Seroepidemiology of leptospirosis in southern Vietnamese children

OBJECTIVE: To estimate the seroprevalence of human leptospirosis in southern Vietnam. METHODS: All pupils (n=961) of two primary schools in two communes in southern Vietnam were screened for the presence of serum Leptospira immunoglobulin (Ig)G. Leptospira IgM was tested in 92 randomly selected samples. IgM and IgG were tested with a commercially available enzyme-linked immunosorbent assay (ELISA). RESULTS: Leptospira IgG was found in 123 (12.8%, 95% CI: 10.8-15.1) children with a male:female ratio of 1.5:1. At the age of 7 years the prevalence was 11%. Log-linear binary regression of the IgG seroprevalence by age showed a mean seroconversion rate of 1.5% (95% CI: 1.23-1.75) per year. Five (5.4%, 95% CI: 2.3-12.1) samples were definitely positive for IgM. Presence of serum Leptospira IgG antibodies was significantly associated with swimming in rivers (RR: 1.745, 95% CI: 1.117-2.724) and wading through water (RR 1.793, 95% CI: 1.181-2.722). CONCLUSION: Our data emphasize the importance of leptospirosis among children in Vietnam, despite the absence of severe disease, and stress the need for adequate and cheap diagnostics.     

A prospective evaluation of four immunodiagnotic assays for human leptospirosis

This was a prospective evaluation of four immunodiagnostic assays for human leptospirosis, including the indirect immunofluorescence test (IFA), the microscopic agglutination test (MAT), the LEPTO dipstick, and the latex agglutination (LA) test. Four hundred ninety-two serum samples were collected from 348 patients who presented with acute fever without localizing signs. The sensitivities of the IFA, MAT, Dipstick, and LA were 91.9, 76.6, 77.4, and 83.1%, respectively. The specificities of these assays were 100.0, 100.0, 89.3, and 83.5, respectively. Even though IFA showed the highest overall sensitivity and specificity, when acute sera were considered, the LA was the most sensitive (28.7%). All 3 genus specific antibody assays had broad reactivity against various serogroups. The MAT is best suited for the reference laboratory, where it can be maintained with the battery of live antigens; the IFA is suited for a laboratory with sophisticated equipment and technical expertise; the Dipstick and LA are suitable for peripheral laboratories which lack expensive equipment and expertise.     

A serological investigation of leptospirosis in sows from central Thailand

Leptospirosis is a major pig-associated zoonosis worldwide. There are also human occupational disease exposure risks. For better public health and sanitation, the prevalence of this disease was investigated. Four hundred sera were obtained from sows in central Thailand during August 2004 to January 2005 and examined with 20 reference leptospira serovars by a microscopic agglutination test (MAT). The results showed that 10% of samples gave a positive reaction. The most prevalent serovar was grippotyphosa which accounted for 55% of all positive cases. Other minor serovars were canicola and a non-pathogenic strain (patoc). It follows that, the sow may be one of the disease transmitting sources for humans in this area. The disease correlation between pigs, humans and the environments should be evaluated.     

Polymerase chain reaction in comparison with serological tests for early diagnosis of human leptospirosis

The aim of this study was to compare the sensitivity and specificity of polymerase chain reaction (PCR) using two primer pairs and combined with blood culture, immunoglobulin M enzyme-linked immunosorbent assay (IgM ELISA), microscopic agglutination test (MAT) and slide agglutination test (SAT) in the diagnosis of human leptospirosis. We analysed 124 serum samples: 60 from patients with confirmed leptospirosis, 20 from patients with other diseases and 44 from healthy individuals. Analysing the first serum sample collected during the first 3-8 days of disease, the sensitivities of the four tests MAT, IgM ELISA, SAT and PCR were, respectively, 69.0%, 79.3%, 72.4% and 62%. In subsequent samples, those same sensitivities were, respectively, 95.4%, 100%, 100% and 72.7% in samples collected from days 9 to 14 and 88.9%, 88.9%, 77.8% and 44.4% in those collected from days 15 to 42. The most specific method (at 100%) was PCR and the least specific (at 89.1%) was IgM ELISA. Although we found PCR to be less sensitive than the serological tests over the course of the disease, our data indicate that PCR was the most sensitive in those initial serum samples presenting no specific antibodies detectable by any of the serological methods tested. We also recommend that PCR can be used in combination with serological tests as we found that this improves the sensitivity of the diagnosis of leptospirosis in the first phase of the disease (93.1-96.5%).     

Use of locally isolated saprophytic Leptospira strain for serological testing of human leptospirosis.

A saprophytic Leptospira isolate recovered from tap water was utilized for serological testing. One hundred-twenty Serum samples comprising 55 cases from PUO/febrile jaundice and 65 samples from apparently healthy individuals were tested by MAT and HA using this environmental saprophytic strain and the results compared with that of Leptospira biflexa semaranga patoc, the standard saprophytic strain commonly employed for sero-diagnosis of leptospirosis. The MAT data showed 96.4 per cent correlation between the two strains. Similarly, the HA results were matching to the extent of 94.5 per cent. Results, therefore, suggest that local saprophytic Leptospira strain may serve as a substitute to serovar patoc for serodiagnosis of leptospirosis.     

Seroepidemiology and serological follow-up of anti-leptospiral IgG in children in Southern Vietnam

A follow-up study was conducted with 23 months interval to investigate the seroepidemiology and persistence of Leptospira IgG antibodies among healthy children in Binh Thuan province, Southern Vietnam. Sera from 262 children (7–13 years of age) were collected and analysed with a commercially available enzyme-linked immunosorbent assay (ELISA) for Leptospira IgG. Seroconversion was observed in 10.4% (22 of 211, 95% CI: 5.6–26.7) of the children, of whom 18 (8.5%) had probably and four (1.9%) had certainly been exposed to Leptospira. Based on the reduction of sero-negatives of 1.9% among children who have been certainly exposed, the annual seroconversion rate, a measure of the incidence rate of Leptospira infections, corresponds to 0.99% (95% CI: 0.39–2.52). In 61% (31 of 51, 95% CI: 47.1–73.0) of the children with past-infection, Leptospira IgG antibodies remain detectable after 2 years. Data from this study indicate that IgG antibody responses against Leptospira may persist at least for 2 years in children without manifestations of leptospirosis. Results of study uncover the true incidence of leptospirosis infection, the dynamics of waxing and waning antibody concentrations and points at a larger burden of clinically non-significant Leptospira infections in Southern Vietnam. This also indicates background reactivity for serological testing and thus serological result of a single serum sample must be carefully interpreted.     

Development of culture-based serological assays to diagnose Babesia divergens infections

Babesioses are hematic tick-borne diseases that induce malaria-like disorders in domestic, wild animals, and humans. Although indirect fluorescent antibody test (IFAT) and enzyme-linked immunosorbent assay (ELISA) commercial kits are available to test the presence of antibodies against most Babesia species, no kit exists to serologically diagnose the infections due to Babesia divergens, one of the most important zoonotic species. To fill this gap and to develop assays to detect animal and human infections, in vitro cultures (microaerophilous stationary phase system) of B. divergens were organized. Infected erythrocytes were adsorbed as corpuscular antigen (CA) on IFAT slides and ELISA microwells. The supernatant medium of the cultures (metabolic antigen, MA) was collected and employed in ELISA and western blot (WB) assays. B. divergens was also used to produce positive sera in Meriones unguiculatus and to infect a calf. Serological tests were set up with sera from experimentally/naturally infected animals, and possible cross-reactions were evaluated using heterologous sera from cattle positive to other piroplasms. Sera from clinically healthy people at risk of infection were also tested. As expected, assays based on the purified MAs from in vitro cultures proved more sensitive and specific than CA-IFAT and CA-ELISA. In fact, MA-ELISA provided satisfactory performances (even if 8.4%-15.7% cross-reactions were evidenced), and the WB developed proved totally sensitive and specific. WB indicated as immunodominant antigens two major protein bands at 33 and 37?kDa, which were also evidenced in 2.2% of the human sera tested, proving the parasite transmission to humans also in Italy.     

不同梅毒血清学检测方法的临床价值

目的:评价常用的4种梅毒血清学试验检测方法在临床诊断中的价值。方法:分别用快速血浆反应素试验(RPR)、胶体金免疫层析法(GICA)、酶联免疫吸附试验(ELISA)和微粒子化学发光法(CMIA)对264例标本进行梅毒血清学试验检测,同时与明胶颗粒凝集法(TPPA)的检测结果进行比较,得出不同检测方法的敏感度和特异性。结果:RPR、GICA、ELISA、CMIA的敏感度分别为67.5%、92.1%、96.0%和98.4%,特异性分别为89.1%、100%、100%和100%。结论:RPR可结合其他方法对梅毒进行联合诊断和对已诊断的患者进行疗效观察;GICA适合快速初筛,检测结果需结合其他方法进一步确认;ELISA和CMIA均可替代TPPA法作为临床诊断试验选用。     

Predictive value of latex agglutination test in serological screening for Toxoplasma gondii

The predictive value of commercial latex agglutination kit (Toxo-Screen DA, bioMerieux) was assessed for use as screening test for Toxoplasma IgG antibody. The sensivity and specificity were also compared with those of the reference standard Sabin-Feldman dye test. Five hundred serum samples were collected from 200 blood donors and 100 each from pregnant women, kidney recipients and HIV infected persons. Eighty (16.0%) out of 500 subjects were positive for Toxoplama IgG antibody by Toxo-Screen DA (bioMerieux) compared with 57 (11.4%) by Sabin-Feldman dye test. The sensivity and specificity of Toxo-Screen DA (bioMerieux) were 100% and 94.8 % respectively which were similar to previous reports from the area of high prevalence of Toxoplasma infection. In present study the positive predictive value of Toxo-Screen DA (bioMerieux) was only 71.3%. The latex agglutination test should be considered as a screening test for Toxoplasma antibody, especially by small laboratories in remote area due to its availability, simplicity, sensitivity and specificity. However, because of its moderate positive predictive value, the test should be used with caution in screening immunocompromised patients and pregnant women living in areas with low prevalence of Toxoplasma infection. Since the number of false seropositive cases would be relatively higher than in a highly prevalent area, confirmation by the dye test would be needed.     

Large scale screening for haemoglobin disorders in southern Vietnam: implications for avoidance and management

In order to obtain an approximate assessment of the public health burden that will be posed by the inherited disorders of haemoglobin in southern Vietnam, several thousand individuals were screened for these conditions. A smaller sample was screened for glucose‐6‐phosphate dehydrogenase (G6PD) deficiency. The important haemoglobin disorders identified were β thalassaemia, haemoglobin E and a variety of different forms of α thalassaemia. There were sufficient G6PD‐deficient individuals to materially affect malaria control programme design. The most remarkable finding was wide variation in the gene frequencies of these conditions among the ethnic groups sampled. The approximate number of babies expected to be born with clinically significant haemoglobin disorders in Vietnam was estimated from the gene‐frequency data. This study emphasizes the importance of wide‐scale population screening, including ethnic subgroups, to establish the requirements for inherited haemoglobin disorder programmes in resource‐limited settings.