Response of small mammal and tick communities to a catastrophic wildfire and implications for tick‐borne pathogens

Abstract

Through their potentially devastating impacts on the environment, wildfires may impact pathogen, vector, and host interactions, leading to changing risks of vector‐borne disease in humans and other animals. Despite established risks for tick‐borne disease and increasing frequency and severity of wildfires in the United States, impacts of wildfire on ticks and tick‐borne pathogens are understudied. In 2015, the large Wragg fire extensively burned a long‐term field site at Stebbins Cold Canyon University of California Reserve (CC). We characterized the tick, reservoir host and pathogen community over a two‐year period after the burn, comparing our findings to pre‐fire data and to data from Quail Ridge Reserve (QR), a nearby unburned site. After the fire, there were 5.5 times more rodent, primarily Peromyscus spp., captures at CC than QR (compared to 3.5 times more pre‐fire). There were significantly fewer dusky‐footed woodrats (Neotoma fuscipes) at both sites post‐fire, likely due to drought but not fire. Pre‐fire tick infestation prevalence on rodents was comparable across sites (12.5% at CC and 9.9% at QR) and remained low at CC post‐fire (13.7%) but was significantly higher at QR (48.0%), suggesting that ticks or their habitat were destroyed during the burn. Normalized difference vegetation indices documented a 16‐fold loss of vegetation post‐ compared to pre‐fire at CC; loss of vegetation and direct impacts on fauna are likely the main drivers of the post‐fire differences in ticks we saw at CC. These data contribute to our understanding of tick‐associated disease risks in our increasingly disturbed landscapes.

Climate Change and Infections on the Move in North America

“…Interestingly, the study found a significant shift in tick genera proportions from predominantly Ixodes spp to more equal proportions of Ixodes and Dermacentor spp at both sites pre- and post-fire: at the Cold Canyon burned site, 100% of the ticks pre-fire were of the Ixodes genus, which shifted to 55.81% Ixodes and 44.19% Dermacentor post-fire; at the Quail Ridge unburned site, 87.5% of the ticks pre-fire were of the Ixodes genus and 12.5% were of the Dermacentor genus, which shifted to 31.25% Ixodes and 68.75% Dermacentor post-fire. 101 The authors also found a significant increase in the number of animals infested with ticks at both sites when considered together, which was primarily driven by an increase at the unburned Quail Ridge site from 9.9% pre-fire to 48% post-fire. 101 Additionally, a longer duration of infestation was seen at the unburned site where animals were only infested during the Spring and Summer pre-fire but through all four seasons post-fire.…”

“… 101 The authors also found a significant increase in the number of animals infested with ticks at both sites when considered together, which was primarily driven by an increase at the unburned Quail Ridge site from 9.9% pre-fire to 48% post-fire. 101 Additionally, a longer duration of infestation was seen at the unburned site where animals were only infested during the Spring and Summer pre-fire but through all four seasons post-fire. 101 The number of small mammal species more than tripled from pre- to post-fire at the burned site, while near doubling from pre- to post-fire at the unburned site.…”

“… 101 Additionally, a longer duration of infestation was seen at the unburned site where animals were only infested during the Spring and Summer pre-fire but through all four seasons post-fire. 101 The number of small mammal species more than tripled from pre- to post-fire at the burned site, while near doubling from pre- to post-fire at the unburned site. These findings suggest that wildland fires alter host and vector habitats and prevalence of disease-carrying ticks by increasing abundance of the host reservoir.…”

“… 100 A 2020 study aimed to characterize the tick, reservoir host, and pathogen communities over a two-year period following a large 2015 wildfire. 101 Ticks were collected from rodents before and after a wildfire at burned (Stebbins Cold Canyon Natural Reserve) and nearby unburned (Quail Ridge Natural Reserve) sites about 6.5km apart in Northern California. All ticks were of either the Ixodes (five species) or Dermacentor (two species) genera.…”

“…These findings suggest that wildland fires alter host and vector habitats and prevalence of disease-carrying ticks by increasing abundance of the host reservoir. 101 …”