General view on Cestodes

Sponsored Ads

Body of a cestode consists of :
A- Scolex provided with organs of fixation
B- Neck, active region for growth of segments
C- Chain of segments starting by:
-Immature segment.
-Mature segment.
-Gravid segment (filled by pregnant uterus full of ova).

Organs of fixation :
- 2 Slit like suckers and 4 cup shaped suckers with or without rostellum.

Development of  coming CESTODES :
1- Adult tapeworms live in the small intestine of DH. All eggs pass mature (hexacanth embryo) in the feces.
2- Egg : Ingested by IH
3- embryo is liberated and penetrate intestinal wall and develops in organs into cystic larval stage.
4- This larvae when ingested by DH it develops into adult in intestine.

Example of cestodes : Taenia

- Bothe T.Saginata and T.Solium heve Same Mature segments squarish, common genital pores are not on same side.
- Gravid segments longer than broader, uterus has 15-20 (T.saginata) or 7 – 11 (T.solium) lateral branches full of eggs. Terminal segments separate to pass with stool or crawl at anal orifice.

Eggs (mature contain embryo) pass with stool of DH (man).
- It is ingested by IH (cattle in T.saginata and pig in T.solium) and embryo is liberated in intestine.

- Embryo pierces intestinal wall to blood vessel to reach muscles of IH to develop into cysticercus bovis containing no hooks (T. saginata) or cysticerus cellulosae containing hooks (T. solium)

Infective stage: Cysticercus bovis (T. saginata) or cysticercus cellulosae (T.solium).
- Mode of transmission is by eating raw or improperly cooked beef meat containing cysticercus bovis (T. saginata) or insufficiently cooked pork meat containing cysticercus cellulosae (T.solium).

- In small intestine of man, Scolex attaches to mucosa and by neck forms adult worm.

Clinical picture :
- Symptomless or associated with abdominal discomfort, vomiting, diarrhea.

- The main complaint is the passage of gravid segments with faeces or their crawling through the anal orifice and migration on the skin causing irritation& itching.

Diagnosis :
I. Clinical diagnosis:
1- history of passing segments.
2- Clinical picture.

II. Laboratory:
1- Stool examination for detection of eggs or gravid segments (diagnostic stages):
- 30-40 μ.
- Thick shell radially striated

- Contains hexacanth embryo

Treatment :
1- Praziquantel:10mg/kg single oral dose.
2- Yomesan: 2gm single dose. It is contraindicated in Taenia solium because it disintegrates gravid segments releasing eggs increasing risk of cysticercosis.

Prevention and control :
1-Treatment of patients.
2- Avoid eating insufficiently cooked meat.
3- Freezing of meat at -10C for 3 weeks kills cysticerci.
4- Proper inspection of meat in slaughter houses.
5- Avoid defecation in soil.

Blood Flukes

Sponsored Ads

General characters :
- Separate sexes.
- Oesophagus bifurcates into 2 simple intestinal caeca that unite again giving a single caecum that ends blindly.
- Male is folded on itself forming a gynecophoric canal and has 4-9 small testes.
- Female is longer than male with a cylindrical body , single ovary and uterus.

Schistosomes.
The main species affect humans :
- Schistosoma haematobium
- Schistosoma mansoni

*Infective stage: Furcocercous cercaria.
*Mode of infection :penetration of skin or buccal mucosa by cercaria.

- Eggs pass mature with urine (S. haematobium) and faeces (S.mansoni).
- Eggs hatch liberating miracidium that enters snail and develops inside to sporocyst and cercaria (NO REDIA).
- Furcocercous cercaria (has forked tail) comes out of snail and swims in water (NO METACERCARIA).

Diagnosis.
I. Clinical diagnosis: Clinical picture.
II. Laboratory diagnosis:
1- Stool (intestinal schistosomiasis) or urine (urinary schistosomaiasis) examination for detection of eggs (diagnostic stage). Eggs don’t not pass in urine or stool
in chronic schistosomiasis when there is fibrosis preventing passage of eggs.
2- Cystoscope or Sigmoidoscope to take biopsy.
3- Serological by detection of antibodies in patient sera.
4- Blood examination: anaemia.

Treatment.
1- Praziquantel: effective in all forms of schistosomiasis both in acute stage and late stages
Dose : 40 mg / kg in a single oral dose
2- Oxamniquine : is effective in S. mansoni only
Dose :30 mg / kg / day on two doses for 2 days
3- Treatment of swimmer’s itch by antipruritic lotions and antibiotics for secondary infections .

Control of schistosomiasis.
I. Measures dealing with man :
1- Treating patients.
2- Health education.
3- Safe water supply.

II. Snail control :
A- mechanical control:
1- Scraping wall of canal to remove weeds and snails.
2- Increase slopes of canal or divert away from population.
B- Biological control: enhance growth of snail enemies like gambusia fish.
C- Chemical control by molluscicide such as Bayluscide

Intestinal Flukes

Sponsored Ads

Heterophyes heterophyes :
- Disease : heterophyiasis
- Geographical distribution: Egypt and far east
- Habitat :small intestine
- DH: man and fish eating animals: dogs and cats (RH)
- 1st IH : snail: Pirenella conica
- 2nd IH : Mugil (boury) and Tilapia (bolty)

Morphology Adult worm :
- Pear shape 1.5 mmx0.5 mm
- Has 3 suckers: oral, ventral and genital sucker around genital pore.
- Two testes beside each other
- One ovary lies anterior to testes
- Simple intestinal caeca

Life cycle of Heterophyes :
- Infective stage: encysted metacercaria in fish muscle
- Mode of transmission is by ingestion of insufficiently cooked or salted fish (less than 10 days) containing encysted metacercaria.
- In the small intestine , metacercaria excysts and lodged between the villi and develops to an adult worm.

Diagnosis :
I. Clinical diagnosis: Clinical picture
II. Laboratory:
Stool examination for egg (diagnostic stage).
- Size:30x17u
- Colour: Golden yellow
- Shell: Thick shell with operculum.
- Content: Miracidium

Treatment :
-Praziquantel: 25 mg/kg/day for 1 or 2 days.

Prevention and control :
1- Avoid eating insufficiently cooked or salted fish.
2- Avoid defecation in water.
3- Snail control.
4- Treatment of patients

Liver Flukes

Sponsored Ads

Fasciola gigantica and hepatica :

- Disease: Fascioliasis.
- Geographical distribution: Worldwide including Egypt.
- Habitat: Bile ducts.
- DH: Man or sheep or cattle (RH) .
- IH: Water snail, Lymnaea cailliaudi (F. gigantica) , Lymnaea truncatula (F. hepatica)

Morphology of  Fasciola gigantica and hepatica :

F.gigantica Adult Worm.

- Larger 2-8 cm

- Less developed shoulders

- Parallel lateral borders.

- Larger ventral sucker

F.hepatica Adult Worm

- 2-3 cm

- Well apparent shoulders.

- Converging lateral borders

- Medial branches of intestinal caeca are small knobs

Life cycle of Fasciola species :

- Eggs pass with faeces to water. Egg develops miracidium and hatches. Miracidium enter snail and develops to sporocyst, redia and leptocercous cercaria (simple tail). Cercaria attaches to grasses and loses tail and forms encysted metacercaria.

- Infective stage: encysted metacercaria on grass or water.

- Mode of transmission is by ingestion of metacercaria found in raw unwashed grass or by drinking of contaminated water.

- Metacercaria excysts in the small intestine and penetrates the intestinal wall to peritoneal cavity and pierces the liver capsule and tissue to settle into the bile ducts to become adults.

Diagnosis :

I. Clinical diagnosis: Clinical picture

II. Laboratory:

1- Stool examination for egg (diagnostic stage).

It is useful in diagnosis of chronic fascioliasis, because adults are not yet developed and eggs are not yet excreted in the acute stage

** False diagnosis may result from eating infected raw liver where ova appears in stool. It can be avoided by preventing patient from eating liver for few days, then repeat examination if egg is still present, then patient is infected with Fasciola.

Treatment :

- Triclabendazole: 10 mg/ kg body weight single oral dose.

Trematodes (Flukes)

Sponsored Ads

General characters of trematodes:
- Body is flattened unsegmented, except female schistosomes (cylindrical).
- No body cavity.
- Organs of fixation in the form of suckers (oral, ventral).
- Hermaphrodites except schistosomes.
- All Trematodes need a snail intermediate host, so part of the life cycle occurs in water.

Digestive system:
- Incomplete digestive tract without anus
- Mouth, surrounded by oral sucker, leads to oesophagus that bifurcates in front of ventral sucker into two intestinal caeca.
- Caeca may be simple or branched.

Genital system:
- Hermaphrodites except Schistosomes.

- Male organs :
Two testes (TE) each gives a vas efferans (VE) that unit to give vas deferens (VD) that passes through a sac called cirrus sac (CS). Vas deferens ends by cirrus (CI) that opens in common genital atrium (GP).

- Female organs :
Single ovary (OV) leading to an oviduct that receives canal from swelling (seminal receptacle where sperms are stored) and common vitelline duct (D) receiving secretions of vitelline glands (VI). Oviduct opens in the ootype (OT). From ootype starts a coiled uterus (UT) that opens in common genital pore (GP).

Fertilization in trematodes:
- Self-fertilization.
- Cross-fertilization

Types of parasites and hosts

Sponsored Ads

According to their habitat (site where parasite lives) :
1.Ectoparasites: live on the surface of their hosts.
2.Endoparasites: live inside the body of their hosts (small intestine, large intestine, etc.).

According to the number of hosts :
1. Monoxenous: needs only one host for the completion of life cycle as Ascaris and Trichuris
2. Heteroxenous: the life cycle is completed in two or more hosts as Heterophyes

According to the association with their hosts :
1. Obligatory: can't survive outside their hosts, i.e. completely dependant on their hosts.
2. Facultative: capable of free living outside their host (change life style between free-living and parasitic) as Strongyloides stercoralis.
3. Temporary: visit the hosts from time to time for its meal & then leaves, as mosquitoes
4. Permanent: always fixed to their hosts.
5. Opportunistic: capable of producing disease in immuno-compromised host as Cryptosporidium.

Types of hosts :
- Final or definitive host (DH): harbors the adult stages or sexually reproducing forms of the parasite.
- Intermediate host (IH): harbors the larval stages or asexually reproducing form.
- Reservoir host (RH): Animal host that harbors the same species and stages as human. It maintains the life cycle of the parasites in nature
- Vector: an arthropod that transmits parasites from one host to another.

Effects of parasitism: Parasite may :
1- Feed on blood as mosquitoes, fleas, lice and ticks.
2- Cause tissue necrosis, ulceration and inflammation
3- Consume host’s food
4- Mechanically obstruct the intestine, bile duct, or lymphatics.
5- Cause pressure atrophy of surrounding tissues.
6- Produce toxin and induce allergy.
7- Disturb body functions causing indigestions, malabsorption and diarrhoea as in intestinal parasites.