It is a virus so long term antibiotics can help reduce secondary infections, and steroids can sometimes make them feel a bit better but there are no guarantees.
It is either treat, wait and see, or have them put down if suffering.
Having had it on the farm, it would be worth vaccinating weaners in future to protect them, or buy from somewhere already vaccinated, and clean and disinfect everything before the next batch.
It is highly unlikely to spread between species.