S. C. Sehgal

Randomized controlled trial of doxycycline prophylaxis against leptospirosis in an endemic area

Leptospirosis occurs as seasonal outbreaks, lasting for about 3 weeks during October-November in North Andaman. A randomized controlled trial was undertaken to assess the efficacy of doxycycline prophylaxis in the prevention of infection and clinical disease due to leptospires during the outbreak period. A sample population of 782 persons, randomized into two groups was given doxycycline 200 mg/week and a placebo. The microscopic agglutination test was done on blood samples collected on day zero, after 6 weeks and after 12 weeks. Infection rates and attack rates of clinical illness were calculated in the two groups based on the serological results. Statistically there was no difference in the infection rates among the two groups. However, a statistically significant difference was observed in the clinical disease attack rates (3.11 vs. 6.82%) between study group and control group. The results of the study indicate that doxycycline prophylaxis does not prevent leptospiral infection in an endemic area, but has a significant protective effect in reducing the morbidity and mortality during outbreaks.

LEPTO Dipstick: a rapid and simple method for serodiagnosis of acute leptospirosis

The LEPTO Dipstick assay is a newly developed test for the diagnosis of leptospirosis and uses a broadly reactive antigen for detecting IgM antibodies. The test was evaluated in the Andaman and Nicobar Islands, using 867 serum samples from known cases of leptospirosis and controls. The efficacy of IgM ELISA was also tested for comparison. The LEPTO Dipstick had a sensitivity of 78.7%, a specificity of 88.3% and a positive predictive value of 91.0%. The test had a good level of agreement with the standard criteria for diagnosis using paired microscopic agglutination tests (kappa = 0.64). These indices were similar to those of IgM ELISA (sensitivity 78.5%, specificity 87.6%, positive predictive value 90.5%, kappa 0.63). Both the LEPTO Dipstick and IgM ELISA had the highest sensitivity during the second, third and fourth weeks of illness (87.6% and 88.2%, respectively). Sensitivities during the first week and after 4 weeks were relatively low but acceptable. The test is very easy to perform and does not require any special skills for its performance. The reagents and dipsticks have a long shelf-life even at room temperature. As the test can be performed without the aid of sophisticated equipment, it is suitable for use at the peripheral level as a rapid screening test for the diagnosis of leptospirosis.

Evaluation of Lepto Dri Dot as a rapid test for the diagnosis of leptospirosis

Lepto Dri Dot is a new card agglutination test developed by the Dutch Royal Tropical Institute for the rapid diagnosis of leptospirosis. We evaluated the test in field conditions in The Andaman Islands. Patients suspected of leptospirosis who attended three primary health centres were included in the study. The test results were compared with blood culture or microscopic agglutination tests on paired serum samples; 74 of 124 patients were diagnosed as having leptospirosis based on these criteria. Lepto Dri Dot had a sensitivity of 67.6% (50/74) and a specificity of 66.0% (33/50) during week 1. During weeks 2-4 the values increased to 85.5% (47/55) and 80% (40/50) respectively. An IgM ELISA was also performed on the serum samples for comparison and this was marginally less sensitive, but more specific, during the first week of illness. The positivity rates for the Dri Dot test during days 2-3, 4-5 and 6-7 were 53.1% (17/32), 75.0% (18/24) and 83.3% (15/18), respectively. The corresponding values for ELISA were 28.1% (9/32), 54% (13/24) and 77.8% (14/18). Both Dri Dot and ELISA showed good agreement with the standard diagnostic criteria after the first week of illness (kappa= 0.65 and 0.74, respectively). The overall concordance of the two tests was 89.5 % (kappa = 0.79). The test does not require special storage or sophisticated equipment and can be performed by relatively low skilled personnel.

Distribution of Shigella enterotoxin genes and secreted autotransporter toxin gene among diverse species and serotypes of shigella isolated from Andaman Islands, India

We studied the prevalence and distribution of the newly described genes for Shigella enterotoxins (ShET1 and ShET2, encoded by set and sen genes) and secreted auto‐transporter toxin (encoded by sat gene) in clinical isolates from the Andaman Islands, India. A total of 153 Shigella isolates obtained from hospitalized patients during 1994–2004 were analysed. These isolates included all the four species of Shigella (S. dyseteriae– 29, S. flexneri– 75, S. sonnei– 38, S. boydii– 5) that belonged to diverse serotypes (including serologically untypable – 6) and each serotype included a wide variety of genotypes. Each isolate underwent polymerase chain reaction (PCR) for detection of set, sen and sat genes employing specific primers. We found the set gene in all S. flexneri 2a and 2b isolates (41 of 41, 100%) but not outside S. flexneri serotype 2. The sen gene was well distributed among all species and serotypes but its presence was apparently low at 49.1% (75 of 153), probably because of the loss of the large plasmid that harbours the gene in 76 of the 78 (97.4%) sen negative isolates. Also, all S. flexneri 2 isolates (including 2a and 2b serotypes) had the sat gene. It was present in 96% (72 of 75) of S. flexneri, in 6.9% (2 of 29) of S. dysenteriae, in 20% (1 of 5) of S. boydii, and in 33.3% (2 of 6) of untypable Shigella, but not in (0 of 38) S. sonnei. This study provides initial data on the prevalence and distribution of of the set, sen and sat genes in a wide variety of Shigella isolated over a 10‐year period. Our results suggest a greater prevalence of the set and sat genes in S. flexneri 2 isolates than previously thought and might help in future pathochip designs.

Serodiagnosis of severe leptospirosis: evaluation of ELISA based on the recombinant OmpL1 or LipL41 antigens of Leptospira interrogans serovar autumnalis.

Abstract ELISA based on the recombinant OmpL1 and LipL41 antigens of Leptospira interrogans serovar autumnalis strain N2 have been developed, for the serodiagnosis of the severe pulmonary form of leptospirosis on the endemic Andaman Islands. The recombinant OmpL1 and LipL41 were produced using Escherichia coli expression systems and then purified before each was evaluated in an IgM-ELISA. The sera tested came from 224 patients who had the severe form of leptospirosis and pulmonary pneumonitis as major symptoms, 148 patients who, although clinically suspected to have severe leptospirosis, had been found seronegative for leptospirosis, 528 patients with diseases other than lepstospirosis, and 704 apparently healthy individuals, all from the Andaman Islands. Among the patients with the severe pulmonary form of leptospirosis, the ELISA based on the recombinant OmpL1 achieved a sensitivity of 91.1%, a specificity of 86.5%, a positive predictive value of 91.1%, and a negative predictive value of 86.5%. The corresponding values for the assay based on the recombinant LipL41 were 89.3%, 89.2%, 92.6%, and 84.6%, respectively. The good performance of both ELISA indicates that either may be routinely used for the diagnosis of severe pulmonary leptospirosis which, at least on the Andaman Islands, occurs soon after the patient has become leptospiraemic. The evaluated ELISA may also be useful for early case detection and for monitoring the effects of treatment.

Epidemiology of hepatitis B infection among the Nicobarese - a mongoloid tribe of the Andaman and Nicobar Islands, India

Andaman and Nicobar Islands, Union Territory of India, is home to six primitive tribes. Preliminary serological studies carried out earlier among the four accessible tribes revealed that hepatitis B virus (HBV) infection is hyper-endemic among them. The present study was carried out to understand important modes of transmission and to identify possible risk factors associated with HBV infection among the Nicobarese tribe. The epidemiology of HBV infection in these islands appears to be distinct with a high prevalence of the chronic carrier state (22.2%) associated with a comparable proportion of the population being anti-HBs positive (26.3%). More than half of the HBsAg and anti-HBs negative individuals have anti-HBc antibodies. Age, past history of hospital admission, intramuscular injections and number of carriers in the tuhet were found to be significantly associated with exposure to hepatitis B virus. Horizontal transmission through close contact with carriers and perinatal route appears to be an important mode of transmission of HBV in this community. Besides this, use of unsafe injections represents an independent risk factor for acquiring HBV infection in this population. Introducing HBV vaccine in the infant immunization programme and improving injection safety would help to control the infection in the tribal community of these islands.

Malnutrition and high childhood mortality among the Onge tribe of the Andaman and Nicobar Islands.

OBJECTIVES A study was conducted among the Onge tribe of the Andaman and Nicobar Islands with the objectives of identifying demographic factors responsible for the decline in their population and assessing their nutritional status, which is an important determinant of child survival. STUDY DESIGN AND SUBJECTS The study included estimation of indices of fertility and child mortality, and assessment of nutritional status. All individuals of the Onge community settled on Little Andaman Island were included. RESULTS The mean total marital fertility rate was estimated to be 5.15 live births per woman and the general fertility rate was 200 live births per 1000 married-woman-years. Although the gross reproduction rate was estimated to be 2.2 female children per married woman, the net reproduction rate was only 0.9 surviving female child per married woman. The mean infant mortality rate during the past 30 years was 192.7 per 1000 live births, and the child survival rate was found to be only 53.2%. A mild to moderate degree of malnutrition was found in 85% of children of pre-school age and severe malnutrition in 10%. The Onges had low intakes of iron, vitamin A and vitamin C. All the screened Onges were found to be infested with one or more intestinal parasites. CONCLUSIONS High childhood mortality appears to be the predominant demographic factor responsible for the decline in the Onge population. The high prevalence of undernutrition and micronutrient deficiency disorders could be important factors contributing to the high childhood mortality.

Leptospiral infection among primitive tribes of Andaman and Nicobar Islands

The Andaman islands were known to be endemic for leptospirosis during the early part of the century. Later, for about six decades no information about the status of the disease in these islands was available. In the late 1980s leptospirosis reappeared among the settler population and several outbreaks have been reported with high case fatality rates. Besides settlers, these islands are the home of six primitive tribes of which two are still hostile. These tribes have ample exposure to environment conducive for transmission of leptospirosis. Since no information about the level of endemicity of the disease among the tribes is available, a seroprevalence study was carried out among all the accessible tribes of the islands. A total of 1557 serum samples from four of the tribes were collected and examined for presence of antileptospiral antibodies using Microscopic Agglutination Test (MAT) employing 10 serogroups as antigens. An overall seropositivity rate of 191% was observed with the highest rate of 53.5% among the Shompens. The seropositivity rates in the other tribes were 16.4% among Nicobarese, 222% among the Onges and 14.8% among the Great Andamanese. All of the tribes except the Onges showed a similar pattern of change in the seroprevalence rates with age. The prevalence rates were rising from low values among children to reach a peak in those aged 2140 years and then declined. Among Onges the seroprevalence rates continued to rise beyond 40 years. In all the tribes, seroprevalence rates were found to be significantly higher among the males. The commonest serogroups encountered were Australis followed by Grippotyphosa, Icterohaemorrhagiae, Pomona and Canicola.

Leptospiral carrier state and seroprevalence among animal population--a cross-sectional sample survey in Andaman and Nicobar Islands.

A study was conducted with the objective of assessing the leptospiral carrier state and seroprevalence among animal population of Andaman and Nicobar Islands. A total of 494 sera samples from different domestic animals and 85 samples from rats (Rattus rattus) were tested by microscopic agglutination test using nine serogroups prevalent in these islands. Antibodies to leptospires were detected in 164 samples giving an overall seroprevalence of (33.11%). The seroprevalence was highest among cows (40.32%). Of 85 rat (Rattus rattus) samples tested for antileptospiral antibodies six (7.1%) were positive. Leptospires were isolated from kidney of two rats and urine of one cow. Isolate from urine of cow was heavily contaminated and was subsequently lost during further subculture. The two isolates were found to be pathogenic, belonging to serogroup Grippotyphosa. The isolates were further characterized by using a set of monoclonal antibodies. The agglutination patterns of isolates were similar to that of ratnapura and valbuzzi, however these did not completely match.

Leptospirosis among schoolchildren of the Andaman & Nicobar Islands, India: low levels of morbidity and mortality among pre-exposed children during an epidemic

Leptospirosis is an important public health problem in the Andaman Islands. The disease is being increasingly reported among children and adolescents in recent times. An attempt was made to find out the level of exposure to leptospires, to estimate the incidence of infection and to identity the risk factors for acquiring infection among children. A sample of 1544 schoolchildren was selected. Presence of anti-leptospiral antibodies was tested using the microscopic agglutination test (MAT). Students were interviewed for behavioural factors. In total, 341 (221 seronegative and 120 seropositive) students were followed up clinically and serologically during a subsequent outbreak. An overall seropositivity rate of 23.6% (95% CI 21.54-25.81) was observed. Infection rate was 33.5% among seronegatives whereas re-infection rate was 16.7% among seropositives during the outbreak that occurred 1 month after the first sample collection. Morbidity and mortality were found to be higher among seronegative individuals than seropositives. More than 90% of leptospiral infections were found to be subclinical or unnoticed. The high level of exposure among the children results in high infection rates and because they have less previous exposure than adults, they do not have sufficient protection to resist clinical illness during outbreaks.