Friday, November 03, 2006
Very Important H5N1 Article
We assessed the clinical response and extent and duration of viral shedding in 5 species of North American ducks and laughing gulls (Larus atricilla) after intranasal challenge with 2 Asian H5N1 HPAI viruses. Birds were challenged at ≈10 to 16 weeks of age, consistent with temporal peaks in virus prevalence and fall migration. All species were infected, but only wood ducks (Aix sponsa) and laughing gulls exhibited illness or died.The duck species tested were mallards, northern pintails, blue-wing teals, redheads and wood ducks. Of the species tested, only laughing gulls and wood ducks were susceptible to HPAI H5N1. The other species got infected but did not become ill or die.
It's a common misconception that HPAI H5N1 kills wild water fowl. It doesn't usually, although the Qinghai strain is notable for having produced some major die-offs. High pathogenicity for avian flu has traditionally been determined by the effect on domestic chickens, and most HPAIs do not even make most wild birds ill. Just because those ducks look good, it doesn't mean that they are not capable of passing an infection lethal to other birds.
Just as in human populations, lethality of diseases depends on the virulence of the particular pathogen, the initial exposure (low levels of exposure may produce no clinical disease, whereas high levels of exposure might produce high death rates or severe clinical illness), and the overall health of the infected organism. Wild bird populations under stress (parasitizations, cross-infections, migration stress, or marginal habitat) might show clinical disease whereas unstressed populations might not.
Among the findings were that cloacal swabs were not a good way to detect infection. Two different viral strains were tested. The first was a Qinghai strain (from Mongolia), which proved to be more virulent. In the first test, virus was detected via cloacal swabs in only 9 out of 15 infected birds. In the second test, virus was detected via cloacal swabs in only 5 out of 15 birds. To boot, the detection via cloacal swab was transient - only a day or a couple of days.
The logical conclusion is that it is rather unlikely that our current testing efforts will find HPAI H5N1 in North America until it is widely disseminated.
But the real kicker is this, which was buried in the discussion:
One wood duck and 1 laughing gull reacted positively for preinoculation antibodies to AIV by the HI test. However, both of these birds were positive at the lowest detectable limit of this test, and these results may have been false-positive due to nonspecific hemagglutination. The wood duck did not become sick after inoculation with the Mongolia/05 isolate. The laughing gull did become ill after inoculation with the Anyang/01 virus, but completely recovered. If these serologic results are true positives, it is possible that the low antibody titers provided some immunologic resistance for these birds.This is a rather startling finding. The ducks used were domestically raised in Oklahoma, and the gulls used were captured in McIntosh County, GA. These findings in the two susceptible species raise at least the possibility that some domestic H5N1 infection might exist already. This study should be repeated on a larger scale. Three wood ducks were tested with the Mongolian strain, and the one that didn't die tested positive on an H5 HI test before infection, although at a very low level. Three laughing gulls were tested with Anyang, and one of those tested positive prior to infection. It's possible that the positive findings were the result of some other H5 strain, and in that case perhaps a cross-reaction did provide some immunity.
This study should blow complacency regarding NA H5N1 right out of the water. It was, btw, done by four scientists, two from UGA and two from the Southeast Poultry Research Lab.
The symptoms in laughing gulls were:
...cloudy eyes, ruffled feathers, weakness, and incoordination, torticollis, or both.Torticollis is twisted or tipped neck, and it is quite remarkable if you have ever seen it. Torticollis is sometimes seen in botulism infections - these symptoms are not unique. Not that I haven't been watching Canadian geese stagger around my property like this for over a year now....
The symptoms in wood ducks were:
cloudy eyes, ruffled feathers, rhythmic dilation and constriction of the pupils, severe weakness, incoordination, tremors, and seizuresReported H5N1 symptoms in geese (Europe) have included apparent blindness. That is a somewhat unusual symptom. In mine (yeah, I have more guts than sense), the effect was that the birds appeared to be able to see light but not to distinguish anything. They seemed to be trying desperately to focus their eyes, until the late stage, when they appeared to be able to see almost nothing at all. Their eyes didn't roll, but they appeared to flex if you looked directly into them.
I was never able to get anyone to test these geese out here, so I just settled for pretty much banning everyone from the property.