1 - do all ticks carry lyme?
2 - do all bites of lyme carrying ticks transfer the disease to the person?
3 - different people take different preventive measures before going in the woods, so that would affect the study as well and how?
Veterinarian checking in to the thread again. Can't speak to human medicine, but for my patients the answers are thusly:
1) Only soft-shelled ticks. In this part of the world, that's the deer tick, Ixodes scapularis. Most recent prevalence I've seen is around 47% of deer ticks are carriers.
2) No. The Borrelia bacterium has to migrate from the body cavity to the salivary glands of the tick, which takes around 24 hours at common near-body temperatures. Most Lyme-carrying rocks will activate it on a bite but not all. Additionally, being bitten by a tick that later tests negative for Lyme doesn't mean you weren't bitten by another tock that had it - so tick-testing is probably of limited value.
3) Similar to the COVID vaccine trials, the point is to see how the vaccine does in a real-world environment. Thus: vaccinate a group of people and give another group a placebo, then wait. COVID had a very high prevalence so they reached significance really quickly. This may take longer, but the fact that it's volunteer- based means it's likely to draw people who are at a higher-than-average risk of exposure.
You're right that intentional inoculation would be more foolproof, but no ethics board would approve that. Also, that would introduce another variable - if they inoculate with one strain, we wouldn't know how it protects from other strains.
PSA: please make sure your dogs are protected from ticks and vaccinated. It's 2023, there's no reason for any dog to get Lyme disease. Oral preventatives are light-years ahead of anything topical.
