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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 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.


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.


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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Copyright: Palmer and Reeder