# 2511
Aquatic waterfowl, most notably ducks, are considered to be the natural reservoir of low-pathogenic avian influenzas. These viruses tend to affect the gut of the bird, rather than their respiratory system, and birds spread the virus by leaving virus laden feces in communal water sources like lakes and ponds.
Avian influenza viruses can survive for days in cold water, promoting the spread of the virus to new hosts.
Ducks have been generally thought to carry the virus asymptomatically, although a new study, reported by Maggie Fox of Reuters, indicates that infected ducks tend to be thinner than uninfected ducks and that they only shed viruses for a few days.
There are a great many unanswered questions, however, over how the highly pathogenic H5N1 virus has spread around the world. Migratory birds, and the poultry trade, are both eyed as likely vectors.
Bird flu makes mallards thin, study finds
03 Dec 2008 01:53:13 GMT
Source: Reuters
WASHINGTON, Dec 2 (Reuters) - Avian flu viruses make mallard ducks thinner than other ducks, a finding that implies they do not spread the germs over long distances, researchers reported on Tuesday.
Their tests of thousands of ducks migrating through Sweden showed the viruses do affect the birds, contrary to conventional wisdom that the pathogens have no effect on them.
And, to their surprise, they found the birds only "shed", or release, virus for a few days, the researchers reported in the Proceedings of the Royal Society B: Biological Sciences.
"Mallard ducks are a main reservoir for low-pathogenic avian influenza virus in nature, yet surprisingly little is known about how infection affects these birds," Jonas Waldenstrom of Sweden's Kalmar University, Albert Osterhaus of Erasmus Medical Center in Rotterdam and colleagues wrote.
A reservoir is a species that hosts a virus without becoming ill, and thus serves to spread it. Avian flu viruses have most often been found in migratory waterfowl, especially mallard ducks.
Over the past several years we've also learned a good deal about other potential, non-avian reservoirs of the highly pathogenic H5N1 virus.
Some earlier blogs on the subject include:+
Reservoir Dogs (Cats, Foxes, and Raccoons)
This study demonstrates that red foxes fed bird carcasses infected with HPAI virus (H5N1) can excrete virus while remaining free of severe disease, thereby potentially playing a role in virus dispersal
Experimental Infection of Cattle with Highly Pathogenic Avian Influenza Virus (H5N1)
Abstract
Four calves were experimentally inoculated with highly pathogenic avian influenza virus A/cat/Germany/R606/2006 (H5N1) isolated from a cat in 2006.
All calves remained healthy, but several animals shed low amounts of virus, detected by inoculation of nasal swab fluid into embryonated chicken eggs and onto MDCK cells. All calves seroconverted.
Hong Kong: Bird Flu Discovered In 4 Markets - Mass Culling To Begin
Of particular concern is that these infected birds were discovered by routine testing, that no unusual bird die offs had been reported, raising the specter that these birds are asymptomatic carriers of the virus.
The Secret Woid Is `Asymptomatic'
On Monday we learned that 2% of the birds sampled in Siberia showed antibodies to the H5N1 virus. These birds, alive and healthy, were exposed at some point in their lives to the virus and either recovered or were never sickened to begin with.
We've seen repeated reports (here, here, here, and here) over the past year from Vietnam, Indonesia, and other parts of the world of asymptomatic birds spreading the disease without showing signs of illness themselves.
