Anian influenza virus and the threat posed to humans

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Avian Influenza

Introduction

Bird flu in most cases begins with discomfort of lower respiratory ways and in unusual cases--from upper respiratory air-ways . Elevated viral titer is isolated from pharynx but not from nose . Initial symptoms of the H5N1 influenza are : high grade fever , mild cold , cough and shortness of breath . Practically all patients develop viral pneumonia complicating to secondary bacterial infection , mild to severe respiratory distress diarrhea , vomiting and abdominal pain

. Conjunctivitis is entity Sometimes gastrointestinal dis develops earlier than respiratory symptoms

Avian influenza viruses are shed in respiratory secretions and feces of birds . Infected ducks , for example , shed virus for at least 30 days Influenza virus from the feces of waterfowl can be recovered from surface water . Avian species develop infection that ranges from asymptomatic to lethal . Avian influenza has caused major outbreaks in poultry farms . Influenza virus can undergo genetic mutations in hemagglutinin or neuraminidase (antigens on the surface of the virus that can lead to epidemics . Much less commonly , a completely new hemagglutinin or neuraminidase emerges - with the new genetic material coming from animals . This genetic shift typically leads to pandemics

Early chronology

1929 - Last evidence (serologic ) of circulation in humans of a swine-like influenza virus

1930 - Isolation of an influenza virus from swine

1933 - First isolation of an influenza virus from humans

Until 1995 , only three of the 15 influenza hemagglutinins that had been identified were known to cause infections in humans . Birds have all 15 identified hemagglutinins and nine neuraminidases . New influenza viruses often emerge from southern China , a region characterized by a large densely settled human population and abundant pigs and ducks living in close proximity to humans

Until events in Hong Kong in 1997 , scientists thought that avian influenza posed no direct threat to humans . In 1997 , after causing influenza outbreaks on chicken farms , avian influenza (H5N1 ) spread to humans (Claas et al . 1998 . Eighteen human cases were confirmed , six of them fatal . Infection was concentrated in children and young adults unlike the pattern in most outbreaks where morbidity and death are most common in older adults . The virus recovered from humans was identical to that found in birds (Subbarao et al . 1998 . Epidemiological studies suggested that there had been multiple independent introductions of the influenza virus into the human population from birds , but that very limited person-to-person spread occurred . At the time of the human cases , there were estimated to be 300-600 live bird markets in Hong Kong , where mixing of different avian species (ducks , chickens pheasants , pigeons , wild birds ) was possible . When the Hong Kong live bird markets were studied , 10 or more of birds were found to be shedding H5N1 , in multiple avian species (geese , chickens , ducks . The birds (more than one million ) were killed , and no additional human cases of H5N1 have been documented . In 1999 , human infection with H9N2 another avian influenza strain widespread in Asia , was also documented for the...