PLAGUE Dan Salkeld Postdoc, Lane Lab Department of Environmental Science, Policy & Management UC Berkeley
Yersinia pestis Many hosts (>200 species) Many fleas (>250 species) Multiple modes of transmission (what are they?)
Yersinia pestis Flea-borne zoonotic disease Important in human history (why?) Most lethal bacterium known to mankind
Third Pandemic introduced plague to USA Current USA distribution of plague
Prairie dogs Cynomys ludovicianus Prairie dog towns/colonies (highly social) Keystone species?
Decline in abundance Habitat loss - Development - Farming
Decline in abundance Eradication efforts Fun
Plague and the black-tailed prairie dog High mortality rate Slow colony recovery Significant threat to remaining prairie dog populations Photo by Kim Pollard
Plague activity on prairie dog colonies on the Pawnee National Grasslands, CO Prairie dog colonies Extinct 2004 Extinct 2005 Plague present in 2005
MYSTERY: where is plague in between the big die-offs? DIE-OFF DIE-OFF MYSTERY QUIESCENT PHASE Colony extinct in 6 weeks Individuals die in 4 6 days Territorial coteries 1 2 years before re-colonisers
environment? Transmission Cycle RODENT HOST FLEA pneumonic carnivores pets HUMANS pneumonic
environment? ALTERNATIVE RODENT HOST? FLEA? Pneumonic? transmission cycle for prairie dogs Carnivores?
HOW DO YOU FIND IT? 1. Nobutos antibodies 2. PCR presence 3. Culture
ARE CARNIVORES IMPORTANT IN THE ECOLOGY OF PRAIRIE DOG PLAGUE?
Carnivore exposure to plague common in USA Map of seroprevalence rates:
Do carnivores and prairie dogs interact? Evidence from scat. 8 grassland colony 7 No. scats/survey 6 5 4 3 2 1 0 coyote Species swift fox
Do carnivores and prairie dogs interact? Evidence of scavenging, using dead guinea pigs. 4 Mean days to discovery 3 2 1 0 active plague grassland Site type
Investigating swift foxes Reintroduction of swift foxes to South Dakota Why test for plague?
Seropositive (i.e. exposed) foxes associated with extinct prairie dog colonies
ARE CARNIVORES IMPORTANT IN THE ECOLOGY OF PRAIRIE DOG PLAGUE? Do carnivores spread plague? Or are they just exposed dead-end hosts? SENTINEL HOSTS: Sign of plague activity and geography in rodents
Introduction to the small mammals of the PNG (smaller than prairie dogs) Thirteen lined ground squirrel Spermophilus tridecemlineatus Northern grasshopper mouse Onychomys leucogaster Ord s kangaroo rat Dipodomys ordii Deer mouse Peromyscus maniculatus
Asian hosts Marmots/tarabagan Susliks Gerbils
Fleas Y. pestis PCR Blood samples Y. pestis antibodies Host measurements
High plague exposure rates in grasshopper mice Seropositive animals ONLY on epizootic colonies Seropositive deer mice and ground squirrels 1 yr after epizootic
How do mice get plague? Prairie dog flea: Oropsylla hirsuta Common on prairie dogs, Infrequently on carnivores Rare on small mammals \
O. hirsuta load (no./mouse) 7 6 5 4 3 2 1 Prairie dog fleas on grasshopper mice active colonies Infrequently found 0 May/Jun Jul/Aug Sep May/Jun Jul/Aug Aug Sep 2004 2005 Session
7 74 3Prairie 41 62 dog fleas on grasshopper mice Loads increase during epizootics O. hirsuta load (no./mouse) 6 5 4 3 2 1 0 2004 plague active colonies extinct 62 extinct 3 74 41 May/Jun Jul/Aug Sep May/Jun Jul/Aug Aug Sep 2004 2005 Session
O. hirsuta load (no./mouse) 7 6 5 4 3 2 1 0 74 3 41 62 8 5 82 Prairie dog fleas on grasshopper mice 2005 plague 2004 plague active colonies 74 41 3 Loads increase during epizootics 62 May/Jun Jul/Aug Sep May/Jun Jul/Aug Aug Sep 2004 2005 Session plague detected 8 82 5
O. hirsuta load (no./mouse) 7 6 5 4 3 2 1 0 Prairie dog fleas on grasshopper mice 74 3 41 62 8 5 82 35 84 Increased loads allow detection/prediction of plague activity? 2005 plague 2004 plague active colonies 84 74 41 3 62 May/Jun Jul/Aug Sep May/Jun Jul/Aug Aug Sep 2004 2005 Session 8 82 35 5 plague confirmed
Is prairie dog to grasshopper mouse transmission only via fleas?
What must grasshopper mice do to maintain plague dynamics? PCR positive fleas Pleochaetis exilis; the grasshopper mouse
Patterns of grasshopper mouse abundance and plague activity Grasshopper mouse abundance in 2004 predicts plague activity in 2005 (18 colonies, logistic regression, P = 0.02) Long-term patterns: (t+1) proportion of colonies extinct 0.4 0.3 0.2 0.1 mice captured colony extinctions 40 30 20 10 grasshopper mouse abundance 0.0 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 Year 0
Grasshopper mice and plague in prairie dogs Die-off High abundance of grasshopper mice results in increased flea movement in prairie dog colony? Increased flea movement increases transmission rate/spatial extent?
Grasshopper mice and plague in prairie dogs Mystery quiescent phase Maybe plague persists in grasshopper mice? Transmission to prairie dogs when grasshopper mouse abundance is high?