Environmental stressors are ubiquitous and can impact disease susceptibility and transmission in complex ways. Stress can alter an individual's phenotype through effects on reproduction, growth, and development, as well as their stress response and immune function. This in turn can influence their susceptibility to disease and ability to transmit disease to others. The timing, duration, and intensity of stress exposure are important factors that may increase or decrease disease risk in complex, nonlinear ways. Research is needed to better understand how stressors like pollution contribute to disease emergence and outbreaks through their effects beyond just susceptibility, and how individual stress profiles impact transmission capacity and recovery from disease.

1. Stress effects on Ranavirus susceptibility and transmission
Robin Warne, Lucas Kirschman & Alessandra Araujo
Southern Illinois University

2. 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 (-) ?

3. Stressors, Glucocorticoids & Disease Transmission
Stress Coping Style
Glucocorticoids
Passive Aggressive
Exploratorybehavior
Foodintake
Transmission(β)
Glucocorticoids
Contaminants Stressor Intensity
•Stressor effects on transmission
unclear
– Altered behavior
– Infectivity

4. 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

5. 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
CORTng/gBW
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

6. Timing of stress exposure may also affect disease
Baseline
ImmuneFunction
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
Predation
Competition
Thermal shock
Pollution
Habitat change

7. 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

8. 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 Chronic
CORT
Metyrapone Positive
Control
Negative
Control
Survival
Treatment
Survival at LD-50 dose
CORT effects on surviving Ranavirus exposure

9. 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

10. • 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

11. 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