At the 15th European Congress of Clinical Microbiology and Infectious Diseases (ECCMID) last year, Professor Albert Osterhaus from Albert Osterhaus of the Erasmus University of Rotterdam (Netherlands) presented a report on possible prospects for the development of the avian flu epidemic in Southeast Asia.

Influenza viruses differ in the type of hemagglutinin and neuraminidase: to date, 15 types of hemagglutinin and 9 types of neuraminidase are described. The H5N1 strains currently circulating in Asia are highly pathogenic to birds, humans and felines.

The professor began his report with a description of an outbreak of bird flu in the Netherlands in 2003 caused by the H7N7 virus, which is not linked to strains recently isolated from Asia. This structural virus had much in common with the virus previously isolated from birds in Italy, and was characterized by high pathogenicity and virulence for birds. During the epidemic, apparently migratory birds infected chickens raised in the open air and, in turn, they transmitted the infection to poultry, those who care for them, their families and a veterinarian who developed fatal influenza pneumonia. A total of 78 cases of human illness were detected during the epidemic: 78 cases of conjunctivitis, 2 cases of systemic flu-like illness, 5 cases of systemic flu-like illness with conjunctivitis (including 1 fatal), and 4 people did not have a clinically distinguishable image of the disease. In 86 cases, infection with birds occurred and in 3 cases, secondary transmission from person to family member.

One fatal case occurred with a veterinarian, who was one of the few in contact with infected birds who had not taken oseltamivir as a preventive measure. Prophylactic administration of the drug has been recommended to all persons in contact with the bird after detecting an epidemic. The patient went to the hospital with a major complaint of headache, but quickly developed severe interstitial pneumonia and died a week later from the time of hospitalization. The H7N7 virus isolated from the patient's lungs (A / Netherlands / 219/03) has accumulated more than 12 mutations compared to the strains which exclusively caused conjunctivitis. This phenomenon, accompanied by an increase in the pathogenicity of influenza viruses, is also observed in the H5N1 strains isolated from humans. Typically for influenza, in 2003, the Netherlands simultaneously spread the H7N7 virus, which causes conjunctivitis, and H3N2, which caused respiratory infections.

Since the H5N1 avian flu epidemic in 1997 in Hong Kong, during which human cases were noted, other subtypes of virus have circulated: H9N2 in Southeast Asia in 1999-2000, H5N1 in Hong Kong in 2003, mentioned above H7N7 in the Netherlands in 2003 and the current outbreak in Southeast Asia H5N1.

The epidemic currently observed has several unique characteristics, including the interspecific pathogenicity of the pathogen. Tigers and leopards at the Bangkok Zoo in Thailand fell ill and some died after eating carcasses of chickens that died from bird flu. This proves the possibility of direct transmission of the virus from one animal species to another. The H5N1 strain, obtained during an epidemic in Hong Kong in 1997, was pathogenic for macaques in which the virus caused the development of necrotizing bronchopneumonia. Posthumously in animals, the virus has been detected in the lymph nodes and blood. Unlike the recent cases of children in Vietnam, no virus has been posthumously released from the brains of infected macaques.

There is no doubt that the H5N1 virus currently in circulation is pathogenic for humans, but free person-to-person transmission has not yet been described. The virus also does not reveal specific genetic markers characteristic of human pathogenic strains. Strains freely transmitted from person to person can appear in one of the scenarios: several (7 or more) consecutive mutations among the circulating strains or the genetic recombination of human and avian influenza viruses, which generally occurs when animals (piglets) are infected, followed by pandemic spread. The agents responsible for the last 3 flu pandemics (the Spanish in 1917, which claimed the lives of more than 50 million people, the Asian flu in 1957 and the Hong Kong flu in 1968) were originally from strains less pathogenic for humans. In fact, other strains of the influenza A virus, rather than the H5N1 of concern today, could cause the next pandemic.

The modern world, comprising both developed and developing countries, is clearly unprepared for a threatening pandemic. Cases have already been described which indicate the imperfection of surveillance measures carried out in influenza outbreaks in humans and animals. Difficult factors include:

The case of the illegal transport of 2 raptors infected with the avian influenza virus from South-East Asia to Belgium is described, where they were found and quarantined at Brussels airport. However, a veterinarian who examined the birds may have been infected by accident.

Given the total lack of immunity to H5N1 in the population, the vaccine will likely contain an adjuvant.

In conclusion, it was noted that in most countries, national influenza pandemic programs have not been sufficiently developed for complex public health areas such as quarantine, public awareness, educational activities and prioritization of vaccination and antiviral therapy.