What sort of virus could have the same effect as Bubonic Plague?
Bubonic plague?
On a more serious note, how do you read 'the same effects'? Bubonic plague was not unknown in the 19th century, and an outbreak in Europe was always possible. That it didn't happen was more luck than skill. But the 19th century version of plague was a very different animal from the virgin-soil pandemic of the 1340s or even the great epidemics of the 1500s and 1600s (so different, in fact, that it is still considered somewhat respectable to try and find a different culprit - an anthrax strain or a hemorrhagic fever - for the 'Black Death'). That was probably partly due to mutation (bacteria change very quickly and lower lethality is a desireable trait if your survival depends on contagion) and partly due to acquired resistances. Plague was not curable until the twentieth century, and it's still not an 'easy' disease.
If you are looking to replicate the effects of a virgin-soil pandemic, I would suggest a hemorrhagic fever out of Africa, with a slightly lower lethality, longer incubation period and higher contagiousness than the usual suspects. It could credibly appear as a completely new threat, untreatable by Victorian medicine, with any of the expeditions that entered the dark continent and spread along the shipping lanes. Ebola kills too quickly - it couldn't do that - but a mid-century fast sailer or steamer could take a slower disease to Alexandria or Lisbon, and from there, its spread would be guaranteed. The first symptom is pain in the joints and easy bruising (no big deal - lots of people suffer from rheumatism) followed by nosebleeds and bleeding gums. Bloody stools are next. Draw this stage out over several weeks - the blood carries the disease and the first symptoms will not be taken seriously. In the catastrophic climax of the disease, the victim bleeds from the nose, mouth, anus, penis or vagina, eyesockets and ears, the joints are stiff with excruciating pain and the skin black and blue with subcutaneous hematoma. This is accompanied by high fever. If the crisis is survived, the patient recovers. Most die, if not from the fever and multiple organ failure, then from dehydration and blood loss. Caring for patients is deadly since the blood is highly infectious. This could kill millions in a previously unknown and terrifying way around the world, worse than cholera.