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Chapter
26
Filariasis
and Elephantiasis
Filariasis
was not, until recently, of great importance to radiologists: the unpleasant
and often life-threatening complications which are part of the clinical
progress of filarial infection did not call for major diagnostic imaging.
Now the development of high-definition ultrasonography and the technique
of lymphoscintigraphy has brought new understanding of filarial diseases,
and added information which is important in the clinical management
of the millions of patients who are afflicted.
It is impossible
to ignore the gross swelling of limbs and other parts of the body which
are the result of filariasis. The name "the elephant disease"
was given by Lucretius (99-55 B. C.), who described the appearance of
people living along the Nile and recognized that the eye disease occurring
elsewhere was a similar illness, "and so different places are hurtful
to different parts and members." He also realized that "we
must absorb at the same time into our body those things as well,"
but it was many centuries later (1589) before Pigafetta first described
Loa loa in a Congolese. Almost 200 years after that (1770) the
worm was isolated from the eye of a Haitian who had brought the infection
to the New World from Africa. Microfilariae were described long before
the life cycle was understood: first in 1863, when Jean-Nicholas Demarquay,
a surgeon, placed a trocar into the left-sided scrotal "tumor"
of a young Cuban man, and then a few years later, when the larval microfilariae
were seen in the urine of a Brazilian patient with hematochyluria and
Otto Wucherer (in 1868) described thread-like transparent worms with
brisk wavy movements. The diagnosis became more accurate when, in 1875,
a British naval surgeon, O'Neill, described filarial dermatitis (onchocerciasis)
in West Africa and started the diagnostic use of skin-snips. In December
1876 another adult nematode was recovered by Joseph Bancroft from a
lymphatic abscess and hydrocele. That parasite, named Filaria bancrofti,
was a female and was seen to emit large numbers of microfilariae. (The
current name, Wuchereria bancrofti, was not formalized until
1921.)
The
life cycle was still unknown until, in 1878, Patrick Manson made a landmark
discovery in the fields of tropical medicine and parasitology: he suggested
that the circulating microfilariae might leave the human host when a
blood-sucking insect was feeding, to then mature and reinfect another
person. While in China, Manson confirmed his hypothesis by allowing
mosquitoes to feed on the blood of his gardener and later dissecting
the mosquitoes to find new larval stages. Manson, however, thought the
larval stages were released into the water in which the mosquito died
and infected man by being swallowed.
It
was not until the late 1890s that the work of Bancroft and others showed
that these potentially infective filiarial larvae actively migrate into
the proboscis of the female mosquito. There the larvae await an opportunity
to enter the human host at the mosquito's next blood meal. Again, it
was many years before the next big step forward in the understanding
of filariasis, which came as a result of the many who were infected
during the World War II campaigns in the Pacific Islands.
Those
who enjoy travel will be glad to know that, in contrast to many other
parasitic infections, filariasis is not a disease of the returning traveler.
Even those people who travel on "Eco-Tours" to remote rural
or urban areas are unlikely to become infected, unless they have been
in contact with infected blood via transfusion (and then filariasis
may be only one of their concerns). The development of clinical filariasis
is thought to occur only in those living for months or years in an endemic
region, with prolonged contact with the infected fly vector.
Filariasis
Filariasis
is the general name for a variety of helminthic infections which are
caused by round worm or nematode parasites. Although there are many
species parasitic in a variety of animals, only eight species infect
humans. Of these, the most significant are Wuchereria bancrofti,
Brugia malayi, and Onchocerca volvulus. A broad spectrum
of disease is caused by these parasites.
Bancroftian, or lymphatic filariasis, is the most widespread and occurs
throughout the tropical world; its most severe form results in elephantiasis.
Malayan filariasis, as the name suggests, is geographically more restricted
but results in similar lymphatic disease. Filariasis is still, widespread
and a major public health problem in the tropical world. It is one of
the six major tropical diseases targeted by the WHO for research, control,
and possible eradication, a program which has met with some success.
For example, in the Sahandang Province of China, the transmission of
infection has been interrupted by a large-scale and vigorous campaign.
But in other parts of the world, progress has not been so dramatic.
Synonyms
Lymphatic
filariasis. Bancroft's filariasis. Wuchereria bancrofti infection.
Filariasis bancrofti. Filariasis malayi. Brugia malayi infection.
Wuchereria malayi infection. Brug's filariasis. Malayan filariasis.
Brugia timori infection. Brugian zoonoses. Sp: Filariasis.
Fr: Filarioses. Ger: Filariosen Erkrankungen durch Filaria.
Definition
Bancroftian
filariasis is infection with Wuchereria bancrofti, Malayan filariasis
is infection with Brugia malayi, and filariasis timori is infection
with Brugia timori.
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