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spacemanv t1_ivnzdhm wrote

The first rash is actually immediately over the bite in 70% of cases, and is a immune mediated superficial skin rash. It actually gets it's characteristic bullseye shape from the center being an immune reaction to the salivary proteins, and the outer ring being the spread of bacteria outwards in the skin. You see them behind the knees because it's easy for ticks to get brushed into skin folds.

The secondary (stage 2) lesions and lymphadenopathy happen after the bacteria spreads from the initial lesion in the weeks following.

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