HLTA01H3 Chapter 1 The Nature of Plagues1/19/2012 11:24:00 AM
Disease can be a personal affair.
pneumonia 肺炎== Legionnaires’ disease== 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 (冷凝
--Unlike infections caused by inhalation (inhalation means entry of disease
during respiratory), aspiration is produced by choking. Secretions in the
mouth get past the choking reflex and instead of going into the esophagus
(食道) and stomach, mistakenly enter the lungs.
--The outbreak of Legionnaires’ disease have been traced to water heaters,
whirlpool baths, respiratory therapy equipment and ultrasonic misters used
in grocery stores.
Toxic shock syndrome TSS= the source of Mary’s infection and the
possibility that it might be spread thru the population as a sexually
transmitted disease (STD).
--TSS is a gender specific disease.
--However, TSS was note an STD, it linked to the use of certain types of
tampons, especially those containing cross-linked carboxymethyl cellulose
with polyester foam, which provided a favorable environment for the toxin-
producing S. aureus.
--The symptoms of TSS are begin with vomiting and high fever followed by
lightheadedness and fainting, the throat felt sore, and the muscles ached. A
day later, a sunburn-like rash（红疹） appeared, and the eyes became
bloodshot. Within 3-4days, victims suffered confusion, fatigue, weakness,
thirst and a rapid pulse, the sin became cool and moist, and breathing
became rapid. This was followed by a sudden drop in blood pressure, if it
remained low enough for a long enough period, circulatory collapse produced
The effects of disease at the personal level can be tragic, but when illness
occurs in many people, it may produce another emotion-fear- for now the
disease might spread rapidly.
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.
E.g. the efficiencies in transportation, fast moving ships, trains, and planes.
New diseases may be related to advances in technology, e.g. TSS resulted
from the improved menstrual tampons. Legionnaires’ disease was the result
of the growth and spread of ―germ‖ thru the hotel’s air-conditioning system.
Incubation period: interval of time required for development of a disease
Latent period: seemingly inactive period between exposure to an infection
and subsequent illness
Parasite virulence: capacity of a parasite to cause disease
Zoonotic infections: animal infections that can be transmitted to humans
The germs that caused SARS, Legionnaires’ disease and TSS are parasites.
Parasites: 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‖ , from the Latin word parasitus, meaning
--Some parasites, such as tapeworms, hookworms the malaria parasite HIV
live inside the body, whereas others (ticks and chiggers) live on the surface.
--Parasites are invariably smaller in mass than their host.
--Parasites often harm their host. However, they will not always kill their
host, 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.
--Some parasites have complex life cycles and may have several hosts. e.g
malaria, the hosts are mosquitoes and humans.
--Parasites produce lots of offspring, thereby increasing the odds that some
will reach new hosts, More offspring will have a greater probability o
reaching a host and setting up an infection. Then m the parasite enhances
its chances for survival. e.g. malaria parasite, the red blood cell-destroying
hookworms and the white blood cell killer HIV.
The movement of a parasite from host to host-whether by direct or indirect
means- is called transmission.
When the transmission of parasites involves living organisms such as flies,
mosquitoes, fleas, lice or snails, these animate intermediaries are called
Transmission by a vector may mechanical or developmental or
contamination of eating utensils (用具), drinking cups, food ,bedclothes,
towels or clothing or in droplet secretions (小滴分泌物).
Parasite and their free-living relatives come in a variety of sizes,
shapes and kinds or species. e.g. bacteria and virus are called micro
parasites. Larger parasites that can be seen without the use of a microscope
are referred to as macro parasites, they are composed of many cells.
Virus: although a virus’s genetic code contains all the info needed for
assembling a new virus, it lacks that which is necessary for reproduction. So
for a virus to reproduce, it must enter a living cell and use the cellular
machinery to replicate itself. Viruses are not completely independent,
they are not alive, and yet they can be killed if their DNA or RNA is
destroyed. Virus are neither cells nor organisms, they are called infectious
microbes or ―germs‖.
Bacteria: are independent existence. Bacteria do not need a host to
reproduce, they can be either free living or parasitic.
Plagues- all diseases outbreaks, irrespective of their cause. When a parasite
invades a host, it establishes an infection and wounds the body.
Contagious: are contagious before symptoms appear, has a short
incubation period, and infrequently requires hospitalization. e.g normal flu.
infectious: infectious only after symptoms appear, longer incubation period
and hospitalization required. e.g SARS
-- infectiousness, may persist even after disease symptoms have
disappeared, the person who are infectious but asymptomatic are called
Forecasting Storms, prediction Plagues
Three factors are required for a parasite to spread from host to host:
1. there must be infectious individuals; 2. there must a susceptible
individuals, and there must be a means for transmission between the two.
Hlta01h3 chapter 1 the nature of plagues1/19/2012 11:24:00 am. -unlike infections caused by inhalation (inhalation means entry of disease during respiratory), aspiration is produced by choking. Secretions in the mouth get past the choking reflex and instead of going into the esophagus ( ) and stomach, mistakenly enter the lungs. -the outbreak of legionnaires" disease have been traced to water heaters, whirlpool baths, respiratory therapy equipment and ultrasonic misters used in grocery stores. Toxic shock syndrome tss= the source of mary"s infection and the possibility that it might be spread thru the population as a sexually transmitted disease (std). -however, tss was note an std, it linked to the use of certain types of tampons, especially those containing cross-linked carboxymethyl cellulose with polyester foam, which provided a favorable environment for the toxin- producing s. aureus. -the symptoms of tss are begin with vomiting and high fever followed by lightheadedness and fainting, the throat felt sore, and the muscles ached.