Photo Credit – FAO
# 6142
With influenza viruses, the only true constant is change.
Viruses must continually evolve and adapt in order to survive. The legacy of infection by a virus is usually some degree of immunity, and if viruses did not evolve they would soon run out of susceptible hosts.
Minor mutations happen all of the time, but most turn out to be evolutionary dead-ends. They confer no biological advantage to the virus, fail to thrive, and die out.
It is only when the right combination of changes occurs that changes the virus’s antigenic profile or enhances transmissibility or replication – or expands its host range – while still remaining `biologically fit’, that a new strain begins to flourish and spread.
And those types of changes can happen very quickly, or they can take years in coming.
It is this evolutionary process that has led to having 20+ clades (major versions) of the H5N1 virus circulating around the world, including the vaccine resistant strain clade 2.3.2.1 (see FAO Warns On Bird Flu) that began to emerge in 2010.
With so many different clades in circulation, it is no wonder we see some variations in the way the virus behaves.
All of which serves as prelude to a long report appearing today in the Indonesian Newspaper Kompas, which talks about a moderation in outward signs of infection among poultry.
Those with long memories may recall we discussed similar concerns back in 2009 (see Bird Flu Symptoms Changing In Indonesia). Three years ago the Dean of Faculty of Veterinary Medicine, Institut Pertanian Bogor was quoted as saying:
“Common signs as cyanosis of wattle, comb or fetlock are not observed anymore. Mortality also decreases so that it’s difficult to differ between ND and AI”
So while perhaps becoming more common today, these changes do not appear to be entirely new.
Included are also some comments by Professor C.A. Nidom, on the dangers of H5N1 reassortment. My thanks to Shiloh on FluTrackers for finding, and translating the following article (original link).
Be warned, this is a machine translation, and so the syntax is a bit mangled.
Can Bird Flu Virus More Dangerous
Asep Chandra | Tuesday, February 14, 2012 | 9:28 pmJakarta, Kompas - The bird flu virus (H5N1) in Indonesia is thought to have changed. The virus is feared more dangerous than before. Further research is needed to ensure the fatality rate of the new virus.
Reports from a number of areas, until Monday (13/Feb), indicating the change. Even so, not yet ascertained the impact of the change.
Head of Animal Husbandry and Animal Health in Central Java Semarang District Whitono reveals, some poultry that died of bird flu now has features that are not as usual, ie no black or bluish spots on the comb or body part that is not hairy.
Meanwhile, Head of Animal Health Animal Husbandry and Animal Health Central Java Eko Sutarti revealed, though not sure about the new virus, characteristics of birds that died of bird flu part shifted. Usually the birds that died of bird flu are marked with blue or black spots on the comb or body parts that are not covered in fur.
Now the poultry that died suddenly without these spots were found positive for bird flu.
Of Brebes, Central Java, reportedly, the body's defense system against virus attacks poultry in the region changed when compared with previous years. This is evident from the clinical symptoms found in cases of chicken deaths in the region last week.
Head of Animal Health and Veterinary Public Health Veterinary Services Brebes Jhoni Murahman say, around 2003, when he first outbreak of bird flu virus in Bradford, clinical symptoms of bird deaths at that time happened very quickly and in large quantities.
Physical signs in birds that died of bird flu is also very clear, that the body was black, very much saliva, swollen heads and blue crest on the head.
However, at present, clinical symptoms are not very visible. Poultry deaths tend to be in unison, but one by one. Body of dead birds as well just turn blue with not a lot of saliva and the head is not swollen.
Chairman of the Avian Influenza Research Center, zoonosis, which is also a lecturer at the Faculty of Veterinary Medicine Airlangga University, Surabaya, CA Nidom, say, the existence of the bird flu virus in Indonesia to worry about. "There are allegations of meetings between the H5N1 virus (bird flu) and pan2009 A H1N1 (swine flu) in Indonesia. This could produce a new type of virus is more dangerous, "he said.
Over the years concerns have been voiced that inconsistent or poorly matched poultry vaccination programs could be driving the evolution of the H5N1 virus.
As new clades emerge, vaccination of birds with existing vaccines may still lessen morbidity and mortality in the flocks, but not prevent infection.
Creating, in a sense, a `stealth' bird flu virus; one that doesn't announce itself with clearly observable symptoms.
And that, one would have to assume, only serves to increase the chances that more people and more poultry will be inadvertently exposed to the virus.
