Vol 27 No 2 December - The Indian Society for Parasitology
Vol 27 No 2 December - The Indian Society for Parasitology
Vol 27 No 2 December - The Indian Society for Parasitology
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JPD : <strong>Vol</strong>. <strong>27</strong> (2), 2003<br />
Trematodes of public health importance<br />
71<br />
<strong>The</strong> second I.H. is a fish (Mugil cephalus, Tilapia<br />
nilotica, Aphanius fasciatus and Acanthogobius<br />
(sps). <strong>The</strong> cercariae which escape from the mollusc<br />
encyst superficially in fishes which constitute the<br />
source of infection <strong>for</strong> man and other mammals.<br />
Infection takes place through eating infected raw fish.<br />
(Faust et al 1975, Hafeez, 1993)<br />
<strong>The</strong>se parasites in the nucosal crypts at the duodenum<br />
and jejunum produce superficial irritation of the<br />
gonads, with excess secretion of mucus and superficial<br />
necrosis of the mucosa. In heavy infections this may be<br />
accompanied by Colicy pains and mucous diarrhoea.<br />
More serious is the occasional deep penetration of the<br />
worms into the mucous coat of the intestine , so that<br />
their minute eggs get into mesenteric venules (or)<br />
lymphatics and are carried to the heart, brain or spinal<br />
cord where they may stimulate granulomatous<br />
reactions with symptoms related to these lesions.<br />
Metagonimus yokogawai<br />
It is probably the most common heterophyid fluke in<br />
the USSR, <strong>No</strong>rthern Siberia, Korea, Japan, Formosa,<br />
Egypt and Bukan states. It was discovered by<br />
yokogawa in 1911 in the gills, scales and muscles of<br />
fresh water fish in Formosa. <strong>The</strong>se flukes usually occur<br />
in the small intestine of man and other definitive hosts<br />
like pigs, dogs, cats, etc. <strong>The</strong> first I.H. is the snail<br />
nd<br />
Semisulcospira libertina and related species, the 2<br />
I.H. are several sps. of fresh water fishes (the Trout<br />
Necoglosscus altivelis, Salmoperri udontobutis and<br />
Leuciscus sps.). <strong>The</strong> cercariae encyst under the scales<br />
or in the tissues of the gills, fins or tails and the final<br />
host gets infection itself by eating these raw fishes.<br />
<strong>The</strong>se minute worms attach to the cell in the mucosal<br />
crypts, usually at the duodenal and jejunal walls of the<br />
small intestine, causing excess secretion of mucus,<br />
superficial erosion of the mucosal and granulomatous<br />
infiltration aroung egg deposits in the stomal tissue.<br />
<strong>The</strong> worms have also been demonstrated deep in the<br />
mucosal layer where they remain until they die but<br />
with out host tissue encapsulation. <strong>The</strong> symptoms<br />
consists of mild to moderate mucous diarrhoea of a<br />
persistant type. Similar observations were also noticed<br />
in man and domestic animals infected with M.<br />
yokogawai in USSR.<br />
HEAPATIC FLUKES<br />
Fasciola hepatica<br />
F hepatica was the first trematode to be described and<br />
was likewise the first one on which the complete<br />
lifecycle was elucidated, by Leuckart in Germany in<br />
1882 and by Thomas in England in 1883. It is<br />
particularly prevalent in sheep raising areas. In several<br />
countries human infection is an increasing clinical and<br />
public health problem. <strong>The</strong> parasite is cosmopolitan in<br />
distribution and occurs in the liver of sheep, goat, cattle<br />
and man.<br />
<strong>The</strong> intermediate hosts are snails of the genus Lymnea.<br />
<strong>The</strong> infection is contracted by ingesting vegetation on<br />
which the cercariae of F. hepatica have encysted. <strong>The</strong><br />
metacercariae encyst in the duodenum migrate<br />
through the intestinal wall into the peritoneal cavity,<br />
penetrate the capsules of the livers traverse its<br />
parenchyma and ultimately settle in the biliary<br />
passage. <strong>The</strong>y begin to liberate eggs in about 3 to 4<br />
months.<br />
<strong>The</strong> migrating immature flukes cause both traumatic<br />
damage and toxic irritation with necrosis of tissues<br />
along their pathway. In the larger bile passages they<br />
produce hyperplasia of the biliary epithelium with<br />
leucocytic infiltration and development of a fibrous<br />
capsule around the ducts.<br />
In sheep it causes a fatal disease called "Liver rot" with<br />
enlargement of the bile duct, cirrhosis of the liver and<br />
ascites. Early symptoms in human infections consists<br />
of right upper quadrant abdominal pain, fever, and<br />
hepatomegaly, biliary colic with coughing and<br />
vomiting, marked Jaundice, generalized abdominal<br />
rigidity, diarrhoea, irregular fever, profuse sweating.<br />
Urticaria, significant eosoniphilia and Loeffler's<br />
syndrome may appear. <strong>The</strong> mature or adolescent<br />
worms have been found in abscess pockets in blood<br />
vessels, lungs, subcutaneous tissues, ventricles of the<br />
brain and orbit, often associated with mature worms in<br />
the bile passage. It was also recorded from a breast<br />
abscess.<br />
Fasciola gigantica<br />
<strong>The</strong> giant liver fluke, differs from F. hepatica in its<br />
greater length, more attenuate shape, shorter anterior