Characterization of the anopheline vector breeding habitats: Implications for elimination of malaria in tribal inhabited Car Nicobar Island

Background & objectives: Malaria is an important public health problem in Andaman & Nicobar archipelago. Among the three districts, Nicobar is the most endemic district where API is >2. In this district, the malaria incidence in Car Nicobar Tehsil has declined steadily over the past 10 years. A renewed initiative to consolidate this gain is being made with the ultimate objective of achieving zero indigenous transmission of malaria in Car Nicobar. So, the present study undertook a close environmental monitoring of water bodies for assessing changes in the risk potential of mosquito vector breeding habitats which can augment the elimination programme. Methods: The breeding habitats of anopheline mosquitoes were sampled in 16 areas of Car Nicobar Island for eight time periods during 2017-2020. Along with anophelines, various associated water parameters (n=60) were estimated, viz. physicochemical (n=13), and biological, which included culicine mosquito immatures, insect predators (n=5), phytoplanktons (n=31) and zooplanktons (n=10). Results: In the 16 study sites, overall 1126 surface water stagnating bodies constituting 21 different habitat types were surveyed. Of these, 17 were positive for anopheline breeding. Water bodies from three villages were consistently found to be positive for anopheline breeding. However, early instars of anopheline larvae were more abundant compared to the late instars. Four anopheline species were recorded, including Anopheles sundaicus, A. barbirostris, A. insulaeflorum and A. subpictus, in which 48 per cent were A. sundaicus. Multivariable analysis indicated that anopheline density was significantly higher in permanent water bodies than in temporary habitats (P<0.05) (high risk of anophelines). The highest pH (?8.2), dissolved solids (?0.39) levels showed significantly (P<0.05) decreased larval densities (lower risk of breeding), adjusted with breeding sites and season. Nitrite levels increased (P=0.022) larval densities. Interpretation & conclusions: The present study facilitated estimating the productive period of a larval habitat enabling target larval sources to reduce adult populations. Implementing larviciding strategy before monsoon season is presumably the most cost-effective strategy. The output can be utilized for environmental monitoring of mosquito breeding risk in other malaria endemic areas, particularly where medium/large water bodies are the predominant breeding sites for malaria vectors.

Diurnally subperiodic filariasis among the Nicobarese of Nicobar district - epidemiology, vector dynamics & prospects of elimination.

In India diurnally subperiodic filariasis (DspWB) is prevalent only in the Nicobar district of Andaman and Nicobar Islands. Studies undertaken at different points of time indicate that this form of filariasis is restricted to a small region in Nancowry group of islands where it is transmitted by mosquito Downsiomyia nivea, a day biting mosquito. Studies on prevalence, distribution, and assessment of endemicity status, vector incrimination, bioecology, host seeking behaviour, population dynamics of the vector, transmission dynamics and clinical epidemiology indicate the prevalence and persistence of this infection in the Nancowry group of islands with perennial transmission. There was no control programme in these islands, until the National programme to eliminate filariasis was launched in 2004. Eight rounds of annual mass drug administration (MDA) with diethyl carbamazine (DEC) + albendazole have been completed. Despite this, microfilaria prevalence remains at above one per cent, the level identified for initiating transmission assessment survey to decide on continuation of MDA further. This necessitates adjunct measures to the ongoing MDA programme in these islands. The vector control options could be an adjunct measure, but the vector is a forest dweller with a unique bio-ecology, therefore, not a technically feasible option. Use of DEC fortified salt for six months to one year could hasten the process of elimination. Although administration of DEC-fortified salt is simple, rapid, safe, and cost-effective, challenges are to be tackled for evolving operationally realistic strategy. Such a strategy requires commitment of all sections of the society, a distribution mechanism that ensures the use of DEC-fortified salt in the Nancowry islands. Here we discuss the plan of action to serve the indigenous communities and operationalizing DEC fortified salt strategy through an inter-sectoral approach involving multiple stakeholders.

Survival of diurnally sub periodic Wuchereria bancrofti in Downsiomyia nivea (Diptera: Culicidae): a density dependent factor from Andaman & Nicobar Islands.

Background & objectives: In India, diurnally sub periodic Wuchereria bancrofti transmitted by Downsiomyia nivea is prevalent only in the Nicobar district of Andaman and Nicobar Islands. The ongoing LF elimination programme aims at transmission interruption by bringing down the microfilarie (mf) load in the community, which has implication on the parasite load in mosquito vector. Therefore, understanding density dependent constraints on transmission assumes significance from control perspective. The present study was undertaken in Teressa Island to understand the density dependent parasite mortality and survival probability of the parasite Do. nivea. Methods: The entomological data collected from Teressa Island, endemic for the diurnally sub periodic form of W. bancrofti were used to examine the parasite loss and its survival up to infectivity. Patterns of parasite distribution in Do. nivea were examined. Results: Distribution patterns of microfilariae were found to be over dispersed in Do. nivea. The later stages of the parasite in the vector were randomly distributed. Distribution pattern of various filarial larval stages suggested that the loss of parasites occurred as development progressed and was maximal between the first and second stages. Further, both the prevalence of infection and the degree of parasite aggregation in the vector population have fallen significantly with development of parasite stage. Interpretation & conclusions: Results indicate the operation of parasite density dependent mortality of vectors or parasite loss or combination of both. The present study with Aedes transmitted filariasis conducted before launching LF elimination programme in the study area indicates a comparable level of parasite regulation in the vector which has similar implications on the transmission threshold. Thus, the consideration of Aedes with Culex in deriving the critical level of antigen positive for making decisions on cessation of mass drug administration (MDA) can be justified. However, with MDA aiming at reducing parasite load in the community, the operation of density dependent factor in the transmission becomes less pronounced in the subsequent rounds of MDA.

Community-centred approach for the control of Aedes spp. in a peri-urban zone in the Andaman and Nicobar Islands using temephos.

Background. Chikungunya fever struck the Andaman and Nicobar Islands in July 2006. From the entomological point of view, dengue and chikungunya are hard to control due to the high prevalence of Aedes aegypti in both urban and rural areas. Mobilizing communities for the control of Aedes aegypti has not been attempted in India. Methods. We did a prospective observational feasibility study in one peri-urban locality (Brookshabad) to assess the Aedes spp. infestation and subsequently test the efficacy of a community-based approach to control Aedes aegypti. An Aedes infestation larval survey was done with the assistance of community volunteers using the single larval survey (SLS) technique. House index, container index and Breteau index reflecting the relative prevalence and infestation levels were estimated. Various information, education and communication (IEC) campaign tools were developed to disseminate information about the prevalent situation. Several talks were organized to sensitize and motivate the people to realize the problem and participate in solving it. A two-pronged strategy, viz. environmental management through source reduction and anti-larval campaign using temephos was adopted to combat Aedes infestation through community involvement. Results. A total of 533 water-holding containers were searched for Aedes larvae, both indoors (188/533, 35.3%) and outdoors (345/533, 64.7%) from 104 (104/235, 44.3%) premises. Of these, 109 containers (95% CI 17.19%–24.03%) were found to support Aedes spp. larval breeding (20.45%). The Breteau index was 104.8%. Aedes aegypti predominated followed by Aedes albopictus. The most abundant water-holding containers supporting Aedes breeding were plastic, metal drums and cement tanks. These waterholding containers were targeted for temephos application by the community volunteers. Forty rounds of temephos applications were carried out during the study period. The number of containers supporting Aedes aegypti breeding reduced significantly within 1 month post-intervention by community volunteers. As a result the Breteau and house indices dropped from 104.8% to 2.7% and 44.23% to 2.6%, respectively. Thereafter, the indices remained at zero level till completion of the study. Conclusion. Larval indices indicate that Aedes aegypti is well established in peri-urban Brookshabad. Predominance of this mosquito species indicates infiltration into the peri-urban locality and beginning of displacement of Aedes albopictus. Epidemiologically, 3 categories of water-holding containers, viz. plastic, metal drums and cement tanks facilitate breeding of Aedes aegypti. Consequently, targeted source reduction as one way of selectively attacking the most important types of containers with temephos is feasible. Community involvement and networking with the residents allowed for a communitycentred approach to combat Aedes aegypti infestation. As an outcome of this approach, the larval indices reduced significantly and remained low. We suggest that a control strategy emphasizing the use of temephos through a community-centred approach should be considered for these islands. However, close monitoring of this approach is warranted for long term sustainability

Leptospirosis: an emerging global public health problem.

Leptospirosis has been recognized as an emerging global public health problem because of its increasing incidence in both developing and developed countries.A number of leptospirosis outbreaks have occurred in the past few years in various places such as Nicaragua, Brazil and India.Some of these resulted due to natural calamities such as cyclone and floods. It is a direct zoonotic disease caused by spirochetes belonging to different pathogenic species of the genus Leptospira. Large number of animals acts as carriers or vectors.Human infection results from accidental contact with carrier animals or environment contaminated with leptospires. The primary source of leptospires is the excretor animal, from whose renal tubules leptospires are excreted into the environment with the animal urine. Majority of leptospiral infections are either sub clinical or result in very mild illness and recover without any complications.However,a small proportion develops various complications due to involvement of multiple organ systems. In such patients, the clinical presentation depends upon the predominant organs involved and the case fatality ratio could be about 40% or more. Febrile illness with icterus, splenomegaly and nephritis (known as Weil's disease), acute febrile illness with severe muscle pain,febrile illness with pulmonary haemorrhages in the form of haemoptysis, jaundice with pulmonary haemorrhages, jaundice with heamaturea, meningitis with haemorrhages including sub conjunctival haemorrhage or febrile illness with cardiac arrhythmias with or without haemorrhages are some of the syndromes. Because of the protean manifestations of leptospirosis it is often misdiagnosed and under-reported. Although the basic principles of prevention such as source reduction,environmental sanitation, more hygienic work-related and personal practices etc., are same everywhere, there is no universal control method applicable to all epidemiological settings. Comprehensive understanding of the eco-epidemiological and cultural characteristics of a community that faces the problem of leptospirosis is an essential prerequisite for evolving an effective and acceptable control measure.

Transmission dynamics of diurnally subperiodic lymphatic filariasis transmitted by Ochlerotatus (Finlaya) niveus in the Andaman & Nicobar Islands.

BACKGROUND & OBJECTIVE: In India diurnally subperiodic filariasis is prevalent only in the Nicobar district of Andaman and Nicobar Islands, with significant health problem. Sample surveys indicated that this form of filariasis is restricted to a small region of Nancowry group of islands with Ochlerotatus niveus as the vector. We therefore carried out a comprehensive study to assess the transmission dynamics of LF in Teressa island in Nicobar district in view of its control and evaluation of interventions. METHODS: Entomological studies were carried out for a period of twelve months covering all the seasons in the year, by means of man landing catches in Teressa Island, an endemic island for this form of filariasis. Parameters viz., the annual biting rate (ABR), annual infective biting rate (AIBR), annual transmission index (ATI), risk of infection index (RII) and annual transmission potential (ATP), which reflect the dynamics and intensity of transmission of filariasis, were estimated. Host efficiency of Oc. niveus was also assessed. RESULTS: The number of vectors biting a person in a year was estimated to be 21851, of which 107 were harbouring infective parasite. Risk of infection intensity was 0.02332. Every person in this study area was at the risk of receiving an estimated number of 22 infective stage larvae per year. The host efficiency index of Oc. niveus indicated that over 40 per cent of the microfilariae ingested were able to develop into infective stages. The ATP was 169 with evidence of year round transmission. The pattern of monthly transmission potential suggested that the intensity of transmission was high during summer months. INTERPRETATION & CONCLUSION: Perennial transmission of subperiodic Wuchereria bancrofti in the typical forest ecosystem was evident in Teressa Island with transmission parameters suggesting that summer is a high risk season for transmission. Personal protection measure is the method of choice to protect from the risk of infection, because of day biting, exophilic and exophagic behaviour of the vector and larvae are not amenable to larvicidal measures. An alternative method to control the transmission would be to use selective or periodic mass chemotherapy to reduce the parasite load in this community.

Aedes aegypti (L) in Port Blair, Andaman and Nicobar islands-distribution and larval ecology.

A comprehensive survey was carried out in the Port Blair town in Andaman and Nicobar islands, in order to study the distribution and relative prevalence of Aedes aegypti during the monsoon (July'1997-October'1997) season using larval survey and adult collection methods. Ae. aegypti was found in all 21 localities surveyed. Spatial variations in distribution was evident which was closely related to population density. The nature of the larval habitats was observed to be similar in all the localities. For both outdoor and in-door containers, breeding preference ratio was highest for mud/brick/cement containers, followed by metal and plastic containers. These findings are correlated with water storage habits of the residents in the localities surveyed.

Efficacy of a Bacillus sphaericus formulation as influenced by the quality of Culex quinquefasciatus breeding waters.

To understand the physico-chemical factors that influence the efficacy of B. sphaericus formulation in the breeding sites of Culex quinquefasciatus, a study was carried out in Mayiladuturai area of Tamil Nadu (India). The factors studied were hydrogen ion concentration (pH), acidity, alkalinity, chlorides, phosphates, total hardness, sulphates, total solids, dissolved solids, suspended solids, nitrate nitrogen, ammoniacal nitrogen, dissolved oxygen, biological oxygen demand (BOD) and chemical oxygen demand (COD). Efficacy of the formulation was assessed in terms of reduction in larval population in the treated habitats. pH of water in the treated sites was around neutral range (mean +/- SD 7.65 +/- 0.23). Phosphate content was low (2.27 +/- 1.34 ppm) whereas chlorides (326.1 +/- 55.8 ppm) and sulphates (38.9 +/- 23.8 ppm) were high. Total hardness ranged from 206 to 462.5 ppm with a mean of 312.1 +/- 80.5 ppm. The chlorides and sulphates, though present in considerable quantity, did not have any influence on the efficacy of B. sphaericus formulation. However, the proportion of insoluble chlorides and sulphates which contribute to total hardness seemed to influence the formulation adversely.

Development of alginate-based slow release formulation of Bacillus sphaericus for controlling Culex quinquefasciatus.

Seven types of formulations were prepared as granules using the larvicidal factor of Bacillus sphaericus and different concentrations of calcium alginate which was used as matrix to immobilize and entrap the active ingredient (ai). All formulations were tested in disused wells against Culex quinquefasciatus at the rate of 15 kg ai per hectare. Among the seven types tested, the type 2 which contained 5% calcium alginate as immobilizing agent, exhibited the maximum larvicidal activity. Persistent control in breeding was noticed for 8 weeks with this formulation type.

Efficacy of Bacillus sphaericus in different breeding habitats of Culex quinquefasciatus.

'Spherifix', an alginate based slow release formulation of Bacillus sphaericus was field tested in different types of breeding habitats of Culex quinquefasciatus at the dose of 15 kg ai/ha at bimonthly interval. The efficacy of the formulation was higher in most of the months except in rainy and post-rainy months. The mean percentage reduction +/-SD during the treatment phase of one year was 31.2 +/- 17.9, 50 +/- 29.4, 28.3 +/- 17.6, 30.3 +/- 21.1, 66 +/- 22.5 and 53 +/- 20.4 in larval density and 49 +/- 20.8, 65.1 +/- 26.1, 30.3 +/- 21.9, 59.8 +/- 22.6, 63.1 +/- 21.9 and 47.7 +/- 24.2 in pupal density respectively in cement tanks, cesspools, cesspits, disused wells, unlined drains and cement lined drains. The reduction in immature density was relatively higher in undisturbed, debris free and shallow habitats such as cesspools, unlined drains and cement lined drains. After withdrawal of treatment, the effect of the formulation could be seen for a period of four months.

Little Andaman Island, a new focus of infection with nocturnally periodic Wuchereria bancrofti.

A filariasis survey was carried out for the first time in the Little Andaman island, covering a population of 12,247 in 12 of the 13 villages. Infection due to Wuchereria bancrofti was found only in 3 villages with microfilaria (mf) rate ranging from 1.02 to 6.45 per cent. Observations on the appearance of mf in peripheral blood showed that the parasite is nocturnally periodic form with a peak at 2000 h. The infection was prevalent only among the settlers from Bihar and Bangladesh and none of the local tribal population was affected. Carriers included 18 males and 4 females. Their age ranged from 6 to 50 yr. Only one of 2788 individuals examined was found to have clinical manifestation. A total of 442 female mosquitoes belonging to eight species were collected and dissected. Natural infection was found only in Culex quinquefasciatus (0.24%). Epidemiological investigations and vector studies indicates local transmission. Thus, this island appears as a new focus of infection.