Stress effects on Ranavirus susceptibility and transmission

Robin Warne, Lucas Kirschman & Alessandra Araujo

Southern Illinois University

Extrinsic stressors

� Nutrition

� Competition

� Predation

� Pollutants

� Climate change

Phenotype

� Reproduction

� Growth

� Development

� Stress response

� Disease susceptibility

� Disease transmission

Environmental stressors are ubiquitous

… as are their effects on disease expression?

Hypothalamus

Pituitary

Interrenal

CRF

ACTH

CORT (-) ?

Stressors, Glucocorticoids & Disease Transmission

Stress Coping Style

Glu

coco

rtic

oid

s

Passive Aggressive

Exp

lora

tory

be

ha

vio

r

Foo

d in

take

Tra

nsm

issi

on

(β

)

Glu

coco

rtic

oid

s

Contaminants Stressor Intensity

•Stressor effects on transmission unclear

– Altered behavior

– Infectivity

Stressor effects on susceptibility & transmission

• Density dependent transmission

• � = Transmission coefficient

• S = Susceptible individuals

• I = Infected Individuals

• � = Force of infection

• Underlying assumptions of the transmission coefficient

– Contact rate increases in proportion to population density

– Assumed to be equally applicable to

all members of the population

•Environmental stressors can increase disease susceptibility

•Stressor effects on transmission unclear

– Altered behavior

– Infectivity

0.8

1

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6

0 1 2 3 4 5 6 7

CO

RT

ng

/g B

W

Days of Infection

Control

Infected

Warne, Crespi, & Brunner (2011) Functional Ecology

Ranavirus, CORT & Developmental Interactions

• Ranavirus infection elevates whole body CORT

– Stress response

– Or CORT mediating immune response

• Infection significantly increased developmental rate

• Infection significantly decreased body condition

• Prometamorphic tadpoles (GS 35-40) had highest mortality

– HPI mediated trade-offs

– Immune system development

Timing of stress exposure may also affect disease

Baseline

Imm

un

e F

un

ctio

n

Duration of Stressor

Minutes-Hours Hours-Days Days-Weeks Weeks-Months

(-)

(+)

Adapted from Martin (2009), General and

Comparative Endocrinology, Vol. 163

Inflammatory cytokines

Acute response

Immunosuppression - negative feedback

PredationCompetitionThermal shock

PollutionHabitat change

Warne, Crespi, & Brunner (2011)

Stress & Immunology

• Wood frog tadpoles exposed to exogenous CORT

– Acute = six hours prior to infection

– Chronic = three days prior to and during infection

– Metyrapone = CORT synthesis blocker

• Then exposed to cultured Ranavirus (104 PFU)

• Livers and spleens dissected at day 2 & 4 post-exposure

• Livers analyzed for viral load via qPCR

• Spleens analyzed for lymphocyte proliferation by PH3-mitotic marker immunohistochemistry staining

Survival Methods

• Following CORT exposure the tadpoles were exposed to Ranavirus at an LD 50 dose (102.5

PFU)

• Animals which reached GS 46 were considered to have survived infection

Acute & chronic CORT effects on Ranavirus infection

Survival varied significantly by

treatment (χ2 =19.93, df=4,

p<0.0005, log-rank test)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Acute CORT ChronicCORT

Metyrapone PositiveControl

NegativeControl

Su

rviv

al

Treatment

Survival at LD-50 dose

CORT effects on surviving Ranavirus exposure

CORT expression varies across a population

• Low CORT profiles of tadpoles associated:

• Greater size & development

• More aggressive accessing of food

Stress effects on transmission

Are Large or small focals better disease

spreaders?

• Focals infected with lethal virus dose

• 24 hour transmission in tub of 9

susceptible tadpoles

• UV filter to inactivate free virions

• Ubiquitous environmental stressors undoubtedly alter disease susceptibility

Environmental stressors are ubiquitous

… as are their effects on disease expression?

• Transmission capacity likely not equivalent across individuals

• Stressors affect individuals differently

• How do individual stress profiles influence not only susceptibility, but transmission and recovery

• How do stressors like pollutants contribute to patterns of disease emergence and outbreaks?

• ….. beyond susceptibility

Research Funding

SIUC New Faculty Start Up Grant

OSPA Seed Grant

Thanks To

Lucas Kirschman

Alessandra Araujo

Seth LaGrange

Tom Egdorf

Jackie Adams

Kelley Fritz

Acknowledgements