Sporotrichosis is a fungal infection that is gotten from thorny plants and bushes. Lesions that end up forming on the hand or skin can be swabbed and cultured to make the diagnosis. There are medications to treat it and I don't know if your brother is taking any at this time. He should be on medication therapy at this time however if the infection has involved the bone then surgery is usually necessary. Please take a look at the website below for more detailed info to help you understand what is going on with your brother.
I hope all will be well with your brother.
It would help if you could give me some more details about your brother. Who told you that his situation could be fatal and why? As you read, if the infection is in the bone or joint it is much more difficult to treat than if it is on the skin. What does the doctor want to do at this point to treat your brother? What medications is he currently using? Does he have any medical problems? Is he diabetic?
Let me say this: This condition is treatable over a long period of time with special medications. If the patient has a suppressed immune system and therefore has difficulty fighting infection then this leads to serious problems. If the infection gets into the lymph system it can be potentially fatal only if bacterial superinfections cause sepsis which is generalized infection in the blood. These are the worst case scenarios. It depends on how far the infection has gone into his body and his immune system's ability to fight back, along with medication. This will determine his prognosis.
People recover from sporotrichosis, with treatment and when it is caught early. Something else may be going on medically in his case.