c. Treatment. An effective drug is hexylresorcinal; however, recently the US
has discontinued marketing hexylresorcinal. If hexylresorcinal is not available or not
effective, use tetrachloroethylene. Another drug used in treatment is niclosamide, but it
may not be as effective as the other two drugs. It is however, more convenient to give.
3-12. LUNG FLUKES
Paragonimus westermani, the lung fluke, is a parasite which uses humans and
other animals as a host. The common name lung fluke comes from the fact that when
infected, a human's lungs are frequently involved. This parasite occurs throughout the
Far East, West Africa, South Asia, Central America, and northern South America.
a. Life Cycle.
(1) Fluke eggs reach the water, either in sputum or feces, and hatch in 3 to
6 weeks. Miracidia penetrate snails and develop. Next, cercariae leave the snails and
encyst in the tissues of crabs and crayfish.
(2) Infection occurs when raw or partially cooked fresh water crabs and
crayfish containing infected larvae are eaten. Pickling of crabs and crayfish in wine,
brine, or vinegar--common practice in Asia--frequently does not kill the infected larvae.
Most larvae migrate through the diaphragm and enter the lung parenchyma. Some
larvae lodge in the peritoneum, the intestinal wall, liver, or other tissues; these usually
do not mature. In rare instances, the larvae migrate to the brain or spinal cord. As the
parasite matures, a capsule of fibrous and inflammatory tissue forms around it and later
swells and ruptures into a bronchiole. Fluid containing eggs, blood, and inflammatory
cells is released in expectorated in the sputum, and the cycle begins again.
b. Signs and Symptoms. Until the flukes mature and begin producing eggs,
the infection shows no signs or symptoms. Gradually, there is a low-grade fever,
cough, or hemoptysis. At first, the cough is dry; later, there is rusty or blood-flecked
viscous sputum. Pleuritic chest pain is common. The condition is chronic and
progresses slowly. People with light infections often do not seem seriously ill. In heavy
infections, there is dyspnea, signs of bronchitis and bronchiectasis, weakness, malaise,
and weight loss. Parasites in the peritoneal cavity or intestinal wall may cause
abdominal pain, diarrhea, and dysentery. Those in the central nervous system,
depending on their location, may cause seizures, palsies, or meningoencephalitis.
c. Treatment. Biothinol can be used for pulmonary infections; it is the drug of
choice. Use antibiotics to control secondary pulmonary infection. An alternative
method of treatment is a new drug, menichlopholan.