Nicholas Woronchuk | California State Polytechnic University | Arcata, California
The genus Rickettsia consists of 35 valid species (Sánchez-Montes et al. 2021) of obligatory intracellular gram-negative bacteria that are primarily transmitted by arthropods (Perlman et al. 2006; Fournier and Raoult 2009; Morand et al. 2020). Rickettsia bacterium are responsible for numerous human febrile diseases including, Rocky Mountain Spotted Fever, ehrlichiosis, spotted fever, typhus fever, and trematode-borne neorickettsiasis (Fournier and Raoult 2009; Morand et al. 2020). Over the past 40 years, the incidence of rickettsial diseases has increased and has seen a continuous increase since 1970 (Morand et al. 2020). In recent years, cases of tick-borne diseases, such as Lyme, have also experienced a rise (Swei et al. 2020). Such trends have been attributed to the onset of climate change (Swei et al. 2020), land-use changes (Morand et al. 2020), changes to vector range (Swei et al. 2020), and globalization (Adams and Kapan 2009; Morand and Walther 2018). Moreover, the incorporation of mammalian pets (e.g. cats and dogs) into the household also increase the likelihood of transmission to humans (Kidd et al. 2008; Smout et al. 2017). As these trends grow in occurrence and extent, the threat of emerging infectious diseases will become an ever more pressing problem (Morand and Walther 2018; Swei et al. 2020).
Emerging infectious diseases (EISs) are those that have appeared in populations where they previously did not exist, are increasing in incidence, or have experienced an increase in geographic range (NIH, 2018). Swei et al. (2020) and Jones et al. (2008) note that at least 60% of emerging diseases are the result of zoonosis, the transmission of a disease from a vertebrate animal to a human (Woolhouse et al. 2001; Woolhouse and Gowtage-Sequeria 2005; World Health Organization, 2020). Swei et al. (2020) also notes that despite 14% of infectious diseases being vector-borne, vector-born zoonotic diseases make up 22% of emerging infectious diseases, a dispassionately high amount (Woolhouse et al. 2001).
The impact of ticks on human diseases around the globe necessitates a standardized method for their collection. Implementing a standardized protocol ensures that data is more easily comparable between different laboratories and can alleviate unknown factors related to their collection. The dissemination of information is thus more easily incorporated into future research related to ticks and tick-borne diseases.
The dragging method (not the flagging method; Fig. 1), a technique designed to collect host-seeking, ‘sit-and-wait’ predatory ticks, will be used in the interior of forested areas with a large canopy cover and leaf litter (Guerra et al. 2002; Salomon et al. 2020). After placing two staked flags on either side of the predesignated 15 m transect line, the collector will walk along the line with a 1-m2 white cloth dragging behind them (Salomon et al. 2020). Every 15 m, the collector will stop, examine the cloth, and remove any ticks (Salomon et al. 2020). Removed ticks will be preserved in a 70-95% ethanol solution (Salomon et al. 2020). The collector will not exceed a distance of 15 m so that ticks will not detach themselves from the cloth before they can be removed with tweezers (Salomon et al. 2020).
From the protocol outlined above, the abundance and densities of each tick species at each life stage can be calculated using the parameters described in the dragging method (Salomon et al. 2020). The length of the transect line will be multiplied by the area of the cloth to calculate the total area dragged (ticks per unit area; Salomon et al. 2020). The total number of ticks collected will be identified by species and life stage and used to calculate abundance and density. In accordance with the procedure described by Salomon et al. (2020), at least 750 m6, either linearly or in a grid, will be covered to provide a strong estimate of density and abundance for the populations and life stages of each tick species. This data will be reported as the number of ticks per 100m2 to standardized abundance data (Salomon et al. 2020).
Ticks are responsible for the transmission of numerous human and animal diseases around the world. Their role in disease ecology is growing in magnitude and requires further investigation as the world continues to change. Creating a method that helps researchers to standardize their research-related ticks improves the quality of research and the subsequent application derived from such research.
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Conservation Ecology @ HSU 