Epidemiological patterns of the import and spread of El Tor cholera]

The paper is a response to the paper by A. K. Akiev published in 1974 in the "Journal of Microbiology Epidemiology and Immunobiology": "Concerning the Epidemiology of El Tor cholera Abroad". The opinion of the author concerning the origin of El Tor infection in 1970, the sources of infection, and the factors of its transmission is critisized. Literature data and personal observations explaining the regularities of importation and spread of El Tor cholera as an intestinal infection are presented; these data are against the view of Akiev on El Tor cholera as a disease with a natural nidality caused by freely living vibrios.     

Purification of El Tor cholera enterotoxins and comparisons with classical toxin.

In 55 clinical isolates of Vibrio cholerae biotype El Tor, cholera toxin (CT) production was higher after growth in liquid medium first under relatively anaerobic conditions followed by excessive aeration (AKI conditions) as compared with growth under the optimal conditions for CT production from V. cholerae of classical biotype (median toxin level being 400 ng ml-1 and 1 ng ml-1 respectively, for the two different growth conditions). Large growth volumes further enhanced El Tor toxin production to levels at or above 3-5 micrograms ml-1 from several strains, which allowed for easy purification of toxin by salt precipitation, aluminium hydroxide adsorption and/or GM1 ganglioside affinity chromatography. However, such purified El Tor CT completely lacked the A subunit when examined by SDS-PAGE or by monoclonal anti-A subunit antibody GM1-ELISA. In contrast, when El Tor CT was prepared from bacteria grown in the presence of specific antiserum against soluble haemagglutinin/protease it contained the A subunit (unnicked) in the same proportion to the B subunit (1A:5B) as classical CT. Immunodiffusion-in-gel tests revealed that the B subunits of El Tor and classical CTs share major epitopes but also have one or more weaker biotype-specific epitopes. The two types of toxin were practically indistinguishable in various GM1-ELISA tests, and antisera raised against El Tor and classical CT, respectively, could also completely neutralize the heterologous as well as the homologous toxin activity in vivo. The results indicate that CTs from El Tor and classical V. cholerae, despite demonstrable epitope differences, are predominantly cross-reactive and give rise to antisera with strong cross-neutralizing activity.     

Comparative Trial of Tetracycline,Chloramphenicol, and Trimethoprim Sulphamethoxazole in Eradication of Vibrio cholera El Tor

A comparison of tetracycline, chloramphenicol, and trimethoprim/sulphamethoxazole showed that all hasten the eradication of Vibrio cholerae from the stools of patients with cholera.A four-day period of tetracycline or trimethoprim/ sulphamethoxazole was adequate for eradicating V. cholerae from the stools of all patients, but three days, as suggested by the W.H.O. Expert Committee, was not. Four days of chloramphenicol therapy was sufficient for most patients, but a minority required up to seven days'' therapy.Purging produced reappearance of V. cholerae in the stools of one-eighth of the patients who had had three successive daily negative stool cultures; such patients are a potential danger to the population.     

Medical genetic study of the population of Uzbekistan. V. The frequency of heterozygous beta-thalassemia in 4 kishlaks of Urgut District, Samarkand Province]

A subject of this investigation is the results of the subtotal examination of 4 villages for the detection of heterozygous beta-thalassemic carriers. 848 persons (55.5% of the registered population) have been examined. The mean frequency of the beta-Th gene was 0.0159, FST-Wahlund--0.00975. Statistically significant differences in the gene frequencies between villages have been revealed (p less than 0.01). The study of genetic distances (by Edwards) has revealed no intertribe differences in gene frequencies. The comparison of findings of the present study with other similar investigations enabled to account for the detected differences in the frequencies of beta-thalassemia as a result of the genetic drift. The importance of choosing populations for the study and methods for detection heterozygous beta-thalassemia are discussed.     

Molecular characterization of Vibrio cholerae outbreak strains with altered El Tor biotype from southern India

Forty-four Vibrio cholerae isolates collected over a 7-month period in Chennai, India in 2004 were characterized for gene traits, antimicrobial susceptibility and genomic fingerprints. All 44 isolates were identified as O1 El Tor Ogawa, positive for various toxigenic and pathogenic genes viz. ace, ctxB, hlyA, ompU, ompW, rfbO1, rtx, tcpA, toxR and zot. Nucleotide sequencing revealed the presence of cholera toxin B of classical biotype in all the El Tor isolates, suggesting infection of isolates by classical CTXΦ. Antibiogram analysis showed a broad-spectrum antibiotic resistance that was also confirmed by the presence of resistant genes in the genomes. All isolates contained a class 1 integron and an SXT constin. However, isolates were sensitive to chloramphenicol and tested negative for the chloramphenicol resistant gene suggesting a deletion in SXT constin. Fingerprinting analysis of isolates by ERIC- and Box PCR revealed similar DNA patterns indicating the clonal dissemination of a single predominant V. cholerae O1 strain throughout the 2004 outbreak in Chennai.     

Long-term survival of E1 Tor cholera vibrios in naturally contaminated sewage]

El Tor cholera vibrios of Ogava serological type were revealed in the sewage of the locomotive shed for 15 months. In experiment with an oil catcher in naturally infected sewage El Tor vibrios survived 36 days, in storage of this sewage at the laboratory--39 days, in the artificially infected sewage of a settlement and of a milk plant--2 and 11 days, respectively, in the oil and disel fuel--14 months. Consequently, El Tor vibrio can survive in the sewage with a high oil product content for a long time.     

Variation in epitopes of the B subunit of El Tor and classical biotype Vibrio cholerae O1 cholera toxin

Variation in epitopes of the B subunit of cholera toxin (CT-B) produced by strains of El Tor and classical biotype Vibrio cholerae O1 was examined using monoclonal antibodies prepared to V. cholerae 569B CT. CT-B epitopes were markedly conserved for V. cholerae classical biotypes. In contrast, epitope variation was observed for El Tor biotypes, which produced both a classical-like CT-B and a unique CT-B lacking at least one epitope common to 569B CT-B. The missing epitope was located outside the GM1 ganglioside-binding site. From results of the study reported here, genetic divergence is exhibited in the El Tor biotype CT-B versus classical CT-B. Furthermore, at least five unique epitopes of V. cholerae 569B CT-B can be defined.     

Expression of cholera toxin under non-AKI conditions in Vibrio cholerae El Tor induced by increasing the exposed surface of cultures

The regulatory systems controlling expression of the ctxAB genes encoding cholera toxin (CT) in the classical and El Tor biotypes of pathogenic Vibrio cholerae have been characterized and found to be almost identical. Notwithstanding this, special in vitro conditions, called AKI conditions, are required for El Tor bacteria to produce CT. The AKI conditions involve biphasic cultures. In phase 1 the organism is grown in a still tube for 4 h. In phase 2 the medium is poured into a flask to continue growth with shaking. Virtually no expression of CT occurs if this protocol is not followed. Here we demonstrated that CT expression takes place in single-phase still cultures if the volume-to-surface-area ratio is decreased, both under air and under an inert atmosphere. The expression of key genes involved in the regulation of CT production was analyzed, and we found that the expression pattern closely resembles the in vivo expression pattern.     

An outbreak of fowl cholera in waterfowl on the Chesapeake Bay

An outbreak of fowl cholera (Pasteurella multocida infection) occurred in waterfowl wintering on the Chesapeake Bay during February to March 1970. Losses were primarily confined to sea ducks: oldsquaws (Clangula hyemalis), white-winged scoters (Melanitta deglandi), goldeneyes (Bucephala clangula), and buffleheads (Bucephala albeola).