The worst part is foreign mosquitoes doing the disease spreading that American mosquitoes won’t do :)
Or is it simply American mosquitoes getting it by sucking the blood of diseased foreigners. There was qa time when immigrants had to undergo very rigorous medical examination and testing, submitting to internment and quarantine for a period long enouh to ensure the individuals were not disease-bearers. If they were, they were not admitted at least until after being free of it. Including iontestinal flora. I bet.