Impact of climate change on temperature variations and extrinsic incubation period of malaria parasites in Chennai, India: implications for its disease transmission potential

Our plain-English summary of Impact of climate change on temperature variations and extrinsic incubation period of malaria parasites in Chennai, India: implications for its disease transmission potential, by P.K. Kripa, P.S. Thanzeen, N. Jaganathasamy, et al (Parasites & Vectors, 2024).

The study

• Authors: P.K. Kripa, P.S. Thanzeen, N. Jaganathasamy, S. Ravishankaran, A.R. Anvikar, A. Eapen
• Journal: Parasites & Vectors
• Published: 2024;17(1):134
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: The global temperature has significantly risen in the past century. Studies have indicated that higher temperature intensifies malaria transmission in tropical and temperate countries. Temperature fluctuations will have a potential impact on parasite development in the vector Anopheles mosquito.

Methods: Year-long microclimate temperatures were recorded from a malaria-endemic area, Chennai, India, from September 2021 to August 2022. HOBO data loggers were placed in different vector resting sites including indoor and outdoor roof types. Downloaded temperatures were categorised by season, and the mean temperature was compared with data from the same study area recorded from November 2012 to October 2013. The extrinsic incubation period for Plasmodium falciparum and P. vivax was calculated from longitudinal temperatures recorded during both periods. Vector surveillance was also carried out in the area during the summer season.

Results: In general, temperature and daily temperature range (DTR) have increased significantly compared to the 2012-2013 data, especially the DTR of indoor asbestos structures, from 4.30 ℃ to 12.62 ℃ in 2021-2022, unlike the marginal increase observed in thatched and concrete structures. Likewise, the average DTR of outdoor asbestos structures increased from 5.02 ℃ (2012-2013) to 8.76 ℃ (2021-2022) although the increase was marginal in thatched structures and, surprisingly, showed no such changes in concrete structures. The key finding of the extrinsic incubation period (EIP) is that a decreasing trend was observed in 2021-2022 compared to 2012-2013, mainly in indoor asbestos structures from 7.01 to 6.35 days, which negatively correlated with the current observation of an increase in temperature. Vector surveillance undertaken in the summer season revealed the presence of Anopheles breeding in various habitats. Anopheles stephensi could be collected using CDC light traps along with other mosquito species.

Conclusion: The microclimate temperature has increased significantly over the years, and mosquitoes are gradually adapting to this rising temperature. Temperature negatively correlates with the extrinsic incubation period of the parasite. As the temperature increases, the development of the parasite in An. stephensi will be faster because of a decrease in EIP, thus requiring relatively fewer days, posing a risk for disease transmission and a hindrance to malaria elimination efforts.

© 2024. The Author(s).

In plain English

This study from Chennai, India, is about malaria, not asbestos disease. "Asbestos" here is one of three roof types (thatched, asbestos and concrete) where temperatures were measured. From September 2021 to August 2022, the authors placed 18 temperature and humidity loggers indoors and outdoors at mosquito resting sites in Besant Nagar. They compared the readings with their 2012–2013 data from the same area. Using a degree-day formula, they calculated the extrinsic incubation period: how long malaria parasites (Plasmodium vivax and P. falciparum) take to develop inside mosquitoes. They also surveyed mosquitoes in summer. The average daily temperature range under indoor asbestos roofs rose from 4.30 °C to 12.62 °C, and outdoors from 5.02 °C to 8.76 °C. Changes under thatched and concrete roofs were smaller or absent. The average incubation period under indoor asbestos roofs fell from 7.01 to 6.35 days, but rose slightly under indoor thatched roofs. Anopheles stephensi was found breeding and in light traps. The authors concluded that rising temperature shortens parasite development and poses a transmission risk. They noted that no experiment with infected mosquitoes was done.

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: Field microclimate monitoring study compared with the authors' earlier 2012–2013 data from the same area, with degree-day calculation of the parasite extrinsic incubation period and summer mosquito surveillance
• Who was studied: Mosquito resting sites in human dwellings in Besant Nagar, Chennai, India, monitored with 18 data loggers (three replicates per roof type, indoors and outdoors) from September 2021 to August 2022, compared with November 2012 to October 2013 data; 518 mosquito breeding habitats surveyed
• Exposure: Microclimate temperature and relative humidity under thatched, asbestos and concrete roofs, indoors and outdoors; asbestos is a roofing material category, not an exposure studied for health effects
• Main results:
  • Average daily temperature range for indoor asbestos structures rose from 4.30 °C in 2012–2013 to 12.62 °C in 2021–2022
  • Average daily temperature range for indoor thatched structures rose marginally, from 4.08 °C to 5.55 °C
  • Average daily temperature range for indoor concrete structures rose from 1.93 °C to 2.95 °C
  • Average daily temperature range for outdoor asbestos structures rose from 5.02 °C in 2012–2013 to 8.76 °C in 2021–2022
  • Average daily temperature range for outdoor concrete structures showed no change (4.46 °C)
  • Average extrinsic incubation period for indoor asbestos structures fell from 7.01 days in 2012–2013 to 6.35 days in 2021–2022
  • Average extrinsic incubation period for indoor thatched structures rose slightly, from 7.57 to 7.74 days
  • Average extrinsic incubation period inside concrete structures fell from 7.10 to 6.96 days
  • In 2021–2022, the highest indoor temperature was under asbestos roofs in summer (34.92 plus or minus 1.78 °C)
  • Temperatures at the local transmission sites were at least 3–4 °C warmer than weather station data
  • Of 518 breeding habitats surveyed, 79 (15.2%) had anopheline mosquitoes; the adults that emerged were An. stephensi
  • Adult collections: one An. stephensi in resting collections, no anophelines in pyrethrum spray collections, and in light traps An. stephensi (8), An. pallidus (3) and An. subpictus (1)
• The authors' conclusion: The authors concluded that the parasite incubation period is negatively correlated with temperature. In their view, global warming and rising temperatures will make parasite development faster, posing a risk for malaria transmission and possibly hindering elimination efforts.
• Limitations the authors state:
  • No real-time experiment exposing infected mosquitoes to varying daily temperatures was conducted, so the implications of the observations are difficult to derive
  • Paaijmans' temperature model could not be used because recorded temperatures exceeded the model's critical upper temperature, so Detinova's degree-day model was used instead
  • Because of COVID-19-related disruption of technical services, few malaria cases were reported in the area during the study period

Topics

Medical terms in this study, explained in our Lexicon: Endemic.

Related studies

• 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 — S. Ravishankaran, A. Asokan, et al. (2022)
• Resting and feeding preferences of Anopheles stephensi in an urban setting, perennial for malaria — S. Thomas, S. Ravishankaran, et al. (2017)
• Immunopathological effects of malaria pigment or hemozoin and other crystals — A. Tyberghein, K. Deroost, et al. (2014)
• Identifying predictors of personal exposure to air temperature in peri-urban India — C. Milà, A. Curto, et al. (2020)
• Phagocytosis of hemozoin (native and synthetic malaria pigment), and Plasmodium falciparum intraerythrocyte-stage parasites by human and mouse phagocytes — P. Olliaro, L. Lombardi, et al. (2000)
• Extreme temperatures, foundation species, and abrupt ecosystem change: an example from an iconic seagrass ecosystem — J.A. Thomson, D.A. Burkholder, et al. (2015)

Browse return to medical research.