Lizards and Lyme disease risk

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Lizards and Lyme disease risk

•  Diana Erazo

•  Luisa Carrillo Rodriguez

•  Marilia Palumbo Gaiarsa

•  Paula Ribeiro Prist

•  Rodrigo Mazzei Carvalho

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Introduction

It is an important public health issue in the US, where it is the most common vector-borne disease

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Introduction

Black-legged tick (Ixodes scapularis) Western black-legged tick (Ixodes pacificus)

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Introduction

Western black-legged tick (Ixodes pacificus)

It’s transmitted to humans

trough ticks’ bites Black-legged tick (Ixodes scapularis)

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Introduction

Western black-legged tick (Ixodes pacificus)

It’s transmitted to humans

trough ticks’ bites Black-legged tick (Ixodes scapularis)

Borrelia burgdorferi

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Spring

Winter Summer

Fall

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Spring

Fall

Winter Summer

Eggs

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Spring

Fall

Winter Summer

Eggs

Larvae

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Spring

Fall

Winter Summer

Eggs

Larvae Nymph

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Spring

Fall

Winter Summer

Eggs

Larvae Nymph

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Spring

Fall

Winter Summer

Eggs

Larvae Nymph

Adults

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Spring

Fall

Winter Summer

Eggs

Larvae

Adults Nymph Eggs

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Spring

Fall

Winter Summer

Eggs

Larvae

Adults Nymph Eggs

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Sceloporus occidentalis

Hosts

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California Kangaroo Rat (Dipodomys californicus) Dusky-footed Woodrat

(Neotoma fuscipes)

Western Grey Squirrel (Sciurus griseus)

Deer Mouse

(Peromyscus maniculatus)

Hosts

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Host competence: ability to sustain the tick population.

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Host competence: ability to sustain the tick population.

Reservoir competence: ability of an infected host to infect a tick.

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Host competence

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Host competence

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Host competence

Lizards hold up to 90 % of the ticks

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Reservoir competence

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Susceptible tick"

Infected tick"

Reservoir competence

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é Host competence ê Reservoir competence

ê Host competence é Reservoir competence

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Objectives

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Objectives

To assess the impacts of experimentally reduced western fence lizard density on abundance and infection prevalence of Ixodes pacificus and on tick distributions

on the remaining hosts Sceloporus occidentalis Ixodes pacificus

ü Abundance

ü Infection prevalence

Other hosts

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Hypothesis

The presence of lizards may act as a barrier for the transmission of lyme disease, due to it high host competence and lower reservoir competence

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Hypothesis

1) If ticks switch to other hosts when lizards are scarce, and feed with equal success, then tick abundance might not decline and infection prevalence

would increase.

Predictions

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would increase.

2) Alternatively, reduced lizard abundance might lower tick abundance if ticks generally fail to find alternative, high-quality hosts

Hypothesis

Predictions

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would increase.

2) Alternatively, reduced lizard abundance might lower tick abundance if ticks generally fail to find alternative, high-quality hosts

If there is a strong preference for lizards – no switch to an alternate host

Hypothesis

Predictions

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Methods

MarinCounty,CA, north of San Francisco

14 long-term 1 ha plots

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Methods

MarinCounty,CA, north of San Francisco

6 experimental removal plots 8 control plots

14 long-term 1 ha plots

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Results

The effect of lizard removals on the density and infection prevalence of questing ticks was evaluated:

ü  Sampling larval ticks in the year of removals (time t)

ü  Nymphal ticks the year after the experimental manipulation

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Results

é Larvae ticks

ü  Nymphal ticks the year after the experimental manipulation

Time t:

were not able to immediately find an alternate blood meal host

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Results

é Larvae ticks were not able to immediately find an alternate blood meal host

lizard removal elevated larval tick burden on female woodrats

é Larval burdens on female N. fuscipes

ü  Nymphal ticks the year after the experimental manipulation Time t:

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Results

The year following lizard removal:

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Results

ê Nymphal ticks

ü 5.19% of larval I. pacificus did switch to a competent reservoir host (N. fuscipes)

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Results

ê Nymphal ticks

ü 5.19% of larval I. pacificus did switch to a competent reservoir host (N. fuscipes) ü The increased larval burden on N. fuscipes was not enough to absorb 94.81% of larvae that would have fed on lizards

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Results

ê Nymphal ticks

ü 5.19% of larval I. pacificus did switch to a competent reservoir host (N. fuscipes) ü The increased larval burden on N. fuscipes was not enough to absorb 94.81% of larvae that would have fed on lizards

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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L= Larvae N=Nymph T=Tick f = hungry a = fed i = infected s=susceptible

Larvae Nymph Tick

fed

hungry

susceptible

infected

L N

T

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L^f

L^as L^ai

N^fs N^fi

N^as N^ai

T

L= Larvae N=Nymph T=Tick f = hungry a = fed i = infected s=susceptible

L L

N

N N

N

T L

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L^f

L^as L^ai

N^fs N^fi

N^as N^ai

T

L= Larvae N=Nymph T=Tick f = hungry a = fed i = infected s=susceptible L

L

N

L

N

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L^f

L^as L^ai

N^fs N^fi

N^as N^ai

T

L

N

L

N

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L^f

L^as L^ai

N^fs N^fi

N^as N^ai

T

L

N

L

N

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L^f

L^as L^ai

N^fs N^fi

N^as N^ai

T

L

N

L

N

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L^f

L^as L^ai

N^fs N^fi

N^as N^ai

T

L

N

L

N

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L^f

L^as L^ai

N^fs N^fi

N^as N^ai

T

L

N

L

N

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µ₁ L^f

L^as L^ai

N^fs N^fi

N^as N^ai

T

µ₂ µ₂

µ₃ µ₃

γ γ

L

N

L

N

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µ₁ L^f

L^as L^ai

N^fs N^fi

N^as N^ai

T

µ₂ µ₂

µ₃ µ₃

γ γ

L

N

L

N

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Larvae

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Larvae

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Larvae

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Larvae

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Larvae

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Larvae

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Larvae

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Nymph

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Nymph

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Nymph

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Nymph

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Nymph

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Nymph

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Nymph

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Nymph

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Hosts

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Hosts

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Hosts

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Hosts

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Hosts

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Hosts

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Hosts

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Hosts

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Hosts

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Humans

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Humans

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Humans

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Ticks

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Ticks

Saturation term

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Ticks

Saturation term

Maintenance term

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Ticks

Saturation term

Maintenance term Eggs

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Final Remarks

•  Transient state;

•  Lizard = barrier

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Final Remarks

•  Transient state;

•  Lizard = barrier

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THANKS!!!

•  Organizers

•  Professors

•  T.As

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Lizards and Lyme disease risk