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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.

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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


  • Yellow fever
  • Typhus not this one
  • West Nile Virus
  • Malaria

As an ARBOR vector

  • 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
mosquito life cycle
Mosquito Life Cycle


Egg - larva - pupa - adult

Larval & pupal stages are aquatic


Gary Larson’s

view on


plague impact yellow fever
Plague impact: Yellow Fever
  • Pathogen:
    • a virus
  • Hosts:
    • monkeys & humans
  • Vector:
    • a mosquito (Aedesaegypti et alia)
  • Reservoir:
    • resistant monkeys in
      • Africa
      • Central America
      • South America
yellow fever
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.

Political impact

All because of a little biting fly

yellow fever trade canals
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 fever1
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.
yellow fever2
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
another disease

Another “Disease”

Another Vector

  • 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)
  • A disease normally expressed in times of war and mass movement of populations
  • A disease expressed during times of the unwashed and unclean
  • 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
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

Contributing factor

as to why France

failed to conquer

Russia in the 19th



Political impact: during WWII

DDT saving lives during WWII

political impact typhoid mary
Political impact: Typhoid Mary

malaria the most important global arbor disease
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



mosquito control
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 perday]
  • 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.
malaria the parasite
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
malaria the parasite1
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.

Infected cells

Selection for Sickle Cell alleles distribution:

  • 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.
malarial mosquitoes
Malarial Mosquitoes
  • Over 100 species of mosquito are capable of vectoring malaria
  • Most capable vectors are in the genus Anopheles
malaria control
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
malaria control today
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
problems with malaria today
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
ethical issues
Ethical Issues

Poverty and Malaria

food for thought
Food for thought!!

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