Canada will check donor blood for West Nile virus if test available
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* Barbara Sibbald

Canadian Blood Services (CBS) hopes to be using a blood test to detect West Nile virus (WNV) by next summer. “In Canada, it is unlikely that either the blood suppliers or the public would accept that an available screening test would not be used to detect a potentially fatal virus that could be transmitted by blood transfusion,” explains Medical Director Heather Hume. 

The CBS decision was announced a week before the death of an Ontario woman who was infected with WNV, which may have been contracted during a blood transfusion. Joyce Kimmel, a 57-year-old cancer patient, died Nov. 21. On Dec. 13, CBS and Héma-Québec took the precautionary step of withdrawing thousands of units of blood products that may have been contaminated with the virus. 

“Even if the Ontario case [was] not [WNV], we know that WNV can be transmitted by blood, and if WNV continues to spread in Canada then we likely will have a [transfusion-related] case — unless donor testing becomes available,” says Hume.

WNV (*CMAJ* 2000;162 [7]:1036) is spread by mosquitoes, but less than 1% of those infected become seriously ill. However, the virus may cause potentially fatal encephalitis in immunocompromised patients.

The possibility of WNV infection is already causing concern among patients being treated for anemia. Durhane Wong-Rieger, president of the Anemia Institute for Research and Education, says the benefits “far outweigh the current treatment risks.”

CBS was initially pessimistic about the possibility of a test being developed to allay fears of infection, but Hume says “it now appears quite likely that there will be a suitable test.” An estimated price is not yet available.

In the meantime, new CBS guidelines to prevent transmission of WNV via the blood supply will rely on disease surveillance after donations are made to determine if blood should be destroyed. This has limited use, since only 20% of infected people develop symptoms.

Between Aug. 28 and Oct. 2, 2002, the US Centers for Disease Control and Prevention reported that 15 patients with confirmed WNV infection were diagnosed after receiving blood components; 3 had received organ transplants. WNV was the probable cause of death for at least 3 of the 4 patients who died. In Canada, WNV patients who have either received blood recently or donated blood shortly before developing their symptoms are deferred from donating for 56 days. In the US, they are deferred for 28 days.

In the US 3495 cases of WNV had been reported by November 2002, resulting in 204 deaths. Canada had 51 confirmed human cases and 2 deaths in 2002. — *Barbara Sibbald*, CMAJ