Lyme Disease Transmission Risk: Seasonal Variation in the Built Environment

Abstract

Seasonal variation in spatial distribution and pathogen prevalence of Borrelia burgdorferi in blacklegged ticks (Ixodes scapularis) influences human population risk of Lyme disease in peri-urban built environments. Parks, gardens, playgrounds, school campuses and neighborhoods represent a significant risk for Lyme disease transmission. From June 2012 through May 2014, ticks were collected using 1 m2 corduroy cloths dragged over low-lying vegetation parallel to walkways with high human foot traffic. DNA was extracted from ticks, purified and presence of B. burgdorferi assessed by polymerase chain reaction amplification. Summer is reported as the time of highest risk for Lyme disease transmission in the United States and our results indicate a higher tick density of 26.0/1000 m2 in summer vs. 0.2/1000 m2 to 10.5/1000 m2 in spring and fall. However, our findings suggest that tick infection rate is proportionally higher during the fall and spring than summer (30.0–54.7% in fall and 36.8–65.6% in spring vs. 20.0–28.2% in summer). Seasonal variation in infected tick density has significant implications for Lyme disease transmission as people are less likely to be aware of ticks in built environments, and unaware of increased infection in ticks in spring and fall. These factors may lead to more tick bites resulting in Lyme infection.

Landscape determinants of density of blacklegged ticks, vectors of Lyme disease, at the northern edge of their distribution in Canada

“…We found a higher abundance of nymphs early in the year, as expected based on tick phenology 29,30 . Interestingly, we also found a higher infection prevalence by B. burgdorferi late in the year, which is similar to findings from another study in Europe 31 , although this trend is not consistently observed in all regions or all years 32 . Our results support a general pattern seen throughout the range of I. scapularis , with the Spring and Fall seasons posing different levels of Lyme disease risk owing to changes in environmental risk and human exposure.…”

Patience is not always a virtue: effects of terrain complexity on the host‐seeking behaviour of adult blacklegged ticks, Ixodes scapularis, in the presence of a stationary host

“…Regardless, nymphal size would make it virtually impossible to mark and observe ticks in the same manner as adults in the present study. Although nymphs are considered to be responsible for much of the transmission of B. burgdorferi to humans in North America (Fish, ), adult I. scapularis should not be dismissed as a significant contributor – they are nearly twice as infected (45.5% of adults compared to 27.5% of nymphs) (Roome et al ., ); are host‐seeking a greater proportion of the year (spring and fall for adults compared to summer for nymphs) (Roome et al ., ); and, as demonstrated by this experiment, can actively and successfully locate stationary hosts.…”

“…The transition of adult I. scapularis ticks to an active‐search approach would likely increase the foraging success of ticks near host animals that have stopped to rest/sleep or feed. As ticks are increasingly found in built environments often constructed for the purpose of human congregation (Roome et al ., ), awareness is required for outdoor activities that involve remaining stationary (napping, picnicking, reading, etc.) in areas where ticks may be present.…”

“…Lyme disease and other tick‐borne diseases, such as babesiosis, anaplasmosis, Rocky Mountain spotted fever and more, pose a significant health risk in the northeastern U.S.A. Ixodes scapularis ticks are the primary vectors for the Lyme disease‐causing bacteria, Borrelia burgdorferi , which is transmitted when saliva from an infected tick enters a host during feeding. Humans are increasingly at risk of tick exposure in built environments traditionally considered ‘safe’, such as school campuses, public parks, backyards and gardens (Roome et al ., ). Understanding tick host‐seeking behaviour can help us understand how to minimize the risk of tick exposure and, thus, infection.…”

Nested Species Distribution Models of Chlamydiales in Ixodes ricinus (Tick) Hosts in Switzerland

“…Bacterial communities within ticks are also known to be influenced by environmental conditions, notably through the modification of tick density, tick behavior, or the vector-host interactions ( 28 – 30 ). For example, B. burgdorferi is most likely found at lower altitudes ( 27 ), infects more ticks collected in forests than in pastures ( 29 , 31 ), and may be favored by forest fragmentation ( 31 , 32 ), whereas Rickettsia bacteria may be more prevalent in ticks in pasture sites showing a shrubby vegetation and a medium forest fragmentation ( 31 ). Environmental factors might provide us with critical information regarding bacterial distribution and thus potential threats to humans.…”