Avian Bird Flu

Avian Bird Flu

The Avian Flu was first recorded in Italy more than 100 years ago in 1878 and due to the massive poultry epidemics, it was then known as "Fowl Plague" (History pp). It was detected in the United States in 1924-1925 and again in 1929 (History). In 1955, it was determined that the virus causing the Fowl Plague was one of the influenza viruses (History).

All influenza viruses affecting domestic animals belong to Type A, which is the most common type that produces serious epidemics in humans (History).

There are two forms of Influenza A, one is highly pathogenic and the other is mildly pathogenic (History). The recent outbreaks in Hong Kong and elsewhere are caused by the Highly Pathogenic Avian A virus, HPAI - subtypes H5 and H7, and is a form that has the ability to be transmitted to humans (History).

Strains of the Avian Flu have cropped up several times in humans during the past 100 years, and at times with disastrous consequences (History1). In 1918, the Spanish Flu pandemic, stemming from the HINI influenza virus, swept the world and killed more than 40 million people (History1). The Asian Flu outbreak in 1957, which is blamed on the H2N2 influenza virus, claimed more than 100,000 lives (History1). In 1968, the N3N2 virus was responsible for the Hong Kong Flu pandemic that claimed more than 700,000 lives (History1).

In 1997, the avian flu virus H5N1 began infecting people in Hong Kong and eventually killed six people (History1). Then again in 1998, two more people were infected in Hong Kong and one died, and in 2003, the N7H7 strain infected 83 people and led to one death (History1). In 2004, the H5N1 and H7N3 strains infected dozens of people in Vietnam and Thailand, and two in Canada, and several of these people died (History1). So far in 2005, strains have been found to infect people in Vietnam, Cambodia, Indonesia, and Thailand, resulting in approximately 60 deaths, and strains are now being detected in animals for the first time in Romania, Greece, Turkey, Russia, and England (History1).

The Avian Flu has received considerable domestic and international attention over the past few years as recent epidemics were found in Japan, South Korea, Belgium, Germany, the Netherlands, and areas of South-east Asia, and reports of outbreaks in Australia, Pakistan, Italy, Chile, and Mexico (History). The impact has been disruptive to the poultry industries as millions of chickens, geese, and turkeys had to be slaughtered to prevent further transmission of this highly contagious disease (History). Aside from the devastation to the poultry industry, the Avian Flu has received unprecedented publicity due to the occurrence in 1997 in Hong Kong, when the Avian Flu virus was detected in humans, marking the first time that the disease was transmitted to humans (History). This outbreak resulted in eighteen people being hospitalized and six human deaths (History). Recently, a major outbreak of the Avian Flu surfaced in Vietnam's and Thailand's poultry industry and within a few weeks, it had spread to ten countries and regions in Asia (History). More than 50 million chickens, ducks, geese and turkeys were slaughtered in an effort to stop the disease from spreading, however 34 people were infected with the virus in Vietnam and Thailand, of which 23 of them died (History).

Though scientists determined that the spread of the Avian Flu virus from fowl to humans are rare occurrences, they do caution that the problem could become significantly worse if the virus mutates into a more lethal form or a form than could pass more easily from humans to humans (History). The World Health Organization, WHO, is especially concerned about the Avian virus's potential to swap genes with a common flu virus, thus creating a lethal form that could spread around the globe within a matter of months (History).

According to the World Health Organization, influenza A viruses have 16 H. subtypes and 9 N. subtypes, yet only viruses of the H5 and H7 subtypes are known to cause the highly pathogenic form of the disease, however not all viruses of the H5 and H7 subtypes are highly pathogenic and not all cause severe disease in poultry (Avian). At present it is understood that H5 and H7 viruses are introduced to poultry flocks in their low pathogenic form, and when allowed to circulate within the poultry populations, then the viruses can mutate, often with a few months, into the highly pathogenic form (Avian). This is the reason why the presence of an H5 and H7 virus in poultry creates alarm, even when the initial signs are mild (Avian).

Although the role of migratory birds in the spread of highly pathogenic avian influenza is not completely understood, wild waterfowl are considered the natural reservoir of all influenza A viruses and have probably carried the viruses, with no apparent harm, for centuries (Avian). However they are known to carry the H5 and H7 subtypes, though usually in the low pathogenic form, and considerable evidence suggests that migratory birds can introduce low pathogenic H5 and H7 viruses to poultry flocks, which then mutate tot he highly pathogenic form (Avian). In the past, highly pathogenic viruses have been isolated from migratory birds on very rare occasions, usually involving a few birds found dead within the flight range of a poultry outbreak, thus suggesting that wild waterfowl are not agents for the onward transmission of these viruses (Avian).

Recent events suggest that it is more likely that some migratory birds are now directly spreading the H5N1 virus in its highly pathogenic form, and further spread to new areas is expected (Avian). The current outbreaks of highly pathogenic Avian influenza, that began in Southeast Asia during 2003, are the largest and most severe on record (Avian). The H5N1 virus has proved to be especially tenacious, for despite the death or destruction of some 150 million birds, the virus is now considered endemic in many parts of Indonesia, Vietnam, Cambodia, China, Thailand and the Lao People's Democratic Republic, and control of the disease in poultry is expected to take several years (Avian).

According to the World Health Organization, the widespread persistence of H5N1 in poultry populations poses two major risks for human health (Avian). First, the risk of direct infection when the virus passes from poultry to humans results in very a severe disease, and of the few Avian viruses that have crossed the species barrier to infect humans, the H5N1 has caused the largest number of cases of severity and death in humans (Avian). Unlike normal seasonal influenza, the disease caused by H5N1 follows a particularly aggressive clinical course, with rapid deterioration and high fatality and primary viral pneumonia and multi-organ failure are common (Avian). During the present outbreak, more than half of those infected have died, and the majority of cases have occurred in previously healthy children and young adults (Avian). The second risk, which is considered of even greater concern, is that the virus, if given opportunities, will change into a form that is highly infectious for humans and has the ability to spread easily from person to person, which could mark the beginning of a pandemic or global outbreak (Avian).

At present, it is believed that the main route to human infection is direct contact with infected poultry, or surfaces and objects contaminated by their faeces (Avian). To date, the majority of human cases have occurred in rural or peri-urban areas where most households keep small poultry flocks, which usually roam freely, often entering homes or sharing outdoor areas where children play, thus providing opportunities for exposure to infected droppings or to contaminated environments (Avian). However, it is believed that exposure most likely occurs during slaughter, de-feathering, butchering, and preparation of poultry for cooking, yet there is no evidence that properly cooked poultry or eggs can be a source of infection (Avian). It is not believed that the virus spreads easily from birds to humans, and although more than 100 human cases have occurred in the current outbreak, this is a small number when compared with the huge number of birds affected and the numerous associated opportunities for human exposure (Avian). Moreover, it is not presently understood why some people, and not others, become infected following similar exposures (Avian).

According to the Centers for Disease Control and Prevention, CDC, the reported symptoms of Avian Flu in humans have ranged from typical influenza-like symptoms, such as fever, cough, sore throat, and muscle aches, to eye infections, pneumonia, acute respiratory distress, viral pneumonia, and other severe and life-threatening complications (Avian1).

CDC reports that there are four different influenza antiviral drugs, amantadine, rimantadine, oseltamivir, and zanamivir, which have been approved by the U.S. Food and Drug Administration for the treatment of influenza, three are approved for prophylaxis, and all four have activity against influenza A viruses (Avian1). Yet, the CDC cautions that sometimes influenza strains can become resistant to these drugs, thus they may not always be effective (Avian1). For example, some of the 2004…