I admit to not having done more than skim the abstract, but couldn't it be just as likely that authoritarian governments cause the spread of disease (and famine, etc.) through ineptitude?
More to the point, I think framing it as "authoritarian governments cause the spread of disease" is misleading. The spread is not caused by accident or economic failure, it's caused by apathy (although obviously a failed state can't fight parasites). The reason hookworm is found in relatively wealthy southeast asian countries is the same as the reason it has been found in rural Alabama; the governments don't care about everyone. It's not accurate to call that authoritarianism and it's misleading to assume it's simply economic failure.