Bird Flu: Human Infection
Bird flu is a disease caused by a specific type of avian (bird)
influenza virus, the so-called H5N1 virus. This virus was first
discovered in birds in China in 1997, and since then has
infected 125 people in Vietnam, Cambodia, Thailand, and
Indonesia, killing 64 of them. It is spread by infected
migratory birds (including wild ducks and geese) to domestic
poultry (primarily chickens, ducks, and turkeys), and then to
humans.
Some infected people have developed abnormal clotting profiles
resulting in excessive bleeding--which was a frequent clinical
symptom in the deadly so-called Spanish influenza of 1918-19,
which killed more than 100 million people worldwide. Indeed,
bird flu shares a number of disturbing characteristics with the
1918-19 influenza virus. These two viruses have, in fact,
recently been shown to be similar genetically. And in a recent
laboratory experiment with mice, the 1918-19 virus was found to
produce 39,000 times more viruses four days after infection than
the regular seasonal human flu strain. The 1918-19 virus killed
100 percent of the mice that were infected with it, compared to
none of the mice infected with the regular flu strain. With a
current "case fatality rate," or death rate of approximately 50
percent in humans, bird flu is obviously also a very deadly
disease.
There are only a few reports in the medical literature
describing the clinical features of bird flu in humans. The
clinical spectrum of H5N1 infection ranges from asymptomatic
infection--where the person doesn't even know he or she is
infected--to fatal pneumonia and multiple organ failure. Some
infected individuals develop liver or kidney dysfunction, and
there were two children who died from the virus that came to
medical attention because of diarrhea and seizures related to
encephalitis (infection of the brain). However, the most common
presentation is one of fever, cough, and trouble breathing.
Approximately 70 percent of patients also have diarrhea, and a
few patients have had only gastrointestinal symptoms (such as
stomach ache, vomiting, and diarrhea) and no breathing problems.
Deaths have generally been in normally healthy people. The first
report in the medical literature of deaths from bird flu was on
12 patients living in Hong Kong. Their median age was nine
years, with a range of one to 60 years. All presented with
fever, and eight had symptoms or signs of upper-respiratory
infections (five had clinical and X-ray evidence of pneumonia
when first diagnosed). Gastrointestinal (GI) symptoms, including
stomach pain, vomiting, and diarrhea, were present in eight
patients. There were a total of five deaths (one died with
Reye's syndrome, which is associated with taking aspirin in
children).
In a study of 10 patients in Vietnam with laboratory-confirmed
avian influenza (H5N1), the mean age of the patients was 13.7
years. For eight of the patients, there was a clear history of
either direct handling of poultry (chickens or ducks) or
exposure to sick poultry in the week before the onset of
illness. All presented in January 2004 with cough, shortness of
breath, and fever, and seven had diarrhea; none had myalgia
(muscle aches)--which is often found in the regular seasonal
flu. Notably, oseltamivir (Tamiflu) was administered to five
patients, four of whom died (treatment was probably started too
late for the medication to be effective--it must be given within
48 hours after onset of symptoms to be effective). In total,
eight of the patients died, for an 80 percent case fatality rate
or death rate.
As is apparent from the descriptions above, the presenting
symptoms of individuals with bird flu are very similar to the
symptoms of the normal seasonal flu. Infections caused by either
the bird-flu virus (H5N1) or the seasonal influenza virus can be
completely asymptomatic--that is, cause no symptoms at all.
Fever, cough, malaise (feeling ill), and gastrointestinal
symptoms are common to both infections. Excessive bleeding
occurs only with bird flu, but currently this symptom doesn't
appear to be common. Difficulty breathing is more common with
severe cases of bird flu, not seasonal flu. Runny nose and
sneezing are found only with colds (or allergies).
The cough in either type of infection is what is referred to in
medicine as "nonproductive"--meaning there is no sputum brought
up when coughing, or if any sputum is brought up, it is white in
color. This type of cough is characteristic of upper respiratory
viral infections. As either type of infection progresses or
worsens, tissues may be damaged, disrupting the normal structure
and function of the infected cells. This in turn may allow
bacteria to grow and also cause damage. When this happens
following a viral infection, it is referred to as a "secondary"
bacterial infection. When this occurs, the color of the sputum
characteristically turns yellow or green. If this happens,
antibiotics are indicated to treat the bacterial infection.
(Antibiotics are not indicated in the treatment of viral
infections, because they don't work.)
It is safe to assume that during a bird-flu pandemic, most
individuals who become infected with the bird-flu virus will
either be asymptomatic--having no symptoms--or their illness
will not be severe enough to require hospitalization. The small
percentage who do become seriously ill will have to be
hospitalized, and treated with either of the two antiviral
agents available, oseltamivir (Tamiflu) or zanamivir (Relenza).
A smaller subset of that group will develop life-threatening
complications such as acute respiratory distress syndrome
(ARDS), which requires treatment with a mechanical ventilator, a
respirator.
Some individuals may develop other serious complications such as
liver failure, kidney failure, neurological problems--such as
seizures, paralysis, psychiatric problems such as delirium or
psychosis, or bleeding problems. However, it is reasonable to
predict that most people infected with the virus will not die
and will not have significant residual symptoms, although a
small percentage will.
Bradford Frank, M.D., M.P.H., M.B.A. The Frank Group P.O. Box
138 Lakewood, NY 14750 www.AvoidBirdFlu.com