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Major Diseases Transmitted by Insects
Malaria
Malaria (an Italian term meaning bad air) is a disease of animals, especially birds, monkeys,
apes, reptiles and humans. Mosquitoes carry the infective protozoan from monkeys and birds
to humans. It occurs in subtropical, tropical and some temperate areas of the world. Traditionally, malaria is found throughout tropical and subtropical and into temperate regions of the
world. Since 1950, malaria has been eliminated from almost all of Europe and North America
and from large areas in Central and South America. It remains a major problem in parts of Africa and in southeastern Asia. About 100 million cases of human malaria develop each year about 1 percent are fatal. Recently, the incidence of malaria has been increasing because of increasing resistance to drugs used to control the Plasmodium pathogen. The primary control
method is vector control by the use of residual insecticides. Since 1638, the infection has been
controlled by treating the patient with an extract from the bark of the cinchona tree, known as
quinine. Quinine, which is somewhat toxic, suppresses the growth of protozoans within the
bloodstream. Synthetic drugs with lower toxicity and greater efficacy have since been developed.
Yellow Fever
Yellow fever is another mosquito-vectored disease. The mosquito infects humans by carrying
the virus from monkey to humans. Although the disease may have originated in West Africa,
the first records are from Central and South America. Outbreaks have since occurred in North
America, Europe and other regions.
The main hosts (and reservoir for the human disease) are treetop dwelling monkeys and normally the mosquitoes that transmit the pathogen do not encounter humans. However, when
logging occurs, the treetops are brought to the forest floor and the disease can be transmitted to
people. For 300 years following the Spanish conquests in Central America, yellow fever was
one of the great plagues of the world. The tropical and subtropical regions of the Americas
were subjected to devastating epidemics, and serious outbreaks occurred as far north as Boston
and as far away as Spain, France, England, and Italy. Yellow fever stymied the first attempt to
construct the Panama Canal. After several years the French led effort was abandoned because
of high worker mortality and sickness. A later American effort was successful when Walter
Reed discovered that Yellow Fever is spread by mosquitoes. He instituted a mosquito control
program and the canal was completed. No treatment is known for yellow fever. But a vaccine
is available and is very effective. It is required for all persons traveling between endemic regions and other locations.
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Typhus (Typhoid Fever)
Rather than being transmitted by a bite from the vector, typhus is transmitted in the insect feces, which is scratched into the skin. When the louse bites, the human it leaves its feces behind. The human scratches the itchy bite and introduces the contaminated feces into the open
wound. The human body louse is the transmitter of Rickettsia carried from rats. Worldwide, it
is associated with people crowded together in filth, cold, poverty, and hunger; with wars and
famine; with refugees; prisons and jails; concentration camps; and ships. Epidemic typhus has
been one of the great disease scourges in human history. Devastating epidemics of typhus occurred intermittently throughout Europe in the 17th, 18th, and 19th centuries. Prominent outbreaks developed during the Napoleonic Wars and during the Irish potato famine of 1846-49.
In the early 20th century, typhus decreased and then practically disappeared from Western Europe as improvements in living conditions and hygiene occurred. However, the disease remained intermittently epidemic in Eastern Europe, the Middle East, and parts of Africa. During
World War I the disease caused 3,000,000 deaths in Russia, several million other deaths in Poland and Romania. In World War II, it again caused epidemics, this time among refugees and
displaced persons, particularly in the German concentration camps. Typhus's role in war has
been so pronounced that the outcomes of conflicts often were decided by typhus rather than
battle. In Napoleon's advance into Russia, he began with 450,000 men. At his retreat into Poland he had 80,000 men, most lost to typhus not battle.
A vaccine was developed during World War II and is generally effective. Pesticides to give
louse control can be applied to clothing in outbreak areas. Despite vaccination and delousing,
typhus is still an ever-present threat to impoverished and destitute peoples in many parts of the
world. Best prevention is avoidance of areas where rats or lice may be present.
Plague
Fleas that carry the bacteria from rodents, especially rats, transmit plague. It occurs worldwide!
Plague occurs in three forms: bubonic, characterized by swelling of the lymph nodes (buboes);
pneumonic, in which the lungs are extensively involved; and septicemic, in which the bloodstream is so invaded that death ensues before the bubonic or pneumonic forms have had time
to appear. The illness in man varies from severe to mere indisposition to violent death. The
mild infections are almost always bubonic; pneumonic and septicemic plague are invariably
severe and almost always fatal unless treated. In the 14th century outbreak known as the Black
Death, the number of deaths was enormous, reaching in various parts of Europe two-thirds or
three-fourths of the population in the first pestilence. It has been calculated that one-fourth of
the population of Europe, or 25,000,000 persons, died from plague during the great epidemic.
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This is three times the fatalities in WWI. The Great Plague of London in 1664-65, resulted in
more than 70,000 deaths in a population estimated at 460,000. An outbreak in Canton Province
in China and Hong Kong in 1894, left 80,000 to 100,000 dead. Within 20 years, the disease
spread from the southern Chinese ports throughout the whole world, resulting in more than
10,000,000 deaths. Plague is primarily a disease of rodents, and infections of man are accidental. When an outbreak in rodents reduces their population, the rat fleas may transfer to humans and bring the disease with them. At first, the cases are sporadic, but under suitable conditions large numbers of persons may be infected.
Trypanosomiasis
Called sleeping sickness in humans, Trypanosomiasis is also a disease of cattle and other animals in Africa, which serve as the reservoir for the protozoa. In cattle, the disease is called nagana. Tsetse flies transmit a protozoa from wild, hoofed animals. Two variations of the disease
occur in central and western Africa. In South America, another version of the protozoan, T.
cruzi, is transmitted by the triatoma bug (kissing bug) and is called Chagas' disease. African
sleeping sickness begins with a chancre at the site of the insect bite, an accelerated heartbeat,
an enlargement of the spleen, and rash and fever. Over the next few months the nervous system
is attacked, with accompanying mood changes, sleepiness, lack of appetite, eventual coma,
and, frequently, death. Sleeping sickness is usually fatal to humans as well as to domestic horses, camels, dogs, and mules. Cattle and sheep usually survive, but do poorly. Sleeping sickness
is endemic in approximately 25% of Africa. The disease has proven to be extremely difficult to
treat and prevent, and control of the flies is not practical. A consequence of the disease is that
much of Africa has remained wilderness and this has allowed many wild animals to survive.
Prevention is the best option. It involves avoidance of bites of tsetse flies.
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Major Diseases Transmitted by Insects
Reading For Content
Name ________________________________________________________
Disease
Where is it
Found?
What type or
organism causes
the disease?
What insect transmits the disease
to
humans?
What is the nonhuman host?
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Insect Transmitters of Organisms That Cause Disease in Humans
Insect Carriers
Mosquitoes
Disease Organisms
Plasmodium (Protozoa)
Virus
Virus
Filaria (Nematode)
Filaria (Nematode)
Filaria (Nematode)
Disease
Malaria
Yellow Fever
Dengue Fever
Encephalitides
Filariasis
Elephantiasis
Black Flies
Filaria (Nematode)
Onchocerciasis
Sand Flies
Leishmania (Protozoan)
Bartonella (Rickettsia)
Virus
Virus
Virus
Kala-azar
Oriental Sore,
Espundia
Verruga
Papataci Fever
Bacillus anthracis
(Bacteria)
Pasteurella tularensis
(Bacteria)
Trypanosoma (Protozoan)
Pastuerella pestis (Bacteria)
Anthrax
African Sleeping Sickness
Bubonic Plague
Rickettsia typhi (Rickettsia)
Endemic Typhus
Horse Flies
Deer Flies
Tsetse Flies
Fleas
Kissing Bugs
Sucking Lice
Lice
Trypanosoma cruzi
(Protozoa)
Pasteurella tularensis
(Bacteria)
Borrelia recurrentis
(Spiroch.)
Rickettsia prowazakii
(Ricket.)
Rickettsia quinatana
(Rickett.)
Tularemia
Chagas' Disease
Tularemia
Relapsing Fever
Epidemic Typhus
Trench Fever
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