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
