helminthic infection

BLOOD FLUKES

These are flukes that reside mainly in the blood vessels of various organs and the schistosomes are the prototype and the commonest flukes in our country.
Schistosomiasis (Bilharziasis)

It is estimated that about 600 million people in 79 countries suffer from schistosomiasis (Bilharziasis). The schistosomes cause intestinal, hepato-splenic, pulmonary, urogenital, cerebral and other forms of schistosomiasis. Schistosome is the only fluke with separate sexes. The female worm lies in the gynecophoral canal of the male. This condition is important for transportation.
There are three medically important species:
1. Schistosoma mansoni: causes intestinal schistosomiasis.
2. Schistosoma haematobium: causes vesical (urinary) schistosomiasis.
3. Schistosoma japonicum: causes intestinal schistosomiasis.

This seems to cause milder disease in man. It causes disease in other vertebrate hosts.

Schistosoma mansoni
Habitat - This species lives in the veins of the intestine.
The snail hosts that harbor S. mansoni are the genera: Biomphalaria.

Morphology
Male: The male ranges in size from 1-1.4 cm in length and the body is covered by coarse tubercles. It has 6-9 testes.

Female:The female is 1.5-2.0 cm in length. The ovary is present in the anterior third and Vitelline glands occupy the posterior two-thirds. It lays about 100-300 eggs daily. The uterus is short containing few ova.



Urinary Schistosomiasis
Etiology - Schistosoma haematobium
Habitat - The worm lives in the veins of the bladder of humans.
The peak prevalence is the 10-14 year age group. The snail hosts that harbor S. haematobium are the genera Bulinus .

Morphology
Male: The male ranges in size from 1-1.5 cm in length. The body is covered by fine tubercles. It has 4-5 testes.
Female: The female ranges in size from 2-2.5 cm in length. The ovary is present in the posterior third. Vitelline glands occupy the posterior thirds. Uterus is long containing many ova. It lays about 20-200 eggs daily.

Schistosoma japonicum


Morphology
Male : The male measures 12–20 mm - 0.5–0.55 mm and has no cuticular tuberculation. There are 6–7 testes.
Female: The female has the ovary at about the middle of the body.

The female adult worm lays about 500-3500 eggs daily. The eggs are ovoid,
bearing only a minute lateral spine or a small knob postero-laterally. It is found in Japan, China, and Philippines, etc.

Life cycle
Adult worms reside in pairs: the female lying in the gynecophoral canal of the male. After fertilization, eggs are passed into the venules. A larval form – the miracidium - develops within the egg. Its lytic enzymes and the contraction of the venule rupture the wall of the venule liberating the egg into the perivascular tissues of the intestine (S. mansoni) or urinary bladder (S. haematobium). The eggs pass into the lumens and organs and are evacuated in the feces (S. mansoni) or the urine (S. haematobium). On contact with fresh water the miracidia hatch from the eggs and swim about until they find the appropriate snail, which they penetrate. After two generations of sporocyst development and multiplication within the snail, the fork-tailed cercariae emerge. Infection to man takes place during bathing or swimming. The cercariae penetrate the skin, are carried into the systemic circulation and pass through to the portal vessels.
Within the intrahepatic portion of the portal system, the worms feed and grow to maturity.

Symptoms and complications
Patients infected with S. haematobium suffer from terminal haematuria and
painful urination . There is inflammation of the urinary bladder (cystitis), and enlargement of spleen and liver.
Patients infected with S. mansoni suffer from cercarial dermatitis (swimmers itch) and dysentery (mucus and blood in stool with tenesmus) as well as enlargements of the spleen and liver.
S. haematobium causes squamous cell carcinoma in the bladder.

Treatment:
Praziquantel: single oral dose of 40 mg/kg divided into two doses.

Prevention:
1. Health education:
A. On use of clean latrines and safe water supply
B. Avoid urination and defecation in canals, avoid contact with canal water

2. Snail control:
A. Physical methods:
i. Periodic clearance of canals from vegetations.
ii. Manual removal of snails and their destruction.
B. Biological methods: Use of natural enemies to the snails such as Marisa.
C. Chemical methods: Molluscides are applied in the canals to kill the
snails. e.g. Endod.

Structures of the three major Schistosome species. Only the male of S. mansoni is shown. The males of the other species differ principally in the number of testes, while that of S. japonicum has a smooth tegument.