Right about now, after months of reports, media hype, and the seeming inexorable march of “bird flu” across the world, the best advice I can offer about avian flu is “Everybody breathe regular.” Avian flu is a topic of great concern and potentially devastating import. It is a matter that we should all take time to educate ourselves about and keep half an eye on. It is not the sort of thing the average person should make vacation plans, let alone life decisions about, at least not yet.

There is understandable and continuous concern among global health authorities about the rapid and deadly spread of “avian influenza” (AI) throughout the world’s bird populations. AI is nothing new. This particular strain, H5N1, has been around for years, and since 1997 there have been a small but steady number of laboratory confirmed human infections with AI.

Nearly all of these cases occurred in people who had direct contact with birds and to date that has been the only way that every human has been infected with AI; from close and familiar contact with birds. What is sometimes lost is that while there have been an increasing number of infected people, they still represent only a tiny fraction of those that can actually be classified as “at risk.”

The purpose of this article is to place the whole avian flu situation into context and offer some perspective. We’ll focus our attention on basic information about AI in bird populations. We’ll also be looking at how humans are affected by avian flu and review the potential for a pandemic of human to human avian flu.

Avian Influenza (AI), sometimes called “Bird Flu” or “Avian Flu,” is a highly contagious viral infection that can infect birds of all species. Scientists first identified the disease over a century ago and it occurs worldwide. Migrating wild birds are known to carry AI in their intestines, usually without becoming ill due to natural resistance.

Over the last few years, AI has been spreading around the world as part of an apparent epizootic (an epizootic is a global outbreak of a disease in animals; a pandemic is a global outbreak of a disease in humans). It appears that migrating birds are spreading the disease to domestic poultry populations. Virtually every human case has resulted from contact with domestic chickens, ducks, or geese.

AI is caused by the “A” type influenza virus which belongs to the Orthomyxovirus family. Several subtypes of influenza A exist. And although it is possible for other species (including humans) to acquire AI infection, it occurs primarily in birds. Influenza infections in birds are divided in two groups based on pathogenicity (ability to cause disease).

The first and most common type of AI is known as Low Pathogenic Avian Influenza (LPAI). It generally causes a mild form of the disease, with mild or no symptoms. Secondary infections or environmental conditions may exacerbate LPAI infections, leading to more serious disease. The symptoms of LPAI in poultry consist primarily of mild respiratory disease, depression, and decreased egg production in laying birds. Current research indicates that some LPAI virus subtypes can mutate into the much more dangerous and virulent Highly Pathogenic Avian Influenza (HPAI).

Clinical signs of HPAI are depression, loss of appetite, cessation of egg laying, nervous signs, swelling and blue discoloration of the wattles (due to disturbance of blood circulation), coughing, sneezing, and diarrhea. Sudden death may occur without any prior symptoms. The incubation periods of both HPAI and LPAI range from a few hours up to three days in individual birds.

HPAI strains can be devastating infections in poultry, sometimes with local mortality rates as high as 100%. Since 1959, when recording first started, there has been a steady increase in reports of HPAI outbreaks in domestic bird populations, though whether this is due to an actual increase in the disease or simply better reporting is unclear.

The H5N1 AI virus subtype is of particular concern. The incidence of H5N1 has been increasing significantly since the first reports of outbreaks on poultry farms in Hong Kong in 1997. As of 2005, both domestic and wild birds are dying in record numbers due to HPAI resulting from infection with H5N1.

All the current evidence suggests that AI viruses are normally spread by wild waterfowl, although gulls and shorebirds have also been implicated. Direct contact between wild birds and poultry does not appear to be necessary for the introduction of the virus into poultry farms. AI is often spread through wild bird excrement that contains the virus. Drinking water may also become a source of infection if contaminated with AI. On farms, AI is transmitted through direct contact of infected poultry with healthy poultry through highly contagious respiratory secretions, saliva, and feces.

AI is also indirectly spread on an individual farm through contact with contaminated farm equipment or even workers. The spread of AI virus from one farm to another usually occurs when infectious excrement is mechanically transferred by farm workers or drivers visiting the farm, moving birds, or delivering food. So ironically, humans are spreading the outbreak to birds and may therefore be setting the stage for the disease to jump to humans.

According to the World Health Organization (WHO), “Avian influenza viruses do not normally infect species other than birds and pigs.” However, there have been a number of confirmed human cases of H5N1 Avian Influenza since the first case was documented in 1997. To date, all these cases have been attributed to direct contact with infected poultry and/or exposure to contaminated surfaces.

The current outbreak began in the middle of 2003 and has seen a steady trickle of laboratory-confirmed human cases of H5N1 Avian Influenza. To date, nine Asian countries have reported outbreaks (listed in order of reporting): the Republic of Korea, Viet Nam, Japan, Thailand, Cambodia, the Lao People’s Democratic Republic, Indonesia, China, and Malaysia. Of these, Japan, the Republic of Korea, and Malaysia have controlled their outbreaks and are now considered free of the disease. Elsewhere in Asia, the virus has become endemic in several of the initially affected countries.

In late July 2005, the virus spread to affect poultry and wild birds in the Russian Federation and adjacent parts of Kazakhstan. Almost simultaneously, Mongolia reported detection of the highly pathogenic virus in wild birds. In October 2005, the virus was reported in Turkey, Romania, and Croatia. In early December 2005, Ukraine reported its first outbreak in domestic birds. Further spread of the virus along the migratory routes of wild waterfowl is, however, anticipated.

Since bird migration is an annual recurring event, countries on the flyways from central Asia will likely face continuous risk of introduction or re-introduction of the virus to domestic poultry flocks.

In humans, influenza viruses are transmitted through the inhalation of infectious respiratory secretions. Another way is through direct contact or indirect contact with contaminated environmental surfaces and subsequent self-inoculation through the respiratory tract or the conjunctiva (the mucous membrane surrounding the eye). Evidence has shown that H5N1 infections in humans have occurred through bird-to-human transmission and possibly through environment-to-human infection. Household clusters have been reported, which raises the question of human-to-human transmission.

Still, H5N1 avian influenza remains largely a disease of birds. Despite the infection of tens of millions of poultry over large geographical areas since mid-2003, fewer than 170 human cases have been laboratory confirmed. All cases have been reported in six countries, all but one of which are in Asia: Cambodia, China, Indonesia, Thailand, Turkey, and Viet Nam. The first patients in the current outbreak, which were reported from Viet Nam, developed symptoms in December 2003. Thailand reported its first cases on 23 January 2004. The first case in Cambodia was reported on 2 February 2005. The next country to report cases was Indonesia, which confirmed its first infection on 21 July. China’s first two cases were reported on 16 November 2005. Confirmation of the first cases in Turkey came on 5 January 2006, followed by the first reported case in Iraq on 30 January 2006. All human cases have coincided with outbreaks of highly pathogenic H5N1 avian influenza in poultry. To date, Viet Nam has been the most severely affected country, with more than 90 cases.

For unknown reasons, most cases have occurred in rural households or on farms on the outskirts of cities where small flocks of poultry are kept. Very few cases have been detected in presumed high-risk groups, such as commercial poultry workers, workers at live poultry markets, cullers, veterinarians, and health staff caring for patients without adequate protective equipment. Another puzzle is the concentration of cases in previously healthy children and young adults, and what if anything these mean.

In January 2005, the World Health Organization (WHO) described the first, “probable secondary human transmission resulting in severe disease” because the case occurred between close family contacts (a mother and her young child in Thailand in September 2004). The exact nature of the transmission is yet to be proven and no similar cases have been identified.

Symptoms of AI H5N1 are fever (less than 38°C), lower respiratory tract symptoms (i.e. cough, difficulty in breathing, chest pain, wheeze) accompanied by an influenza-like illness. There may be upper respiratory tract symptoms (i.e. sneezing, nasal congestion). Unlike some other types of influenza, conjunctivitis is not common in cases of H5N1. There have been reports of gastrointestinal tract distress, pleuritic pain (the pleura is the membrane covering the lungs), and bleeding from the nose and gums in some cases. The incubation of H5N1 in humans is usually between two to four days, but can take up to eight days (which is longer than other types of human influenza).

During the 20th century, there were three severe influenza pandemics: the “Spanish Flu” of 1918, another in 1957 (the “Asian Flu), and the so-called “Hong Kong Flu” of 1968. A milder epidemic of “Russian Flu” occurred in 1976-78.

The 1918 pandemic killed about 50 million worldwide in a few months. Researchers have shown that the virus causing the pandemic was, like the H5N1 virus, from an avian source. A role for bird strains has also been shown in the 1957 and 1968 epidemics, both of which killed a million people in the course of a year.

Since the latest outbreaks of H5N1 began in mid-2003, the virus has become endemic (i.e. firmly established) in Southeast Asia, and new cases of AI in birds in West Asia and Europe suggest the virus is spreading. In addition, studies of the virus suggest that since it was first detected in humans in 1997, the H5N1 virus has mutated in ways that might allow it to move more easily from birds to humans.

Having said all that, the truth is that the unpredictable behavior of influenza viruses makes it impossible to predict either the timing or severity of the next pandemic. This particular strain of virus has been active for 8 years, and 91 deaths in three years out of a world population of 6 billion is a remarkably low death rate. In any event for a pandemic to occur, the virus would need to establish effective transmissibility from person to person; something it has yet to do.

The influenza vaccine that is developed each year for seasonal flu does not protect against the H5N1 virus. Researchers worldwide are working to develop one, but there is caveat. In order to be effective the vaccine must closely match the virus that causes the pandemic. That virus will only manifest itself when the pandemic occurs, and so it will not become commercially available until several weeks or months after the onset of the global outbreak, and may very well likely not be available when it is most needed.

Similarly, there is no known “cure” for AI H5N1. Since it is a viral infection (rather than bacterial), antibiotics are not effective against it. Antiviral drugs may decrease the severity of symptoms and possibly shorten the duration of the illness. Two drugs, oseltamivir (commercially known as Tamiflu) and zanamivir (commercially known as Relenza), have been shown in laboratory studies to reduce the severity and duration of illness caused by seasonal influenza and should work against H5N1 in humans. However the efficacy of these drugs depends on their administration within 48 hours after symptom onset.

To date, no agency or government has issued any warning against international travel. However, individuals traveling to affected countries should avoid settings where they will come into contact with wild birds, poultry farms, or markets that are selling live animals. For the latest updates regarding Avian Influenza, go to the WHO website at http://www.who.int/csr/disease/

There is no epidemiological data that suggest AI can be transmitted to humans through properly cooked food (even if the food was contaminated with the virus prior to cooking). There have, on the other hand, been cases of AI infection in humans that might have consumed dishes containing raw blood.

Basically this means that you should cook poultry and poultry products evenly and thoroughly. Similarly, because H5N1 virus can survive at very low temperatures, you should practice good hygiene when handling refrigerated or frozen meat, especially in areas where outbreaks of AI have occurred.

The basic rules you should follow include:

So what does this all mean for you and your family? The truth is that at present, most concerns and media (as well as governmental and scientific) reports have focused on potentialities, rather than realities.

Only a small number of people have been infected with AI in the past three years, and an even tinier number have died. The current H5N1 outbreak is indeed wreaking havoc and sowing death and destruction in its inexorable movement around the globe, but the principal victims are birds, which have been dying in the tens of millions.

If this virus, or a mutation of it, effectively crosses the species barrier and then becomes transmissible from person to person, the ensuing pandemic will likely spread quickly; modern day air travel will guarantee that and the virus will have spread worldwide before we are even aware it is there.

But the nature of that pandemic is unknown. While it is almost certain to cause widespread illness, how severe will it be? It may be a virulent strain with the ability to slaughter the strong and vigorous similar to what happened in 1918. Or it may simply behave in the severe, but comparatively mild manner of the Asian and Hong Kong flu epidemics, killing influenza’s preferred targets: the very young, the very old, and the weak.

There will be no effective vaccine in the early days, weeks, and months and the odds are that the supply of effective anti-virals will be limited, and even when available restricted to those most at risk.

During the 20th century, influenza pandemics caused millions of deaths, hundreds of millions of illnesses, social disruption, and profound economic losses worldwide. When the next influenza pandemic does strike we can be almost certain that far more people will be ill and unable to work for a few days than will likely die. In one conservative scenario it has been calculated that the world will face up to 100 million outpatient visits, and more than 25 million hospital admissions. The impact of these absences will snarl the wheels of commerce, cut down the number of healthcare providers, and take their toll in a dozen little ways, from sick teachers and empty classrooms, to vacant shops and businesses, reduced emergency personnel, and so forth.

This is what a future pandemic can do. So planning for it and understanding how we will meet it is the best thing we can do and the one thing we must focus our efforts on.

Read Also:

• Keeping an Eye on Bird Flu