Climate Change And Vector Borne Diseases Ppt To Pdf
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Climate change is expected to alter the geographic and seasonal distributions of existing vectors and vector-borne diseases [Likely, High Confidence]. Ticks capable of carrying the bacteria that cause Lyme disease and other pathogens will show earlier seasonal activity and a generally northward expansion in response to increasing temperatures associated with climate change [Likely, High Confidence]. Longer seasonal activity and expanding geographic range of these ticks will increase the risk of human exposure to ticks [Likely, Medium Confidence].
Rising temperatures, changing precipitation patterns, and a higher frequency of some extreme weather events associated with climate change will influence the distribution, abundance, and prevalence of infection in the mosquitoes that transmit West Nile virus and other pathogens by altering habitat availability and mosquito and viral reproduction rates [Very Likely, High Confidence]. Alterations in the distribution, abundance, and infection rate of mosquitoes will influence human exposure to bites from infected mosquitoes, which is expected to alter risk for human disease [Very Likely, Medium Confidence].
Vector-borne pathogens are expected to emerge or reemerge due to the interactions of climate factors with many other drivers, such as changing land-use patterns [Likely, High Confidence]. The impacts to human disease, however, will be limited by the adaptive capacity of human populations, such as vector control practices or personal protective measures [Likely, High Confidence].
Beard, C. Eisen, C. Barker, J. Garofalo, M. Hahn, M. Hayden, A. Monaghan, N. Ogden, and P. Schramm, Ch. Vector-borne diseases are illnesses that are transmitted by vectors , which include mosquitoes, ticks, and fleas.
These vectors can carry infective pathogens such as viruses, bacteria , and protozoa , which can be transferred from one host carrier to another. In the United States, there are currently 14 vector-borne diseases that are of national public health concern. These diseases account for a significant number of human illnesses and deaths each year and are required to be reported to the National Notifiable Diseases Surveillance System at the Centers for Disease Control and Prevention CDC.
In , state and local health departments reported 51, vector-borne disease cases to the CDC Table 5. Case counts are summarized based on annual reports of nationally notifiable infectious diseases.
Median and range values encompass cases reported from to for babesiosis and from to for dengue. Vectors and hosts involved in the transmission of these infective pathogens are sensitive to climate change and other environmental factors which, together, affect vector-borne diseases by influencing one or more of the following: vector and host survival, reproduction, development, activity, distribution, and abundance; pathogen development, replication, maintenance, and transmission; geographic range of pathogens, vectors, and hosts; human behavior; and disease outbreak frequency, onset, and distribution.
The seasonality, distribution, and prevalence of vector-borne diseases are influenced significantly by climate factors, primarily high and low temperature extremes and precipitation patterns. Collectively, these changes may contribute to an increase in the risk of the pathogen being carried to humans.
Climate change is likely to have both short- and long-term effects on vector-borne disease transmission and infection patterns, affecting both seasonal risk and broad geographic changes in disease occurrence over decades.
However, models for predicting the effects of climate change on vector-borne diseases are subject to a high degree of uncertainty , largely due to two factors: 1 vector-borne diseases are maintained in nature in complex transmission cycles that involve vectors, other intermediate zoonotic hosts, and humans; and 2 there are a number of other significant social and environmental drivers of vector-borne disease transmission in addition to climate change. For example, while climate variability and climate change both alter the transmission of vector-borne diseases, they will likely interact with many other factors, including how pathogens adapt and change, the availability of hosts, changing ecosystems and land use , demographics, human behavior, and adaptive capacity.
The risk of introducing exotic pathogens and vectors not currently present in the United States, while likely to occur, is similarly difficult to project quantitatively. These include West Nile virus, dengue virus, and chikungunya virus. In the case of the dengue outbreak in southern Florida, climate change was not responsible for the reintroduction of the virus in this area, which arrived via infected travelers from disease- endemic regions of the Caribbean.
This chapter presents case studies of Lyme disease and West Nile virus infection in relation to weather and climate. Although ticks and mosquitoes transmit multiple infectious pathogens to humans in the United States, Lyme disease and West Nile virus infection are the most commonly reported tick-borne and mosquito-borne diseases in this country Table 5. In addition, a substantial number of studies have been conducted to elucidate the role of climate in the transmission of these infectious pathogens.
These broad findings, together with the areas of uncertainty from these case studies, are generalizable to other vector-borne diseases. In the eastern United States, Lyme disease is transmitted to humans primarily by blacklegged deer ticks. Lyme disease is a tick-borne bacterial disease that is endemic commonly found in parts of North America, Europe, and Asia. It is primarily transmitted to humans in the eastern United States by the tick species Ixodes scapularis formerly I.
If left untreated, infection can spread to joints, the heart, and the nervous system. Although the reported incidence of Lyme disease is greater in the eastern United States compared with the westernmost United States, 20 , 21 in both geographical regions, nymphs small immature ticks are believed to be the life stage that is most significant in pathogen transmission from infected hosts primarily rodents to humans Figure 5. The summer is a period of parallel increased activity for both blacklegged and western blacklegged ticks in the nymphal life stage the more infectious stage and for human recreational activity outdoors.
Infection rates in humans vary significantly from year to year. The geographic and seasonal distributions of Lyme disease case occurrence are driven, in part, by the life cycle of vector ticks Figure 5. Humans are only exposed to Lyme disease spirochetes B. Aside from short periods of time when they are feeding on hosts less than three weeks of their two- to three-year life cycle , ticks spend most of their lives off of hosts in various natural landscapes such as woodlands or grasslands where weather factors including temperature, precipitation, and humidity affect their survival and host-seeking behavior.
In general, both low and high temperatures increase tick mortality rates, although increasing humidity can increase their ability to tolerate higher temperatures.
In summary, weather-related variables can determine geographic distributions of ticks and seasonal activity patterns. However, the importance of these weather variables in Lyme disease transmission to humans compared with other important predictors is likely scale-dependent. In general, across the entire country, climate-related variables often play a significant role in determining the occurrence of tick vectors and Lyme disease incidence in the United States for example, Lyme disease vectors are absent in the arid Intermountain West where climate conditions are not suitable for tick survival.
However, within areas where conditions are suitable for tick survival, other variables for example, landscape and the relative proportions within a community of zoonotic hosts that carry or do not carry Lyme disease-causing bacteria are more important for determining tick abundance, infection rates in ticks, and ultimately human infection rates.
Because the presence of tick vectors is required for B. Minimum temperature appears to be a key variable in defining the geographic distribution of blacklegged ticks. The probability of a given geographic area being suitable for tick populations increases as minimum temperature rises. Maximum temperatures also significantly affect where blacklegged ticks live. Declines in rainfall amount and humidity are also important in limiting the geographic distribution of blacklegged ticks.
Ticks are more likely to reside in moister areas because increased humidity can increase tick survival. Climate variables have been shown to be strong predictors of geographic locations in which blacklegged ticks reside, but less important for determining how many nymphs live in a given area or what proportion of those ticks is infected. For example, in a single county in northern coastal California with strong climate gradients, warmer areas with less variation between maximum and minimum monthly water vapor in the air were characteristic of areas with elevated concentrations of infected nymphs.
Though there are links between climate and tick distribution, studies that look for links between weather and geographical differences in human infection rates do not show a clear or consistent link between temperature and Lyme disease incidence. Temperature and precipitation both influence the host-seeking activity of ticks, which may result in year-to-year variation in the number of new Lyme disease cases and the timing of the season in which Lyme disease infections occur.
However, identified associations between precipitation and Lyme disease incidence, or temperature and Lyme disease incidence, are limited or weak. Birds such as the house finch are the natural host of West Nile virus. The peak period when ticks are seeking hosts starts earlier in the warmer, more southern, states than in northern states.
The effects of temperature and humidity or precipitation on the seasonal activity patterns of nymphal western blacklegged ticks is more certain than the impacts of these factors on the timing of Lyme disease case occurrence. Host-seeking activity ceases earlier in the season in cooler and more humid conditions. In many woodlands, ticks can find refuge from far-subzero winter air temperatures in the surface layers of the soil.
To project accurately the changes in Lyme disease risk in humans based on climate variability, long-term data collection on tick vector abundance and human infection case counts are needed to better understand the relationships between changing climate conditions, tick vector abundance, and Lyme disease case occurrence. West Nile virus is maintained in transmission cycles between birds the natural hosts of the virus and mosquitoes Figure 5.
The number of birds and mosquitoes infected with WNV increases as mosquitoes pass the virus from bird to bird starting in late winter or spring. Human infections can occur from a bite of a mosquito that has previously bitten an infected bird. Mosquito vectors and bird hosts are required for WNV to persist, and the dynamics of both are strongly affected by climate in a number of ways.
Geographical variation in average climate constrains the ranges of both vectors and hosts, while shorter-term climate variability affects many aspects of vector and host population dynamics. Unlike ticks, mosquitoes have short life cycles and respond more quickly to climate drivers over relatively short timescales of days to weeks. Impacts on bird abundance are often realized over longer timescales of months to years due to impacts on annual reproduction and migration cycles.
WNV has been detected in 65 mosquito species and more than bird species in the United States, 85 although only a relatively small number of these species contribute substantively to human infections. Three Culex Cx. Bird species that contribute to WNV transmission include those that develop sufficient viral concentrations in their blood to transmit the virus to feeding mosquitoes.
Impacts of Climate and Weather. WNV is an invasive pathogen that was first detected in the United States just over 15 years ago, which is long enough to observe responses of WNV to key weather variables, but not long enough to observe responses to climate change trends. Climate change may influence mosquito survival rates through changes in season length, although mosquitoes are also able to adapt to changing conditions.
For example, mosquitoes that transmit WNV are limited to latitudes and altitudes where winters are short enough for them to survive. Even during diapause, very harsh winters may reduce mosquito populations, as temperatures near freezing have been shown to kill diapausing Cx. During the warmer parts of the year, Culex mosquitoes must have aquatic habitat available on a nearly continuous basis because their eggs hatch within a few days after they are laid and need moisture to remain viable. The breeding habitats of WNV vectors vary by species, ranging from fresh, sunlit water found in irrigated crops and wetlands preferred by Cx.
WNV has become endemic within a wide range of climates in the United States, but there is substantial geographic variation in the intensity of virus transmission. Part of this geographic variation can be attributed to the abundance and distributions of suitable bird hosts. Climate change has already begun to cause shifts in bird breeding and migration patterns, 99 but it is unknown how these changes may affect WNV transmission. Temperature is the most studied climate driver of the dynamics of WNV transmission.
It is clear that warm temperatures accelerate virtually all of the biological processes that affect transmission: accelerating the mosquito life cycle, , , , , increasing the mosquito biting rates that determine the frequency of contact between mosquitoes and hosts, , and increasing viral replication rates inside the mosquito that decrease the time needed for a blood-fed mosquito to be able to pass on the virus.
Precipitation can create aquatic breeding sites for WNV vectors, , and in some areas snowpack increases the amount of stored water available for urban or agricultural systems, which provide important habitat for WNV vectors, , although effects depend on human water management decisions and vary spatially. The impact of year-to-year changes in precipitation on mosquito populations varies among the regions of the United States and is affected by the typical climate of the area as well as other non-climate factors, such as land use or water infrastructure and management practices.
However, despite the short history of WNV in the United States, there are some lessons to be learned from other mosquito-borne diseases with longer histories in the United States. Louis encephalitis virus SLEV were first identified in the s and have been circulating in the United States since that time. WEEV outbreaks were associated with wet springs followed by warm summers. Despite climatic warming that would be expected to favor increased WEEV and SLEV transmission, both viruses have had sharply diminished incidence during the past 30 to 40 years.
Several other mosquito-borne pathogens, such as chikungunya and dengue, have grown in importance as global health threats during recent decades; however, a link to climate change induced disease expansion in the United States has not yet been confirmed.
These examples demonstrate the variable impact that climate change can have on different mosquito-borne diseases and help to explain why the direction of future trends in risk for WNV remain unclear. Despite the growing body of work examining the connections between WNV and weather, climate-based seasonal forecasts of WNV outbreak risk are not yet available at a national scale.
Identification, taxonomy, systematics and molecular phylogenetics of parasites and arthropod vectors. Surveillance of indigenous and invasive arthropod vectors of public and veterinary health relevance: distribution, abundance and bionomics. Assessment of vector-pathogen relationships and the risk of pathogen transmission and associated disease. Impact of environmental change on the transmission dynamics of parasites and the biology, ecology and distribution of intermediate hosts and vectors. Emergence, re emergence and globalisation of vectors, pathogens and hosts and One Health. Parasitic and vector-borne diseases of humans, wildlife and domestic, farm and companion animals including studies on immunology, immunopathology, diagnosis and control.
Vector-borne diseases account for over 17% of all infectious diseases. Source: PPT on Health Climate change and WHO, Figure from Arc c.
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OVERVIEWS: VECTOR-BORNE DISEASE IN HUMANS, PLANTS, AND ANIMALS
If your institution subscribes to this resource, and you don't have a MyAccess Profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus. Please consult the latest official manual style if you have any questions regarding the format accuracy. This new climate has already altered the epidemiology of some infectious diseases. In some cases climate change may establish conditions favoring the emergence of infectious diseases, while in others it may render areas that are presently suitable for certain diseases unsuitable. This chapter presents the current state of knowledge regarding the known and prospective infectious-disease consequences of climate change. The term climate change refers to long-term alterations in temperature, precipitation, wind, humidity, and other components of weather. Over the past 2.
Climate change is expected to alter the geographic and seasonal distributions of existing vectors and vector-borne diseases [Likely, High Confidence]. Ticks capable of carrying the bacteria that cause Lyme disease and other pathogens will show earlier seasonal activity and a generally northward expansion in response to increasing temperatures associated with climate change [Likely, High Confidence]. Longer seasonal activity and expanding geographic range of these ticks will increase the risk of human exposure to ticks [Likely, Medium Confidence]. Rising temperatures, changing precipitation patterns, and a higher frequency of some extreme weather events associated with climate change will influence the distribution, abundance, and prevalence of infection in the mosquitoes that transmit West Nile virus and other pathogens by altering habitat availability and mosquito and viral reproduction rates [Very Likely, High Confidence]. Alterations in the distribution, abundance, and infection rate of mosquitoes will influence human exposure to bites from infected mosquitoes, which is expected to alter risk for human disease [Very Likely, Medium Confidence]. Vector-borne pathogens are expected to emerge or reemerge due to the interactions of climate factors with many other drivers, such as changing land-use patterns [Likely, High Confidence].
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