Effects of environmental change on emerging parasitic diseases

Abstract

Ecological disturbances exert an in¯uence on the emergence and proliferation of malaria and zoonotic parasitic diseases, including, Leishmaniasis, cryptosporidiosis, giardiasis, trypanosomiasis, schistosomiasis, ®lariasis, onchocerciasis, and loiasis. Each environmental change, whether occurring as a natural phenomenon or through human intervention, changes the ecological balance and context within which disease hosts or vectors and parasites breed, develop, and transmit disease. Each species occupies a particular ecological niche and vector species sub-populations are distinct behaviourally and genetically as they adapt to man-made environments. Most zoonotic parasites display three distinct life cycles: sylvatic, zoonotic, and anthroponotic. In adapting to changed environmental conditions, including reduced nonhuman population and increased human population, some vectors display conversion from a primarily zoophyllic to primarily anthrophyllic orientation. Deforestation and ensuing changes in landuse, human settlement, commercial development, road construction, water control systems (dams, canals, irrigation systems, reservoirs), and climate, singly, and in combination have been accompanied by global increases in morbidity and mortality from emergent parasitic disease. The replacement of forests with crop farming, ranching, and raising small animals can create supportive habitats for parasites and their host vectors. When the landuse of deforested areas changes, the pattern of human settlement is altered and habitat fragmentation may provide opportunities for exchange and transmission of parasites to the heretofore uninfected humans. Construction of water control projects can lead to shifts in such vector populations as snails and mosquitoes and their parasites. Construction of roads in previously inaccessible forested areas can lead to erosion, and stagnant ponds by blocking the¯ow of streams when the water rises during the rainy season. The combined effects of environmentally detrimental changes in local landuse and alterations in global climate disrupt the natural ecosystem and can increase the risk of transmission of parasitic diseases to the human population. q

A comparative evaluation of endemic and non-endemic region of visceral leishmaniasis (Kala-azar) in India with ground survey and space technology

“…The physiographical characteristics of the surface environment derived from the land cover data play an important role in the dynamics of leishmaniasis transmission (Defries & Townshend 1999). Different land cover classification approaches vary in their potential for discernment and consequently in their utility for meeting specific needs (e.g., the identification of all examples of a particular habitat) (Rogers 1991, Patza et al 2000, Franklin & Wulder 2002. FA analysis results corroborated breeding preferences of P. argentipes by landscape elements.…”

Serologic evidence of Leishmania infection in free-ranging wild and domestic canids around a Brazilian National Park

“…Environmental changes influencing this transmission can be of natural or anthropogenic origin, including human activities expansion, habitat fragmentation, reforestation, climate warming and pollution, and the emergence of diseases also involve biodiversity loss and increasing emergence and incidence of zoonosis (Patz et al 2000, Daszak et al 2001.…”

“…Courtenay et al 1994). Although it is a confirmed natural reservoir, and many times blamed for supporting the wild and peri-urban disease cycle (see Patz et al 2000), the crab-eating fox is not important for the maintenance of leishmaniasis, contributing with only 9% of the transmission, while domestic dogs contribute with 91% (Courtenay et al 2002). These authors propose that C. thous populations cannot maintain the transmission cycle independently without the presence of domestic dogs, and is improbable that they introduce the parasite into infection-free dog populations.…”

Ocorrência de Giardia, Cryptosporidium e microsporídios em animais silvestres em área de desmatamento no Estado de São Paulo, Brasil

“…As alterações ambientais, aqui representadas pelo desmatamento para a construção de duas represas, podem comprometer nichos ecológicos de forma a criar condições que permitam a disseminação de doenças, incluindo as zoonoses parasitárias (PATZ et al, 2000). Nesse sentido, a identificação de agentes patogênicos nos animais de áreas que sofreram tais intervenções pode ser fundamental para o entendimento de sua epidemiologia e até mesmo para a adoção de medidas preventivas.…”