Part 1.
Even though Spain (SP) and Austro-Hungary (AH) are the two main Earth Powers on Venus (bypassing the "Scramble for Mars" that broke out between Britain (UK), Germany (GE,) France (FR,) and America (USA.))
There were other Colonial presences on Venus – for Britain and France it was primarily the two scientific research stations conceded by treaty and the "Plantations" of Belgian financiers working for the King of Belgium (which the Crafty Belgian had won as quid pro quo for letting the Belgian Government take over the Congo Free State from the King in 1901 due to pressure from Britain, France, Germany, and America on Spanish claims of the entire planet (disputed by Austro-Hungary of course though most of Europe tended to only give lip service to AH claims at best.)
America (after losing the Spanish American War due to previously unsuspected Spanish development of "alien" Technology) had no claims to venus by treaty but they had an asiento to provide food stuffs to Spain's Venusian colonies (Spain saw the potential power of the USA and decided a generous treaty was better than an embittered and embarrassed enemy) and a small party of American scientists help developed the less classified products that Spain provided to a world in fear of the "infections" that Earth suffered from due to smugglers from Venus to Earth.
When incidents of "WereWolves, Vampires, and Zombies" became all too real in London, Paris, New York, Mexico City, Moscow, Berlin, Constantinople, and (initially and especially) Vienna there was a frenzy of Apocalyptic cults that grew up in response to the terrors unleashed. Spanish (and American) scientists pressured the Spanish government successfully to 'bite the bullet' and officially announce the "plagues" were known diseases that were known to occur from contact from "micro insects" in the Venusian coastal swamps (the observations of Ignaz Semmelweis earlier were vindicated beyond all doubt in Spanish/American Labs on Venus then further developed in British, French and German research centers.)
British and French Intelligence Services eventually produced evidence that it was a group of AH smugglers who brought the plague to Europe. "Aztlán Reconquista" Mexican radicals diseased Martyrs caused the infection to spread to New York then ironically to Mexico City via their transporters.
The serums to control (no cures to exist to this date) the effects of the causative agents from Venus were able (with great effort and high costs) to be reproduced on Venus. Unfortunately (except to Spanish Government coffers) all attempts to create the medical agents here on Earth have failed despite intense efforts of the Best Non-Spanish Scientists.
The initial smugglers were apparently eventually determined to be Austro-Hungarian freelancers (though many had ties to the AH government.) Reports that the causative agents were in some cases intentionally spread by AH intelligence services are vehemently denied by Vienna.