Tuesday, April 05, 2005

H7 in North Korea

Reports from Pyongyang, North Korea today seem to indicate that the unidentified bird flu strain afflicting North Korean poultry is of the H7, not H5, sub-type. AP says this has been confirmed by FAO, but New Scientist says evidence is "indirect" (according to a different FAO source), where "indirect" means the North Koreans prepared a vaccine from the sick birds and the vaccinated birds showed antibodies to H7.

If the infection is with H7 subtype this would seem to be good news as human cases with H7 have not been particularly severe. H7N2 has been reported in poultry in the US (Delaware) and H7N7 caused a large outbreak in poultry in 2003 in The Netherlands which jumped to humans. Most cases manifested as conjunctivitis ("pink eye") and a small number (3) showed typical influenza-like symptoms (cough, fever, muscle aches). The only serious case involved a veterinarian who visited one of the farms and developed fatal respiratory distress syndrome.

Relatively mild disease, yes. But the fly in the ointment is that this avian virus also showed itself to be quite transmissible to and among people. Eighty-three cases were reported initially among poultry workers with three possible subsequent transmissions to family members. A follow-up blood study with 500 farmers, their families and workers involved in the massive cull initially showed no antibodies to H7, even in those with confirmed infection. It turned out the hemagglutination assay (to see if a subject's blood serum made red blood cells clump together, a standard test for prior infection) worked with horse red blood cells, not the standard turkey rbcs. Even using horse rbcs, only about 50% of the previously infected patients showed agglutination, still not very sensitive. Using the modified assay, Dutch investigators estimated that at least 1000 and perhaps as many as 2000 people may have been infected. More importantly, close family contacts of poultry workers had a 59% seroprevalence of H7 antibodies, suggesting person to person transmission on large scale. Some other pertinent technical results:
. . . having measurable antibodies was associated with having conjunctivitis (RR 1.72; 95% CI 0.99-2.99), and a lower proportion of the exposed persons who took prophylactic antiviral medication developed antibodies (corrected OR 0.48; 95% CI 0.25-0.89).

Neither poultry farmers nor those engaged in controlling the epidemic complied satisfactorily with preventive measures. Only 6% of farmers reported consistent use of facial masks and 1% reported consistent use of goggles while working with infected poultry. In cullers, compliance was only slightly better: 25% consistently used facial masks and 13% used goggles. The results of the epidemiological study suggest that oseltamivir protected against conjunctivitis (corrected OR=0.14; 95% CI=0.08C0.27) as well as against infection without specific symptoms. No protective effect was demonstrable for safety goggles or mouth-nose masks.
Meanwhile, the North Koreans are declaring the outbreak over (Right. Maybe they want to sell me a bridge over the Yalu?). Even if true, questions remain, as New Scientist notes:
But this is a mystery, as an outbreak of H7 has never been recorded in east Asia before. “The North Koreans say they have destroyed all the sick chickens, and the outbreak is now over,” says [the FAO scientist]. “That’s good for the Koreans. But we’d like a sample of tissue from the infected birds so we can isolate the virus.”

A genetic sequence might help trace the strain’s origins, and whether it has mixed with other Asian strains.
So the evidence has been destroyed? I'll bet it's still there. The problem will be getting it before it migrates elsewhere.