Weather and climate effects on Lyme disease exposure

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Lyme disease is spread to humans through the bite of infected ticks. The tick population is affected by weather and climate. Many factors determine tick population densities as well as diseased population densities of ticks so that no single factor can determine likelihood of exposure to tick-borne disease. [1] Overall climate [2] and primary host population [3] determine the localities where ticks will thrive. However, studies have been conducted which correlate tick population to climate change and their behavior to weather patterns. Ticks are parasites which carry a myriad of infectious diseases that depend on the species of tick. [4] Overall climate is more determinate of tick population and daily weather has a subtle effect on the spread of tick-borne disease. Being mindful of daily weather patterns and vigilantly avoiding exposure to ticks reduces human exposure to Lyme disease. [5]

Contents

Lyme disease number of cases reported by county 2007 Lyme disease reported cases 2007.jpg
Lyme disease number of cases reported by county 2007
Peak summer weather July 2007. Warm humid air from the tropics meeting with cooler air over the eastern United States. Moisture condenses and forms clouds that trail up the Northeast illustrating the transfer of heat and humidity to the northeastern United States from equatorial waters. The cloud formations coincide with reported cases of Lyme from 2007. 2007sat 7.gif
Peak summer weather July 2007. Warm humid air from the tropics meeting with cooler air over the eastern United States. Moisture condenses and forms clouds that trail up the Northeast illustrating the transfer of heat and humidity to the northeastern United States from equatorial waters. The cloud formations coincide with reported cases of Lyme from 2007.

Tick entomology

After the larvae have fed, they drop off the host and molt to nymphs. The nymphs then overwinter and their activity almost completely ceases until late spring. They emerge the following year in May, June, and July. This emergence is just before the new generation of larvae hatch, allowing the nymphs to transmit tick-borne disease to new generations of hosts. This increases the possibility that the next generation of larvae will also become infected. Nymphs usually attach and feed on small mammals and birds. After feeding, nymphs drop off and molt to adults that will reappear in the fall of the same year. Adults seek medium to large mammalian hosts, primarily deer. Once adulthood is reached, ticks no longer hibernate during the winter and may become active on warm winter days. [6]

Climate

The incidence of Lyme disease is tied to many factors including climate. Certain regions worldwide supply the proper conditions for ticks to flourish. Ticks like habitats with at least 85% humidity and can only practice host questing at temperatures greater than 7 °C (45 °F). [7] In order to find microclimates that are suitable ticks will use thermoreceptors to detect these proper conditions. [7] One region with especially suitable climate for ticks is the northeastern United States. This region is part of a temperate and humid zone [8] presenting the ideal conditions for tick survival. It is also important to consider that warmer temperatures that are favourable for plant growth create an ideal condition for vegetation to thrive and these temperatures are beginning to arise in earlier spring due to climate change. This can lead to earlier tick emergence and questing behaviour which in return allows for extended periods of human-tick interactions. [9]

Climate change

Climate change could affect ticks in a variety of ways. Süss et al. (2008) lists the following as possible changes to tick populations due to increased temperature brought on by global climate change: [7]

  1. an acceleration of the ticks' developmental cycle
  2. an extension of the ticks' developmental cycle
  3. an increase in egg production
  4. an increase in population density
  5. a shift in risk areas

Many of these changes could potentially increase the Lyme disease incidence and pose a threat to human populations, especially in the eastern half of the United States.

Vegetation Growth

It is also important to consider how vegetation levels in tick habitats effect tick behaviour and density of tick populations. Vegetation levels vary with the different seasons in terms of how dense and how much of it is present in tick habitats. Ticks thrive in environments with enough moisture to keep them sustained and far from desiccation. [10] Habitats with more vegetation tend to contain more moisture as plants are constantly driving water into their roots from soil and transpiring that water within the atmosphere. Although precipitation heavily contributes to moisture levels, areas with more dense vegetation are able to retain that moisture more easily than deserted regions with less vegetation. Also, compacted undergrowth of vegetation allows for ticks to have shelter from environmental stressors like high temperatures and direct sunlight. It also provides a habitat in which the ticks can utilize their questing state to wait for a host to pass through. The density of vegetation and how it changes from Summer to Winter significantly affect tick populations. In the regions where the preferred tick habitats and vegetation are more prevalent, there is more opportunity for ticks to seek out hosts due to higher populations of ticks in those areas. [10]

Rainfall and temperature

In addition to climate, seasonal weather variations have a strong effect on tick populations. Changes in temperature and precipitation from year to year affect the Lyme disease incidence. Multiple studies have shown that there is a correlation between the amount of precipitation and the incidence of Lyme disease. After nymph ticks feed on and infect their host with Lyme disease they lose their ability to effectively control their water content. [11] During a year with very little precipitation many ticks may die following feeding because of this loss of water regulatory control. [11] These nymph ticks that have died out will never reach adulthood and lay eggs. Two years later their offspring nymph tick population will be reduced and thus Lyme disease incidence will also decrease. [11] Schauber et al. (2005) also suggests a similar tie between lagged precipitation as measured by the Palmer Hydrologic Drought Index and Lyme disease incidence in the northeastern United States. [12]

In addition to direct effects on nymph tick populations summer precipitation may also be a factor for controlling the population of the ticks' primary host – the white-footed mouse. [11] Decreased rainfall in the summer months may also decrease the amount of vegetation available for mice populations to eat in order to sustain themselves during the winter. [13] It thus follows that a decrease in rainfall may decrease the population of the ticks' primary host and thus reduce tick populations and Lyme disease incidence.

Subak (2003) proposes that a link between human behavior and precipitation could be another factor in Lyme disease incidence. [11] In the northeastern United States when the summer weather is especially hot and dry, it may disincline people from outdoor activity. [11] In fact, Subak (2003) found a link between dry conditions and a decreased Lyme disease incidence during late summer months in the northeast United States. [11]

Temperature may also play a role in Lyme disease incidence. Schauber et al. (2005) found a positive correlation between the mean summer temperature and the rate of Lyme disease in the northeastern United States. [12] Additionally, Subak (2003) suggests that there may also be a relationship between warmer winters and increased Lyme disease. [11] This study discovered a tentative link between warmer winter weather lagged one year and Lyme disease incidence. [11] A more moderate winter may increase the survival of the white-footed mouse host allowing for increased tick populations in the spring and summer. [11] These warmer winter temperatures may also allow for more adult tick activity during winter and cause an increase in nymph populations the following year. [11]

Risk

Reported Cases of Lyme Disease by Month of Illness Onset United States, 1992-2004 RptdMthOfillness.jpg
Reported Cases of Lyme Disease by Month of Illness Onset United States, 1992–2004

Vulnerability to Lyme

Outdoor activities tend to take place under fair weather conditions, which are those that ticks thrive in. [14] Populations of the nymphal stage, the stage which most commonly transmits Lyme to humans, [15] are highest during the late spring and early summer, [15] directly preceding the months when greatest number of reported cases of Lyme disease occur. [16]

Typical summer outerwear consists of shorter garments that enable ticks greater exposure to skin. Tick saliva has immunosuppressive properties [17] that shut off the body's response, which would alert the body to the tick's presence. This allows ticks to remain attached for an extended period of time while feeding, increasing the probability of disease transmission. [18]

Mitigating exposure

A number of different methods have been shown to mitigate exposure to Lyme disease. Individuals who practice diligence in ticks removal and exposure reduction techniques will be resilient to the risks of contracting Lyme disease, [19] but further risk reduction can be attained by observance of the daily weather since ticks use a number of host seeking techniques that the weather can affect. [20] ticks are able to detect hosts by their shadow. [20] On bright sunny days, shadows contrast greatly with the surrounding brightly lit areas. [21] Wearing light colored clothing on these days reduces risk of ticks exposure by reducing the contrast. Conducting outdoor activities on overcast or slightly foggy days also reduces shadow detection since contrast with the surroundings is minimized. [21]

Ticks can detect the odor of a host. [20] On breezy days remaining downwind from prime ticks habitats will minimize scent detection. [22] Ticks seek hosts only at temperatures above 7 °C (45 °F). [7] Risk of exposure at temperatures below these is extremely minimal.

Related Research Articles

<span class="mw-page-title-main">Tick</span> Order of arachnids in the arthropod phylum

Ticks are parasitic arachnids of the order Ixodida. They are part of the mite superorder Parasitiformes. Adult ticks are approximately 3 to 5 mm in length depending on age, sex, species, and "fullness". Ticks are external parasites, living by feeding on the blood of mammals, birds, and sometimes reptiles and amphibians. The timing of the origin of ticks is uncertain, though the oldest known tick fossils are from the Cretaceous period, around 100 million years old. Ticks are widely distributed around the world, especially in warm, humid climates.

<span class="mw-page-title-main">Lyme disease</span> Infectious disease caused by Borrelia bacteria, spread by ticks

Lyme disease, also known as Lyme borreliosis, is a tick-borne disease caused by species of Borrelia bacteria, transmitted by blood-feeding ticks in the genus Ixodes. The most common sign of infection is an expanding red rash, known as erythema migrans (EM), which appears at the site of the tick bite about a week afterwards. The rash is typically neither itchy nor painful. Approximately 70–80% of infected people develop a rash. Early diagnosis can be difficult. Other early symptoms may include fever, headaches and tiredness. If untreated, symptoms may include loss of the ability to move one or both sides of the face, joint pains, severe headaches with neck stiffness or heart palpitations. Months to years later, repeated episodes of joint pain and swelling may occur. Occasionally, shooting pains or tingling in the arms and legs may develop.

Tick-borne diseases, which afflict humans and other animals, are caused by infectious agents transmitted by tick bites. They are caused by infection with a variety of pathogens, including rickettsia and other types of bacteria, viruses, and protozoa. The economic impact of tick-borne diseases is considered to be substantial in humans, and tick-borne diseases are estimated to affect ~80 % of cattle worldwide. Most of these pathogens require passage through vertebrate hosts as part of their life cycle. Tick-borne infections in humans, farm animals, and companion animals are primarily associated with wildlife animal reservoirs. Many tick-borne infections in humans involve a complex cycle between wildlife animal reservoirs and tick vectors. The survival and transmission of these tick-borne viruses are closely linked to their interactions with tick vectors and host cells. These viruses are classified into different families, including Asfarviridae, Reoviridae, Rhabdoviridae, Orthomyxoviridae, Bunyaviridae, and Flaviviridae.

<span class="mw-page-title-main">Tick-borne encephalitis</span> Medical condition

Tick-borne encephalitis (TBE) is a viral infectious disease involving the central nervous system. The disease most often manifests as meningitis, encephalitis or meningoencephalitis. Myelitis and spinal paralysis also occurs. In about one third of cases sequelae, predominantly cognitive dysfunction, persist for a year or more.

<span class="mw-page-title-main">White-footed mouse</span> Species of mammal

The white-footed mouse is a rodent native to North America from southern Canada to the southwestern United States and Mexico. In the Maritimes, its only location is a disjunct population in southern Nova Scotia. It is also known as the woodmouse, particularly in Texas.

<i>Ixodes holocyclus</i> Species of tick

Ixodes holocyclus, commonly known as the Australian paralysis tick, is one of about 75 species in the Australian tick fauna and is considered the most medically important. It can cause paralysis by injecting neurotoxins into its host. It is usually found in a 20-kilometre wide band following the eastern coastline of Australia. Within that range, Ixodes holocyclus is the tick most frequently encountered by humans and their pets. Because the same area includes Australia's most densely populated regions, bites on people, pets and livestock are relatively common.

<i>Dermacentor variabilis</i> Species of tick

Dermacentor variabilis, also known as the American dog tick or wood tick, is a species of tick that is known to carry bacteria responsible for several diseases in humans, including Rocky Mountain spotted fever and tularemia. It is one of the best-known hard ticks. Diseases are spread when it sucks blood from the host. It may take several days for the host to experience symptoms.

<i>Babesia</i> Genus of protozoan parasites

Babesia, also called Nuttallia, is an apicomplexan parasite that infects red blood cells and is transmitted by ticks. Originally discovered by the Romanian bacteriologist Victor Babeș in 1888, over 100 species of Babesia have since been identified.

Powassan virus (POWV) is a Flavivirus transmitted by ticks, found in North America and in the Russian Far East. It is named after the town of Powassan, Ontario, where it was identified in a young boy who eventually died from it. It can cause encephalitis, inflammation of the brain. No approved vaccine or antiviral drug exists. Prevention of tick bites is the best precaution.

<span class="mw-page-title-main">Microbiology of Lyme disease</span>

Lyme disease, or borreliosis, is caused by spirochetal bacteria from the genus Borrelia, which has 52 known species. Three species are the main causative agents of the disease in humans, while a number of others have been implicated as possibly pathogenic. Borrelia species in the species complex known to cause Lyme disease are collectively called Borrelia burgdorferisensu lato (s.l.), not to be confused with the single species Borrelia burgdorferi sensu stricto, a member of the complex, which is responsible for nearly all cases of Lyme disease in North America.

Andrew Spielman was a prominent American public health entomologist and Professor of Tropical Public Health in the Department of Immunology and Infectious Disease at the Harvard School of Public Health (HSPH).

<i>Ixodes scapularis</i> Species of tick

Ixodes scapularis is commonly known as the deer tick or black-legged tick, and in some parts of the US as the bear tick. It was also named Ixodes dammini until it was shown to be the same species in 1993. It is a hard-bodied tick found in the eastern and northern Midwest of the United States as well as in southeastern Canada. It is a vector for several diseases of animals, including humans and is known as the deer tick owing to its habit of parasitizing the white-tailed deer. It is also known to parasitize mice, lizards, migratory birds, etc. especially while the tick is in the larval or nymphal stage.

<i>Ixodes ricinus</i> Species of tick

Ixodes ricinus, the castor bean tick, is a chiefly European species of hard-bodied tick. It may reach a length of 11 mm (0.43 in) when engorged with a blood meal, and can transmit both bacterial and viral pathogens such as the causative agents of Lyme disease and tick-borne encephalitis.

<i>Amblyomma americanum</i> Species of tick

Amblyomma americanum, also known as the lone star tick, the northeastern water tick, or the turkey tick, is a type of tick indigenous to much of the eastern United States and Mexico, that bites painlessly and commonly goes unnoticed, remaining attached to its host for as long as seven days until it is fully engorged with blood. It is a member of the phylum Arthropoda, class Arachnida. The adult lone star tick is sexually dimorphic, named for a silvery-white, star-shaped spot or "lone star" present near the center of the posterior portion of the adult female shield (scutum); adult males conversely have varied white streaks or spots around the margins of their shields.

<span class="mw-page-title-main">Human granulocytic anaplasmosis</span> Medical condition

Human granulocytic anaplasmosis (HGA) is a tick-borne, infectious disease caused by Anaplasma phagocytophilum, an obligate intracellular bacterium that is typically transmitted to humans by ticks of the Ixodes ricinus species complex, including Ixodes scapularis and Ixodes pacificus in North America. These ticks also transmit Lyme disease and other tick-borne diseases.

<i>Ixodes pacificus</i> Species of arachnid

Ixodes pacificus, the western black-legged tick, is a species of parasitic tick found on the western coast of North America. I. pacificus is a member of the family Ixodidae. It is the principal vector of Lyme disease in that region. I. pacificus larvae and nymphs typically feeds on lizards and small mammals, while adults typically feed on deer. It is an ectoparasite that attaches itself to the outside of its host and feeds on the host's blood. It can have a heteroxenous lifestyle or monoxenous life cycle depending on how many hosts it feeds on in each cycle. I. pacificus has a four-stage life cycle that takes around 3 years to complete. These stages include egg, larva, nymph, and adult. They prefer dense woodland habitats or areas of brush and tall grass.

<span class="mw-page-title-main">Deer tick virus</span> Pathogenic member virus of Powassan virus

Deer tick virus (DTV) is a virus in the genus Flavivirus spread via ticks that causes encephalitis.

Disease ecology is a sub-discipline of ecology concerned with the mechanisms, patterns, and effects of host-pathogen interactions, particularly those of infectious diseases. For example, it examines how parasites spread through and influence wildlife populations and communities. By studying the flow of diseases within the natural environment, scientists seek to better understand how changes within our environment can shape how pathogens, and other diseases, travel. Therefore, diseases ecology seeks to understand the links between ecological interactions and disease evolution. New emerging and re-emerging infectious diseases are increasing at unprecedented rates which can have lasting impacts on public health, ecosystem health, and biodiversity.

<span class="mw-page-title-main">Climate change and infectious diseases</span> Overview of the relationship between climate change and infectious diseases

Global climate change has increased the occurrence of some infectious diseases. Infectious diseases whose transmission is impacted by climate change include, for example, vector-borne diseases like dengue fever, malaria, tick-borne diseases, leishmaniasis, zika fever, chikungunya and Ebola. One mechanism contributing to increased disease transmission is that climate change is altering the geographic range and seasonality of the insects that can carry the diseases. Scientists stated a clear observation in 2022: "The occurrence of climate-related food-borne and waterborne diseases has increased ."

<i>Ixodes angustus</i> Species of tick

Ixodes angustus is a species of parasitic tick, whose range encompasses the majority of Canada and the United States, along with parts of northern Mexico. I. angustus is a member of the Ixodidae (hard-bodied) family of ticks. It is most abundant in cool, moist biomes such as riparian, boreal or montane zones. I. angustus is a host generalist and has been discovered feeding on more than 90 different host species, including humans and domestic dogs. I. angustus has been identified as a potential vector for Lyme disease but is not considered a principal vector due to the relative rarity with which it feeds on humans.

References

  1. ↑ Ginsberg, Howard S., Eric L. Rulison, Lorenza Beati, Russell Burke, Graham J. Hickling, Kaetlyn Kerr, Isis Kuczaj, Roger A. LeBrun, Genevieve Pang, Cathy Scott, and Jean I. Tsao. Effects of Environmental Variables on Abundance and Phenology of Immature Ixodes Scapularis (Acari: Ixodidae). http://www.nps.gov/caco/naturescience/upload/Ginsberg_Poster.pdf. National Park Service. Web. 30 November 2011.
  2. ↑ Frans Jongejan, Frans. "Ticks, Diseases and Climate Change". http://www.rtcc.org/2007/html/res_edu_uou.html. Utrecht Centre for Tick-borne Diseases. 2007. Retrieved 2011-11-28.
  3. ↑ N.L. Breisch, N.L. and Thorne, B.L.. "Lyme Disease and the Deer Tick in Maryland". Maryland Cooperative Extension Fact Sheet 595. http://extension.umd.edu/publications/pdfs/fs595.pdf. 2001. Retrieved 2011-11-30.
  4. ↑ "Ticks : Environmental Health : NYC DOHMH." New York City Department of Health and Mental Hygiene. http://www.nyc.gov/html/doh/html/ehs/ehstick.shtml. 2011. Web. 30 November 2011.
  5. ↑ "Ticks | Health Department | City of Alexandria, VA." City of Alexandria, Virginia. http://alexandriava.gov/health/info/default.aspx?id=27984. City of Alexandria Health Department, 28 June 2011. Web. 30 November 2011.
  6. ↑ Stafford III, Kirby C. "Tick Management Handbook." Maine Medical Center Research Institute. The Connecticut Agricultural Experiment Station, 2007. http://www.ct.gov/caes/lib/caes/documents/publications/bulletins/b1010.pdf. Web. 10 December 2011.
  7. 1 2 3 4 Süss J, Klaus C, Gerstengarbe FW, Werner PC (2008). "What makes ticks tick? Climate change, ticks, and tick-borne diseases". J Travel Med. 15 (1): 39–45. doi: 10.1111/j.1708-8305.2007.00176.x . PMID   18217868.
  8. ↑ Major Biomes Map. Soil climate map, USDA-NRCS, Soil Survey Division, World Soil Resources, Washington D.C. (1999). http://soils.usda.gov/use/worldsoils/mapindex/biomes.html. Retrieved 11 December 2011.
  9. ↑ Eisen, Rebecca J.; Eisen, Lars (1 January 2024). "Evaluation of the association between climate warming and the spread and proliferation of Ixodes scapularis in northern states in the Eastern United States". Ticks and Tick-borne Diseases. 15 (1): 102286. doi:10.1016/j.ttbdis.2023.102286. ISSN   1877-959X.
  10. 1 2 Berger, Kathryn A.; Ginsberg, Howard S.; Dugas, Katherine D.; Hamel, Lutz H.; Mather, Thomas N. (14 April 2014). "Adverse moisture events predict seasonal abundance of Lyme disease vector ticks (Ixodes scapularis)". Parasites & Vectors. 7 (1): 181. doi: 10.1186/1756-3305-7-181 . ISSN   1756-3305. PMID   24731228.
  11. 1 2 3 4 5 6 7 8 9 10 11 Subak, Susan. Effects of Climate on Variability in Lyme Disease Incidence in the Northeastern United States. American Journal of Epidemiology, Vol. 105, No. 6 (2003): 531–538.
  12. 1 2 Schauber, Eric M. Richard S. Ostfeld and Andrew S. Evans, Jr. What Is the Best Predictor of Annual Lyme Disease Incidence: Weather, Mice, or Acorns? Ecological Applications, Vol. 15, No. 2 (Apr., 2005): 575–586
  13. ↑ Jones, C.J. and U.D. Kitron. Populations of Ixodes scapularis (Acari: Ixodidae) Are Modulated by Drought at a Lyme Disease Focus in Illinois. Journal of Mecial Entomology, Vol 37, No. 3 (2000): 408–415
  14. ↑ "Making Lyme Disease Take a Hike." Advance for Nurse Practitioners June (2001): 116. Nurse Practitioners and Physicians Assistants. http://nurse-practitioners-and-physician-assistants.advanceweb.com/sharedresources/advancefornp/resources/DownloadableResources/np_0601_lyme.pdf. Web. 5 December 2011.
  15. 1 2 "CDC – Transmission – Lyme Disease." Centers for Disease Control and Prevention. https://www.cdc.gov/lyme/transmission/index.html. 12 April 2011. Web. 5 December 2011.
  16. ↑ "CDC – Cases by State – Lyme Disease." Centers for Disease Control and Prevention. https://www.cdc.gov/lyme/stats/chartstables/casesbymonth.html. 9 Sept. 2010. Web. 5 December 2011.
  17. ↑ Kotsyfakis, M. "Antiinflammatory and Immunosuppressive Activity of Sialostatin L, a Salivary Cystatin from the Tick Ixodes Scapularis." Journal of Biological Chemistry 281.36 (2006): 26298–6307. Print.
  18. ↑ "Lyme Disease." American Lyme Disease Foundation. http://www.aldf.com/lyme.shtml. 26 April 2010. Web. 5 December 2011.
  19. ↑ "CDC – Tick-Borne Diseases – NIOSH Workplace Safety and Health Topic." Centers for Disease Control and Prevention. https://www.cdc.gov/niosh/topics/tick-borne/. 22 Sept. 2011. Web. 5 December 2011.
  20. 1 2 3 "CDC – Tick Life Cycle and Hosts – Ticks." Centers for Disease Control and Prevention. https://www.cdc.gov/ticks/life_cycle_and_hosts.html. 8 March 2011. Web. 5 December 2011.
  21. 1 2 Hale, Nathan Cabot. Abstraction in Art and Nature. New York: Dover, 1993. Print.
  22. ↑ National Resource Council. Odors from Stationary and Mobile Sources. Washington, 1979.

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