While I don't have information on the epidemiology of the Spanish Flu, I can answer the first half of your question.

The precise origin of the Spanish Flu is debated, in part because of the debate on when it actually "became" Spanish Flu. An outbreak of influenza in China in 1889 has been suggested as the possible "starter" virus which evolved into flu. Oxford et al (2005) argued that the Flu started in the British army in Etaples (Northern France) because of a relatively severe influenza outbreak there in late 1916/early 1917, in large part because of several contemporary sources in 1919 that described the two outbreaks as "fundamentally the same condition" (Abrahams et al, 1919). A much less common--but still not unreasonable--theory is that the flu originated in what is now Vietnam and Laos and was brought to Europe with a contingent of 50,000 Indochinese soldiers.

The most accepted theory for the origin of Spanish Flu is somewhere in the United States, particularly a prison in New York (there was an influenza outbreak in New York in February of 1918, but again--when does Spanish Flu become Spanish Flu, and not just influenza? However, there seems to be a body of evidence suggesting that this was Spanish Flu or something very similar) or a training camp in Kansas in March. Camp Funston is widely considered the most likely start of the pandemic, as 1,100 soldiers were infected with influenza, many of whom later went to Europe where they carried the pathogens.

Because we cannot ascribe a particular date to Spanish Flu beyond early 1918, and because we didn't have the same global information sharing, it is likely we will never know exactly which influenza strain (whether it be a modified version of the Chinese outbreak of 1889 or was a purely American variation, or whether it really started in France, etc) caused the pandemic.

Even at the time though, doctors didn't blame the Spanish, and in fact, almost no lay people did either that I could find evidence for. The name Spanish Flu came about in large part because Spain was neutral during the First World War (unlike America, France, Britain, and Germany, where the disease was really starting to take off). Therefore, the Spanish press reported on the disease well before other nations did, as they were not concerned about enemies knowing about illness amongst their army. The war incidentally probably also helped the disease become the pandemic it was, as soldiers from all corners of the world came together, allowing numerous strains of influenza to mix, and carried it home when the war ended in November of that year.