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Blood (Intracellular) and Other Tissue Protozoa 105

control lies in control of the vector populations. This in- head is slightly swollen and has two circles of well-
cludes removal of breeding sites and killing of the large defined papillae. The tail of B. malayi is ventrally curved.
populations of mosquitoes by insecticides. Because hu- Sexual differences exist, with the adult female B. malayi
mans are the only host for this species of parasite, remov- being approximately 8 cm long by 0.3 mm wide and the
ing infected persons to other nonendemic regions will also male about 2 cm long and 0.1 mm wide (Amaya, 2003).
stifle the source of infected victims for the insect vectors.
Symptoms
BRUGIA MALAYI
B. malayi produces a condition marked by infection and
Brugia malayi is found in rural areas of Asia, in addi- swelling of the lymphatic system. The disease is primar-
tion to isolated pockets in countries extending from the ily caused by the presence of worms in the lymphatic
west coast of India to New Guinea, the Philippines, and vessels and the resulting host response. Signs of infec-
Japan. (Amaya, 2003). The habitat in which B. malayi tion are essentially the same as those seen in bancroftian
flourishes is in the rural freshwater swamp forests in (W. bancrofti) filariasis, including fever, lymphadenitis,
Southeast Asia, and its intermediate host is that of one lymphangitis, lymphedema, and potentially a second-
of several genera of mosquitoes. In open swamp and ary bacterial infection. Lymphadenitis, or swelling of the
irrigated fields and hill forests of South and East Asia, lymph nodes, is commonly a sign of many diseases and
B. malayi uses the mosquitoes of the genera Mansonia, occurs as an early manifestation of filariasis, occurring
Aedes, Anopleles, and Culex. In the intermediate host, frequently in the inguinal area before the worms mature.
B. malayi occupies the stomach, thorax muscles, and Lymphangitis, inflammation of the lymphatic ves-
the proboscis or piercing part of the mosquito. The only sels, is in response to the infection and occurs early in
definitive hosts the organism utilizes that may be bitten the course of infection in response to worm develop-
by the mosquito include human, monkeys, forest carni- ment, molting, death, or accompanying bacterial and
vores (meat-eating creatures), and domestic cats. The fungal infection. Abscess formation and ulceration of the
organism enters the wound before migrating to the lym- lymph nodes occasionally occur during B. malayi infec-
phatic system through the bloodstream where it remains tion. Repeated inflammatory reactions cause dilation of
throughout its adult life (Amaya, 2003). blood vessels and thickening of the affected lymphatic
The impact of B. malayi on human health can be vessels, interrupting the fluid balance between tissues
considerable. Infections by B. malayi frequently contrib- and the circulatory system. Elephantiasis resulting from
ute to both physical and mental disabilities. The physi- B. malayi infection most often affects the lower extremi-
cal disabilities come in the form of the inflammation and ties of the legs and arms. B. malayi infections rarely affect
marked swelling of the lymph nodes, normally from the the genitalia as frequently as with bancroftian infection.
waist down, due to the blockage of the lymphatic circu- Most infections appear asymptomatic but will vary
lation. Mental disabilities often ensue and chiefly stem among individuals. Those living in endemic areas with
from psychological stress based on a lack of mobility and microfilaremia may never present with overt symptoms
the attitudes they experience from social contacts when but in some individuals, the infective load is inconse-
their physical appearance is drastically altered. Two quential as a severe inflammatory response may be elic-
genera of mosquito, Mansonia and Aedes, are vectors for ited by only a few worms.
B. malayi, which are also implicated in transmitting
other diseases (Figure 4-20). For instance, Aedes aegypti Life Cycle
is also known to transmit both yellow fever and dengue,
among other diseases. The reproductive cycle of B. malayi begins when a mos-
quito, the intermediate host of a species in the genera
Morphology Mansonia, Anopleles, and Aedes, acquires the sheathed
microfilaria parasite in its blood meal. The microfilar-
The adult Brugia malayi is a long and slender organism iae penetrate the gut wall of the mosquito where they
with a smooth cuticle, kinked, and has a long cephalic lose their sheath and migrate to the muscles of the
space having a length-to-width ratio of about 2:1. The thorax. After 10 to 20 days, in which they undergo three