Environmental Changes and Infectious Disease

1. Environmental Changes and Infectious Disease

2. Introduction • Changes in the ecosystem contribute to infectious disease in some regions of the world. • Caused by either natural occurrence or through human interference. • Developing nations in Sub-Sahara Africa, Latin America, South America, and Asia are primarily affected by these environmental changes.

3. Overview of environmental changes • Climate: • Temperature • Rise in average temperatures • Rainfall • Increase in precipitation • Intense weather patterns: • Heat waves • Droughts • Floods

4. Overview of environmental changes con’t • Land • Deforestation • Loss of trees in tropical rainforests • Soil degradation: • Soil erosion • Overgrazing and cultivation • Construction • Human settlements • Roads

5. Factors influencing environmental changes • Global warming: • Emission of “greenhouse gases” by automobiles, industrial factories, and other sources. • Agricultural development: • Clearing of forests for farming and ranching. • Efforts to irrigate water-poor lands.

6. Factors influencing environmental changes con’t • Human intrusion into environment: • Construction of reservoirs, dams, and roads to accommodate development. • Logging of tropical forests. • Expansion of human population.

7. Specific infectious diseases • Vector-borne: • Mosquito • Malaria • Yellow fever • Dengue fever • Filariasis • West Nile virus

8. Infectious disease con’t • Other vectors • Leishmaniasis (sand flies) • Trypanosomiasis (Tsetse fly) • Onchocerciasis (Blackfly) • Loiasis (Chrysops fly) • Lyme Disease (Deer tick)

9. Filariasis (elephantiasis) Vector: Mosquitoes, Blackflies

10. LeishmaniasisVector: Sand fly Symptoms: Ulcers and wearing away (erosion) in the mouth, tongue, gums, lips, nose, and inner nose

11. Trypanosomaisis (Sleeping SicknessVector: Tsetse Fly Symptoms: high fever, weakness and headache, joint pains and pruritus (itching). Eventually patients central nervous system invaded causing sleep-like unconsciousness leading to death.

12. Onchocerciasis (River Blindness) Vector: Black Flies In addition to visual impairment or blindness, onchocerciasis causes skin disease, including nodules under the skin or debilitating itching.

13. Lyme DiseaseVector: Ticks High Lyme Disease risk Woodland suburban housing (NE USA) High tick density and high tick infection prevalence  infected deer Complex life- cycle of tick Many competent reservoir species  less dilution by incompetent reservoir species Expanding mouse populations Less diversity of vertebrate predators and viral hosts Poor inter-species regulation Forest fragmentation, hunting (wolves, passenger pigeons) Adapted from: R. Ostfeld

14. Malaria Vector: Mosquitoes Symptoms: high fevers, shaking chills, and flu-like illness. Causes anemia leading to death in some cases

15. Connecting environmental changes to infectious disease • Environmental changes can adversely affect human health by providing: • Breeding areas and habitat for vectors and animal intermediates. • Adaptation of vectors to new habitats. • Increased interaction between pathogen and host.

16. Impact of environmental changes on infectious disease • Temperature and rainfall: • Small increases in existing low temperatures have been shown to exert increased transmission of malaria. • Malaria incidence is on the rise in higher altitude areas, such as highlands, due to temperature changes. Source: Patz, et. al. (2000)

17. Deforestation

18. Impact of environmental changes on infectious disease con’t • Deforestation: • Causes resurgence of malaria, yellow fever and other mosquito-borne viruses. • Poor, subsistence farmers cutting down more tropical rainforests to have more land to cultivate creates more breeding opportunities for mosquitoes carrying malaria. )

19. Impact of environmental changes on infectious disease con’t • Removal of the forest canopy has created pools for the expansion of mosquito breeding habitats. • New mosquito species, such as An. Gambiae, have become associated with malaria transmission around deforested areas. • The removal of intact forest has resulted in the emergence of newly recognized pathogens. • Human activity in previously inaccessible areas provides more interaction between vectors and hosts Source: Norris

20. Impact of environmental changes on infectious disease con’t • Replacement of deforested areas with cocoa, coffee, oil palms, or mango trees provide a habitat for tsetse flies. • Deforestation decreases predators that would otherwise keep hosts of the Lyme disease tick population down. Source: Patz, et. al.

21. Impact of environmental changes on infectious disease con’t • Urbanization: • Storm water handling systems provide breeding sites for mosquitoes when surface waters are scarce. . • Discard materials, such as tires, cans, and barrels can provide a breeding habitat for mosquitoes. Source: Norris (2004).

22. Impact of environmental changes on infectious disease con’t • Other impacts:. • Movement by humans, who do not have protective immunity and are unaware of preventive measure against vectors, in remote areas. • Animal and vector adaptability to changing environments and competition among species. Source: Part, et. al.

23. Conclusion • Without a doubt, the changes in the world’s ecosystems contribute to the cycle of infectious disease. • In particular, human activities, such as deforestation, increased development agricultural lands, and movement of humans into previously inaccessible areas. • Changes in climate, such as greater rainfall, are another driver for increased cases of infectious disease.

24. Conclusion con’t • Human activities and natural occurrences provide habitats for vectors and reservoirs, but also allow humans and animals more contact with infectious disease.

25. References • Norris, D. E. (2004). Mosquito-borne Diseases as a Consequence of Land Use Change. EcoHealth, 1, 19-24. • Patz, J.A., et. al. (2000). Effects on Environmental Change on Emerging Parasitic Disease. International Journal for Parasitiology, 30, 1395- 1405. • Sutherst, R. W. (2001). The Vulnerability of Animal and Human Health to Parasites Under Global Change. International Journal for Parasitology, 31, 933-948.

26. Adapted from Powerpoint presentation by William R. Barnett • PUBH 605