Pest, Plagues & Politics
Lecture 20
Medical Entomology
Key Points:
Medical Entomology
• How did Yellow fever impact trade
• Why did Napoleon’s campaign to Russia fail
• How did Typhoid Mary impact US immigration
laws?
• What is currently the most dangerous ARBOR
disease globally
The mosquito - the most dangerous animal
in the world
Why??
•
•
•
•
Yellow fever
Typhus not this one
West Nile Virus
Malaria
As an ARBOR vector
MOSQUITOES
• Order = Diptera (“two wings)
– Family = Culicidae
• 3,000 species worldwide
• 150 species in the U.S.
• Aquatic in their immature life stages
• Female mosquitoes require a blood meal for
egg development
• Male mosquitoes do NOT feed on blood
– nectar feeders
For your interest
Mosquito Life Cycle
Holometabolous
Egg - larva - pupa - adult
Larval & pupal stages are aquatic
For your interest
Gary Larson’s
view on
mosquitoes
For your interest
Plague impact: Yellow Fever
• Pathogen:
– a virus
• Hosts:
– monkeys & humans
• Vector:
– a mosquito (Aedes aegypti et alia)
• Reservoir:
– resistant monkeys in
• Africa
• Central America
• South America
For your interest
Yellow Fever
• Today of historical significance
– <400 cases a year worldwide
• Before the 20th century a major problem
– to North America via the slave trade
– 1647: 6,000 fatalities among Europeans
(Barbados)
– 1741: 20,000 British soldiers dead of a force
of 27,000 in South America
– 1802: 29,000 French soldiers dead of a force
of 33,000 in Haiti
• an influence for the French to sell the Louisiana
Territories to the U.S.
For your interest
Political impact
All because of a little biting fly
For your interest
Yellow Fever & Trade Canals
• Yellow fever (& malaria)
were major causes for the
French to abandon both
the Suez (1869) and
Panama Canal projects
• The U.S. took both over &
by “defeating” arbor
disease we conquered both
Big Ditches
Yellow Fever
• Yellow Fever and the Panama Canal
–“We have three diseases to contend with
in building this canal; malaria - yellow
fever and cold feet.”
• Mr. Stephens - American CEO of the project.
For your interest
Yellow Fever
• An urban problem in Colonial America
and the U.S. for 200 years
– e.g. 1879 - epidemic in over 100 population
centers of eastern U.S. left 20,000 dead of the
“Black Vomit”
– Note: Aedes aegypti is somewhat of a coyote
of the mosquito world and thrives in urban
environments
For your interest
For your interest
Another “Disease”
Another Vector
TYPHUS
• Also known as “classic typhus,” louse-borne
typhus, “war fever,” & “jail fever”
• Pathogen
– A bacteria
– Rickettsia (R. prowazekii)
• Host
– Homo sapiens
• Vector
– the human body louse
• (Pediculus humanus humanus)
TYPHUS
• A disease normally
expressed in times of
war and mass
movement of
populations
• A disease expressed
during times of the
unwashed and
unclean
For your interest
TYPHUS
• Route of infection
– healthy louse bites an infected human
– rickettsiae enter louse’s gut
– rickettsiae penetrate the epithelial lining of
the louse’s gut and reproduce
– gut cells rupture and release rickettsiae into
the lumen & ultimately into the feces
– transmitted to the next human via the louse
feces
• NOT via the bite or saliva of the louse.
Political impact: TYPHUS
• 420 BC: first recorded typhus epidemic in
Athens
• 1566: Germans attacking the Ottoman
Empire in Hungary - typhus breaks out
among the Germans and they go home
• 1741: Austria cedes Prague to the French
after 30,000 Austrian soldiers die from
typhus
• WWI: an estimated 2 - 3 million typhus
caused deaths
For your interest
Contributing factor
as to why France
failed to conquer
Russia in the 19th
century.
Russian invasion during 1812-13
Typhus Risk Areas – High red, Low green
For your interest
Political impact: during WWII
DDT saving lives during WWII
For your interest
Political impact: Typhoid Mary
http://en.wikipedia.org/wiki/Typhoid_Mary
MALARIA: The most important global
arbor disease
• Infecting ca. 300,000,000 persons (right
now)
– 5% of the world’s population
– a child dies every 30 seconds from malaria
– an adult dies every 30 seconds from malaria
– two million fatalities per annum
– 90% of all cases in sub-Saharan Africa
“During the last 150 years, the Western world has
virtually eliminated death due to infectious disease.
Smallpox was eradicated, tuberculosis and
polio were in decline and, WITH THE EXCEPTION
OF MALARIA, so were all of the other major
infectious health threats of the 20th century.”
Levins, et al. 1994. American Scientist
For your interest
MALARIA
http://www.childinfo.org/malaria_progress.html
For your interest
MALARIA
http://blog.lib.umn.edu/mccl0222/gdes_4365w/2010/10/poverty-environmental-nahil-khalife.html
For your interest
Mosquito Control
• Vector Control
Basic reproduction rate of malaria
How many female offspring will a mosquito produce
m(a) = relative rate of a given mosquito population
that will bite on a given day
p = proportion of female mosquitoes surviving daily
pn = proportion surviving with plasmodial parasite
• [Java: 1 infectious bite per week per human –
areas of Africa where it is 1 infectious bite per
day]
For your interest
MALARIA
• Generally restricted to humid regions
where the average temperature is
>61°F.
– equals about 45% of the earth
• Continued global warming could result in
60% of the earth hosting malaria.
For your interest
MALARIA - the parasite
• Caused by a unicellular Plasmodial
parasite
– Plasmodium falciparum - malignant or
tertian malaria
• chills and fever every two days
– Plasmodium vivax - benign malaria
– Plasmodium ovale - similar to P. vivax, but
limited to a small geographical area
– Plasmodium malariae - quartian malaria
• chills and fever every three days
For your interest
MALARIA - the parasite
• Plasmodia are parasites of human red blood
cells
• Plasmodia are parasites of the gut
epithelium in the vector (mosquito)
• The life cycle of this parasite is involved
and complicated……very complicated.
For your interest
Infected cells
Selection for Sickle Cell alleles
distribution:
http://anthro.palomar.edu/synthetic/synt
h_4.htm
For your interest
Malaria
• Malaria: from the Italian language for
“bad air”
• 1897: Ronald Ross proves that mosquitoes
are involved in the transmission of malaria
• 1899: The Italian team of Grassi, Bignami
& Bastianelli prove that human malarial
parasites are vectored by Anopheline
mosquitoes.
For your interest
Malarial Mosquitoes
• Over 100 species of
mosquito are capable
of vectoring malaria
• Most capable vectors
are in the genus
Anopheles
For your interest
Malaria Control
• Disease control via anti-malarial drugs
– drug resistance a big problem
– “Gin & Tonic Please”
• Disease prevention via a vaccine
– the hoped for “magic bullet” which, while
not yet achieved, is continually sought
• Disease prevention via mosquito control
– a very complex subject
For your interest
Malaria Control Today
• Anti-malaria drugs (wide spread resistance)
– Suppressives
• Quinine
• Mefloquine
• Malarone
• Chloroquine
• Doxycycline & Tetracycline (antibiotics)
– Causals
• Primaquine (only one available in U.S.)
• Mosquito control
For your interest
Problems with malaria today
• Loss of effective insecticides for mosquito
control.
– U.N. WHO receives an exemption for DDT
in a proposed world wide ban
• Loss of effective anti-malarial drugs
– resistance development
• Failure to develop an effective vaccine
– and maybe things are changing in this arena
For your interest
Ethical Issues
Poverty and
Malaria
http://sspp.proquest.com/archives/vol2iss2/0512-022.pattanayak.html
Food for thought!!
Disease
Mortality
Research $
per fatality
TB
2,000,000
$13
Malaria
1,000,000
$65
Asthma
180,000
$789
HIV/AIDS
300,000
$3,274
1990 Data from the Wellcome Trust (world’s largest philanthropy)
Key Points:
Medical Entomology
• How did Yellow fever impact trade
• Why did Napoleon’s campaign to Russia fail
• How did Typhoid Mary impact US immigration
laws?
• What is currently the most dangerous ARBOR
disease globally