Highly Pathogenic Avian Influenza Virus HPAI H7N7 - 2003 Epidemic in Europe
2. How the Virus Spread from Poultry to People and Pigs
Avian 'Flu Risk to Other Species - Cats, Dog, Cattle, Horses, Rodents, Pigs
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Veterinarian Dies in Livestock Influenza Epidemic
On April 19, 2003, the Dutch Health Ministry reported that a 57-year-old male veterinarian had died as result of Avian Influenza (AI) infection. The vet developed pneumonia two days after working with AI-infected poultry and died soon afterwards in hospital. He had apparently not been taking anti-viral medication (see below).
There was concern that this human mortality case might indicate a shift of the virus genome towards increased virulence for people, but a Dutch health ministry spokesman told Reuters new agency "We now know there's no mutation of the virus, we know for sure that the vet died of the original bird flu. It's very good to know that".
History of the 2003 Epidemic
In less than two months, an epidemic of highly pathogenic avian influenza (also known as AI and classical fowl plague) due to an influenza A virus subtype H7N7 (HPAI H7N7) has devastated the Dutch poultry industry and spread to Belgium. The epidemic began on March 1st 2003 near Barneveld in poultry which had first developed symptoms on February 28th. Most of the initial outbreaks were in free-range poultry farms. Three turkey farms in Dinteloord, near Roosendaal, in the province of Brabant were early hosts for the virus.
In efforts to control spreading of the virus, the Dutch Agriculture Ministry has culled 25 million birds - almost 25% of the total poultry in The Netherlands. Over 1,000 farms have been affected by control measures.
Spread to Pigs
On April 16th 2003, the Dutch Agriculture Minister, Cees Veerman, reported that the virus had spread to swine. Antibodies to the new virus were found in swine on five farms in the Gelderland Valley which also had infected poultry. There is no evidence, however that the virus can spread from pig to pig. Also, none of the seropositive pigs have shown any clinical signs. However, all transportation of pigs in the Gelderland Valley Limburg and parts of North Brabant has been banned as a precautionary measure. In Belgium and the Netherlands, movement of pigs had already been banned from known infected farms.
The seropositive pigs appeared to have recovered from infection - no live virus was found.
An Agriculture Ministry spokesman is quoted as saying that the danger that new viruses created inside pigs could jump to humans is "not hypothetical".
Restrictions on general pig movements in the control zones of the country have now been lifted because investigations indicate that there is little risk of transmission by pigs.
Precautions against human infection
People undertaking slaughter of infected chickens, pigs and turkeys have been vaccinated against human influenza virus and are also receiving antiviral drug treatment. The aim is not only to to protect them against infection by the bird influenza virus, but also to avoid a new and more virulent virus being formed from mixing (reassortment) of human and avian influenza viruses in someone with co-infection of viruses.
The Outbreak Management Team (OMT) are recommending the antiviral preparation oseltamivir (Tamiflu) to prevent illness in people coming into contact with the virus and to protect others coming into contact with infected individuals e.g. close family members and medical personnel.
Human Infections Reported
Up to April 25th 2003, the avian flu virus has affected 82 farmworkers and slaughtermen. An additional human infection case has occurred in Belgium. Affected people have shown symptoms ranging from conjunctivitis to mild 'flu. Even more alarming is the apparent human-to-human spread of the virus - to the wife and child of one infected man, who have not themselves had direct contact with poultry.
Surveillance of wild birds
Scientists at the Erasmus University in Rotterdam have looked for the virus in 85 samples from 24 avian species collected in the Gelders Valley without finding the virus. However, 4 tame ducks and 3 mute swans sampled in the vicinity of three infected poultry farms in Renswoude, were found to be infected with HPAI H7N7. The seven infected birds were "kept animals" that lived around farms.
Origin of the HPAI H7N7 influenza virus
The origin is uncertain but we are told by a Dutch epidemiologist that one theory is that the outbreaks may have originated in the south-west of the Netherlands near a lake district called Biesbos. A surveillance survey found three poultry farms which were seropositive for low pathogenicity AI (avian influenza virus). One of these farms had free-range poultry and was adjacent to canals with many wild waterfowl. The farm is reported to have had a hatchery service man who also served flocks in the Gelderse Valley. It is possible that the low pathogenicity avian influenza strain mutated to a HPAI strain after infecting poultry the Gelderse Valley.
However, according to virologist Prof Dr A. Osterhaus of the Erasmus University in Rotterdam his group have previously (1-2 years earlier) found the HPAI H7N7 virus type in migrating ducks and water fowl. It seems likely that wild waterfowl are a reservoir of the virus.
Similar virus strains (H7N1, H7N3) have been isolated in Italy over the past four years from different strains of virus in the poultry farms. In Italy turkey flocks have also played a reservoir role for the virus.
International Spread of HPAI H7N7
A/H7 associated conjunctivitis developed in four Netherlands poultry workers from Poland and one from Belgium. While the risk is low, they indicate the risk of spread by humans to other countries. There has been preventive depopulation of poultry flocks in Germany along the border with the Netherlands, although there have so far been no suspected or confirmed AI infections in German poultry.
Twentieth century pandemics of human influenza include Spanish flu in 1918, Asian flu in 1957, Hong Kong flu in 1968, and Russian flu in 1977. Some of viruses involved originated in animals.
An epidemic of AI H5N1 led to destruction of all poultry in Hong Kong in 1997. Six people died in this outbreak. The virus returned in February 2002 and a further death has since occurred.
The British Medical Association advise rest in bed and the drinking plenty of cold fluids. Painkillers, such as paracetamol, and anti-pyretics such as aspirin (acetylsalicilic acid) may help to ease aching muscles and fever. Antiviral drugs, e.g. amantadine, may be used in severe cases but need to be taken within 24 hours of onset of symptoms. Zanamivir, administered inhaler, can shorten the duration of symptoms but does not give protection against serious complications.
Medical attention should be sought if there is difficulty in breathing or fever lasting more than 48 hours.
In uncomplicated cases in animals or people, influenza symptoms last less than a week usually, although a cough sometimes persists for 2 weeks or more. Fatigue and depression may also persist beyond the acute stage. In severe epidemics of highly virulent viruses, deaths from secondary pneumonia may occur.
Vaccination is sometimes recommended for people in high-risk or high-exposure (e.g. health workers) groups, but not usually for babies. Vaccines typically prevent illness in about two-thirds of people who are vaccinated annually. Vaccine effectiveness is undermined by the variety of flu viruses that may occur and the possibility of virus mutating so that the vaccine loses effectiveness. The World Health Organization advises each year. on which strains of virus are expected to be a probem in particular regions. Bird and animal vaccines are also available, but not yet for the new H7N7 strain.
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