26.05.2005

A Organização Mundial de Saúde (OMS) alertou que uma pandemia da gripe do frango é inevitável e orientou governos do mundo inteiro a tomar providências para conter o contágio de humanos pela doença. Treze pessoas morreram no Vietnã desde dezembro por causa do vírus, e a Tailândia e o Cambódia também registraram mortes ligadas à gripe do frango. Segundo a OMS, é altamente provável que haja uma pandemia da doença entre seres humanos.

Experiências passadas indicam que uma pandemia está se aproximando. No último século, houve três surtos graves de gripe. O primeiro, batizado de gripe espanhola, foi em 1918 e matou 50 milhões de pessoas no mundo todo. A gripe asiática foi o segundo grande surto, provocando um milhão de mortes. Finalmente, veio a gripe de Hong Kong em 1969, deixando mais um milhão de vítimas.

Os sintomas da gripe do frango são parecidos com os de outros tipos de gripe – febre, mal estar, garganta inflamada e tosse. Também é comum a ocorrência de conjuntivite.
Todas as atenções estão voltadas para o sudeste asiático, onde a gripe do frango matou 32 dos 45 humanos infectados com a doença desde 1997.
As pessoas pegam a doença por meio de contato próximo com aves infectadas vivas. Os pássaros expelem o vírus nas fezes, que depois de secas, pulverizam-se, sendo inaladas com o ar pelos seres humanos.

Mas há receios de que o vírus da gripe do frango pode sofrer uma mutação em contato com o da gripe humana, o que permitiria que o vírus fosse transmitido de uma pessoa para outra.
Epidemiologistas dos Estados Unidos e da Holanda pediram a criação de uma força-tarefa internacional para combater o que eles receiam que pode se transformar em um surto global de gripe que poderia matar milhões de pessoas.
Em artigo publicado na revista científica Nature, os cientistas da Universidade de Minnesota, nos Estados Unidos, e do Centro Médico Erasmus, na Holanda, dizem que apenas uma resposta unificada evitaria uma catástrofe que, entre outros efeitos, poderia afetar a economia mundial.

Why H5N1 is of particular concern
Of the 15 avian influenza virus subtypes, H5N1 is of particular concern for several reasons. H5N1 mutates rapidly and has a documented propensity to acquire genes from viruses infecting other animal species. Its ability to cause severe disease in humans has now been documented on two occasions. In addition, laboratory studies have demonstrated that isolates from this virus have a high pathogenicity and can cause severe disease in humans. Birds that survive infection excrete virus for at least 10 days, orally and in faeces, thus facilitating further spread at live poultry markets and by migratory birds.
The epidemic of highly pathogenic avian influenza caused by H5N1, which began in mid-December 2003 in the Republic of Korea and is now being seen in other Asian countries, is therefore of particular public health concern. H5N1 variants demonstrated a capacity to directly infect humans in 1997, and have done so again in Viet Nam in January 2004. The spread of infection in birds increases the opportunities for direct infection of humans. If more humans become infected over time, the likelihood also increases that humans, if concurrently infected with human and avian influenza strains, could serve as the “mixing vessel” for the emergence of a novel subtype with sufficient human genes to be easily transmitted from person to person. Such an event would mark the start of an influenza pandemic.

Influenza pandemics: can they be averted?
Based on historical patterns, influenza pandemics can be expected to occur, on average, three to four times each century when new virus subtypes emerge and are readily transmitted from person to person. However, the occurrence of influenza pandemics is unpredictable. In the 20th century, the great influenza pandemic of 1918–1919, which caused an estimated 40 to 50 million deaths worldwide, was followed by pandemics in 1957–1958 and 1968–1969.
Experts agree that another influenza pandemic is inevitable and possibly imminent.
Most influenza experts also agree that the prompt culling of Hong Kong’s entire poultry population in 1997 probably averted a pandemic.

Several measures can help minimize the global public health risks that could arise from large outbreaks of highly pathogenic H5N1 avian influenza in birds. An immediate priority is to halt further spread of epidemics in poultry populations. This strategy works to reduce opportunities for human exposure to the virus. Vaccination of persons at high risk of exposure to infected poultry, using existing vaccines effective against currently circulating human influenza strains, can reduce the likelihood of co-infection of humans with avian and influenza strains, and thus reduce the risk that genes will be exchanged. Workers involved in the culling of poultry flocks must be protected, by proper clothing and equipment, against infection. These workers should also receive antiviral drugs as a prophylactic measure.
When cases of avian influenza in humans occur, information on the extent of influenza infection in animals as well as humans and on circulating influenza viruses is urgently needed to aid the assessment of risks to public health and to guide the best protective measures. Thorough investigation of each case is also essential. While WHO and the members of its global influenza network, together with other international agencies, can assist with many of these activities, the successful containment of public health risks also depends on the epidemiological and laboratory capacity of affected countries and the adequacy of surveillance systems already in place.

While all these activities can reduce the likelihood that a pandemic strain will emerge, the question of whether another influenza pandemic can be averted cannot be answered with certainty.