FILARIASIS
[Brugia malayi]
[Brugia timori] [Wuchereria bancrofti]
What
is filariasis?
Filariasis
is a disease caused by parasitic worms called filariae. Filariae are microscopic roundworms
that dwell in the blood and tissues of humans. The most important filarial diseases
for humans are lymphatic filariases, in which the adult worms are found
in the lymphatic system. The
lymphatic form of filariasis will be the focus of the site. Lymphatic is also referred to sometimes
as “elephantiasis.” Elephantiasis
is actually an extreme clinical feature of filariasis that has become strongly
associated with the disease.
Taxnomic
breakdown:
Nematoda (Phylum) > Secernentea (Class) > Spirurida (Order) >
Filarioidea
(Superfamily)
How does one get
filariasis?
Lymphatic filariasis spreads
from person to person by mosquito bites. As the mosquito bites, infective filarial larva are
deposited on a person’s skin, penetrate the skin and develop to maturity
in the lymph vessels.
Adults produce highly adapted eggs called microfilariae that
travel to the blood. Microfilaria
are again ingested by the same species of mosquito when it bites, infecting the
insect. The process continues
cyclically.
Who is affected by filariasis?
|
Endemic |
Uncertain |
Non-endemic |
Usually it takes many
insect bites over several months to get filariasis. People that live or stay for long
periods of time in tropical or sub-tropical areas where the disease is
common are at the greatest risk. These
regions include central Africa, the Nile delta, Madagascar, Turkey, the Middle
East, India, Pakistan, Sri Lanka, Myanmar, Thailand, Malaysia, Vietnam, South
Korea, Indonesia, the Philipines, Timor, Southern China, Haiti, Dominican
Republic, Guyana, French Guinea, and Costal Brazil. Short-term tourists are at a very low
risk.
What happens to those affected by filariasis?
© 2001-04, Dermatlas
Often times, symptoms will
not develop until after adult worms die.
For lymphatic filariases, fluid collects in the lymph vessels causing
swelling in the arms, breasts, legs, and groin area (for men). This swelling is called lymphedema. Swelling and decreased lymph function
can adversely affect the body’s immune response to germs and other
infections. Increased
infections in skin and lymph lead to hardening and thickening of the skin,
called elephantiasis. Chyle
may occur in the urine, giving the urine a milky appearance (chyluria).
What is used to treat filariasis?
Ivermectin
Diethylcarbamazine
(DEC) is an effective drug for killing microfilariae, but is
slower in killing adult worms. It
is usually administered at the rate of 6 mg/kg of body weight. DEC has been applied to table
salt in both China and Tanzania as a mass treatment program. Ivermectin may be taken
concordantly with DEC for better long-term suppression of
microfilaremia. Superficial wounds
can be treated with antibacterial cream to prevent further infection. Surgery has also been employed for treatment
of scrotal elephantiasis and hydrocele.
How does one avoid getting filariasis?
Avoiding
and controlling the disease vector, mosquito, is the most effective prevention.
Sleep under a
mosquito net in endemic areas
Use insect
repellent between dusk and dawn or other peak vector hours
Eliminating
vector habitat (i.e. puddles and stagnant pools of water)
Insecticide-impregnated
materials
Taking a yearly
preventative dose of ivermectin or DEC
can also kill any circulating worms before clinical symptoms develop. This should only be practiced in “at
risk” populations in endemic areas.
Created by Eric Crossen and
Nicole Sandoval Human
Biology 103 Parasites and Pestilence
Spring
2004 Instructor:
D. Scott Smith, MD