1. oaks, moths, mice, gypsy moths, and lyme disease
The Ecology of Lyme Disease
oaks, moths, mice, gypsy moths, and lyme disease

3. Gypsy Moth Defoliation (1975-2008)

4. The white-footed mouse can regulate gypsy moth populations

5. While gypsy moth populations have been down the incidence of Lyme disease has increased
What is going on?

7. Lyme Disease Biology
Caused by the spirochete bacteria Borrelia burgdorferi
Vectored by ticks (in California Ixodes pacificus)
Vector: any agent that carries and transmits an infectious agent

8. A Community of Borrelia Hosts
western fence lizard
eastern chipmunk
dusky-footed woodrat
white-footed mouse
Target Hosts
our best friends
mom and dad
white-tail deer

9. Erythema migrans (~70% cases)
Lyme Disease Symptoms
Within a few days:
Skin rash 3-30 days after tick bite
Within days or weeks:
Fatigue
Chills
Fever
Headache
Muscle and joint aches
Swollen lymph nodes
Bell’s Palsy (loss of muscle tone on one side of the face)
Long-term neurological problems:
Problems with concentration
Short-term memory loss
Severe arthritis and joint pain
Erythema migrans (~70% cases)

10. did it just appear in the 1970s?
Lyme Disease History
did it just appear in the 1970s?
1883: The first record of a condition like Lyme Disease
1921: Joint problems disease is associated with Ixodes scapularis ticks
1975: Cluster of cases of rashes and swollen joints in Lyme, Connecticut
1982: Borrelia burgdorferi is discovered by Dr. Willy Burgdorfer

11. To establish that an organism causes disease, is must be:
How do you show that a particular microbe causes a disease?
Koch’s postulates
To establish that an organism causes disease, is must be:
found in all cases of the disease examined, while absent in healthy organisms
prepared and maintained in a pure culture (some practical difficulties here)
capable of producing the original infection (some ethical difficulties here)
retrievable from an inoculated animal and cultured again

12. Tick life cycle (Ixodes scapularis)

13. one chance to pick up Borrelia infection before nymphal stage
Risk to humans determined by:
density of nymphal ticks
infection prevalence in nymphal ticks
human behavior
feeding
mostly deer
Eggs uninfected
Adult Stage
Larvae uninfected
Nymphal Stage
feeding
one chance to pick up Borrelia infection before nymphal stage
feeding
humans are at risk

14. How Does the Host Community Affect Disease Risk
disease risk = lyme disease cases
Increased Disease Risk
Decreased Disease Risk
Amplification
Adding a species to a community increases the total abundance of hosts for the pathogen, increasing the disease risk to the target host
Dilution
Adding a species to a community decreases the abundance of more competent hosts, decreasing the disease risk to the target host
Each tick feeds only once per stage
Feedings spent on poorly-competent hosts are wasted for the disease
Competence (for hosts)
The efficiency with which a host acquires and spreads a pathogen

15. How Does the Host Community Affect Disease Risk
disease risk = lyme disease cases
White footed mice are a preferred host = more ticks
White footed mice are a competent host = more infected ticks

16. How Does the Host Community Affect Disease Risk
disease risk = lyme disease cases
Increased mammal diversity = more ticks, less ticks, who knows
Increased mammal diversity = less infected ticks

17. Biodiversity and Disease Risk

18. Biodiversity and Disease Risk

19. Tick life cycle (Ixodes pacificus)

20. Reservoir competence
Hosts differ in their efficiency at acquiring and spreading the Borrelia spirochete
highly competent
somewhat competent
totally incompetent
dusky-footed woodrat
Neotoma fuscipes
deer mouse
Peromyscus maniculatus
western fence lizard
Sceloporus occidentalis

21. The Lizard That Fights Lyme Disease
Proteins found in the blood of S. occidentalis kill the Borrelia spirochete

22. Tick life cycle (Ixodes pacificus)

23. The Lizard That Fights Lyme Disease

24. Prevalence of the Borrelia spirochete ≈ 30% - 60%

26. Does the Forest Community Affect Disease Risk?

27. Does the Forest Community Affect Disease Risk?

28. What about gypsy moths?

29. Red oaks (Quercus rubra) mast every 3-5 years
Mast production, or masting, refers to the synchronous, episodic production of heavy seed crops by a population of plants
Red oaks (Quercus rubra) mast every 3-5 years
What are the ecological benefits of masting?

30. Type II Functional Response
Handling-Mediated Specialization

32. disease risk is maximized 2 years following mast production
Tick life cycle (Ixodes scapularis)
disease risk is maximized 2 years following mast production