Type of
helminths
Nematoda:
Roundworms,
Body is
cylindrical with
pointed end,
male and
female
separate
Habitat
Life cycle
Worms
Ascaris
lumbricoides
Strongyloides
stercoralis
Hookworms
Trichuris trichiura
Enterobius
vermicularis
Habitat
s.
intestine
s.
intestine
s.
intestine
l. intestine
l. intestine
Direct:
1. Host → egg → infective egg → host eg. Ascaris lumbricoides
2. Host → egg → Larva → penetration of the skin
eg. Hookworms (Ancylostoma duodenale and Necator americanus
Indirect:
>Two hosts to complete the life cycle eg. Fasciola hepatica, Schistosoma
haematobium
Cestoda:
Tapeworms,
Body is
flattened,
segmented
and
hermaphrodite
Specific
Taenia saginata
Taenia solium
Diphyllopothrium
latum
Echinococcus
granulosis
Common
Beef TW
Pork
Fish
> Man is the definitive host: Taenia saginata & Taenia solium
> Man is the intermediate host:
1. Echinococcus granulosus life cycle begins when eggs exit the human's body via its feces.
2. Outside its host's body, the egg eaten by the intermediate hosts (cattle, pig)
3. Once inside the intermediate host, the tapeworm hatches from the egg and develops into a larva.
4. The human becomes infected by the tapeworm larva after eating undercooked beef or pork contaminated
with tapeworm larvae.
5. Once inside the human, the tapeworm larva develops into an adult within the human's intestines, and the
cycle continues.
Trematoda:
Flukes, is
flattened, nonsegmented,
leaf-like and
Hermaphrodite
(except
Schistosoma
sp.).
Liver
Intestinal
Lung
Blood
Schistosoma
Dog
Fasciola hepatica
Clonorchis sinensis
Opisthorcus spp.
Fasciolopsis buski
Echinostoma
trivolvis
Heterophyes
heterophyes
Paragonimus
westermani
haemotobium
mansoni
japonicum
1. A fluke begins its life in an egg.
2. After hatching → miracidium it infects an intermediate host, such as snail
3. The fluke develops into larva within the snail's body.
4. Human infection begins by penetration of skin by cercaria (eg.
Schistosoma sp.) or ingestion of metacercaria (other flukes).
5. The fluke develops into an adult within its human host's intestine.
6. Fluke eggs are returned to the local water supply after passing through the human's faeces or urine, and the
cycle begins again.
Direct: Not required intermediate host to complete its life cycle. eg. Ascaris lumbricoides, Trichuris trichiura.
Indirect: Required one or two intermediate hosts to complete its life cycle.
➢ One intermediate host Fasciola hepatica, Schistosoma haematobium
➢ Two intermediate hosts Clonorchis sinensis
Medical importance:
Factors: Number & Species of the Parasite
Habitat
Age & Immune status of the host
-anemia: Sucking blood, Intestinal bleeding
(Hookworms), B12 deficiency → Tapeworms
- Malnutrition → Intestinal Helmiths eg. Strongyloides stercoralis
- Loss of Weight
- Intestinal obstruction → Ascaris lumbricoides
- Intestinal perforation and peritonitis → Ascaris lumbricoides and Trichuris trichiura
- Lymphatic obstruction → Filarial worms
(Elephantiasis)
-Visceral & Cutaneous Larva Migrans (VCLM) → Tissues damage
- Jaundice and liver cirrhosis ……. Fasciola hepatica
- CNS damage (larval stages → Taenia solium)
- Cancer of liver & Urinary bladder (Schistosoma spp.
Prevention and control
-
Health education
Wash hands with soap and water before handling food.
Avoid eating undercooked meat.
When traveling to countries where sanitation and hygiene are poor, avoid water or food that may be contaminated.
-
Wash, peel or cook all raw vegetables and fruits before eating.
Do not use human feces as fertilizer.
Prevent defecation outside toilets.
Mass chemotherapy.
Diagnosis
1-Direct faecal smear
2- Concentration methods (sedimentation and floatation)
3- Serological test (ELISA)
4- X – ray and CT – Scan
5- Histopathology and biopsy
6- PCR
-
Skin vesicles created by the penetration of
Schistosoma cercariae