Great question - the prevalence of various serovars in a given area can change over time, but it's rare to see an odd Central American serovar become endemic in e.g. North America - they are fairly region-specific.

As far as species-specificity - each serovar has a presumed natural reservoir, a "maintenance host". That doesn't mean that it only affects certain species, it's just that some serovars infect a host without causing severe disease. Swine serve as maintenance hosts for serovars pomona and bratislava, for example, and dogs are maintenance hosts for canicola - one of the serovars in your dog's vaccine. The other in your vaccine is icterohemorrhagiae, for which rodents serve as a maintenance host.

How dangerous is it for a dog to work as a ratter? I think that vaccinating is a good place to start, but I'd go with the tetravalent vaccine, personally. It includes serovar grippotyphosa, which also has rodents as a maintenance host, as well as pomona (cattle/pigs). Clinical leptospirosis is not super common in dogs, but dogs exposed to rodents would be at the highest risk. I had a coonhound I used to hunt with, and I would always keep her up to date on her lepto vaccine. It was somewhat common where I lived at the time - upstate NY. Cases seem to be on the rise in NYC even, with an outbreak earlier this year linked to a dog park in Brooklyn.

I wish there were a good reference for serovar distribution in the US, sounds like maybe something someone should work on. There are maps with case distribution online, but not serovar distribution.

The vaccine for animals is, frankly, not very good. It covers just a handful of serovars out of the hundreds of serovars identified; serovars most commonly reported in North America. And that coverage is not great, with some potential for infection and disease in vaccinated animals. Bacterin vaccines in general are imperfect, often requiring frequent boosters.

Which brings us to your question - the vaccine for animals wouldn't be that good in humans, either - the majority of cases in people involve one of the ~200 serovars outside of North America - Asia, Central/South America, etc.

Prophylactic antibiotics (doxycycline most often) can instead be provided for people visiting areas/participating in activities with high risk.

In short, it's a disease of developing areas (low pharmaceutical investment) that's tough to develop a broad and effective vaccine against because of the wide range of serovars, with a cheap and easy antibiotic preventative available for those who want it.

E: I did find that at least one lab is working on a universal lepto vaccine: https://elifesciences.org/articles/64166

A protein I work with has a plasma membrane localization sequence, but we delete it because it's unnecessary for our studies 👍

There are a whole host of these signal peptides routing proteins all over the cell: https://en.wikipedia.org/wiki/Signal_peptide

You got it. They'll most often have a nuclear localization sequence - a "tag" of a short length of amino acids that tell the cell "this one goes to the nucleus."

https://en.wikipedia.org/wiki/Nuclear_localization_sequence

Or insect, or mammalian, depending on the application.