Biology 103 - Microbes and You

Lecture 14 Outline

The Black Plague (history; animal vectors; malaria, rabies)


Tick sizes

Plague ridden hand

Bubonic plague buboe

Black Death era burial art

Black Death era burning Jews art

Black Death art

Plague ridden feet

Black Death flagellants

A flea

Lyme disease life cycle

Map of Lyme Disease in US

Malarial mosquito

Yersinia pestis, The plague bacteria

Black Death physician with mask

The plague life cycle

Spread of plague in Europe

Black Death art

Yersinia pestis

Black Death era burial

Extent of plague in Europe

Plague flea

Fat rat

Red flea

Rocky Mountain Spotted Fever rash

Plague enters Europe through shipping

The Plague
several plagues throughout history; Justinian plague (558 AD), Black Death (1348-1350), pandemic of 1663, Austria 1711, Balkans 1770, Surat 1994
the Black Death of the middle ages is the most famous of the plagues
30% of the population of Europe was killed in two years
this terrorized the population, abandoned farms lead to food shortages, dead officials cause governments to be chaotic
the people had a fatalistic view of life and questioned their faith
death by plague is horrible and rapid
the disease is caused by a bacterium, Yersinia pestis
after infection, once a fever has started, the patient may be dead within 12-15 hours
the disintegration of bodily functions leads to massive necrosis (death) of tissues
the fingers and toes literally turn black and large painful buboes (swellings) form in the lymph glands of neck, groin and armpit

Transmission of plague
under the unsanitary conditions of the middle ages it is not surprising that disease was rampant
plague virus became endemic in the rat population of Europe
fleas that bit the rat and then a man would transmit the bacterium
the rats acted as a reservoir, maintaining the bacterial population
the flea was the vector that transmitted the Yersinia from rat to man
the bacterium actually grows in the flea and blocks its digestive tract
the flea gets very hungry, but when it bites its next host, it can't swallow the blood and regurgitates back into the host
once in the animals blood, the bacterium moves to the lymph nodes and survives in phagocytes
an overwhelming infection ensues
the victim is often dead within a week
there are three types of plague:
bubonic - the least deadly form, limited to buboes and lymphatic system
septicemic - infection of the blood and quite deadly
pneumonic - lung infection - 100% fatal - death within hours or days
bubonic and septicemic plague don't spread easily - these must be transferred by the flea
pneumonic plague is very contagious and is spread by aerosols from coughs or physical contact
it is the pneumonic plague that caused the medieval pandemic to be so devastating
today plague occurs, is endemic in some wild rodent populations, but can be treated with antibiotics or vaccines

malaria is caused by a protozoan parasite called Plasmodium
it is an obligate intracellular parasite and must live within host cells during a phase of its life cycle
sexual reproduction occurs in mosquitoes, producing sporozoites
these sporozoites are transferred to the human host via a mosquito bite
the sporozoites travel to the liver and make thousands of merozoites
the merozoites then grow and reproduce in red blood cells
eventually merozoites again get into a mosquito and then undergo sexual reproduction
the merozoites in the blood produce waste products
these waste products actually cause the malarial disease of recurrent fevers

List of other diseases transmitted to humans from animals
Yellow fever - mosquito transmission
Schistosomiasis - transmitted through a phase in snail in polluted water - the parasite infects humans and acts like a fluke (sucking blood) - 200 million infected in Africa and Asia
Toxoplasma godii - feline vector - 40% infected in US - toxoplasmosis is harmless in healthy folks, but dangerous in AIDS patients and pregnant women
Trypanosomiasis - Tse Tse fly vector - sleeping sickness - attacks the central nervous system - can change surface antigens 100 times during infection, thus evading the immune system
Chagas' disease - kissing bug or rodent vector - trypanosome parasite - 50% infected in rural South America
Rabies - animal vector - transmitted through bites, causes fatal encephalitis. initial bite has few virus and does not elicit an immune response, but then rapid growth causes an overwhelming infection. vaccination must be given soon after infection as immunity doesn't last
Hantavirus - mouse urine - hemorrhagic fever, attacks kidneys. an emerging disease

Ticks as vectors
Babesia - like malaria, but transmitted by ticks
Borrelia - relapsing fever - a spirochete bacterium - changes antigenic coat with each fever cycle to rise again
Lyme disease is also caused by a Borrelia spirochete that is transmitted by the Ixodes tick
the tick acts as the vector and field mice represent the reservoir
the multi-year life cycle of the tick shown, infection moving from the mouse population into humans and deer
Lyme disease causes a characteristic bull's eye rash, then flu symptoms
if treated now, cure is likely
if not treated then heart and nervous system problems ensue
these can lead to death

A couple of other diseases
Typhus - transmitted in the feces of louse, generally found in unsanitary conditions disease caused by Rickettsias leads to fever, rash, stupor and without treatment, death
typhus is endemic in rat populations
Rocky mountain spotted fever - tickborne typhus
transmitted by ticks, causes a less deadly typhus disease
transmitted from tick to tick in tick eggs

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