CHAPTER 1: THE NATURE OF PLAGUES
Statistical studies of Legionnaires disease revealed that all who became ill had spent a
significantly longer period of time in the lobby of the Bellevue-Stratford Hotel than those
who remained healthy. Air was implicated as the probable pathway of spread of the disease,
and the most popular theory was that infection resulted from aspiration of bacteria (called
Legionella) in aerosolized water from either cooling towers or evaporative condensers.
Unlike infections caused by inhalation, aspiration is produced by choking. Secretions in the
mouth get past the chocking reflex and, instead of going into the esophagus and stomach,
mistakenly enter the lungs. Protective mechanisms that normally prevent aspiration are
defective in older people, smokers, and those with lung disease.
Toxic shock syndrome (TSS) a gender-specific disease. It is not an STD; it is ultimately
linked to the use of certain types of tampons, especially those containing cross-linked
carboxymethyl cellulose with polyester foam, which provided a favourable environment for
the toxin-producing S. aureus. By the late 1980s, these tampon brands were removed from
the market, and the number of deaths from TSS declined dramatically.
The 2003 outbreak of SARS (severe acute respiratory syndrome) it began in February
2003 when a 64 year old Chinese physician who was working in a hospital in Guandong
Province in southern China traveled to Hong Kong to attend a wedding and became ill. He
had a fever, a dry cough, a sore throat, and a headache. Unconcerned, he felt well enough to
sightsee and shop with his brother-in-law in Hong Kong; however, during that day his
condition worsened, and he had difficulty in breathing. Seeking medical attention at a nearby
hospital, he was taken immediately to the intensive care unit and given antibiotics, anti-
inflammatory drugs, and oxygen. This was no avail, and several hours later he suffered
respiratory failure and died. The brother-in-law, who was in contact with him for only 10
hours, suffered from the same symptoms 3 days later and hospitalized. Again, all measures
failed, and he died 3 weeks after being hospitalized.
SARS quickly spread and ultimately coming to Canada by a 72 year old Chinese-Canadian
businessman who had returned to Hong Kong for a family reunion and had stayed overnight
in the same hotel and on the same floor as the physician.
Over the next 4 months, the SARS survivors sowed the seeds of infection that led to more
than 8000 cases and 800 deaths in 27 countries, representing every continent.
Our world is much more vulnerable than it was in the past.
New and old diseases can erupt and spread throughout the world more quickly because of the
increased and rapid movements of people and goods.
We can move far and wide across the globe, and the vectors of disease can also travel great
distances. Aided by fast-moving ships, trains, and planes, they introduce previously remote
diseases into our midst (such as West Nile virus infection, SARS, influenza, and mad cow
Living off Others
The germs that caused SARS, Legionnaires disease, and TSS are parasites.
Within the range of all that lives, some entities are unable to survive on their own and
require another living being for their nourishment. These life-dependent entities that feed at
the table of the rich are called parasites (Latin parasites, meaning food). Parasitism is the intimate association of 2 different kinds of organisms (species) wherein
one benefits (the parasite) at the expense of the other (the host), and as a consequence of
this, parasites often harm their hosts.
Though parasites can be describes by the one thing they are best known for causing harm
they come in many different guises (Pg. 5 Fig. 1.2 & 1.3). Some may be composed of a
fragment of genetic material wrapped in protein, such as a virus. Others (bacteria, fungi,
protozoa) consist of single cell, and some are made up of many cells (roundworms,
flatworms, mosquitoes, flies, ticks). Some parasites, such as tapeworms, hookworms, the
malaria (Plasmodium falciparum), and the human immunodeficiency virus (HIV), live
inside the body, whereas others (ticks and chiggers) live on the surface.
Parasites are invariably smaller in mass than their host.
Some parasites have complex life cycles and may have several hosts. In malaria, the hosts
are mosquitoes and humans, in blood fluke disease, the curse of the Pharaohs, the hosts
are humans and snails.
All parasites whether they are large or small cause harm to their host, though not all kill
their host outright. This is because resistance may develop in any population of hosts, and
not every potential host will be infected some individuals may be immune or not
susceptible because of a genetic abnormality or the absence of some critical dietary factor
(e.g., vitamin deficiency).
To succeed in a hostile world where individual hosts are distinct and separate from one
another, parasites need to disperse their offspring or infective stages to reach new hosts. To
meet this requirement they produce lots of offspring, thereby increasing the odds that some