That is the way to avoid the disease. Offal is more likely to be infected than meat, but any part of the fish could harbor these critters. Sometimes salmon poisoning is difficult to distinguish from parvo. Diagnosis is usually done by looking for the fluke eggs in fecal samples. It is a more difficult task to look for the rickettsial organisms, but lymph node aspirates can be examined.
Treatment is intensive fluid and antibiotic therapy in a veterinary hospital.
Tetracycline antibiotics are effective if instituted early enough. So I cannot provide diagnoses, or really tell you to ignore or treat a given problem. I hope the information provided guides you in making good health care decisions for your pets.