John B. Hewlett

John B. Hewlett

Jan 27, 2019

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Why does research on Timber rattlesnakes matter? How could it impact you?

A transmittered male Timber rattlesnake (Crotalus horridus) we call "Neil" coiled at the base of a tree. Photo by John B. Hewlett, 2018.

The primary aim of my research is to better understand the disease dynamics of an emerging fungal pathogen in snakes, Ophidiomyces ophiodiicola, that results in high levels of mortality in infected individuals. But why does this research matter? And why should you care?

To better understand the downstream consequences of an emerging disease in snakes we have to take a deeper look at the pieces that compose the ecological jig-saw puzzle, including predator and prey relationships.

People who live in rural areas or are outdoor enthusiasts are no stranger to ticks and chiggers, the parasitic arachnids that enjoy a meal of your blood after a summer's walk through the woods, or in some cases your own backyard. Ticks require this 'blood meal' to complete their life cycle which occurs in four stages: egg, larvae, nymph and adult. Disease transmission typically occurs when an infected tick, the host of Rickettsial (Spotted fever and Typhus) disease or Lyme disease (caused by the bacterium Borrelia burgdorferi), that is at the nymph or adult stage bites a human. Humans are not reservoirs for these diseases so the ticks must acquire the bacteria that cause them through a blood meal from an infected organism and small mammals such as mice, rats, rabbits, chipmunks, voles, and squirrels act as competent reservoir hosts for these pathogens.

Figure 1.) The Woodland Vole ( Microtus pinetorum ) acts a competent reservoir for Rickettsia. Photo by John B. Hewlett, 2017.

Figure 2.) The White-footed mouse ( Peromyscus leucopus ) is a well known competent reservoir for the spirochete Borrelia burgdorferi that causes Lyme Disease. Photo by John B. Hewlett, 2017.

The CDC has reported that during a 13 year study period between 2004 and 2016 the number of vector-borne diseases transmitted to humans as a result of mosquitoes, ticks and fleas more than tripled over the study period with a total of over 642,000 cases being reported [1.] At the same time we are currently experiencing a dramatic decrease in biodiveristy worldwide as well as a general homogenization of the natural world through the introduction of species outside of their native ranges. There is evidence to indicate that a reduction in small mammal predators results in an increase in Lyme disease risk [2.] Models from the University of Maryland also suggest that Timber rattlesnakes (Crotalus horridus), as a predator of small mammals, may reduce tick-borne disease transmission (specifically Lyme Disease) in the Northeastern United States [3.]  

Figure 3.) A photomicrograph of tick larvae found in Timber rattlesnake feces. Photo by John B. Hewlett, 2018.

Figure 4.) John Hewlett examining a Timber rattlesnake fecal sample for parasites in the lab.

In our own research we have attempted to quantify parasite burden and diversity in Timber rattlesnake fecal samples. We have seen that the majority of fecal samples obtained to date have contained tick larvae or nymphs that were presumably on the animals mammalian prey and subsequently passed through the digestive tract after feeding. Though anecdotal at this point, this supports the hypothesis that small mammal predators such as Timber rattlesnakes may indirectly benefit human health.

A large male Timber rattlesnake that is a part of the study we call "Buzz" consuming an adult Eastern Gray squirrel ( Sciurus carolinensis   ). Photo by John B. Hewlett, 2018.

Timber rattlesnakes have faced many threats as a result of habitat loss, fragmentation and direct persecution. However, as of 2006, they now face a new one in the form of Ophidiomyces ophiodiicola and areas that have seen infections have witnessed dramatic population declines as a result. If we lose this piece of our natural heritage, we may be more vulnerable to potentially devastating tick-borne diseases such as, but not limited to, Lyme Disease, Rocky Mountain Spotted Fever, Ehrlichiosis , and Tularemia.

  1. Rosenberg R, Lindsey NP, Fischer M, et al. Vital Signs: Trends in Reported Vectorborne Disease Cases — United States and Territories, 2004–2016. MMWR Morb Mortal Wkly Rep 2018;67:496–501. DOI: http://dx.doi.org/10.15585/mmwr.mm6717e1

  2. Levi, T., Kilpatrick, A. M., Mangel, M., & Wilmers, C. C. (2012). Deer, predators, and the emergence of Lyme disease. Proceedings of the National Academy of Sciences, 109(27), 10942-10947. doi:10.1073/pnas.1204536109

  3. Kabay, E., M. Caruso, N., and Lips, K. (2013). Timber Rattlesnakes may reduce incidence of Lyme disease in the Northeastern United States.


 

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About This Project

Snake fungal disease, SFD, is widespread in snake populations across eastern North America. SFD causes skin lesions and often leads to death. We hypothesize increased stress and stress reactivity in timber rattlesnakes makes them more susceptible to SFD and makes it harder for snakes to fight off the disease. We will tag and track 20 timber rattlesnakes to test this hypothesis. We will also use these data to see how SFD influences snake habitat selection and movement patterns.

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