Existing Drug Effective Against Bird Flu, Research Finds - US Department of State

CDC - Influenza (Flu) |Avian Flu

Overview of Influenza

In the United States each year we average 36,000 deaths and 114,000 hospitalizations. Approximately 10%-20% of the population becomes infected with the influenza.

3 types of influenza viruses exist, A, B, and C.

Influenza A is found in humans and animals (including ducks, chickens, pigs, whales, horses, and seals.

Influenza B is found only in humans

Influenza C causes a mild respiratory illness and is not thought to cause epidemics.

Current subtypes of influenza A viruses found in people are A (H1N1) and A (H3N2).
Influenza B is not divided into subtypes.
Each year’s influenza vaccine includes A (H1N1), A (h3N2) and B.

Influenza A subtypes are divided into subtypes based on two proteins on the surface of the virus: the hemagglutinin (H) and the neuraminidase (N). There are 15 different hemagglutinin subtypes and 9 different neuraminidase subtypes, all of which have been found among wild birds. Wild birds are the primary natural reservoir for all subtypes of influenza A viruses and are thought to be the source of all subtypes of influenza A viruses in all other animals.

Pigs can be infected with both human and avian influenza viruses in addition to swine influenza viruses. Because pigs are susceptible to avian, human and swine influenza viruses they potentially may be infected with viruses from different species (e.g., ducks and humans) at the same time causing an Antigenic Shift. Antigenic shifts are an abrupt, major change in the influenza A virus and most people have little or no protection against the new virus.

Antigenic Drifts are small changes in the virus that happen continually over time. A person infected with a particular flu virus strain develops antibody against that virus, as newer virus strains appear, the antibodies against the older strains no longer recognize the newer virus and reinfection can occur. This is one reason why people can get the flu more than one time. One or two of the three virus strains in the influenza vaccine are updated each year to keep up with changes in the circulating flu viruses.

Influenza B viruses only experience Antigenic Drifts.

Influenza A (H5N1) Avian Influenza

History

In 1997, 18 persons in Hong Kong were hospitalized because of influenza A (H5N1) infections and six of them died. This was the first time an avian influenza virus had ever been found to transmit directly from birds to humans. Scientists determined that the virus spread primarily from birds to humans, though rare person to person infection was noted.

In 1999, Influenza A (H9N2) were confirmed in two children in Hong Kong. Both recovered and no additional cases were confirmed. Several additional human cases of H9N2 were reported from mainland China in 1998-99.

In 2003, two (family member) residents of Hong Kong who traveled to China developed influenza A (H5N1) virus infections and one of them died. How or where these 2 family members were infected was not determined. Another family member died of a respiratory illness in China, but no testing was done.

Also in 2003 Avian influenza A (H7N7) infections among poultry worker and their families were confirmed in the Netherlands during an outbreak of avian flu among poultry. More than 80 cases of H7N7 were reported (the symptoms were mostly confined to eye infections, with some respiratory symptoms), and 1 patient died. There was evidence of some human to human transmission.

Also during 2003, an H9N2 infection was confirmed in a child in Hong Kong. The child was hospitalized but recovered.

During 2003, an outbreak of avian influenza A (h5N1) was reported among poultry in South Korea. In the second week of January, Japan reported the deaths of 6,000 chickens on a single farm in the western part of Honshu due to Influenza A (H5N1) virus infection. No human cases have been reported in either of these outbreaks.

Current

In Vietnam, large outbreaks of influenza A (H5N1) have been reported among poultry in the southern and northern regions of the country. WHO has reported that the H5N1 strain implicated in the outbreak has now been sequenced. All genes are of avian origin, indicating that the virus that caused the death in the three confirmed cases had not yet acquired human genes. The acquisition of human genes increases the likelihood that a virus of avian origin can be readily transmitted from one human to another.

The human deaths in Viet Nam coincide with historically unprecedented epidemics, in bird populations of highly pathogenic H5N1 avian influenza in Viet Nam, the Republic of Korea, and Japan. The outbreak in birds is the first in Japan since 1925 and the first ever documented in Vietnam and the Republic of Korea.

Candidate vaccines were developed last year, for protection against the H5N1 virus strain which caused two cases and one death in Hong Kong last February.

If the virus isolated from the fatal cases in Viet Nam proves sufficiently similar to the 2003 H5N1 in Hong Kong, the existing candidate vaccines could expedite the availability of a new vaccine.

Enhanced U.S. Influenza Surveillance

At this time, CDC recommends enhanced surveillance efforts by state and local health departments, hospitals, and clinicians to identify patients who have been hospitalized with unexplained pneumonia, ARDS, or severe respiratory illness And who have traveled to Vietnam, South Korea, and Japan within 10 days from onset of symptoms.

Symptoms of Avian Influenza in Humans

The reported symptoms of avian influenza in humans have ranged from typical influenza-lie symptoms (e.g., fever, cough, sore throat and muscle aches) to eye infections, pneumonia, acute respirator distress, viral pneumonia, and other severe and life threatening complications.

Pandemic Influenza

Influenza A viruses that experience an antigenic shift and acquire a new H or H+N create a new or Novel Virus to which the general population has no immunity. The novel influenza A virus also must spread easily from person to person and cause serious disease for a pandemic to occur.

Influenza B viruses do not undergo antigenic shifts and do not cause influenza pandemics.

The last two pandemics viruses were combinations of bird and human influenza viruses. Many people believe that these new viruses emerged with an intermediate host, such as a pig, was infected by both human and bird influenza A viruses at the same time. Events in Hong Kong in 1997 however, showed that this is not the only way that humans can become infected with a novel virus. Sometimes an avian influenza virus can Jump the species barrier and move directly from chickens to humans and cause disease.

It is estimated that an average pandemic could progress from a Novel Virus Alert (which is our current status do to the situation in Vietnam) to a Pandemic in a matter of months. This time frame could be much longer if the disease is not readily contagious, or it could be shorter if the virus spreads quickly.

The 1918 Spanish Flu is an example of a worst case scenario because the strain was highly contagious and quite deadly. This pandemic killed more Americans than all the wars of the 20th century.