Abstract
BackgroundTick-borne disease is the result of spillover of pathogens into the human population. Traditionally, literature has focused on characterization of tick-borne disease pathogens and ticks in their sylvatic cycles. A limited amount of research has focused on human-tick exposure in this system, especially in the Northeastern United States. Human-tick interactions are crucial to consider when assessing the risk of tick-borne disease since a tick bite is required for spillover to occur.MethodsCitizen scientists collected ticks from the Northeastern US through a free nationwide program. Submitted ticks were identified to species, stage, and sex. Blacklegged ticks, Ixodes scapularis, were tested for the presence of Borrelia burgdorferi sensu lato (s.l.) and hard-tick relapsing fever Borrelia. Seasonality of exposure and the citizen science activity during tick exposure was recorded by the citizen scientist. A negative binomial model was fit to predict county level CDC Lyme disease cases in 2016 using citizen science Ixodes scapularis submissions, state, and county population as predictor variables.ResultsA total of 3740 submissions, comprising 4261 ticks, were submitted from the Northeastern US and were reported to be parasitizing humans. Of the three species submitted, blacklegged ticks were the most prevalent followed by American dog ticks and lone star ticks. Submissions peaked in May with the majority of exposure occurring during every-day activities. The most common pathogen in blacklegged ticks was B. burgdorferi s.l. followed by hard-tick relapsing fever Borrelia. Negative binomial model performance was best in New England states followed by Middle Atlantic states.ConclusionsCitizen science provides a low-cost and effective methodology for describing the seasonality and characteristics of human-tick exposure. In the Northeastern US, everyday activities were identified as a major mechanism for tick exposure, supporting the role of peri-domestic exposure in tick-borne disease. Citizen science provides a method for broad pathogen and tick surveillance, which is highly related to human disease, allowing for inferences to be made about the epidemiology of tick-borne disease.
Highlights
Tick-borne disease is the result of spillover of pathogens into the human population
Tick submissions Between January 2016 and August 2017, a total of 3740 submissions were received from the Northeastern US and were reported by the citizen scientist to be biting/questing on a human, with an average of 1.1 ticks per submission, accounting for 4261 ticks. 58 (1%, 58/4261) ticks were unidentifiable at the species level due to decomposition or loss of key morphological characteristics
I. scapularis accounted for 60% of the total (2574/4261), though this proportion varied across states (e.g., I. scapularis accounted for 37% of submissions in New Jersey (149/404) and 75% in Rhode Island (35/47))
Summary
Tick-borne disease is the result of spillover of pathogens into the human population. Tick-borne pathogens are transmitted and maintained through a complex cycle of tick vectors, with multiple life stages and a wide diversity of reservoir hosts. B. burgdorferi sensu stricto (s.s.), the causative agent of Lyme disease, is transmitted to Ixodes scapularis during the larval and nymph life stages, during which the tick is primarily is feeding on small mammal hosts. Porter et al Int J Health Geogr (2019) 18:9 progresses to the adult stage, it feeds predominantly on larger mammals, which are considered incidental hosts for B. burgdorferi [3]. Humans and domesticated animals are incidental hosts in this cycle, that become infected when tick-borne pathogens spillover from their usual reservoir hosts through the bite of an infected tick [3, 4]
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