Darwin Chronicles

April 2006

On the lookout for avian influenza in the United States

The feds enhanced surveillance for early detection of highly pathogenic avian influenza in wild migratory birds in the United States, according to an announcement made at a recent press conference in Washington.

This unifies efforts of federal, state, regional and local wildlife agencies, which have been monitoring H5N1 virus in migratory birds for several years and comes as the spring migration of birds is under way. Avian influenza continues across Asia, Europe and the Middle East. Public health officials said it is only a matter of time until the virus is seen in the United States.

“It is increasingly likely that we will detect the highly pathogenic H5N1 strain of avian flu in birds within the U.S. borders, possibly, as early as this year,” said Interior Secretary Gale Norton at the press conference.

Health officials have been looking for H5N1 since it first appeared in Hong Kong in 1997. Government agencies have tested more than 12,000 migratory birds in the Alaska flyway, 4,000 migratory birds in the Atlantic flyway and 1,100 migratory birds in the Pacific flyway. There have been 22 avian influenza isolates identified in the Pacific flyway birds, but none have been highly pathogenic, authorities said.

Preventing the spread of highly pathogenic H5N1 in domestic poultry operations is greatly enhanced if the United States can rapidly detect the pathogen as it is introduced into wild migratory birds here, officials said.

“A detection of the more dangerous high pathogenic H5N1 in wild birds would not mean that commercial poultry – that is, birds raised for consumption – would be affected,” said Agriculture Secretary Mike Johanns. “The U.S. poultry industry is much better positioned to deal with bird flu than many countries currently affected by the highly pathogenic H5N1 virus.”

He added that the industry’s practices and consolidation make it easier to respond to a lethal virus. “In many countries struggling with the virus, chickens are commonly raised in yards and even inside houses. In the United States, chickens, turkeys and eggs produced for human consumption are typically raised in very controlled environments.

The interagency plan outlines five strategies for early detection of the virus in wild migratory birds: investigating disease outbreaks in wild birds; expanding live wild bird monitoring; monitoring of birds killed by hunters; using sentinel animals; and conducting environmental sampling of water and bird feces.

Because Alaska is at the crossroads of bird migration flyways, scientists believe the strain of highly pathogenic H5N1 affecting Southeast Asia would most likely arrive there if it spread to North America through migratory birds, according to a Department of Agriculture press release. The plan recommends a prioritized sampling system with emphasis in Alaska, elsewhere in the Pacific Flyway and the Pacific islands, followed by the Central, Mississippi and Atlantic Flyways. The wild bird monitoring plan is part of the U.S. president’s National Strategy for Pandemic Influenza Preparedness; $29 million has been allocated in pandemic flu funding to implement the wild bird monitoring plan.

However, Health and Human Services (HHS) Secretary Mike Leavitt noted that highly pathogenic H5N1 is still a disease of birds. “While there is no evidence that the virus is passing from person to person, we do see this virus circulating in birds all over the world. It is a highly lethal virus when it gets into human beings, and there is no human immunity ... it has killed this far 98 people in the world, and it has a mortality rate of about 50%.”

Leavitt said HHS is monitoring to spot disease outbreaks at home and abroad; developing vaccines and vaccine manufacturing capability and stockpiling both vaccines and antivirals.

“A pandemic involves much more than just public health officials. This is a matter that requires the attention of elected political leaders, of employers, of school leaders ... all need to be engaged and actively involved,” he said.

To assist local efforts, HHS is holding planning summits in all 50 states and providing checklists to local and state governments, businesses, schools, home health care providers, religious and community organizations and individuals and families.

Various forms of low pathogenicity avian influenza have existed in the United States since the early 1900s. They can cause varying degrees of illness in birds and have not posed a public health threat. — Marie Rosenthal

BSE reported in Alabama cow

An Alabama cow tested positive for bovine spongiform encephalopathy (BSE), according to the Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS).

Two tests were used to confirm the diagnosis: western blot and the immunohistochemistry. At press time, APHIS was conducting an epidemiological investigation to trace the animal’s origin. It had been on the Alabama farm less than a year. One of the first steps will be the recovery and examination of the carcass.

The cow, initially reported to be a Santa Gertrudis, is now believed to be a red crossbred (possibly crossed with a Santa Gertrudis or similar breed). This animal was nonambulatory on the farm and examined by a local veterinarian. The veterinarian returned to the farm the following day, euthanized the animal and collected a sample, which was submitted for testing. The animal was buried on the farm at that time.

This animal did not enter the animal or human food chain. Human and animal health in the United States is protected by a system of interlocking safeguards, which ensure the safety of U.S. beef. The most important of these safeguards is the ban on specified risk materials from the food supply and the FDA’s ruminant-to-ruminant feed ban.

As part of USDA’s BSE enhanced surveillance program, more than 650,000 samples have been tested since June 2004. To date, only two of these highest risk animals have tested positive for the disease as part of the surveillance program, for a total of three cases of BSE in the United States.

Lack of surface receptor hinders human H5N1 transmission

The H5N1 avian influenza virus may not have the right stuff to become a pandemic, according to a recent study done by researchers at the University of Wisconsin (UW) and the University of Japan.

Differences in the cells of the lower respiratory tract makes it difficult for human-to-human transmission of this particular strain, according to virologist Yoshihiro Kawaoka.

By examining human tissue, Kawaoka and colleagues found that receptor cells favored by this virus are clustered deep in the lung, rather than in the upper respiratory tract (URT), where human influenza viruses tend to be. Being so deep in the lungs, people are less likely to shed virus when they are symptomatic, according to a release from the UW. The findings were reported in the journal Nature.

The group noted that the cells in the URT lacked the surface receptors that enable avian H5N1 virus to dock with the cell.

This means the H5N1 must undergo a change to the virus’ hemagglutinin surface protein to become a human pandemic strain, said Kawaoka, a professor of pathobiological sciences at the UW-Madison School of Veterinary Medicine.

In other news, UW-Madison recently announced plans to launch a new Institute for Influenza Viral Research.