, , ,

Malaria morbidity and mortality (1) is typically a function of:

  • Vector control as in control of malaria-infected mosquitoes.
  • Ease of access to medical service, accurate and timely diagnosis, and Artemisinin-based combination therapies.
  • Rural-to-Urban human population shift.
  • Clean housing, ample nutrition, hygienic water management.

In other words, more resources spent, better malaria control. After all, malaria and poverty go hand in hand. Obviously w.r.t. climate change, vector control or capacity of mosquitoes to breed and spread is the weakest link in the chain.

Increased emission of greenhouse gases into the atmosphere triggers climate change. In turn, this affects temperature, rainfall and relative humidity, the same variables that influence the habitats of vectors like mosquitoes (2, 3, 4).

  • More humans now live in cities, a change that in turn parallels the range of anthropophilic mosquitoes such as Aedes aegypti and Aedes albopictus (5).
  • For example, each degree increase in temperature per century has increased the Northern Italy and Alps habitat of the tiger mosquito, Aedes albopictus (6).
  • Tiger mosquito habitat is also expanding along the East and West coasts of the US (7).
  • The tiger mosquito in particular has relevance for human diseases because of key features that make it an optimal disease-spreading agent
    • Thrives in both urban and rural human habitats.
    • Flexible breeding sites.
    • Vast geographic range that includes both US coasts, Southern Europe, South America, Africa and Southern Asia.
  • During drought, again an increasing feature of climate change, we store water for longer periods, with fewer changes and cleaning, in turn leading to greater mosquito breeding and disease outbreaks (8, 9, 10).

Climate change and Malaria
Do temperature, rainfall and relative humidity affect malaria transmission? Epidemiological and lab studies suggest yes.

  • When annual average relative humidity is <60%, malaria transmission is strongly inhibited (11).
  • As temperatures increase, mosquitoes proliferate faster and bite more (12).
  • At 19oC, immature Plasmodium vivax takes 30 days to develop fully inside the mosquito At 28oC? Only 13 days (13).

Could climate change-related environment changes impact mosquito-borne diseases? Studies suggest yes.

  • One study (14) showed that coastal brackish water increases can influence mosquito-borne diseases in two ways
    • Increase local density of salt-tolerant mosquitoes like Anopheles sundaicus and Culex sitiens.
    • Make freshwater mosquitoes such as Anopheles culiefaciens, Anopheles stephensi, Aedes aegypti, Aedes albopictus salt-tolerant.
  • The compelling human relevance of this study?
    • For one, >50% of the global human population lives on land <60km from the seashore (14).
    • For another, coastal area population density is projected to increase from 87 persons per sq. km in 2000 to 134 persons per sq. km in 2050 (15).
    • Human population density is likely to increase particularly in tropical areas, where mosquito-borne diseases like malaria are already endemic.
    • Thus, as a result of climate change-related changes in relative water salinity, both mosquito breeding grounds and salt-adapted mosquito species could expand. In turn, they increase likelihood of spread of mosquito-borne diseases.
  • In the final analysis, climate change-related changes have the capacity to both augment and reduce spread of malaria as this table suggests (16; see figure below).

Climate change and Chikungunya
Let’s consider another mosquito-borne disease likely to spread due to climate change, Chikungunya.

  • With clinical symptoms similar to Dengue fever, this novel arbovirus was first isolated in 1952 among eastern Tanzania’s Makonde people suffering from a febrile illness similar to Dengue.
  • Named Chinkungunya which in the native Makonde language means ‘that which bends up‘, obviously a reference to the body contortions associated with its characteristic severe arthralgia (17, 18, 19).
    • ~2 to 6 days incubation following bite of an infected mosquito.
    • Starts with abrupt onset high fever for 1 to 7 days, crippling myalgias and lower back pain.
    • Severe arthralgias of ankles and wrists, conjunctivitis, maculopapular rash.
  • Infectious bites have a nearly 100% transmission rate (20).
  • Rarely fatal, complete recovery expected but with likely chronic arthritis for several months to years (21, 22).
  • For decades Chikungunya was known to cause episodic outbreaks in Africa, India and southeast Asia without much notice from global health monitors until 2005 when an outbreak on the French island of Reunion spread to India affecting at least 1.4 million people (23, 24, 25).
  • Many features were different about the 2005 outbreak
    • Mortality of 0.3 to 1/1000 symptomatic cases, much higher than in previous Chikungunya epidemics (26).
    • Hepatic failure, spontaneous hemorrhage, vertical mother-infant transmission (27, 28, 29).
    • Chronic, persistent arthritis with symptoms lasting even two years later (30, 31), leading to considerable disability, and public health and economic burden (32).
    • In the 2005 Reunion outbreak, Chikungunya switched vectors to the tiger mosquito, Aedes albopictus (33, 34). What are the implications of this switch?
    • Where previously, Chikungunya was primarily associated with woodland (sylvatic) mosquitoes such as Aedes africanus, A. furcifer, A. luteocephalus, A. neoafricanus, A. taylori (35, 36) that have limited habitat distribution, now it can spread faster and further, piggybacking on the vast range of the tiger mosquito (37, 38).
  • Is climate change the cause of Chikungunya’s increased severity? Maybe not. What’s apparent though is that its vector switch enables it to capitalize on the climate change-induced increased spread of Aedes albopictus. As a result, Chikungunya is likely to become endemic worldwide (5, 39, 40).

Climate change and Cholera

  • Vibrio cholerae, a bacterium, causes cholera. It associates with planktons and tiny crustaceans (copepods) for its survival, reproduction and transmission (41).
  • As sea surface temperatures rise, phytoplanktons increase, in turn causing the increase of cholera’s reservoir, i.e.  zooplanktons such as copepods (42).
  • For example, cholera outbreaks in coastal Bangladesh have been linked to plankton increases associated with local sea surface temperature increase (43).


  1. Gubler, Duane J., et al. “Climate variability and change in the United States: potential impacts on vector-and rodent-borne diseases.” Environmental health perspectives 109.Suppl 2 (2001): 223. Page on nih.gov)
  2. Bai, Li, Lindsay Carol Morton, and Qiyong Liu. “Climate change and mosquito-borne diseases in China: a review.” Global Health 9.10 (2013): 1-22.Page on biomedcentral.com
  3. Lee, Su Hyun, et al. “The effects of climate change and globalization on mosquito vectors: evidence from Jeju Island, South Korea on the potential for Asian Tiger Mosquito (Aedes albopictus) influxes and survival from Vietnam rather than Japan.” PloS one 8.7 (2013): e68512. Page on plosone.org
  4. Eisen, Lars, and Chester G. Moore. “Aedes (Stegomyia) aegypti in the continental United States: a vector at the cool margin of its geographic range.” Journal of medical entomology 50.3 (2013): 467-478.
  5. Le Anh, P. Nguyen, et al. “Abundance and prevalence of Aedes aegypti immatures and relationships with household water storage in rural areas in southern Viet Nam.” International health 3.2 (2011): 115-125.
  6. Roiz, David, et al. “Climatic factors driving invasion of the tiger mosquito (Aedes albopictus) into new areas of Trentino, northern Italy.” PLoS One 6.4 (2011): e14800. Page on plosone.org
  7. Rochlin, Ilia, et al. “Climate change and range expansion of the Asian tiger mosquito (Aedes albopictus) in Northeastern USA: implications for public health practitioners.” PloS one 8.4 (2013): e60874. Page on plosone.org
  8. Subra, R. “The regulation of preimaginal populations of Aedes aegypti L.(Diptera: Culicidae) on the Kenya coast. I. Preimaginal population dynamics and the role of human behaviour.” Annals of tropical medicine and parasitology 77.2 (1983): 195-201.
  9. Chretien, Jean-Paul, et al. “Drought-associated chikungunya emergence along coastal East Africa.” The American journal of tropical medicine and hygiene 76.3 (2007): 405-407. Page on usda.gov
  10. Islam, Mohammad Nazrul, et al. “Prevalence of Malaria, Dengue, and Chikungunya Significantly Associated with Mosquito Breeding Sites.” The Journal of IMA 43.2 (2011): 58. Page on researchgate.net
  11. Yang, Guo-Jing, et al. “Mapping and predicting malaria transmission in the People’s Republic of China, using integrated biology-driven and statistical models.” Geospatial health 5.1 (2010): 11-22. Page on geospatialhealth.net
  12. Epstein, Paul R. “Is global warming harmful to health?.” Scientific American 283.2 (2000): 50-57. Page on vcharkarn.com
  13. Liu, F. M., et al. “Effect of temperature on the development of Anopheles sinensis and the disease transmitted.” Chin J Vector Biol Cont 9 (1998): 185-187.
  14. Ramasamy, Ranjan, and Sinnathamby Noble Surendran. “Global climate change and its potential impact on disease transmission by salinity-tolerant mosquito vectors in coastal zones.” Frontiers in physiology 3 (2012). Page on nih.gov
  15. Page on unep.org
  16. Stanaway, Jeffrey D., and Jonathan D. Mayer. “Climate Variability and Change and Its Effects on Malaria.” Geography Research Forum. Vol. 31. 2011. Page on bgu.ac.il
  17. Robinson, Marion C. “An epidemic of virus disease in Southern Province, Tanganyika territory, in 1952–1953.” Transactions of the Royal Society of Tropical Medicine and Hygiene 49.1 (1955): 28-32. Page on suz.free.fr
  18. Mason, P. J., and A. J. Haddow. “An epidemic of virus disease in Southern Province, Tanganyika Territory, in 1952–1953: An additional note on Chikungunya virus isolations and serum antibodies.” Transactions of the Royal Society of Tropical Medicine and Hygiene 51.3 (1957): 238-240.
  19. Lumsden, W. H. R. “An epidemic of virus disease in Southern Province, Tanganyika territory, in 1952–1953 II. General description and epidemiology.” Transactions of the Royal Society of Tropical Medicine and Hygiene 49.1 (1955): 33-57.
  20. Burt, Felicity J., et al. “Chikungunya: a re-emerging virus.” The Lancet 379.9816 (2012): 662-671. Page on hospitalameijeiras.sld.cu
  21. Robinson, Marion C. “An epidemic of virus disease in Southern Province, Tanganyika territory, in 1952–1953.” Transactions of the Royal Society of Tropical Medicine and Hygiene 49.1 (1955): 28-32. Page on suz.free.fr
  22. Rodrigues, F. M., et al. “Etiology of the 1965 epidemic of febrile illness in Nagpur city, Maharashtra State, India.” Bulletin of the World Health Organization 46.2 (1972): 173. Page on whqlibdoc.who.int
  23. Chikungunya and Dengue in the south west Indian Ocean
  24. Renault, Philippe, et al. “A major epidemic of chikungunya virus infection on Reunion Island, France, 2005–2006.” The American journal of tropical medicine and hygiene 77.4 (2007): 727-731. A Major Epidemic of Chikungunya Virus Infection on Réunion Island, France, 2005-2006
  25. Pialoux, Gilles, et al. “Chikungunya, an epidemic arbovirosis.” The Lancet infectious diseases 7.5 (2007): 319-327. Page on hospitalameijeiras.sld.cu
  26. Burt, Felicity J., et al. “Chikungunya: a re-emerging virus.” The Lancet 379.9816 (2012): 662-671. Page on hospitalameijeiras.sld.cu
  27. Gérardin, Patrick, et al. “Multidisciplinary prospective study of mother-to-child chikungunya virus infections on the island of La Reunion.” PLoS Med 5.3 (2008): e60. Page on plosmedicine.org
  28. Economopoulou, A., et al. “Atypical Chikungunya virus infections: clinical manifestations, mortality and risk factors for severe disease during the 2005–2006 outbreak on Reunion.” Epidemiology and infection 137.04 (2009): 534-541. Page on edoc.rki.de
  29. Borgherini, Gianandrea, et al. “Outbreak of chikungunya on Reunion Island: early clinical and laboratory features in 157 adult patients.” Clinical Infectious Diseases 44.11 (2007): 1401-1407. Early Clinical and Laboratory Features in 157 Adult Patients
  30. Enserink, Martin. “Massive outbreak draws fresh attention to little-known virus.” Science 311.5764 (2006): 1085-1085.
  31. Queyriaux, Benjamin, et al. “Clinical burden of chikungunya virus infection.” The Lancet infectious diseases 8.1 (2008): 2-3)
  32. Gérardin, Patrick, et al. “Perceived morbidity and community burden after a Chikungunya outbreak: the TELECHIK survey, a population-based cohort study.” BMC medicine 9.1 (2011): 5. Page on biomedcentral.com
  33. Schuffenecker, Isabelle, et al. “Genome microevolution of chikungunya viruses causing the Indian Ocean outbreak.” PLoS Med 3.7 (2006): e263. Page on plosmedicine.org
  34. Charrel, Rémi N., Xavier de Lamballerie, and Didier Raoult. “Chikungunya outbreaks-the globalization of vectorborne diseases.” New England Journal of Medicine 356.8 (2007): 769. Page on researchgate.net
  35. Jupp, P. G., and B. M. McIntosh. “Aedes furcifer and other mosquitoes as vectors of chikungunya virus at Mica, northeastern Transvaal, South Africa.” J Am Mosq Control Assoc 6.3 (1990): 415-420. Page on biodiversitylibrary.org
  36. Diallo, Mawlouth, et al. “Vectors of Chikungunya virus in Senegal: current data and transmission cycles.” The American journal of tropical medicine and hygiene 60.2 (1999): 281-286. Page on ajtmh.org
  37. Rezza, G., et al. “Infection with chikungunya virus in Italy: an outbreak in a temperate region.” The Lancet 370.9602 (2007): 1840-1846.
  38. Pagès, Frédéric, et al. “Aedes albopictus mosquito: the main vector of the 2007 Chikungunya outbreak in Gabon.” PLoS One 4.3 (2009): e4691. Page on plosone.org
  39. Dhiman, Ramesh C., et al. “Climate change and threat of vector-borne diseases in India: are we prepared?.” Parasitology Research 106.4 (2010): 763-773;
  40. Ditsuwan, Thanittha, et al. “Assessing the spreading patterns of dengue infection and chikungunya fever outbreaks in lower southern Thailand using a geographic information system.” Annals of epidemiology 21.4 (2011): 253-261. Page on researchgate.net
  41. Lipp, Erin K., Anwar Huq, and Rita R. Colwell. “Effects of global climate on infectious disease: the cholera model.” Clinical microbiology reviews 15.4 (2002): 757-770. Page on paho.org
  42. Rita, R. “Cholera and climate: a demonstrated relationship.” Transactions of the American Clinical and Climatological Association 120 (2009): 119. Page on nih.gov
  43. Kanungo, S., et al. “Cholera in India: an analysis of reports, 1997-2006.” Bulletin of the World Health Organization 88.3 (2010): 185-191. Page on www.who.int