Unit 2: Eastern Deciduous Forest and Lyme Disease. Video 1.

Unit 2: Eastern Deciduous Forest

  • Unit 2 focuses on the Eastern Deciduous Forest, using it as a narrative to teach ecological concepts.
  • The unit aims to address the question: What does it take to create and maintain a healthy ecosystem?
  • The lectures contain ecological concepts presented in a way that allows you to use a lot of concepts while at the same time learning about them.

Lyme Disease: A Case Study

  • Lyme disease was first discovered in Lyme, Connecticut, in 1977 when a mother noticed her children exhibiting arthritis-like symptoms.
  • It is a vector-transmitted disease, meaning it spreads through parasites or insects (primarily ticks), not through aerosol transmission.

Symptoms and Diagnosis

  • Bull's-Eye Rash: A migratory rash appears in 70-80% of cases; its absence doesn't rule out Lyme disease.
  • Other Symptoms: Fever, fatigue, headache, muscle/joint aches.
  • Lyme disease is often called "the great imposter" because its symptoms mimic other illnesses.
  • Misdiagnosis can be common, especially when doctors don't initially consider Lyme disease.
  • In areas where Lyme is prevalent (e.g., Northeast US), doctors often test for it early on.

Causative Agent and Transmission

  • Causative Agent: The bacterium Borrelia burgdorferi, a spirochete with a filament.
  • Vector: The deer tick (Ixodes scapularis), also known as the black-legged tick or bear tick.
  • Deer ticks use various warm-blooded animals (mice, birds, deer) as hosts, feeding on their blood.
  • 300,000 to 350,000 people are affected every single year with Lyme disease.

Prevalence and Distribution

  • Lyme disease is concentrated in the Northeast and upper Midwest of the United States, with some cases on the West Coast.
  • It's been reported in ticks on every continent except Antarctica.
  • It most commonly occurs in temperate deciduous forest areas.

Prevention and Precautions

  • Appropriate Clothing: Wear pants and long-sleeve shirts in tick-prone habitats (forests with undergrowth, leaf litter).
  • Insecticides: Treat clothing with permethrin or buy clothing with permethrin already embedded.
  • Repellents: Use bug repellents containing DEET on your skin.
  • Body Checks: After being in tick areas, check for ticks in folds of skin, hairlines, underarms, around ears, backs of knees, groin, and belly button.
  • Proper Tick Removal: Use the approved tick removal methods. Don't squeeze the abdomen, as this can inject fluids (potentially containing the spirochete) into your body.

Tick Lifecycle

The lifecycle of the deer tick has four different stages: egg, larva, nymph, and adult. The adult females are usually a little bit larger than the adult males.

  • The deer tick's lifecycle lasts two years.
  • Egg: Adult female lays eggs (which don't contain the bacteria), then dies.
  • Larva: Larvae hatch clean and feed on small birds and rodents.
  • Nymph: Larvae molt into nymphs (overwinter dormant).
  • Adult: Nymphs emerge and feed in the spring/summer on larger animals, including humans.
  • Adults feed in the fall, overwinter, and then mate and lay eggs in the spring before dying.

Risk Factors

  • Lyme disease risk is higher from nymphs than adult ticks because nymphs are smaller and less easily detected.
  • Nymphs are about the size of a poppy seed.
  • Each of the larva, nymph, and adult will take one blood meal and then drop off their host. They will either go ahead and overwinter, molt, or reproduce.
  • Not all ticks carry the Borrelia burgdorferi bacterium.
  • Effective reservoirs (hosts that readily transmit the bacteria to ticks) include the white-footed mouse (40-80% transmission) and the eastern chipmunk (50% transmission).
  • Transmission is most concerning from the reservoir host to immature ticks (larva or nymph).

Deer and Acorn Connection

  • Adult ticks feed on deer, but deer are not very effective reservoirs.
  • Deer congregate where there are acorns (nuts of oak trees).
  • Ticks are congregating in these areas too.
  • Acorns also attract mice, which are better reservoirs for the bacteria.
  • Increase acorns falling -> Increase deer -> Increased tick eggs -> Increase mice
  • It's the second summer after acorns fall is when people are at greatest risk to get Lyme disease.

Increased Risk Factors Since 1977

  • Increased residential development near forests.
  • Forest fragmentation increases edge habitat, which is great for mice and deer.
  • Loss of predators for deer and mice further increases their numbers.
  • Lyme disease risk is ten times greater in small forest fragments.
  • Building residential areas in direct contact with forests increases the concentration of white-footed mice and deer. This concentrates the occurrence of Lyme disease in forests.

Climate Change Implications

  • Milder winters enable ticks to remain more active and potentially shift their feeding cycles.
  • Shifting of feeding cycle can make it more likely to survive the entire summer as an adult and bite someone.
  • This blurring of seasonal stages makes avoiding Lyme disease more challenging.

Concept Map

  • (Not part of the assignments, but recommended.)
  • The recommendation is to create a concept map showing the spirochete's relationship with hosts, vectors, and other relevant factors.