April 5, 2005 (CIDRAP News) ?The strain of avian influenza responsible for the deaths of 219,000 poultry in North Korea is not the same as the lethal H5N1 strain many experts fear could cause a worldwide pandemic.

Tests conducted by the United Nations Food and Agriculture Organization (FAO) have confirmed that the virus in North Korea is an H7 strain, although further subtyping has not been completed, according to an Associated Press (AP) story today.

An FAO official said the discovery marks the first time an H7 outbreak has been identified in Asia, where H5N1 has caused poultry outbreaks in nine Asian countries and 50 human deaths in 3 countries since 2003.

The FAO´s Hans Wagner traveled to North Korea when news of the outbreak surfaced in late March. "We have a new situation because H7 has so far not occurred in Asia," Wagner told Reuters television in Beijing today, following his trip.

"We want to know: How did it come to such a large farm with relatively good biosecuirty measures?" the AP quoted Wagner as saying. Three factory-style farms within 3 miles of Pyongyang, the North Korean capital, have been affected, news services said.

Wagner described North Korean officials as "very cooperative" and said they had approved testing of bird samples by labs in China, Britain, and Australia, according to the AP.

News of the outbreak has generated concern about its possible effects on North Korea´s poultry industry. The impoverished, secretive Communist state was thought to have about 25.5 million poultry in 2004, following a massive push to re-establish a local food supply. North Korea has seen widespread famine as a result of many factors, including natural disasters and bad harvests in the mid-1990s. The country has depended on foreign aid to feed its people.

By North Korea´s official reckoning, famine has killed 200,000 people; international estimates range from 1.5 million to 3 million deaths, according to a 2000 estimate by the nonprofit group Medecins Sans Frontieres (MSF).

No human illness cases have been reported in connection with the North Korean outbreak, but H7 viruses have been known to spread from poultry to people before. A recent World Health Organization (WHO) report lists 93 human cases, including one death, as the result of H7 infections. All but four of these were linked with a major avian flu outbreak in the Netherlands in 2003.

Although H7 viruses have made people ill, the cases have not been as severe as those in the current H5N1 outbreak in Southeast Asia. In most cases the symptoms, if any, were limited to conjunctivitis, according to the WHO. However, in the Dutch outbreak in 2003, a 57-year-old veterinarian died.

Follow-up research on the Dutch outbreak suggested there were high rates of transmission of the virus from chickens to people and secondary transmission from person to person. At least 50% of people exposed to infected poultry in the outbreak were later found to have H7 antibodies, according to a 2004 report by the Dutch National Institute for Public Health and the Environment (RIVM).

Further, 59% of people who hadn´t had contact with infected poultry but had household contact with an infected poultry worker had H7 antibodies, according to the RIVM. In all, researchers estimated that 1,000 to 2,000 people were infected with H7N7 in that outbreak, far more than the 89 cases officially reported.

"This suggests that the population at risk for avian influenza was not limited to those with direct contact to infected poultry, and that person-to-person transmission may have occurred on a large scale," the researchers concluded.

Four H7 subtypes H7N1, H7N4, H7N3, and H7N7 have been identified in highly pathogenic avian influenza poultry outbreaks, according to the WHO. It´s not yet clear which H7 subtype has sickened birds in North Korea. Further subtyping of the virus is pending, news services reported today.

See also:

WHO report "Avian Influenza: Assessing the Pandemic Threat"
http://www.who.int/csr/disease/influenza/en/H5N1-9reduit.pdf

RIVM´s final analysis of the H7N7 outbreak in 2003
http://www.eurosurveillance.org/ew/2005/050106.asp

H7 related Chinese scientific journal can be foud at : http://www.flu.org.cn/scn/news/2005465268.htm (Chinese)

the only serology report of antibody level against H7 in regional population (Wuxi city, Jiangsu Province) can be found at http://www.flu.org.cn/scn/resources/2005466878.htm (Chinese) 

OIE Report

AVIAN INFLUENZA IN KOREA (DEMOCRATIC PEOPLE´S REPUBLIC OF ~)

Immediate notification

Information received on 7 and 8 April 2005 from Dr Ri Gyong Gun, Director of the Veterinary and Anti-Epizootic Bureau, Ministry of Agriculture, Pyongyang:

Report date: 5 April 2005.

Reason for immediate notification: first occurrence of a listed disease⁽¹⁾ in the country.

Precise identification of agent: avian influenza virus type A subtype H7.

Date of first confirmation of the event: 26 March 2005.

Date of start of the event: 25 February 2005.

Nature of diagnosis: clinical and laboratory.

Diagnosis:

Source of outbreak: unknown or inconclusive.

Control measures undertaken:

- control of arthropods;

- control of wildlife reservoirs;

- partial stamping out;

- quarantine;

- movement control inside the country;

- screening;

- vaccination;

- disinfection of infected premises/establishment(s).

Vaccination in response to the outbreak:

Treatment of affected animals: no.

Additional details:

Respiratory distress syndrome was observed among the chickens in one of the blocks (the block has a capacity of 19,000 to 24,000) of the Hadang poultry farm, notably when there was a built up of poisonous fumes in the block caused by a power failure that occurred during the night of 23 to 24 February 2005. Air vents were opened to improve ventilation and provide fresh air, but from the next day some layers began to die.

Samples were sent for examination to the Veterinary Diagnostic Laboratory of the Pyongyang Poultry General Complex on 28 February and strict anti-epizootic measures were taken.

The Diagnostic Laboratory of the General Complex conducted tests between 28 February and 5 March but was unable to identify the precise cause of the disease. It then informed the National Veterinary and Anti-epizootic Emergency Committee and sent samples and isolates to the Central Veterinary Diagnostic Laboratory.

The National Veterinary and Anti-epizootic Emergency Committee organised the incineration and burying of all the chickens in the infected blocks and, with a view to identifying the disease, authorised the Central Laboratory to inject all the chickens in the unaffected blocks and in neighbouring chicken farms with an inactivated vaccine obtained by inoculating eggs with material from internal organs of dead chickens into embryonated eggs.

The Central Laboratory conducted general examinations several times between 5 and 15 March, but was unable to obtain a definite identification of the virus subtype due to the lack of standard sera and suitable testing kits, but was able to confirm that the disease was influenza type A.

With the help of Government measures, tests continued and the virus subtype was eventually confirmed, using the PCR⁽³⁾ technique, as avian influenza virus subtype H7 at the Institute of Cell and Gene Engineering, National Academy of Sciences, on 26 March.

The disease outbreak could eventually be officially announced in the country on 27 March.

Tests are currently under way to determine the N subtype of the virus.

On or around 5 March, an outbreak of the disease also occurred at the neighbouring Sopo and Mangyongdae chicken farms, which proved to be caused by the same subtype that affected the Hadang chicken farm.

At Hadang chicken farm a total of over 151,968 layer chickens in the eight blocks were destroyed. At the Sopo and Mangyongdae farms the damage was less extensive thanks to the vaccination that had already been conducted, only three blocks with a total of 51,820 chickens being lost at Sopo and only a single block with over 15,000 chickens being lost at Mangyongdae poultry farm.

A total of over 218,882 chickens were culled and buried during the disease outbreaks. No clinical signs of the disease have been detected since 7 March 2005.

All the necessary anti-epizootic measures have been taken, including a ban on movements into and out of the affected area, in accordance with the provisions of the Terrestrial Animal Health Code. There has been great awareness of the disease among the human population in the affected area. Public health surveillance has been stepped up, especially for those involved in the destruction and burying of infected chickens. To date there have been no reported cases of human infection.

Investigations are under way throughout the country to try to determine the full extent of infection in poultry farms and in various wild bird populations.

As this disease event was one of the first of its kind ever to have occurred in the Democratic People´s Republic of Korea, it took some time to make the correct diagnosis. The inexperience of the veterinary experts, the inadequate facilities and apparatus and the lack of reagents, such as standard sera, caused by the country´s recent economic difficulties had a negative effect on the conduct and timing of the diagnostic procedures.

The anti-epizootic measures taken on this occasion to eradicate the disease were in accordance with the technical standards of the OIE, but the lack of facilities such as reagents, apparatus and standard sera resulted in poor identification of virus subtype H7, though it was diagnosed as H7 by PCR⁽³⁾ analysis at the Veterinary Institute of the Academy of Agricultural Sciences and the Institute of Cell and Gene Engineering, Academy of National Sciences.

On 4 April 2005, an FAO⁽⁴⁾ expert visiting the Democratic People´s Republic of Korea initially confirmed the virus as subtype H7.

(1) Note by the Animal Health Information Department: the listed disease is suspected to be highly pathogenic avian influenza

(2) ELISA: enzyme-linked immunosorbent assay

(3) PCR: polymerase chain reaction

(4) FAO: Food and Agriculture Organization of the United Nations