Truncated seasonal activity patterns of the western blacklegged tick (Ixodes pacificus) in central and southern California

MacDonald, Andrew J.; Briggs, Cheryl J.

doi:10.1016/j.ttbdis.2015.10.016

Cited by 28 publications

(63 citation statements)

References 36 publications

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“…Measurements of relative humidity, while thought to be an important driver of tick survivorship during the summer dry season [13, 14], were not collected at the plot-level. However, weather station data from the region indicate that high summer- and winter-time temperatures are negatively correlated with measures of relative humidity [16], suggesting that plot-level temperature and habitat characteristics alone are a good proxy for this metric of microclimatic conditions.…”

Section: Methodsmentioning

confidence: 99%

“…This method is effective for collection of ixodid ticks and provides a proxy for human risk of tick encounter. An area of 500 m 2 was sampled on each sampling event in each of the 24 plots, which were sampled weekly to bi-weekly from late November to early June, the period of seasonal activity for I. pacificus in southern California [16] in order to determine both peak and average density of each life stage of I. pacificus in each plot. All 24 plots across the three reserves were sampled during the 2013–2014 and 2014–2015 seasons.…”

Section: Methodsmentioning

confidence: 99%

“…Given the low densities of nymphal I. pacificus observed in previous studies [16, 17], we expected to find elevated densities of nymphal ticks to be narrowly associated with dense oak woodland habitat, higher in elevation, with dense leaf litter in the understory, which together promote microclimatic conditions found to be important to nymphal tick abundance in northern California [10, 11, 14, 15]. Similarly, we expected elevated adult tick density to be associated with dense oak woodland, or forest edge habitats where deer, important reproductive hosts for adult ticks, tend to forage.…”

Section: Introductionmentioning

confidence: 92%

“…However, there is evidence that suggests these abiotic and environmental factors may not be predictive of entomological risk in central and southern California where nymphal I. pacificus questing behavior appears to differ markedly from that observed in Lyme-endemic northwestern California [16, 17]. Densities of questing nymphal I. pacificus are extremely low in oak woodland sites in southern California [16, 17] relative to infestation of western fence lizards ( Sceloporus occidentalis ), a key host for juvenile I. pacificus and an effective sentinel animal for detecting juvenile tick activity in this region [17].…”

Section: Introductionmentioning

confidence: 99%

“…Densities of questing nymphal I. pacificus are extremely low in oak woodland sites in southern California [16, 17] relative to infestation of western fence lizards ( Sceloporus occidentalis ), a key host for juvenile I. pacificus and an effective sentinel animal for detecting juvenile tick activity in this region [17]. This suggests both that: (i) risk of human exposure to nymphal I. pacificus in southern California is relatively low and likely to be highly localized to areas with habitat types, abiotic conditions and host assemblages that promote nymphal questing activity; and (ii) due to comparatively high densities of questing adult I. pacificus relative to nymphs, possibly due to differences in questing behavior in the nymphal stage [16], exposure to adult female ticks may present greater risk in central and southern California than exposure to nymphal ticks [16, 17]. …”

Section: Introductionmentioning

confidence: 99%

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Lyme disease risk in southern California: abiotic and environmental drivers of Ixodes pacificus (Acari: Ixodidae) density and infection prevalence with Borrelia burgdorferi

et al. 2017

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BackgroundTick-borne diseases, particularly Lyme disease, are emerging across the northern hemisphere. In order to manage emerging diseases and predict where emergence will likely occur, it is necessary to understand the factors influencing the distribution, abundance and infection prevalence of vector species. In North America, Lyme disease is the most common vector-borne disease and is transmitted by blacklegged ticks. This study aimed to explore the abiotic and environmental drivers of density and infection prevalence of western blacklegged ticks (Ixodes pacificus) in southern California, an understudied and densely populated region of North America.ResultsOver the course of this two-year study, densities of I. pacificus adults were consistently positively associated with host availability for juvenile ticks and dense oak woodland habitat. Densities of nymphal and larval I. pacificus, on the other hand were primarily predicted by host availability for juvenile ticks in the first year of the study, and by habitat characteristics such as dense leaf litter in the second year. Infection with the causative agent of Lyme disease, Borrelia burgdorferi (sensu stricto), and related spirochetes was not predicted by the abiotic conditions promoting I. pacificus populations, but rather by diversity of the tick community, and in particular by the presence of two Ixodes tick species that do not generally feed on humans (Ixodes spinipalpis and Ixodes peromysci). Borrelia spp. infection was not detected in the I. pacificus populations sampled, but was detected in other vector species that may maintain enzootic transmission of the pathogen on the landscape.ConclusionsThis study identified dense oak woodlands as high-risk habitats for I. pacificus tick encounter in southern California. The shift in relative importance of host availability to habitat characteristics in predicting juvenile tick abundance occurred as California’s historic drought intensified, suggesting that habitat providing suitable microclimates for tick survivorship became centrally important to patterns of abundance in the face of deleterious abiotic conditions. These results underscore the need for further investigation of the effects of climate change on tick-borne disease in California. Finally, despite low risk of human Lyme disease infection posed by I. pacificus in southern California, evidence of infection was found in other tick species, suggesting that enzootic transmission of tick-borne borreliae may be occurring in southern California, and involve parallel enzootic cycles with other tick and host species but not necessarily humans.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Lyme disease risk in southern California: abiotic and environmental drivers of Ixodes pacificus (Acari: Ixodidae) density and infection prevalence with Borrelia burgdorferi

et al. 2017

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Risk of vector tick exposure initially increases, then declines through time in response to wildfire in California

et al. 2018

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Abstract. Identifying the effects of human-driven perturbations, such as species introductions or habitat fragmentation, on the ecology and dynamics of infectious disease has become a central focus of disease ecologists. Yet, comparatively little is known about how the ecology of zoonotic disease systems responds to catastrophic disturbance events such as wildfires or hurricanes. In California, wildfire disturbance is centrally important to the ecology of forests and oak woodlands and is projected to increase in severity and extent under future climate change. Here, taking advantage of a recent wildfire as a natural experiment, we investigate the effects of wildfire disturbance on the ecology of tick-borne disease in California oak woodlands. We find that wildfire leads to elevated abundance of questing adult and nymphal western blacklegged ticks (Ixodes pacificus) in the year following fire, relative to unburned control plots, but that vector tick abundance declines sharply in the following two years. We find that the abundance of non-competent hosts (western fence lizards) for the Lyme disease bacterium is unaffected by fire, but that the abundances of important reproductive hosts (deer) for ticks and reservoir hosts (dusky-footed woodrats) for tick-borne pathogens are significantly negatively affected by fire. We found ticks and hosts infected with Borrelia burgdorferi sensu lato only within the burn extent and only in the year following the wildfire, though rates of infection were exceedingly low representing little risk to humans. In aggregate, due to the differential effects of this catastrophic disturbance event on different key host species and vector tick life stages in the transmission of tick-borne pathogens, we conclude that wildfire may potentially increase risk of exposure to vector ticks in the first year following wildfire in California, but that risk is dampened substantially in following years due to tick population declines and loss of key reservoir hosts from the system.

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Mixed transmission modes promote persistence of an emerging tick‐borne pathogen

et al. 2020

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Pathogens utilize different modes of transmission to maximize transmission success. In vector‐borne disease systems, both vertical and horizontal modes of transmission are common, but the relative contribution of these modes is not well understood but may be determined by host genetics, physiology, or environmental conditions. This study focuses on an emerging tick‐borne relapsing fever pathogen, Borrelia miyamotoi, that can be transmitted both vertically and horizontally. The enzootic cycle of this pathogen has not been described in the western USA where it was recently found in the tick species, Ixodes pacificus. Our field surveys found that all three life stages of I. pacificus carry the pathogen, and therefore, all stages pose some level of disease risk to humans. The prevalence of infection increases with each life stage suggesting that horizontal transmission is important in the persistence of this pathogen in the enzootic cycle. In support of this finding, we found that small mammal hosts that are frequently parasitized by juvenile stages of I. pacificus were infected with B. miyamotoi and may therefore function as a source of horizontal transmission and enzootic maintenance of this disease. Our data show that in the western USA B. miyamotoi is maintained in natural populations by both transovarial transmission and transmission from blood meal hosts and that synchronous phenology of juvenile stages of I. pacificus may facilitate the transmission dynamics of B. miyamotoi and other vertically transmitted, vector‐borne pathogens.

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Truncated seasonal activity patterns of the western blacklegged tick (Ixodes pacificus) in central and southern California

Cited by 28 publications

References 36 publications

Lyme disease risk in southern California: abiotic and environmental drivers of Ixodes pacificus (Acari: Ixodidae) density and infection prevalence with Borrelia burgdorferi

Lyme disease risk in southern California: abiotic and environmental drivers of Ixodes pacificus (Acari: Ixodidae) density and infection prevalence with Borrelia burgdorferi

Risk of vector tick exposure initially increases, then declines through time in response to wildfire in California

Mixed transmission modes promote persistence of an emerging tick‐borne pathogen

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