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Blood (Intracellular) and Other Tissue Protozoa 101

milky. This condition was recorded by William Prout in and these larvae only appear in the bloodstream at night,
his 1849 book On the Nature and Treatment of Stomach when they may be transmitted, via an insect bite, to an-
and Renal Diseases (Cox, 2002). other host. But a single bite is usually not sufficient to
The larval microfilariae were first seen in the fluid transmit an infection by one of the species of the caus-
from a hydrocele by the French surgeon Jean-Nicolas ative organisms; therefore, for the most part, short-term
Demarquay in 1863 and in urine by Otto Henry travelers to an endemic region are usually safe. A series of
Wucherer in Brazil in 1866 (Cox, 2002). However, the multiple bites over a period of time is required to estab-
role of the microfilariae in urine and blood remained a lish an infection. As a result, those individuals who are
mystery until Timothy Lewis, a Scottish physician work- regularly active outdoors at night and those who spend
ing in India confirmed the presence of microfilariae in more time in remote jungle areas are at an increased risk
both urine and blood and showed their significance in of contracting the filariasis infection.
the development of elephantiasis. The adult worm was
described by Joseph Bancroft in 1876 and named Filaria Causes and Symptoms of
bancrofti in Bancroft’s honor by the British helmintholo- Filariasis
gist Thomas Spencer Cobbold (Cox, 2002).
In cases of lymphatic filariasis, the most common form
Disease Transmission of the disease, the disease is caused by the adult worms
actually living in the lymphatic vessels near the lymph
In an interesting development, while working on the life nodes. There they distort the vessels and cause local
cycle of the organisms causing filariasis, Manson was inflammation. In advanced stages, the worms can com-
led astray regarding the finding of an intermediate host. pletely obstruct the blood and lymph vessels, causing the
This assumption was based on the belief that the infec- surrounding tissue to become enlarged. In bancroftian
tion leading to filariasis was caused by drinking con- filariasis, the legs and genitals are most often involved,
taminated water. Later, when working in China, Manson whereas the Malayan variety affects the legs below the
found microfilariae in the blood of dogs and humans and knees. Repeated episodes of inflammation lead to block-
hypothesized that these parasites in the blood might be ages of the lymphatic system, especially in the geni-
transmitted by a bloodsucking insect such as the mos- tals and legs. This causes the affected area to become
quito. Following this lead, he fed mosquitoes with the grossly enlarged, with thickened, coarse skin, leading to
blood of his gardener, who was harboring the parasites, elephantiasis.
and found larval stages in the mosquitoes (Cox, 2002). In conjunctival filariasis, the larval forms of the
But Manson erroneously thought that the parasites es- worms migrate to the eye and can sometimes be seen
caped from the mosquito and into the water and that moving beneath the skin or beneath the white part of
humans acquired infection from this contaminated wa- the eye (conjunctiva). If untreated, this disease can cause
ter by drinking the parasitic-laden water or by penetra- river blindness, or onchocerciasis (Figure 4-19). Symp-
tion of the skin. But the true mode of transmission was toms vary, depending on what type of parasitic worm has
not certain until assumptions made by the Australian caused the infection, but all infections usually begin with
parasitologist, Thomas Bancroft, were followed up by chills, headache, and fever between three months and
Manson’s assistant, George Carmichael Low, who dem- one year after the insect bite. There may also be swelling,
onstrated the presence of microfilariae in the mouthparts redness, and pain in the arms, legs, or scrotum. Areas of
of mosquitoes in 1900, completing the history of the de- pus (abscesses) may appear as a result of dying worms or
velopment of lymphatic filariasis (Cox, 2002). a secondary bacterial infection.

How the Disease of Filariasis Is Laboratory Diagnosis
Contracted
The disease is diagnosed by taking a patient history, per-
The larval form matures into an adult worm within six forming a physical examination, and by screening blood
months to one year and can live between four and six specimens for specific proteins produced by the immune
years. Each female worm can produce millions of larvae, system in response to this infection (antibodies). Early