What are the pre-requisites for developing Erysipelas? My Grandfather William John Springett, Adelaides brother, died an early death due to Anasarca. My mother told me it was something he picked up in the Middle East during WW1. Both diseases seem to be quite rare nowadays.
Since erysipelas is a bacterial infection, the only real prerequisite is to pick up the relevant bacterium. The bacterium that causes most cases of erysipelas is called "Streptococcus pyogenes"; this is also responsible for cases of scarlet fever which can lead to rheumatic fever. Both types of infection still exist these days but are far less common than they used to be; it's not 100% certain why this should be the case, but better general hygiene standards are at least in part to thank for this. Antibiotics (which of course didn't exist in Adelaide's day) also help to cut strep infections, but it's thought as well that the bacterium may be mutating/evolving in a way that makes it less toxic to humans.
So lack of hygiene would play a part in the incidence of strep infections, but is not a pre-requisite -- erysipelas is still around today and you don't have to live in a filthy house to get it!
I had to look up "anasarca" too; it's not a term with which I was familiar. Having done so, it looks to me as though the term could be interchangeable with "dropsy" - an accumulation of oedema (fluid) throughout the body. This could manifest in various ways - the commonest (still around) is swollen ankles. Fluid can also collect around the lungs. In more severe cases it can collect in other areas eg inside the abdominal cavity. Oedema like this has a large number of possible causes. The only one that comes to mind as the consequence of an infection would be again caused by our new/old friend Streptococcus - scarlet fever, caused by strep, used to not-infrequently lead on either to rheumatic fever or to glomerulonephritis (a type of kidney disease). The latter can obviously cause accumulation of oedema/fluid in the body if the kidneys are damaged. Rheumatic fever can do so by causing damage to the heart valves so the heart can no longer pump efficiently. So it's possible that William picked up a strep infection in ww1 but the family may have assumed that to be the case as it was not uncommon; it might not have true. (Heavy alcohol intake can cause similar problems for example!)
As I mentioned, streptococcus may be changing in a way beneficial to humans as a host, and that probably accounts largely for the dramatic reduction in heart and kidney disease caused by strep.
