Emergence of Schoengastiella ligula as the vector of scrub typhus outbreak in Darjeeling: Has Leptotrombidium deliense been replaced.

Background: Following a suspected outbreak of scrub typhus in Kurseong, Darjeeling, the Armed Forces Medical College, Pune was requested by the National Institute of Epidemiology and the State authorities to undertake investigation of the ongoing scrub typhus outbreak and suggest containment measures. Materials and Methods:The epidemic team undertook clinical, entomological and serological studies to understand the local disease pattern and delineate high risk areas, host diversity by rodent trapping using Sherman traps, mite fauna diversity, abundance and vector species identification by phase contrast microscopy for preparation of electronic database and rodent and human serological studies by Weil Felix and PCR. Results:The results indicate no association of scrub typhus with age and sex (P=0.37 and 0.74 respectively). The maximum cases occurred amongst the tea garden workers (73%) in the age group of 25-44 years. The predominant clinical presentation was fever (100%) with headache (75%), lymphadenopathy (45%) and presence of eschar (76.7%). The dominant host species (50% of trapped rodents) was shrew Suncus murinus, the index animal for scrub typhus, which contributed maximally to the vector abundance (52.96%) with a chigger index of 61.56. The trombiculid mite Schoengastiella ligula was the vector species much against the expected mite vector Leptotrombidium deliense, in the area. The study found the presence and abundance of vector species which corroborated well with the occurrence of cases in the various localities within the subdivisions. Conclusion:The study thus establishes Schoengastiella ligula as the vector of scrub typhus outbreak in Kurseong, Darjeeling. Preventive and containment measures with emphasis on reduction of man - vector contact were suggested to the state authorities to contain the outbreak.

Insecticide treated bednet strategy in rural settings: can we exploit women's decision making power?

Use of insecticide treated bednets in prevention of malaria is a widely propagated global strategy, however, its use has been reported to be influenced and limited by many variables especially gender bias. A cross sectional field epidemiological study was conducted in a rural setting with two outcome variables, 'Bednet use'(primary outcome variable) and 'Women's Decision Making Power' which were studied in reference to various predictor variables. Analysis reveals a significant effect on the primary outcome variable 'Bednet use' of the predictor variables- age, occupation, bednet purchase decision, women's decision making power, husband's education and knowledge about malaria and its prevention. The study recommends IEC on treated bednets to be disseminated through TV targeting the elderly women who have better decision making power and mobilizing younger women who were found to prefer bednets for prevention of mosquito bites for optimizing the use of treated bednets in similar settings.

Efficacy of Fipronil and Propoxur in the control of German cockroaches (Dictyoptera: Blatellidae).

A field trial for comparative evaluation of chemicals Fipronil gel, Propoxur spray and bait was carried out. The results in the Fipronil treated area indicate a reduction of 89%, 100% and 98% in cockroach infestation by days 7, 30 and 60, whereas the reduction in Propoxur spray treated area during the same period was 88%, 91% and 87% respectively. Propoxur bait was not found to be effective in reducing the cockroach infestation; rather a build up of the cockroach infestation was noticed in the treated site. The study reports the efficacy of Fipronil gel treatment over conventional insecticidal formulations in the control of cockroach infestation in cookhouses of urban households.

Laboratory evaluation of repellents against Leptotrombidium deliense, vector of scrub typhus.

BACKGROUND & OBJECTIVES: Scrub typhus, a rickettsial disease transmitted by larvae of Leptotrombidium deliense, is of special importance to the Armed Forces personnel, due to the heightened risk to this disease during movement in mite endemic areas during exercise/war. The disease is best prevented by the use of personal protective measures including repellents. Studies were undertaken to determine the relative efficacy of repellents: diethyl toulamide (DEET), dibutyl phthalate (DBP) with an indigenously developed repellent diethyl phenyl acetamide (DEPA) against the larval trombiculid mite. METHODS: The repellents were tested for persistence on impregnated cloth prior to washing, post washing and ironing by means of a specially fabricated testing kit. Acaricidal efficacy estimation was performed on the treated fabrics and topical application efficacy of repellents on mice was evaluated by a novel animal testing model. RESULTS: DEET and DEPA were found to provide maximum protection (repellence and acaricidal efficacy), could withstand two launderings of the impregnated uniform and also had superior efficacy on topical application (8 h). Ironing was found to significantly reduce the repellence of DEET and DBP. INTERPRETATION & CONCLUSION: The findings of this study point towards the superiority of DEPA and DEET for impregnation of the uniform cloth as well as for topical application for the prevention of scrub typhus amongst the troops.

Differential efficacy evaluation of formulations of Bacillus thuringiensis Var israelensis against mosquitoes: a laboratory investigation.

The efficacy evaluation of three formulations; wettable powder (W.P.) floating pellet and beads of Bacillus thuringiensis Var israelensis (Bti), revealed a greater susceptibility of the early larval instars of mosquitoes to Bti, sensitivity of anophelines to floating pellet, culicines to bead and equal efficacy and faster kill of W.P. to all the mosquitoes tested. A greater persistence of the slow release formulations, floating pellet and beads for 49 and 28 days against anophelines and culicines respectively was observed in contrast to a maximum persistence for 21 days in case of W.P. formulation.

Evaluation of some risk factors for ischaemic heart disease under a matched pairs case-control design.

A pair-wise matched case-control study was carried out in 200 male patients of ischaemic heart disease (IHD). The cases were matched with an equal number of controls in respect of the variables viz., age and socio-economic status. The objective was to quantify the risk of developing IHD for some of the leading risk factors under the univariate and multivariate situations. The analysis revealed that of the factors (smoking, overweight, hypertension, diabetes, serum cholesterol and family history) considered, the smoking habit of the individual, presence of family history of the disease and overweight were the significant risk factors responsible for the development of the disease. The estimated odds ratios were found to be 3.29, 2.60 and 2.00 respectively.

Epidemiological study of an outbreak of cholera in Delhi cantonment.

An epidemiological study was undertaken to investigate an outbreak of cholera in Delhi Cantonment during May 1991. The study design was a hybrid design using a retrospective Case-Control method superimposed on a population based cross-sectional approach. A total of 9 cases of cholera, confirmed in the laboratory as Vibrio cholerae, 0-1, Eltor, Ogawa were identified using population based survey and compared with 33 controls from the same source population. The overall Incidence rate was 0.71% and showed a significant rising trend with age. There was no morality. Assessment of water supply, sanitary conditions of cook houses and disposal system of night soil could not provide any clue to the source of infection. Subsequently, all the food handlers were subjected to rectal swab examination. Two of them, working in the same messes from where cases had occurred, were found positive for Vibrio cholerae (0-1, Eltor, Ogawa). Immediate control measures by way of isolation and treatment of carriers promptly abated the outbreak. Role of carriers in outbreak of cholera has been highlighted.