# 2654
This is something we've discussed before; the changing clinical picture of H5N1 infection in domesticated birds. A few earlier blogs on the subject can be found here, here, and here.
HPAIs (Highly Pathogenic Avian Influenzas) often reside silently in waterfowl, but almost always produce serious, usually lethal symptoms in poultry.
At least, that's how things used to be.
Asymptomatic infections in poultry, once rare, are now becoming more common. And even among those birds that do show symptoms, they often present with less apparent symtomology.
The following comes from a relatively new, but very welcome resource on the Internet. The Bird Flu Information Corner, a weblog developed based on collaboration work between Kobe University, Japan and Institute of Tropical Disease, Airlangga University, Indonesia.
Indonesia recent avian derived flu virus shows unspecific signs.
January 13, 2009
Poultry disease expert from Gajah Mada University also expert member of Komnas FPBI, Charles Rangga Tabbu said that bird flu mutation in Indonesia has established new concern. Recent circulating virus shows alternation of clinical signs and tissue disruption compare to 2003 isolates.
“We are having difficulty to diagnose bird flu in field. It was easier to diagnose before”, said Charles. Ones can’t determine diagnosis only by observation and palpation, only by laboratory confirmation, as this pathologist from Gajah Mada University explained.
This statement is confirmed by Dean of Faculty of Veterinary Medicine, Institut Pertanian Bogor. “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”, he said. Wayan also explained that this is because birds exposed to virus after they’re vaccinated. Suboptimal immunity in bird’s body allows virus infecting and developing in birds and followed by virus shedding.
Further news can be viewed at Kompas, Indonesia local newspaper here.
The newspaper article referred to at the end of this report appears in KOMPAS, and is dated today (January 13th, 2009). It is written in Indonesian (Bahasan), but I present an excerpt and a link to a machine translation below.
Clinical symptoms of Bird Flu No More Specific
Kompas/P Raditya Mahendra Yasa Compass / P Raditya Mahendra Yasa
Officials from the Department of Animal Husbandry in Semarang, Central Java, squirt disinfectant around the stall owned by citizens Medoho, Eastern District of Semarang, on Tuesday (11/11). Spraying is done to control and prevent the bird flu virus in these regions.
Tuesday, 13 January 2009 | 08:05 WIB
JAKARTA, KOMPAS - bird flu virus mutation memapar the poultry in Indonesia since 2003 has caused a new problem. Poultry fell ill that bird flu virus is now no longer show clinical symptoms of the more specific so difficult recognized.
Likewise opinion poultry disease experts from Gadjah Mada University, who is also member of the panel of experts Control Committee of the National Bird Flu and pandemic influenza Facing Preparedness (Komnas FBPI), Charles Rangga Tabbu, when contacted last week in Yogyakarta.
According to him, the problem of avian influenza (AI) in the new Indonesia is a virus that attacks the birds now klinisnya symptoms vary with the year 2003. Similarly, damage to the poultry network.
"We have difficulties diagnose bird flu in poultry in the field.,” Formerly the birds fell ill easily recognizable, but not now, "said Charles who is also Chairman of the Association of Veterinarians poultry Indonesia. Subklinis difficult to guess the form of the symptoms and not specific.
According to him, the clinical symptoms that can not be observed with the naked eye or hold the fuselage."It should be done in the lab examination," said the lecturer at the Faculty of Veterinary Medicine pathology UGM this.
In the good old days, if a chicken got bird flu, it died quickly. The virus could wipe out a large flock, literally overnight. The signs of infection were dramatic, usually leaving little doubt as to the diagnosis.
But in the past couple of years we've seen a moderation of symptoms in some regions, and in some cases, completely asymptomatic poultry.
Yet these birds can still be infected, and shed the virus.
Exactly why some poultry tolerates infection with the virus today, when five years ago it killed the birds, isn't known for sure. One possibility is some small change in the virus. But that isn't the only possibility.
We do know that cross-immunity can occur when poultry are exposed to the H9N2 virus, which rarely produces illness in poultry.
Khalenkov A, Perk S, Panshin A, Golender N, Webster RG. - Division of Virology, Department of Infectious Diseases, St. Jude Children's Research Hospital, 262 Danny Thomas Place, Memphis, TN 38105-3678, USA.
The continued evolution of H9N2 and H5N1 viruses and their spread and re-emergence across Eurasia raise concern that prior H9N2 virus infection may limit the detection of subsequent H5N1 infection in gallinaceous poultry by attenuating the severity of disease.
Vaccination of birds with a poorly matched vaccine may lessen morbidity and mortality in the flocks, but not prevent infection.
Whatever the cause, it is a worrisome development.
A `stealth' bird flu virus, one that doesn't announce itself with clearly observable symptoms, has a much greater chance of spreading silently to healthy flocks.
And that, one would have to assume, increases the opportunity for people to become unknowingly exposed to infected birds.
