers visited each child every 4th d and collected morbidity data on symptoms suggesting URI (cough, fever, nasal discharge) for the preceding 3 d by recall. On the day of visit they examined each child reporting cough and/or fever to record the temperature, presence of nasal discharge, rate of respiration and presence of chest indrawing. Anthropometry for all children was conducted monthly. Cell-mediated immune competence was assessed by a multiple antigen skin test at baseline and thereafter every 3 months. The incidence of URI was 5.3 episodes per child-year observed. Approximately three-quarters of the study children were below -2 Z-score weight for age and height for age, and a quarter below -2 Z-score weight for height. During different test periods 9-21% of the study children did not respond to any of the test antigens. In a regression model children < -2 Z-score for weight for height had 16% [odds ratio (OR) 1.16, 95% confidence interval (CI) 1.03-1.31, p = 0.01] higher risk of developing URI. Anergic children had 20% higher risk (OR 1.20, CI 1.05-1.38, p = 0.009) of URI than immunocompetent children. The study demonstrated that wasting and depressed cell-mediated immunity (CMI), but not stunting, were associated with the incidence of URI among rural Bangladeshi children.

Comparison of immune responses in patients infected with Vibrio cholerae O139 and O1

Vibrio cholerae O139 has recently emerged as the second etiologic agent of cholera in Asia. A study was carried out to evaluate the induction of specific immune responses to the organism in V. cholerae O139-infected patients. The immune responses to V. cholerae O139 Bengal were studied in patients by measuring antibody-secreting cells (ASC), as well as vibriocidal and antitoxic antibodies in the circulation. These responses were compared with those in patients with V. cholerae O1 disease. Strong immunoglobulin A (IgA) and IgM ASC responses were seen against the homologous lipopolysaccharide or serogroup of V. cholerae. The magnitude and isotype of the responses were similar in O139- and O1-infected patients. Vibriocidal antibody responses were seen against bacteria of the homologous but not heterologous serogroup, and these responses reflect the lack of cross-protection between the infections caused by the two serogroups. The two groups of patients showed comparable cholera toxin-specific ASC responses, with the IgG isotype dominating over the IgA isotype, as well as comparable antitoxic immune responses in plasma. These results suggest that despite having a polysaccharide capsule, V. cholerae O139 induces systemic and intestine-derived ASC responses in peripheral blood comparable to those seen in patients with V. cholerae O1 disease.

Evaluation of Peru-15, a new live oral vaccine for cholera, in volunteers

A new live oral cholera vaccine, Peru-15, was studied for safety, immunogenicity, and excretion in 2 groups of healthy volunteers. Twelve inpatient volunteers received freshly harvested vaccine in doses of either 10(7) or 10(9) cfu. Subsequently 50 outpatient volunteers received freeze-dried vaccine in doses of 10(8) or 10(9) cfu or placebo in a three-cell, double-masked, placebo-controlled trial. The strain was well tolerated at all dose levels, and it stimulated high levels of vibriocidal antibodies in most inpatient volunteers and in all outpatient volunteers. Although antitoxin responses were less frequent and of lower magnitude than the vibriocidal responses, antitoxin responses were seen in >60% of the outpatient volunteers. About 60% of the volunteers excreted the vaccine in their feces; however, fecal excretion did not correlate with serologic responses. It is concluded that Peru-15 is a safe and immunogenic oral vaccine for cholera.

Comparison of alternative buffers for use with a new live oral cholera vaccine, Peru-15, in outpatient volunteers

During development of Peru-15, a new live oral vaccine for cholera, the role of buffer needed to be evaluated. Generally, oral bacterial vaccines are acid labile and need to be administered by using a formulation which protects them from gastric acid. We compared three different buffers for use with Peru-15, including a standard bicarbonate-ascorbic acid buffer, Alka-Seltzer, and a new electrolyte-rice buffer, CeraVacx. Saline served as the control. Thirty-nine healthy adult volunteers received Peru-15 (10(8) CFU) with one of the three buffers or saline in a double-masked study. The volunteers were monitored for symptoms for 7 days after the dose, serum was tested for antibody responses by vibriocidal antibody and immunoglobulin G antitoxin enzyme-linked immunosorbent assays, and stool samples were tested for excretion of the vaccine strain. Side effects were minimal in all groups. All 30 volunteers who took Peru-15 with a buffer showed significant rises in vibriocidal antibody titer. The magnitude of the rises was higher in the CeraVacx group than in the other two buffer groups. Four of nine volunteers who took the vaccine with saline also showed increased titers, but they were lower than those in any of the three buffer groups. Excretion of the vaccine strain was similar in the buffer groups, but excretion was not associated with the magnitude of the vibriocidal responses. Excretion of Peru-15 was not detected in the saline group. We conclude that buffer does amplify the serological response to Peru-15 and that CeraVacx may provide benefits not provided by other buffers.

Detection of non-culturable Shigella dysenteriae 1 from artificially contaminated volunteers' fingers using fluorescent antibody and PCR techniques

Epidemiological studies have demonstrated that hands may be an important vehicle for transmission of shigellosis. The present study was carried out to find out the survival potential of Shigella dysenteriae 1 on fingers of volunteers. Finger surface was inoculated with 10(5) cfu of S. dysenteriae 1 and then the bacteria were detected using conventional culture, PCR and fluorescent antibody (FA) techniques after different time intervals. It was found that S. dysenteriae 1 survived for up to one hour in culturable form but up to four hours in non-culturable form on human fingers. The non-culturable S. dysenteriae was detected by PCR and FA techniques. This study elaborates on the role that fingers have in the transmission of shigellae.

Acute respiratory infections in children: a community-based longitudinal study in rural Bangladesh

A community-based logitudinal study conducted in Matlab, a rural area in Bangladesh, investigated acute respiratory infections (ARI) among children. A cohort of 696 children under 5 years of age was followed for 1 year yielding 183,865 child-days of observation. Trained field workers visited the study children every fourth day. Data on symptoms suggesting ARI, such as fever, cough, and nasal discharge, were collected for the preceding 3 days by recall. To determine the type and severity of ARI, the field workers conducted physical examinations (temperature, rate of respiration, and chest indrawing) of children reporting cough and/or fever. The overall incidence of ARI was 5.5 episodes per child-year observed; the prevalence was 35.4 per hundred days observed. Most of the episodes (96 per cent) were upper respiratory infections (URI). The incidence of acute lower respiratory infections (ALRI) was 0.23 per child per year. The incidence of URI was highest in 18-23-month-old children, followed by infants 6-11 months old. The highest incidence of ALRI was observed in 0-5-month-old infants followed by 12-17-month-old children. Among 559 children who were followed for 6 months or longer, about 9 per cent did not suffer any URI episode and about 16 per cent suffered one or more ALRI episodes. About 46 per cent of URI and 65 per cent of ALRI episodes lasted 15 days or more. The incidence rates of URI were higher during the monsoon and pre-winter periods, and that of ALRI at the end of the monsoon and during the pre-winter periods. Sociodemographic variables were not associated with the incidence of URI or ALRI. The study documents ARI to be a major cause of morbidity among rural Bangladeshi children.

Serotypes of Streptococcus pneumoniae causing invasive childhood infections in Bangladesh, 1992 to 1995

One hundred sixty-five invasive Streptococcus pneumoniae strains were isolated from children under five at Dhaka Shishu (Children's) Hospital during the period 1992 to 1995. Ninety-four strains were from cerebrospinal fluid, and 71 were from blood. More than 91% of the strains were isolated from patients aged 24 months or less. Predominant serotypes were, in descending order 7F, 12F, 14, 15B, 18, 5, and 22A. These comprised 70% of all isolates. The marked differences in serotype distribution in different countries indicate the need for a sentinel surveillance study for the countries of South Asia, particularly Bangladesh, China, India, and Pakistan.

Antimicrobial resistance in organisms causing diarrheal disease

Antimicrobial resistance is becoming increasingly important in the treatment of enteric infections, particularly those due to Shigella, Vibrio cholerae, enterotoxigenic Escherichia coli (associated with traveler's diarrhea), and Salmonella typhi. The rate of antimicrobial resistance is highest in the developing world, where the use of antimicrobial drugs is relatively unrestricted. Of greatest immediate concern is the need for an effective, inexpensive antimicrobial that can be used safely as treatment for small children with dysentery due to Shigella, primarily Shigella dysenteriae type 1.

Monoclonal antibodies to the enterotoxin of Bacteroides fragilis: production, characterization, and immunodiagnostic application

A monoclonal antibody, ICT11, specific for the toxin of enterotoxigenic Bacteroides fragilis (ETBF) neutralized the cytotoxic effect of the toxin on human colonic cell line HT-29/C1. In an evaluation using 115 diarrheal stool specimens and culture as the "gold standard," the assay showed a sensitivity of 85% and a specificity of 100%. An ICT11-based sandwich enzyme-linked immunosorbent assay showed a sensitivity of 100% and a specificity of 98% for direct detection of toxin from stool samples compared with those of culture. Thus, ICT11-based assays will be useful for screening for ETBF.

Vibrio cholerae O139: how great is the threat of a pandemic?

The emergence of the new strain Vibrio cholerae O139 and its rapid spread in Bangladesh and India together with its detection in several other countries, have raised the question whether this constitutes the beginning of the eighth pandemic of cholera, and if so, how large a threat it poses. In an attempt to answer this question, epidemic spread patterns of Vibrio cholerae O139 strain in Bangladesh were studied. Initially the epidemic moved quickly and affected the entire coastal and estuarine tidal plains of southern Bangladesh. In the flood plains of the northern regions it affected mostly the north-eastern and north-central areas, at a slower pace than in the southern areas. In the beginning the new strain totally displaced both biotypes (classic and El Tor) of Vibrio cholerae O1. Nearly 2 years after its initial detection, striking differences in the distribution of V. cholerae O139 and O1 were observed. In most northern areas, the new strain was replaced by V. cholerae O1, whereas in the southern coastal regions, the O139 strain continues to dominate epidemics. The study suggests that the O139 strain may become endemic in the coastal ecosystem. The threat of a pandemic, therefore, may not be as large as it first seemed.

Association between nutritional status, cell-mediated immune status and acute lower respiratory infections in Bangladeshi children

OBJECTIVE

To investigate the association between nutritional status, cell-mediated immune status and the incidence of acute lower respiratory infections (ALRI).

DESIGN

Community-based longitudinal study.

SETTING

Three villages in rural Bangladesh at Matlab.

SUBJECT

696 children aged 0-59 months were followed up for a year.

METHODS

Trained field workers visited all children every fourth day and collected morbidity data for the preceding three days by recall. To determine the type and severity of respiratory infections, the field workers physically examined each child reporting a cough. Anthropometric status was determined monthly and cell-mediated immune status by skin tests was assessed at the beginning of the study and thereafter every 3 months.

RESULTS

The incidence of ALRI was 23 episodes per 100 child-years. A total of 73-78% of the children were below -2 z score weight for age, 15-30% were below - 2 z score weight for height, and 68-76% were below -2 z score height for age. In logistic regression models, malnutrition as assessed by weight-for-height status [odds ratio (OR) 0.66, 95% confidence interval (CI) 0.45-0.96, P = 0.03] or weight-for-age status (OR 0.64, 95% CI 0.45-0.92, P = 0.02) was significant predictor of ALRI. Anergic children had a higher risk of ALRI which approached to be statistically significant (OR 1.81, 95% CI 0.92-3.55, P = 0.08).

CONCLUSIONS

Improvement of nutritional and cell-mediated immune status in rural Bangladeshi children should reduce the incidence of ALRI.