Lyme DZ Life Cycle of The Tick Vector

1. Uninfected larvae:

   • Yr1 Spring

   • The uninfected egg hatches and develops into uninfected larvae

2. Infected larvae:

• Yr1 Summer

• 1st blood meal: the uninfected larva feeds on an infected field mouse (natural reservoir) and becomes infected with Borrelia burgdorferi

3. Infected larvae (dormant):

• Yr1 Fall/Winter

• Drops off the mouse to the ground and stays dormant (cold weather, no field mice around)

4. Infected nymph:

   • Yr2 Spring

   • The infected larva comes out of dormancy and develops into an infected nymph
      

5. Infected nymph → uninfected human/pet:

   • Yr2 Summer

   • 2nd blood meal on a human/pet who is usually outdoors

   • The human/pet gets Lyme Disease

6. Infected adult:

   • Yr2 Fall

   • The nymph drops off the human/pet and develops into an infected adult tick
      

7. Infected adult → uninfected deer:

   • Yr2 Fall

   • 3rd blood meal on a deer, which infects the deer with B. burgdorferi

   • The adult ticks mate

8. Uninfected eggs:

   • Yr1 Spring

   • The infected adult female lays uninfected eggs in the ground (no transovarian passage, unlike RMSF)

Key takeaways:

• Mouse = reservoir (where the tick gets infected)
  
  

• Nymph = main stage that infects humans
  
  

• Deer = mating host (keeps the tick population going)
  
  

• Eggs are always clean, so every generation has to get infected again from mice (unlike RMSF)

Pathway:

8 Egg → 1 Larva → 2 Infected larva (mouse) → 3 Dormant → 4 Nymph → 5 Human 🦠 → 6 Adult → 7 Deer (mate) → 8 Egg

Why is the nymph the main threat to humans?

It’s tiny and easy to miss, and it feeds in summer when people are outdoors.

How many blood meals, and on which hosts?

3: Mouse → Human/pet → Deer (small → medium → big)

Fill in the blank diagram: boxes 1–8.

1 Uninfected larva, 2 Infected larva (mouse), 3 Dormant, 4 Nymph, 5 Human/pet, 6 Adults, 7 Deer, 8 Eggs