Chapter 1, 2, review.docx
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HLTA01-Plagues and People
Chapter 1, 2, 3 –Cumulative Review
Plague: “plaga” to strike a blow with wounds
When a parasite invades a host it establishes an infection and wounds the body
Parasites – organism that grows, feeds, and is sheltered on or in a different organism and that
does not contribute to the survival of its host
o Parasites are life dependent entities who feed at the table of the rich, from the latin word
parasites, meaning food
o Parasitism-obtaining the resources they need for growth and reproduction (eating ,
o -intimate association of two different kinds of organisms wherein one benefits (the
parasite) at the expense of the other (the host)
o When parasites often harm their hosts it is called a DISEASE
o Single cell-bacteria, fungi, protozoa
o Multicellular-roundworms, flatworms, mosquitoes, flies, ticks
o Tapeworms, hookworms, malaria parasite, 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, Ex. A malaria parasite that lives within a
red blood cell is 1/5000 of an inch in diameter
If only 10% of your blood cells were infected, the total mass of the malaria parasite would not
occupy a thimble, but could shortly destroy enough of your red blood cells, leading to death
Not all parasites end up killing their host, because resistance may develop in any population of
hosts and not every potential host will be infected (some individuals may be immune or
susceptible because of a genetic abnormality or the absence of some dietary factor such as a
Parasites produce lots of offspring, increasing the odds that some will reach new hosts, which
increases the probability of setting up an infection. By doing this, the parasite enables the chances
for survival. Ex. When a malaria infected mosquito feeds, it injects its saliva with a dozen of the
thousands of parasites that are present in his salivary glands
Malaria cell invades a liver cell and produces about 10,000 offspring, which intern affects the red
blood cell and in two weeks , a parson will be infected by 100,000 parasites which could lead to
Hookworms- live attached to the lining of the small intestine and they suck blood. Female
hookworms can live in the intestine for 10 years or more producing 10,000 eggs each day
AIDS- causing virus, HIV and after it invades a specific kind of white blood cell T-helper
lymphocyte it replicates and a million viruses will be produced in a few short days (empty vs.
Any environment other than a living host is inimical to the health and welfare of the parasite.
Some parasites have spores, eggs, or cysts that enable them to move from one host to another
akin to “island hopping”. Hookworms, tapeworms, blood flutes, and pinworms have eggs that are
able to survive outside the body
Virus – ultimate micro-parasite – smaller than bacteria; neither cells not organisms; can only
reproduce within their host
o Type of parasite composed of a fragment of genetic material wrapped in a protein
o Smaller than bacteria and can be seen with a electron microscope ( X10,000)
o In order for a virus to reproduce it must enter a living cell and use the cellular machinery
to replace itself
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o Can be killed if the DNA and RNA is destroyed
o Not cells or organisms
Microparasites- reproduce within their hosts and are sometimes referred to as infectious
microbes, or germs
A microparasite is a parasite that complete a full life cycle within one host and can be transmitted
directly to conspecific hosts. They often reproduce within a host's cells and are generally too
small to be seen with the naked eye. Most are viruses, bacteria and fungi with a smaller number
being protists. Examples include salmonella and HIV.
Macro-parasites – composed of many cells; cycles through transmission stages (eggs
and larvae) which pass into the external environment. ( do not multiply within an infected
Macroparasites are parasites that are large enough to be seen with the naked eye, in contrast to
microparasites. They grow in the host but multiply by producing infective stages (transmission
stages) that are released from the host, allowing the parasite to spread to other hosts. These
generally include ticks, mites, nematodes, flatworms, etc., and can be either external parasites
(ectoparasitic) or internal parasites (endoparasitic).
Transmission - movement of a parasite from host to host (direct or indirect)
o Vectors- when transmission involves living organisms such as flies, mosquitoes, ticks,
fleas, lice or snails
o Mechanical- bit wound of a mosquito or fly
o Developmental- parasites that grow and reproduce in snails, mosquitoes
o May occur through contamination of eating utensils, drinking cups, needles, bedclothes,
towels or clothing
o Legionnaires disease, spread through a fine mist of water in the air conditioning system
o SARS- transmission was person to person via droplet secretions in the nose and mouth
Bacteria 1-5 picometeres in size are prokaryotes that can be free living or parasitic, they can
be in rods (bacilli), spheres (cocci) and spiral
Protozoa 5-15 picometres in size are once celled eukaryotes that can lead an independent
existence (freshwater amoeba) or parastitic (entam loeba) that causes amebic dystentry
Bacteria and protozoa are too big to be seen with a microscope
Incubation period-interval of time required for development of a disease
Incubation period: In medicine, the time from the moment of exposure to an infectious agent until
signs and symptoms of the disease appear.
Exposure --presence of symptoms of parasite within the host.
In a vector, it is the time between entrance of an organism into the vector and the time
when that vector can transmit the infection. For Eg.:Once ingested by a mosquito, malaria
parasites must undergo development within the mosquito before they are infectious to
humans. The time required for development in the mosquito (the extrinsic incubation
period) ranges from 10 to 21 days, depending on the parasite species and the temperature.
If a mosquito does not survive longer than the extrinsic incubation period, then she will
not be able to transmit any malaria parasite
o the flu has a 2-4 day incubation period
o SARS has a longer (3-10) day incubation period, hospitalization is required
Latent period-seemingly inactive period between exposure to an infection and subsequent
illness, or that between the instant of stimulation and the beginning of response.
Virus latency (or viral latency) is the ability of a pathogenic virus to lie dormant (latent) within a
cell, denoted as the lysogenic part of the viral life cycle. A latent infection is a phase in certain
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viruses' life cycles in which after initial infection, virus production ceases. However, the virus
genome is not fully eliminated
A "latent period" is the lag time between exposure to a disease-causing agent and the onset of
the disease the agent causes. In infectious diseases it is often identical to the incubation period,
but not always. A disease may have incubated but remains latent, or dormant, within the body.
For instance, the latent period between exposure to HIV (human immunodeficiency virus)
infection and the onset of AIDS (acquired immunodeficiency syndrome) may be many years,
although invasion of the body by HIV does cause a transient primary infection two to three
weeks after initial exposure.
Parasite virulence-capacity of a parasite to cause disease
Zoonotic infections - animal infections that can be transmitted to humans
- Typhoid Mary, seemed a healthy woman when a health inspector knocked on her door in 1907,
yet she was the cause of several typhoid outbreaks. Since Mary was the first "healthy carrier" of
typhoid fever in the United States, she did not understand how someone not sick could spread
- Typhoid fever is caused by Salmonella typhi, a bacillus found in human urine and feces.
There are about a thousand strains of salmonella, including the ones responsible for most
mild food poisoning. All are transmitted by contact with human or animal waste.
Symptoms of typhoid include fever, severe intestinal rumblings, diarrhea, and listlessness.
Typhoid has been a major killer for centuries. There were about 215,000 battle deaths
during the U.S. Civil War (both sides), but 283,000 deaths from other causes, mostly
dysentery and typhoid.
- Mary Mallon was a carrier of typhoid. Although it was (and is) widely believed that she
herself never became sick with the disease
- She was a healthy carrier of typhoid germs. She was unaffected by the disease but could still
spread it. Hence, Mary was compelled to live in solitary confinement
Forecasting Storms, Predicting Plagues
- Understanding weather factors allows for better tracking and predicting of storms, similarly,
recognizing the elements that required for a parasite to spread in a population helps us predict the
course a disease may take
Spread from HOST to HOST- transmission may also occur through direct contact (mosquitoes) or ticks (
in Lyme disease) or by indirect contact (measles, influenza, SARS)
1) Infectious individuals
2) Susceptible individuals
3) Transmission from 1 to 2
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