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??

As an ARBOR vector• Yellow fever• Typhus not this one

• West Nile Virus• Malaria

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

Larval & pupal stages are aquatic

Mosquito Life Cycle

HolometabolousEgg - larva - pupa - adult

Gary Larson’sview onmosquitoes

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

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.

All because of a little biting fly

Political impact

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.

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 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

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

Contributing factoras to why France failed to conquerRussia in the 19th

century.

Russian invasion during 1812-13

Typhus Risk Areas – High red, Low green

DDT saving lives during WWII

Political impact: during WWII

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 hasvirtually eliminated death due to infectious disease.Smallpox was eradicated, tuberculosis andpolio were in decline and, WITH THE EXCEPTIONOF MALARIA, so were all of the other majorinfectious health threats of the 20th century.”

Levins, et al. 1994. American Scientist

MALARIA

http://www.childinfo.org/malaria_progress.html

MALARIA

http://blog.lib.umn.edu/mccl0222/gdes_4365w/2010/10/poverty-environmental-nahil-khalife.html

Mosquito Control• Vector Control

Basic reproduction rate of malariaHow many female offspring will a mosquito producem(a) = relative rate of a given mosquito population

that will bite on a given dayp = proportion of female mosquitoes surviving dailypn = proportion surviving with plasmodial parasite

• [Java: 1 infectious bite per week per human – areas of Africa where it is 1 infectious bite per day]

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.

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 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: http://anthro.palomar.edu/synthetic/synth_4.htm

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.

Malarial Mosquitoes

• Over 100 species of mosquito are capable of vectoring malaria

• Most capable vectors are in the genus Anopheles

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• 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

• 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

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