Impact of the experimental removal of lizards on Lyme disease risk

The distribution of vector meals in the host community is an important element of understanding and predicting vector-borne disease risk. Lizards (such as the western fence lizard; Sceloporus occidentalis ) play a unique role in Lyme disease ecology in the far-western United States. Lizards rather than mammals serve as the blood meal hosts for a large fraction of larval and nymphal western black-legged ticks ( Ixodes pacificus —the vector for Lyme disease in that region) but are not competent reservoirs for the pathogen, Borrelia burgdorferi . Prior studies have suggested that the net effect of lizards is to reduce risk of human exposure to Lyme disease, a hypothesis that we tested experimentally. Following experimental removal of lizards, we documented incomplete host switching by larval ticks (5.19%) from lizards to other hosts. Larval tick burdens increased on woodrats, a competent reservoir, but not on deer mice, a less competent pathogen reservoir. However, most larvae failed to find an alternate host. This resulted in significantly lower densities of nymphal ticks the following year. Unexpectedly, the removal of reservoir-incompetent lizards did not cause an increase in nymphal tick infection prevalence. The net result of lizard removal was a decrease in the density of infected nymphal ticks, and therefore a decreased risk to humans of Lyme disease. Our results indicate that an incompetent reservoir for a pathogen may, in fact, increase disease risk through the maintenance of higher vector density and therefore, higher density of infected vectors.

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Lyme disease risk not amplified in a species-poor vertebrate community: Similar Borrelia burgdorferi tick infection prevalence and OspC genotype frequencies

Infection Genetics and Evolution ◽

10.1016/j.meegid.2014.04.014 ◽

2014 ◽

Vol 27 ◽

pp. 566-575 ◽

Cited By ~ 24

Author(s):

S.L. States ◽

R.J. Brinkerhoff ◽

G. Carpi ◽

T.K. Steeves ◽

C. Folsom-O’Keefe ◽

...

Keyword(s):

Lyme Disease ◽

Borrelia Burgdorferi ◽

Disease Risk ◽

Infection Prevalence ◽

Genotype Frequencies ◽

Tick Infection ◽

Lyme Disease Risk

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Why Lyme disease is common in the northern US, but rare in the south: The roles of host choice, host-seeking behavior, and tick density

PLoS Biology ◽

10.1371/journal.pbio.3001066 ◽

2021 ◽

Vol 19 (1) ◽

pp. e3001066

Author(s):

Howard S. Ginsberg ◽

Graham J. Hickling ◽

Russell L. Burke ◽

Nicholas H. Ogden ◽

Lorenza Beati ◽

...

Keyword(s):

Lyme Disease ◽

Disease Risk ◽

Host Choice ◽

Infection Prevalence ◽

The South ◽

The North ◽

Host Seeking ◽

Tick Infection ◽

Seeking Behavior ◽

Clear Shift

Lyme disease is common in the northeastern United States, but rare in the southeast, even though the tick vector is found in both regions. Infection prevalence of Lyme spirochetes in host-seeking ticks, an important component to the risk of Lyme disease, is also high in the northeast and northern midwest, but declines sharply in the south. As ticks must acquire Lyme spirochetes from infected vertebrate hosts, the role of wildlife species composition on Lyme disease risk has been a topic of lively academic discussion. We compared tick–vertebrate host interactions using standardized sampling methods among 8 sites scattered throughout the eastern US. Geographical trends in diversity of tick hosts are gradual and do not match the sharp decline in prevalence at southern sites, but tick–host associations show a clear shift from mammals in the north to reptiles in the south. Tick infection prevalence declines north to south largely because of high tick infestation of efficient spirochete reservoir hosts (rodents and shrews) in the north but not in the south. Minimal infestation of small mammals in the south results from strong selective attachment to lizards such as skinks (which are inefficient reservoirs for Lyme spirochetes) in the southern states. Selective host choice, along with latitudinal differences in tick host-seeking behavior and variations in tick densities, explains the geographic pattern of Lyme disease in the eastern US.

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Modeling the role of songbirds and rodents in the ecology of Lyme disease

Canadian Journal of Zoology ◽

10.1139/z00-162 ◽

2000 ◽

Vol 78 (12) ◽

pp. 2184-2197 ◽

Cited By ~ 34

Author(s):

Antonia R Giardina ◽

Kenneth A Schmidt ◽

Eric M Schauber ◽

Richard S Ostfeld

Keyword(s):

New York ◽

Lyme Disease ◽

Ixodes Scapularis ◽

New York State ◽

Original Data ◽

Etiologic Agent ◽

Host Community ◽

Infection Prevalence ◽

Tick Infection ◽

Tick Vectors

Small rodents such as the white-footed mouse (Peromyscus leucopus) and the eastern chipmunk (Tamias striatus) efficiently transmit Borrelia burgdorferi, the etiologic agent of Lyme disease, to feeding ticks, whereas other hosts of ticks are less efficient reservoirs of B. burgdorferi. We examined the roles of ground-foraging and ground-nesting songbirds as alternative hosts for ticks, focusing on their potential to dilute the infection prevalence of ticks (Ixodes scapularis, the black-legged tick) with B. burgdorferi. We developed a mathematical model based on the relative use by ticks of rodent and bird hosts across varying host densities. We parameterized the model for sites in southeastern New York State using original data and for the northeastern United States using published values. Our results indicate that American robins (Turdus migratorius), ovenbirds (Seiurus aurocapillus), veeries (Catharus fuscescens), and wood thrushes (Hylocichla mustelina) have a low capacity to dilute the prevalence of tick infection, particularly when rodents are at moderate to high densities. We attribute this result to low use by ticks of birds and a low density of birds relative to that of rodents. Only when rodents constitute less than ca. 10-20% of the combined rodent and songbird host community are birds capable of substantially reducing the infection prevalence of ticks. In years or habitat types in which the density of rodents is low but that of ground-dwelling songbirds is high, the risk of human exposure to Lyme disease may reduced because birds dilute the infection prevalence of tick vectors.

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Diversifying forest communities may change Lyme disease risk: extra dimension to the dilution effect in Europe

Parasitology ◽

10.1017/s0031182016000688 ◽

2016 ◽

Vol 143 (10) ◽

pp. 1310-1319 ◽

Cited By ~ 15

Author(s):

SANNE C. RUYTS ◽

EVY AMPOORTER ◽

ELENA C. COIPAN ◽

LANDER BAETEN ◽

DIETER HEYLEN ◽

...

Keyword(s):

North America ◽

Lyme Disease ◽

Borrelia Burgdorferi ◽

Disease Risk ◽

Severe Disease ◽

Dilution Effect ◽

Ixodid Ticks ◽

Infection Prevalence ◽

Host Diversity ◽

Pine Stands

SUMMARYLyme disease is caused by bacteria of theBorrelia burgdorferigenospecies complex and transmitted by Ixodid ticks. In North America only one pathogenic genospecies occurs, in Europe there are several. According to the dilution effect hypothesis (DEH), formulated in North America, nymphal infection prevalence (NIP) decreases with increasing host diversity since host species differ in transmission potential. We analysedBorreliainfection in nymphs from 94 forest stands in Belgium, which are part of a diversification gradient with a supposedly related increasing host diversity: from pine stands without to oak stands with a shrub layer. We expected changing tree species and forest structure to increase host diversity and decrease NIP. In contrast with the DEH, NIP did not differ between different forest types. Genospecies diversity however, and presumably also host diversity, was higher in oak than in pine stands. Infected nymphs tended to harbourBorrelia afzeliiinfection more often in pine stands whileBorrelia gariniiandBorrelia burgdorferiss. infection appeared to be more prevalent in oak stands. This has important health consequences, since the latter two cause more severe disease manifestations. We show that the DEH must be nuanced for Europe and should consider the response of multiple pathogenic genospecies.

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Faculty Opinions recommendation of Impact of the experimental removal of lizards on Lyme disease risk.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.13357252.14726615 ◽

2011 ◽

Author(s):

Graeme Cumming

Keyword(s):

Lyme Disease ◽

Disease Risk ◽

Experimental Removal ◽

Lyme Disease Risk

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Borrelia burgdorferi (Spirochaetales: Spirochaetaceae) Infection Prevalence and Host Associations of Ticks Found on Peromyscus spp. in Maryland

Journal of Medical Entomology ◽

10.1093/jme/tjab206 ◽

2021 ◽

Author(s):

Julia E Poje ◽

Jose F Azevedo ◽

Nisha Nair ◽

Kurayi Mahachi ◽

Lexi E Frank ◽

...

Keyword(s):

Lyme Disease ◽

Borrelia Burgdorferi ◽

Disease Risk ◽

Ixodes Scapularis ◽

Sensu Stricto ◽

Infection Prevalence ◽

Private Land ◽

Tissue Samples ◽

Wild Mice ◽

Significant Difference

Abstract Lyme disease, caused by Borrelia burgdorferi sensu stricto and most commonly transmitted by Ixodes scapularis Say (Ixodida: Ixodidae), is the most common tick-borne disease in Maryland. Because B. burgdorferi s.s. is maintained in enzootic cycles among wild mice (Peromyscus spp) and Ixodes spp ticks, differing patterns of parasitism of ticks on mice could impact the infection prevalence with B. burgdorferi. We determined the infection prevalence of Peromyscus spp as well as questing and partially engorged nymphal ticks collected at six sites on private land in five counties in Maryland from May to August 2020. Questing nymph infection prevalence (NIP) was 14%. We trapped 1258 mice and collected 554 ticks and 413 ear tissue samples. The prevalence of infested Peromyscus spp varied based on host age and sex, with older and male mice more likely to be infested. We detected a significant difference amongst the proportion of attached Ixodes and the location of trapping. Similarly, the prevalence of B. burgdorferi infected Peromyscus spp mice varied between locations (average mouse infection prevalence was 40%), with the highest prevalence in locations where Ixodes were the most commonly found ticks. The B. burgdorferi infection prevalence in partially engorged I. scapularis nymphs retrieved from Peromyscus spp was ~36% which lends further support to the host infection prevalence. Local differences in distribution of infected vectors and reservoirs are important factors to consider when planning interventions to reduce Lyme disease risk.

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Experimental Evidence for Opposing Effects of High Deer Density on Tick-Borne Pathogen Prevalence and Hazard

10.21203/rs.3.rs-586674/v1 ◽

2021 ◽

Author(s):

Sara Louise Gandy ◽

Elizabeth Kilbride ◽

Roman Biek ◽

Caroline Millins ◽

Lucy Gilbert

Keyword(s):

Lyme Disease ◽

Disease Risk ◽

Dilution Effect ◽

High Density ◽

Infection Prevalence ◽

Vegetation Height ◽

Deer Density ◽

Pathogen Prevalence ◽

Tick Reproduction ◽

The Impact

Abstract Background: Identifying the mechanisms driving disease risk is challenging for multi-host pathogens, such as Borrelia burgdorferi s.l., the tick-borne bacteria causing Lyme disease. Deer are tick reproduction hosts but do not transmit B. burgdorferi s.l., whereas rodents and birds are competent transmission hosts. Here, we use a long-term deer exclosure experiment to test three mechanisms for how high deer density might shape B. burgdorferi s.l. prevalence in ticks: increased prevalence due to higher larval tick densities facilitating high transmission on rodents (M1); alternatively, reduced B. burgdorferi s.l. prevalence because more larval ticks feed on deer rather than transmission-competent rodents (dilution effect) (M2), potentially due to ecological cascades, whereby higher deer grazing pressure lowers vegetation which decreases rodent abundance thus reducing transmission (M3).Methods: In a large enclosure where red deer stags were kept at high density (32.5 deer/km²), we used an experimental design consisting of eight plots of 0.23ha, four being fenced to simulate the absence of deer and four that were accessible to deer. In each plot we measured the density of questing nymphs and nymphal infection prevalence in spring, summer and autumn and quantified vegetation height and density, and small mammal abundance Results: Prevalence tended to be lower, though not conclusively so, in high deer density plots compared to exclosures (predicted prevalence of 1.0% vs 2.2%), suggesting that the dilution (M2) and cascade (M3) mechanisms might outweigh the increased opportunities for transmission (M1). Presence of deer at high density led to lower vegetation and fewer rodents, consistent with an ecological cascade. However, Lyme disease hazard (density of infected I. ricinus nymphs) was five times higher in high deer density plots due to tick density being 18 times higher.Conclusion: High densities of tick reproduction hosts such as deer can drive up vector-borne disease hazard, despite the potential to simultaneously reduce pathogen prevalence. This has implications for environmental pathogen management and for deer management, although the impact of intermediate deer densities now needs testing.

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Lyme Disease Risk of Exposure to Blacklegged Ticks (Acari: Ixodidae) Infected with Borrelia burgdorferi (Spirochaetales: Spirochaetaceae) in Pittsburgh Regional Parks

Journal of Medical Entomology ◽

10.1093/jme/tjz140 ◽

2019 ◽

Vol 57 (1) ◽

pp. 273-280 ◽

Cited By ~ 2

Author(s):

Alison E Simmons ◽

Anna B Manges ◽

Tashi Bharathan ◽

Shannon L Tepe ◽

Sara E McBride ◽

...

Keyword(s):

Lyme Disease ◽

Borrelia Burgdorferi ◽

Disease Risk ◽

Disease Incidence ◽

The United States ◽

Sensu Stricto ◽

Urban Landscapes ◽

Infection Prevalence ◽

Risk Of Exposure ◽

Lyme Disease Risk

Abstract Lyme disease is the most commonly reported vector-borne illness and sixth most commonly reported notifiable infectious disease in the United States. The majority of cases occur in the Northeast and upper-Midwest, and the number and geographic distribution of cases is steadily increasing. The blacklegged tick (Ixodes scapularis Say) is the principal vector of the Lyme disease spirochete (Borrelia burgdorferi sensu stricto) in eastern North America. Although Lyme disease risk has been studied in residential and recreational settings across rural to urban landscapes including metropolitan areas, risk within U.S. cities has not been adequately evaluated despite the presence of natural and undeveloped public parkland where visitors could be exposed to B. burgdorferi-infected I. scapularis. We studied the occurrence of I. scapularis and infection prevalence of B. burgdorferi in four insular regional parks within the city of Pittsburgh to assess Lyme disease risk of exposure to infected adults and nymphs. We found that the density of I. scapularis adults (1.16 ± 0.21 ticks/100 m2) and nymphs (3.42 ± 0.45 ticks/100 m2), infection prevalence of B. burgdorferi in adults (51.9%) and nymphs (19.3%), and density of infected adults (0.60 ticks/100 m2) and nymphs (0.66 ticks/100 m2) are as high in these city parks as nonurban residential and recreational areas in the highly endemic coastal Northeast. These findings emphasize the need to reconsider, assess, and manage Lyme disease risk in greenspaces within cities, especially in high Lyme disease incidence states.

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