Page 210 - parasitology for medical and clinical laboratoryprofessionals

190 CHAPTER 8

Geographic location and clinical data assist in differenti- duodenum and migrate into the bile duct and gallblad-
ation between the eggs of C. sinensis and O. felineus. The der where they attach and develop into adults, which are
eggs are operculated and possess prominent opercular capable of laying eggs after 3 to 4 weeks.
‘shoulders’ and abopercular (opposite the operculum)
knobs. The eggs are distinctly embryonated when passed Disease Transmission
in feces.
It is estimated that up to 1.5 million people in Russia
Symptoms are infected with the Siberian liver fluke. Inhabitants of
Siberia and perhaps other regions of the world acquire
Opisthorchiasis, the disease caused by Opisthorchis the infection by consuming raw or slightly salted and
felineus, is quite variable in severity, ranging from frozen fish.
asymptomatic infection to severe illness. Human cases
of opisthorchiasis may affect the liver, pancreas, and Laboratory Diagnosis
gallbladder and, if not treated, cirrhosis of the liver may
result. Cirrhosis from this infection leads to an increased Diagnosis is based on microscopic identification of eggs
statistical prevalence of liver cancer even years later. in stool specimens. However, the eggs of Opisthorchis are
Approximately 2 weeks after flukes enter the body of the practically indistinguishable from those of Clonorchis,
host, the parasites infect the biliary tract and produce and differentiation is based on geography and clinical
symptoms of infection that include fever, general malaise, data such as the involvement of the biliary system. Using
skin rash, and gastrointestinal discomfort. Severe anemia the oil immersion objective providing a microscopic
and liver damage may severely incapacitate an individual power of 1000×, structural features are somewhat easily
for up to 2 months. visualized in Opisthorchis.
Severity of the disease ranges from an asymptomatic
state to severe medical conditions. Early detection and Treatment and Prevention
treatment are of the essence in preventing unwarranted suf-
fering, and the resulting consequences of a long-standing Treatment of opisthorchiasis is generally with a single
infection. Opisthorchiasis in humans may result in damage dose of praziquantel, the basic drug used for this infec-
to the liver, the pancreas, and the gallbladder. An increased tion. Prevention, as in most parasitic infections, requires
risk exists in the development of liver cancer in chronic good personal and food preparation sanitation, and the
cases, as well as cirrhosis of the liver. Treatment with a sin- ingestion of only thoroughly cooked fish.
gle dose of an effective medication is most often sufficient,
but again, prevention is the best course of action.
PARAGONIMUS WESTERMANI
Life Cycle This fluke is known primarily as the lung fluke and may
be parasitic to a number of mammals other than humans,
The adult flukes deposit fully developed eggs that are including dogs, cats, pigs, mink, and perhaps others. A
passed in the feces. After ingestion by a snail of an ac- diet of poorly cooked crabs or crayfish provide the basic
ceptable species as the first intermediate host, the eggs way of contracting this disease, which is primarily found
release miracidia, which undergo several developmental in parts of Asia. The history of these infections as dis-
stages in a snail’s body, developing from sporocysts, to eases begins with the discovery of the worms and contin-
rediae, and then to cercariae. The cercariae are then re- ues with the elaboration of the life cycles. P. westermani
leased from the snail upon which they penetrate the flesh was discovered in the lungs of a human by B. S. Ringer in
of freshwater fish as the second intermediate host. There 1879, a finding that he subsequently shared with others.
they encyst as metacercariae in the muscles or under the Eggs in the sputum were recognized independently by
scales of the fish. Mammalian definitive hosts that in- Manson and Erwin von Baelz in 1880. Manson also sug-
clude cats, dogs, and various other fish-eating mammals gested that a snail might act as an intermediate host and
including humans become infected by ingesting raw or a number of Japanese scientists reported on the whole
undercooked fish containing metacercariae. After inges- life cycle in a species of snail, Semisulcospira, between
tion by the definitive host, the metacercariae excyst in the 1916 and 1922 (Cox, 2002).