Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Dengue fever

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In 1928, de Broglie was appointed professor of theoret-

ical physics at the University of Paris’s Faculty of Science. De

Broglie was a thorough lecturer who addressed all aspects of

wave mechanics. Perhaps because he was not inclined to

encourage an interactive atmosphere in his lectures, he had no

noted record of guiding young research students.

During his long career, de Broglie published over

twenty books and numerous research papers. His preoccupa-

tion with the practical side of physics is demonstrated in his

works dealing with cybernetics, atomic energy, particle accel-

erators, and wave-guides. His writings also include works on

x rays, gamma rays, atomic particles, optics, and a history of

the development of contemporary physics. He served as hon-

orary president of the French Association of Science Writers

and, in 1952, was awarded first prize for excellence in science

writing by the Kalinga Foundation. In 1953, Broglie was

elected to London’s Royal Society as a foreign member and,

in 1958, to the French Academy of Arts and Sciences in

recognition of his formidable output. With the death of his

older brother Maurice two years later, de Broglie inherited the

joint titles of French duke and German prince. De Broglie died

of natural causes on March 19, 1987, at the age of ninety-four.

See alsoElectron microscope, transmission and scanning;

Electron microscopic examination of microorganisms;

Microscope and microscopy

DEFECTS OF CELLULAR IMMUNITY•see

IMMUNODEFICIENCY DISEASE SYNDROMES

DEFECTS OFT CELL MEDIATED IMMU-

NITY•seeIMMUNODEFICIENCY DISEASE SYNDROMES

DDengue feverENGUE FEVER

Dengue fever is a debilitating and sometimes hemorrhagic

fever (one that is associated with extensive internal bleeding).

The disease is caused by four slightly different types of a virus

from the genus Flavivirusthat is designated as DEN. The four

antigenic types are DEN-1, DEN-2, DEN-3, and DEN-4.

The dengue virus is transmitted to humans via the bite

of a mosquito. The principle mosquito species is known as

Aedes aegypti. This mosquito is found all over the world, and,

throughout time, became adapted to urban environments. For

example, the mosquito evolved so as to be capable of living

year round in moist storage containers, rather than relying on

the seasonal patterns of rainfall. Another species, Aedes

albopictus(the “Tiger mosquito”), is widespread throughout

Asia. Both mosquitoes are now well established in urban cen-

ters. Accordingly, dengue fever is now a disease of urbanized,

developed areas, rather than rural, unpopulated regions.

The dengue virus is passed to humans exclusively by

the bite of mosquito in search of a blood meal. This mode of

transmission makes the dengue virus an arbovirus (that is, one

that is transmitted by an arthropod). Studies have demon-

strated that some species of monkey can harbor the virus.

Thus, monkeys may serve as a reservoir of the virus.

Mosquitoes who bite the monkey may acquire the virus and

subsequently transfer the virus to humans.

The disease has been known for centuries. The first

reported cases were in 1779–1780, occurring almost simulta-

neously in Asia, Africa, and North America. Since then, peri-

odic outbreaks of the disease have occurred in all areas of the

world where the mosquito resides. In particular, an outbreak

that began in Asia after World War II, spread around the world,

and has continued to plague southeast Asia even into 2002. As

of 2001, dengue fever was the leading cause of hospitalization

and death among children in southeast Asia.

Beginning in the 1980s, dengue fever began to increase

in the Far East and Africa. Outbreaks were not related to eco-

nomic conditions. For example, Singapore had an outbreak of

dengue fever from 1990 to 1994, even after a mosquito control

program that had kept the disease at minimal levels for over

two decades. The example of Singapore illustrates the impor-

tance of an ongoing program of mosquito population control.

The disease is a serious problem in more than 100 coun-

tries in Africa, North and South America, the Eastern

Mediterranean, South-East Asia, and the Western Pacific.

Unlike other bacterial or viral diseases, which can be

controlled by vaccination, the four antigenic types of the

dengue virus do not confer cross-protection. Thus, it is possi-

ble for an individual to be sickened with four separate bouts of

dengue fever.

Following the transfer of the virus from mosquito to

humans, the symptoms can be varied, ranging from nonspe-

cific and relatively inconsequential ailments to severe and fatal

hemorrhaging. The incubation period of the virus is typically 5

to 8 days, but symptoms may develop after as few as three

days or as many as 15 days. The onset of symptoms is sudden

and dramatic. Initially, chills tend to develop, followed by a

headache. Pain with the movement of the eyes leads to more

generalized and extreme pain in the legs and joints. A high

fever can be produced, with temperatures reaching 104° F

[40° C]. Also, a pale rash may appear transiently on the face.

These symptoms can persist for up to 96 hours. Often,

the fever then rapidly eases. After a short period when symp-

toms disappear, the fever reappears. The temperature elevates

rapidly but the fever is usually not as high as in previous

episodes. The palms of the hands and soles of the feet may

turn bright red and become very swollen.

In about 80% of those who are infected, recovery is

complete after a convalescent period of several weeks with

general weakness and lack of energy. However, in some 20%

of those who are infected a severe form of dengue fever devel-

ops. This malady is characterized by the increased leakage of

fluid from cells and by the abnormal clotting of the blood.

These factors produce the hemorrhaging that can be a hallmark

of the disease, which is called dengue hemorrhagic fever. Even

then, recovery can be complete within a week. Finally, in some

of those who are infected, a condition called dengue shock syn-

drome can result in convulsions. In addition, a failure of the cir-

culatory system can occur, resulting in death.

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