TBI’s Increasing and Spreading
Tick Borne Infections (TBI’s) were tested in 9 national parks in this study.
As a patient and advocate, I wish researchers would carefully choose their wording when reporting results. For instance the authors state: “Ba. microti occurred at just 20% of the parks. http://jme.oxfordjournals.org/content/early/2016/12/28/jme.tjw213. That wording will bias people into thinking it isn’t significant, but 20% is nothing to sniff at, particularly when you are one of the 20%. Also, that is what they discovered. Someone else may discover something else and if time is any indicator, that number will probably rise. I would also like to see Bartonella strains added to the pathogen list. Interesting to note: there are 210 cases of locally acquired Zika in the Continental U.S., yet Congress is considering appropriating billions of dollars toward it. https://www.cdc.gov/zika/intheus/maps-zika-us.html, http://www.usatoday.com/story/news/2016/01/28/who-warns-zika-spread/79451430/, http://www.usatoday.com/story/news/politics/2016/05/25/zika-funding-mired-congress/84914934/
Abstract
Tick-borne pathogens transmitted by Ixodes scapularis Say (Acari: Ixodidae), also known as the deer tick or blacklegged tick, are increasing in incidence and geographic distribution in the United States. We examined the risk of tick-borne disease exposure in 9 national parks across six Northeastern and Mid-Atlantic States and the District of Columbia in 2014 and 2015. To assess the recreational risk to park visitors, we sampled for ticks along frequently used trails and calculated the density of I. scapularis nymphs (DON) and the density of infected nymphs (DIN). We determined the nymphal infection prevalence of I. scapularis with a suite of tick-borne pathogens including Borrelia burgdorferi, Borrelia miyamotoi, Anaplasma phagocytophilum, and Babesia microti. Ixodes scapularis nymphs were found in all national park units; DON ranged from 0.40 to 13.73 nymphs per 100 m2. Borrelia burgdorferi, the causative agent of Lyme disease, was found at all sites where I. scapularis was documented; DIN with B. burgdorferi ranged from 0.06 to 5.71 nymphs per 100 m2. Borrelia miyamotoi and A. phagocytophilum were documented at 60% and 70% of the parks, respectively, while Ba. microti occurred at just 20% of the parks. Ixodes scapularis is well established across much of the Northeastern and Mid-Atlantic States, and our results are generally consistent with previous studies conducted near the areas we sampled. Newly established I. scapularis populations were documented in two locations: Washington, D.C. (Rock Creek Park) and Greene County, Virginia (Shenandoah National Park). This research demonstrates the potential risk of tick-borne pathogen exposure in national parks and can be used to educate park visitors about the importance of preventative actions to minimize tick exposure.
In the eastern United States, the blacklegged tick, Ixodes scapularis Say, is the primary vector of Borrelia burgdorferi, the causative agent of Lyme disease, which is the most commonly reported vector-borne disease in the United States (Mead 2015). Ixodes scapularis also vectors other pathogens that can cause potentially serious disease, including Borrelia miyamotoi, Anaplasma phagocytophilum, and Babesia microti (Barbour and Fish 1993, Homer et al. 2000, Jin et al. 2012, Krause et al. 2015). Established blacklegged tick populations are nearly continuous across counties in the Northeastern and North-Central United States where the majority of I. scapularis-borne disease cases are reported (Mead 2015, Eisen et al. 2016). The risk of acquiring Lyme disease is influenced by spatio-temporal variation in the density of host-seeking infected nymphs (Diuk-Wasser et al. 2012). This metric often correlates with Lyme disease incidence, though to varying degrees (Mather et al. 1996, Stafford et al. 1998, Falco et al. 1999, Pepin et al. 2012). Human behavior, including time spent in tick-infested areas or engaged in behaviors that enhance or reduce the likelihood of encounters with ticks (Orloski et al. 2000, Connally et al. 2009), also influences the likelihood of acquiring Lyme disease and may explain some of the lack of concordance between measures of density of infected host-seeking nymphs and Lyme disease incidence (Pepin et al. 2012).
Understanding where people may come into contact with infected vector-competent ticks is central to mitigating tick-borne disease risk. For example, in the Mid-Atlantic and Northeastern United States, peridomestic exposure to I. scapularis likely occurs frequently (Falco and Fish 1988, Maupin et al. 1991, Klein et al. 1996, Connally et al. 2006, Feldman et al. 2015), whereas in the North-Central United States, recreational exposures are believed to be more common than peridomestic exposures (Kitron and Kazmierczak 1997, Paskewitz et al. 2001). Regardless of geographic region, previous studies have demonstrated a risk of human exposure to infected host-seeking I. scapularis nymphs in recreational settings (Falco and Fish 1989, Schulze et al. 1992, Oliver and Howard 1998, Paskewitz et al. 2001, Han et al. 2014, Prusinski et al. 2014, Ford et al. 2015). National parks are popular recreation destinations and may represent areas of elevated acarological risk, yet one cannot adequately infer the risk of tick-borne disease for park visitors or employees from the epidemiological surveillance conducted at the county spatial scale (Eisen et al. 2013). National parks often vary ecologically from surrounding areas, and thus the density of infected ticks may differ between settings; further, human behavior within the parks may differ from behavior in surrounding communities.
In this study, we sought to characterize the acarological risk, that is, the risk of human exposure to tick-borne pathogens, in national parks in the Eastern United States. We surveyed frequently used trails in national park units across six Northeastern and Mid-Atlantic States and the District of Columbia, ranging from Maine in the north to Virginia in the south. Our collection efforts focused on the nymphal stage of I. scapularis. This stage likely poses the greatest threat of transmission of B. burgdorferi and other pathogens to humans, as peak activity of questing nymphs occurs in late spring and early summer which coincides with peak onset of human disease (Piesman 1989, Fish 1993, Falco et al. 1999, Mead 2015). Here, we describe the diversity of ticks collected by drag sampling during summer months, density of host-seeking I. scapularis nymphs, and diversity and prevalence of B. burgdorferi, B. miyamotoi, A. phagocytophilum, and Ba. microti infection in I. scapularis nymphs.
