Does the roof type of a house influence the presence of adult Anopheles stephensi, urban malaria vector? - evidence from a few slum settings in Chennai, India

Our plain-English summary of Does the roof type of a house influence the presence of adult Anopheles stephensi, urban malaria vector? - evidence from a few slum settings in Chennai, India, by S. Ravishankaran, A. Asokan, N.A.J.A. Justin, et al (Parasitology Research, 2022).

The study

• Authors: S. Ravishankaran, A. Asokan, N.A.J.A. Justin, S. Thomas, V. Joshua, M.T. Mathai, A. Eapen
• Journal: Parasitology Research
• Published: 2022;121(1):105-114
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

In an urban setting, it is a difficult task to collect adult Anopheles stephensi, unlike the immature stages, due to various reasons. A longitudinal study was undertaken from January 2016 to April 2017, with CDC light traps to collect adult Anopheles stephensi and other mosquito species in houses located in a few slums of Chennai, India. A total of 203 trap collections were made indoors from human dwellings having different roof types, as well as outdoors. Three to four trap collections were made at night (18:00 to 06:00 h) once a week. Overall, Culex quinquefasciatus (64%) was the predominant mosquito species captured, followed by An. stephensi (24%). In 98 of the 203 trap collections (48.3%), at least one female An. stephensi was trapped. In all, 224 female An. stephensi were trapped, of which the majority were collected during monsoon and winter seasons. Compared to outdoors, 10% more An. stephensi, the majority of them unfed, were collected indoors, with relatively more contribution coming from asbestos-roofed houses (71.4%), followed by thatched-roof houses (47.3%). Overall, 2.2% positivity for Plasmodium vivax was detected in An. stephensi through Circumsporozoite-ELISA. Binary logistic regression model indicated that season (winter and monsoon), asbestos-roofed dwelling, lesser number of rooms in a house, and more members in a family were significant predictor variables for the odds of trapping an An. stephensi. The study brought out significant factors associated with the presence of An. stephensi in urban slums setting in Chennai, where malaria is declining. The findings would help in devising targeted, effective vector control interventions for malaria elimination in urban settings.

© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.

In plain English

This study concerned malaria mosquitoes, not asbestos health effects. Asbestos appeared mainly as a roofing material. From January 2016 to April 2017, the authors ran overnight light traps inside and outside houses in three slums of Chennai, India, to catch the mosquito Anopheles stephensi. Of 203 trap collections, 98 (48.3%) caught at least one female An. stephensi. Altogether 224 females were caught, 124 indoors and 100 outdoors. The mosquito was caught in 15 of 21 collections at asbestos-roofed houses, in 79 of 167 at thatched-roof houses and in none at tiled-roof houses. Five of the 224 (2.2%) tested positive for Plasmodium vivax. In a statistical model, the odds of trapping the mosquito were higher in winter and monsoon than summer, in houses with fewer rooms and in larger households. Compared with non-asbestos roofs (thatched, tiled and concrete), asbestos roofs had an odds ratio of 5.67 (95% confidence interval 1.64 to 19.56). Indoor versus outdoor placement was not statistically significant. The authors concluded that this mosquito preferred asbestos and thatched roofs because they offered easier entry and room to hide.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Longitudinal field study collecting mosquitoes with CDC miniature light traps, analysed with chi-square tests and binary logistic regression
• Who was studied: Mosquitoes trapped in and around houses in three urban slums of Besant Nagar, Chennai, India (Ururkuppam, Odaikuppam and Kakkan Colony), January 2016 to April 2017. There were 203 light trap collections: 107 indoors and 96 outdoors.
• Exposure: Not an asbestos exposure study. The factor compared was house roof type (thatched, tiled, asbestos, concrete), grouped as asbestos versus non-asbestos for analysis. Season, indoor or outdoor placement, number of rooms, household size and weather were also examined.
• Main results:
  • At least one An. stephensi was trapped in 98 of 203 collections (48.3%).
  • 964 mosquitoes of all species were collected, including 224 (23.2%) female An. stephensi.
  • Indoor collections caught 124 An. stephensi and outdoor collections caught 100.
  • An. stephensi was captured at 71.4% (15/21) of asbestos-roofed houses and at 47.3% (79/167) of thatched-roof houses (chi-square test, p=0.03).
  • No An. stephensi were trapped at tiled-roof houses.
  • Unfed mosquitoes were the largest group of trapped An. stephensi (43.8%).
  • Of the 224 An. stephensi tested by ELISA, five (2.2%) were positive for Plasmodium vivax.
  • In the logistic regression, asbestos-roofed houses had an odds ratio of 5.665 (95% CI 1.64 to 19.564, p .006) for trapping An. stephensi. The comparison group was non-asbestos roofs (thatched, tiled and concrete).
  • Compared with summer, winter had an odds ratio of 10.31 (CI 1.93 to 55.11) for trapping An. stephensi.
  • Compared with houses of 3 or more rooms, one-room houses had an odds ratio of 5.28 (CI 1.95 to 14.34). Households with 5 or more members were also associated with higher odds.
  • Indoor versus outdoor trap placement was not statistically significant in the model (odds ratio 1.089, 95% CI 0.529 to 2.24, p .817).
• The authors' conclusion: The authors concluded that asbestos and thatched structures were the preferred roofs for An. stephensi, because these roofs allowed easier entry and gave space for hiding.
• Limitations the authors state:
  • Trap placement was not uniform across months and dwelling types, because of operational difficulties.
  • No blood meal analysis was done on fed mosquitoes, because the specimens were damaged and might have been contaminated.

Related studies

• Resting and feeding preferences of Anopheles stephensi in an urban setting, perennial for malaria — S. Thomas, S. Ravishankaran, et al. (2017)
• Impact of climate change on temperature variations and extrinsic incubation period of malaria parasites in Chennai, India: implications for its disease transmission potential — P.K. Kripa, P.S. Thanzeen, et al. (2024)
• Immunopathological effects of malaria pigment or hemozoin and other crystals — A. Tyberghein, K. Deroost, et al. (2014)
• Does the Presence of Asbestos-Containing Materials in Buildings Post-construction and Before Demolition Have an Impact on the Exposure to Occupants in Non-occupational Settings? — R. Singh, A.L. Frank (2023)
• A neglected aspect of the epidemiology of sleeping sickness: the propensity of the tsetse fly vector to enter houses — G.A. Vale, A. Chamisa, et al. (2013)
• Identifying predictors of personal exposure to air temperature in peri-urban India — C. Milà, A. Curto, et al. (2020)

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