دانلود رایگان مقاله پیش بینی حجم جستجوی گوگل خطر بیماری لایم

Abstract

Lyme disease is a major zoonosis in the northern hemisphere. It is caused by the spirochete Borrelia burgdorferi, transmitted by ticks (genus Ixodes), and the abundance of infected tick nymphs determines the risk of the disease in humans. In eastern USA, fluctuations in oak (Quercus spp.) acorn production (including mast seeding) determine rodent abundance, which has been linked with Lyme borreliosis risk in humans. However, the predictive power of masting on Lyme disease risk in other systems has never been tested. We used a combination of field and Internet data to trace the ecological chain reaction that links acorn production by oaks and Lyme borreliosis risk in European forests. We found a positive relationship between oak acorn production (Q. robur and Q. petraea) in year T and the number of Lyme borreliosis incidences in year T + 2. Acorn production was also positively correlated with Google search volume for the terms “tick” and “Lyme disease” two years later. Our results suggest that acorn production influences tick population, leading to fluctuations in the intensity of interactions between humans and ticks that can be seen in Google search dynamics. Thus, mast seeding together with the volume of specific Internet web searches appears to be a promising tool that could be used to alert public.

Discussion

Risk of acquiring Lyme disease by humans is directly linked with the abundance and distribution of questing ticks. Thus, it is essential to understand factors shaping tick population dynamics. We used a combination of three sources of the data: National Institute of Hygiene in Poland on Lyme disease incidence, Polish State Forests on oak acorn crop, and Google Trends, and demonstrated that oak acorn production is associated with the Lyme disease risk in humans. The increase in Google searches for “tick” two years after a good acorn year most likely reflects the increase in the number of humans bitten by ticks. Increase in this internet search coincided with the number of diagnosed cases of Lyme disease which supports the contention that focal search terms indicate fluctuating disease risk. Host importance for the total tick infection prevalence depends on the proportion of parasite population fed by the host (Brunner & Ostfeld 2008; Ostfeld 2010). Rodent hosts have a great impact on tick infection prevalence in the eastern US because they are abundant and heavily infested with ticks (Keesing et al. 2009; Ostfeld 2010). Moreover, they are highly competent vectors (Mather, Wilson, Moore, Ribeiro, & Spielman 1989) that are inefficient in killing ticks while grooming (Keesing et al. 2009). Hence, larvae that feed on rodents have a high probability of getting infected and to survive until molting into a nymph (Keesing et al. 2009). All these characteristics also hold for European rodents. They reach extreme densities after mast years (Jensen 1982; Pucek et al. 1993; Zwolak et al. 2016), may harbor numerous tick individuals (Harrison, Scantlebury, & Montgomery 2010; Kiffner, Vor, Hagedorn, Niedrig, & Rühe 2011; Perkins, Cattadori, Tagliapietra, Rizzoli, & Hudson 2003), and are a highly competent reservoir of Borrelia spirochete (Gern et al. 1998; Hanincova et al. 2003). Moreover, survival of ticks feeding on rodents might be exceptionally high. For example, the percentage of larvae that reaches full engorgement while feeding on wood mouse (Apodemus sylvaticus) ranges from 72 to 100% (Randolph 1979). Importantly, the positive effect of rodent numbers on abundance of infected nymphs in Europe has been already established (Beytout et al. 2007; Paziewska, Zwolinska, ´ Harris, Bajer, & Sinski ´ 2010; Sinski ´ et al. 2006), such as the impact of infected nymph number on Lyme disease risk (Beytout et al. 2007; Hubálek et al. 2003; Jaenson et al. 2009). Here, we added oak mast seeding to the picture, likely providing a more comprehensive view on ecological phenomena shaping temporal variation in risk of acquiring Lyme disease by humans in Europe.