An 8 year old Canadian boy being treated at Toronto’s Hospital for Sick Children got two severe allergic reactions within a week, perplexing the doctors treating him. They later came to know that he had earlier undergone a blood platelet transfusion as a part of his undergoing treatment for medulloblastoma, a type of brain cancer. They say the newly acquired allergy to fish and peanuts might be a result of this transfusion.

Doctors say that the boy, who was earlier able to eat fish and peanut butter without any allergic reaction before the transfusion, developed an anaphylactic reaction after eating salmon. Four days later, a similar reaction was brought about by a peanut butter cup.

A thorough investigation later revealed that one of the donors whose blood the boy received had severe allergies to peanuts, tree nuts, shellfish and other fish. He first tested positive for the presence of all those allergens but was later able to reintroduce these foods into his diet without triggering off any reactions.

Dr. Stacy Dorris, an allergist at Vanderbilt University Medical Center who was not involved with the boy’s treatment, said blood products are often pooled, meaning several donors contribute to each bag.

“There had to be a high enough concentration from a single donor” to produce enough antibodies to cause these reactions. I think it’s exceedingly rare,” Dorris said.

Officials at the Canadian Blood Services told the media that all potential blood donors at blood donation clinics are asked if they are experiencing any allergy symptoms and sent back if they reply in the affirmative. They are requested to come at a later date to avoid the risk of passing on the same allergies to recipients of their blood.

The agency however does not ask people if they suffer from any food allergies. Nor is it considering doing so in the future because that, say experts, could jeopardize the country’s blood supply.