The latest news form the research area is pretty heartening. Two important developments were reported this week in the research journals. One deals with developing a vaccine to avian flu, the other with subclinical (symptomless) infections of avian flu in humans during a flu outbreak in Netherlands. Join me on the flip.
Tian et al reporton the development of a flu vaccine for birds. In the introduction to the research, the authors clearly summarize why they undertook this work and the potential positive impact it could have.
Wild birds are regarded as natural reservoirs for avian influenza viruses. Free-range domestic waterfowl have chances to contact with both wild birds and domestic animals, including poultry and mammals, such as pigs, and therefore can function as intermediate hosts to transmit the avian influenza viruses from wild birds to other hosts. H5N1 avian influenza viruses have circulated in domestic waterfowl in certain southeast Asia countries for a number of years, and these waterfowl usually do not show any disease signs, even when they carry viruses that are highly pathogenic for chickens. If active surveillance is not rigorously carried out, these viruses will not be detected unless they cause disease outbreaks or are transmitted to sensitive hosts, such as chickens or turkeys. It is quite common in southern China and other Asia countries that pigs and ducks are housed in close proximity, especially in farming villages, where families typically own a small number of pigs and ducks. This proximity creates the opportunity for viruses to transmit between ducks and pigs and to adapt to mammalian hosts.
So the goal is to put up a barrier to this virus up to block its transmission from wild birds to domestic flocks and thereby prevent it crossing eventually into humans.
The researchers used reverse genetics to generate a recombinant H5N1 virus that has low pathogenicity, yet high immunogenicity. In other words, it would no longer cause disease, but would be protective against more virulent strains of flu virus. This was used to create a vaccine using the classic process of growing them in eggs. Testing of the vaccine showed that it was protective for chickens, ducks and geese. The success of this method indicates that it is possible to generate an effective vaccine to this virus. It is pretty likely that this vaccine or a very similar one would be possible in humans, and protective. However, the strength of the immune response, and the length of protection was different for each species. In all cases,
the birds were capable of surviving a challenge with the influenza virus. Second, the information obtained during the reverse genetics process will make it easier to develop future vaccines to H5N1 strains that may mutate to be capable of infecting humans.
A second study, by Meijer et. al. looked at the movement of a highly pathogenic avian influenza A(H7N7) virus in The Netherlands. During that outbreak 89 persons were found to have confirmed cases of the illness. The question the authors wanted to answer was, how widespread was viral infection in humans. Did every person infected with the viral strain become deathly ill, or were there many who contracted the virus, but did not show any symptoms, or at least did not come in for treatment? They approached this by testing a population exposed to the virus, either through infected poultry or humans. What they found, was frankly shocking. Of the 508 subjects exposed to influenza-infected poultry, 49% had antibody to the virus, indicating an active infection or one in the recent past. Also, 63% of 64 individuals exposed to ill humans were seropositive for H7N7. Take in the significance of this. Many people had subclinical infections of this avian flu virus. It is very likely the same thing is true for H5N1 strains and it should be investigated. If it turns out that H5N1 also causes subclincal infections, and I see no reason this won't be true, this will greatly reduce the population that would be at risk in a H5N1 pandemic. However, millions would still get sick, but at least half the population would not. Not great, but better than everyone being susceptible to serious illness from infection with the H5N1 influenza.