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

Gypsy Moth Defoliation (1975-2008)

The white-footed mouse can regulate gypsy moth populations

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

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

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

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)

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

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

Tick life cycle (Ixodes scapularis)

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

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

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

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

Biodiversity and Disease Risk

Biodiversity and Disease Risk

Tick life cycle (Ixodes pacificus)

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

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

Tick life cycle (Ixodes pacificus)

The Lizard That Fights Lyme Disease

Prevalence of the Borrelia spirochete ≈ 30% - 60%

Does the Forest Community Affect Disease Risk?

Does the Forest Community Affect Disease Risk?

What about gypsy moths?

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?

Type II Functional Response Handling-Mediated Specialization

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