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Vol.
XXIX No. 44
October 30,
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Avian Flu of Death
Amit Sen Gupta
IN the last two years about 60 deaths in four
countries (Indonesia, Vietnam, Thailand and Cambodia) have been reported due to
the dreaded avian flu. On the face of it, not something that would appear to
be a cause for major concern. Yet there is widespread panic across the world. Is
this mere scare-mongering or do we really stand on the precipice of the next
global pandemic of influenza?
Avian flu is influenza caused by varieties of the
virus that primarily cause infection in birds. Pandemics of influenza are
different from seasonal outbreaks or epidemics of influenza. Seasonal
outbreaks are caused by subtypes of influenza viruses that already circulate
among people, whereas pandemic outbreaks are caused by new subtypes, by subtypes
that have never circulated among people, or by subtypes that have not circulated
among people for a long time.
DEVASTATION BY PREVIOUS PANDEMICS
To understand the genesis of the panicky reaction we
need to go back almost ninety years in time. The First World War was in its last
stages and the world would soon start rebuilding. The War was to end in the
destruction of an estimated 15 million human lives including both military and
civilian deaths. Very few people realised then that the globe was on the edge of
another disaster one that in two years would kill more than three times the
number of people who died in the First World War. Between 1918-1919 an estimated
50 million people died due to an infection caused by a tiny virus which can be
seen only with the help of very powerful microscopes. Named the “Spanish flu
this pandemic which raged across the globe was caused by a strain of the
Influenza A virus. Many people died within the first few days after infection,
and others died of secondary complications. Nearly half of those who died were
young, healthy adults. The devastation in terms of number of deaths would be
matched only twenty years later by the Second World War. Though the 1918-19
pandemic was the worst ever, there have been very several serious outbreaks of
influenza pandemics in the twentieth century, including in1957-58 (called the
Asian flu”) and in 1968-69 (called the Hong Kong flu).
INFLUENZA A DEADLY KILLER
It might still be puzzling for many people how an
influenza epidemic can be so deadly. Most people have had one or more episodes
of influenza in their lifetime, usually without major consequences. The answer
lies in something that is common to all the three great pandemics of influenza
in the twentieth century. All three pandemics were caused by types of influenza
virus that had genetic material derived from influenza viruses that primarily
affect birds also called avian influenza viruses.
Pandemic viruses which cause the worst devastation
emerge as a result of a process called “antigenic shift, which causes an abrupt
or sudden, major change in influenza A viruses. Changes results in a new
influenza A virus subtype. The appearance of a new influenza A virus subtype is
the first step toward a pandemic; however, to cause a pandemic, the new virus
subtype also must have the capacity to spread easily from person to person. Once
a new pandemic influenza virus emerges and spreads, it usually becomes
established among people and moves around or circulates for many years as
seasonal epidemics of influenza. The bird flu virus in some cases can suddenly
become capable of infecting human populations (that is it jumps species) —
for whom it becomes an entirely new and deadly virus.
When a new subtype of the virus establishes itself in
the human population it causes very severe infection because the human body has
no immunity to the virus. After a few years the population develops complete or
partial immunity and the virus causes only sporadic epidemics in low or
non-immune population pockets. Gradually the sporadic outbreaks too die down,
but may resurface decades later as immunity levels to the virus go down in the
population. For example, we still see today cases of influenza caused by the
subtype that was responsible for the 1918-19 pandemic.
RAGING PANDEMIC IN BIRD POPULATION
So the primary attention today is
naturally focused on the epidemic that has been raging in the avian (bird)
population across the world. In domestic poultry, infection with avian influenza
viruses causes two main forms of disease, distinguished by low and high extremes
of virulence. The so-called low pathogenic form commonly causes only mild
symptoms (ruffled feathers, a drop in egg production) and may even go
undetected. The highly pathogenic form is far more dramatic. It spreads very
rapidly through poultry flocks, causes disease affecting multiple internal
organs, and has a mortality that can approach 100 per cent, often within 48
hours.
The current outbreaks in the bird
population, of avian influenza, which began in South-east Asia in mid-2003, are
the largest and most severe on record. Never before in the history of this
disease have so many countries been simultaneously affected, resulting in the
loss of so many birds.
The causative agent, the H5N1 virus, has
proved to be especially tenacious. Despite the death or destruction of an
estimated 150 million birds, the virus is now considered endemic in many parts
of Indonesia and Viet Nam and in some parts of Cambodia, China, Thailand, and
possibly also the Lao Peoples Democratic Republic. Control of the disease in
poultry is expected to take several years.
From mid-December 2003 through early
February 2004, poultry outbreaks caused by the H5N1 virus were reported in eight
Asian nations (listed in order of reporting): the Republic of Korea, Viet Nam,
Japan, Thailand, Cambodia, Lao Peoples Democratic Republic, Indonesia, and
China. Most of these countries had never before experienced an outbreak of
highly pathogenic avian influenza in their histories.
In early August 2004, Malaysia reported
its first outbreak of H5N1 in poultry, becoming the ninth Asian nation affected.
Russia reported its first H5N1 outbreak in poultry in late July 2005, followed
by reports of disease in adjacent parts of Kazakhstan in early August. Deaths of
wild birds from highly pathogenic H5N1 were reported in both countries. Almost
simultaneously, Mongolia reported the detection of H5N1 in dead migratory birds.
In October 2005, H5N1 was confirmed in poultry in Turkey and Romania. Outbreaks
in wild and domestic birds are under investigation elsewhere.
Japan, the Republic of Korea, and
Malaysia have announced control of their poultry outbreaks and are now
considered free of the disease. In the other affected areas, outbreaks are
continuing with varying degrees of severity.
The role of migratory birds in the
spread of highly pathogenic avian influenza is not fully understood. Wild
waterfowl are considered the natural reservoir of all influenza A viruses. They
have probably carried influenza viruses, with no apparent harm, for centuries
and it is believed that wild waterfowl are not agents for the onward
transmission of these viruses. Recent events however make it likely that some
migratory birds are now directly spreading the new avian flu virus in its highly
pathogenic form to other birds. Further spread to new areas is expected.
THREAT TO HUMANS
The widespread persistence of H5N1 in
poultry populations poses two main risks for human health. The first is the risk
of direct infection when the virus passes from poultry to humans, resulting in
very severe disease. Of the few avian influenza viruses that have crossed the
species barrier to infect humans, H5N1 has caused the largest number of cases of
severe disease and death in humans. Unlike normal seasonal influenza, where
infection causes only mild respiratory symptoms in most people, the disease
caused by H5N1 follows an unusually aggressive clinical course, with rapid
deterioration and high fatality. In the present outbreak, more than half of
those infected with the virus have died. Most cases have occurred in previously
healthy children and young adults. However, only about 100 human cases have
occurred in the current outbreak — a very small number compared with the huge
number of birds affected and the numerous opportunities for human exposure.
Direct contact with infected poultry, or surfaces and objects contaminated by
their faeces, is presently considered the main route of human infection. The
other good news is that human-to-human transmission of the H5N1 virus is still
rare and in no instance has the virus spread beyond a first generation of close
contacts or caused illness in the general community.
But the real danger lies in the
possibility that given enough opportunities the virus may (probably will)
change into a form that is highly infectious for humans and spreads easily from
person to person. Such a change could mark the start of a global outbreak (a
pandemic). A pandemic can start when three conditions have been met: a new
influenza virus subtype emerges; it infects humans, causing serious illness; and
it spreads easily and sustainably among humans. The H5N1 virus meets the first
two conditions — the prerequisites for the start of a pandemic have therefore
been met save one: the establishment of efficient and sustained human-to-human
transmission of the virus. The risk that the H5N1 virus will acquire this
ability will persist as long as opportunities for human infections occur. These
opportunities, in turn, will persist as long as the virus continues to circulate
in birds, and this situation could endure for some years to come.
ROCHE TRIES TO CASH IN
Though there is a substantial amount of research on
developing a vaccine, it is unlikely to be available soon. There are anti-viral
drugs which do not prevent the infection but can mitigate the severity of
infection. The most effective is a new drug called oseltamivir (commercially
known as Tamiflu). Tamiflu is marketed at present by Roche, who hold the Patent
for this drug till 2016. Roche has till now refused to voluntarily license the
drug to other companies to manufacture. Clearly the damocles sword of millions
of deaths are not what Corporations are really concerned about. Recently the
Indian company Cipla announced that it was ready to put the generic version of
the drug on the market anywhere in the world where it would be allowed to market
it. Roche countered by saying that it would take years to develop the
manufacturing process for any new company, but soon backtracked from this
statement. Clearly, if Roche doesnt give in, this is an open and shut case for
issuing of compulsory licenses to produce the drug. Recently the Indian
government has said that it wouldnt hesitate to issue a license, and one hopes
it will follow up its promise with actions.
Meanwhile the world waits with bated breath. The
scientific community has long held that a new influenza pandemic is round the
corner. What we still do not know is if this is the one.
