Question (I)                                                          (Total 9 marks)

 

(1) Cysticercosis and Hydatid disease                            (1 mark)

Taenia solium and Echinococcus granulosus            (1 mark)

Mode of infection of cysticercosis → Ingestion of eggs of T. solium by one of the following ways:

• Contaminated food or drink with eggs (Heteroinfection)

• Hand to mouth infection in a patient having adult worms in his intestine (External autoinfecction)

• In a patient having adult worms in his intestine, some detached segments may ascend by antiperistaltic movements to the stomach then descend again to the intestine where they hatch and cause cysticercosis (Internal autoinfection)

                                                                                        (2 marks)

Mode of infection of hydatid disease → Man is infected by ingestion of eggs through:

• Hand to mouth from fur of infected dogs while playing with them.
• Food or drink contaminated with faeces of infected dogs.                (2 marks)

(2) a- T.solium, T.saginata                                  (2 marks)

b- T. saginata or T.solium                                   (2 marks)

c- Cysticercus bovis in beef + drawing OR

Cysticercus cellulosae in pork + drawing            (2 marks)

 

 

Question (II)                                               (Total 6 marks)

 

a- Mechanism of autoinfection in Taeniasis solium

- External autoinfection: hand to mouth in a patient having adult worms in his intestine

- Internal autoinfection : in a patient having adult worms in his intestine, some detached segments may ascend by antiperistaltic movements to the stomach then descend again to the intestine where they hatch and cause cysticercosis. (1 mark)

 

Mechanism of autoinfection in Hymenolepiasis nana:

 

- External autoinfection: hand to mouth in a patient having adult worms in his small intestine                                                      (1 mark)

 

 

b- Taenia egg:

Size: 30-40µ

Shape: spherical with radially striated shell

Color: yellowish brown

Content: hexacanth onchosphere                                (1 mark)

Both eggs are similar so we must differentiate them by Ziel-Neelsen stain (acid-fast stain) where T. saginata egg is stained well but T. solium egg is not. (1 mark)

 

c- Both scolecies globular, have 4 suckers with a rostellum. H. nana has a circle of hooks while H. diminuta has no hooks                       (2 marks)

 

 

Question (III)                              (Total 10 marks)

 

(1) a- Echinococcus granulosus and Dipylidium caninum.      (2 marks)

b- Cysticercosis and Hydatid disease.                         (2 marks)

 

 

(2) a- I.H. :the host where young stages of the parasite lives e.g. pork in Taenia solium          (1.5 marks)

b- Exogenous cyst occurs as a result of herniation of germinal layer to the outside of hydatid cyst.       (1.5 marks)

c- Autoinfection: an infected person that becomes reinfected by the same parasite either externally (hand to mouth) or internally e.g. T.solium (1.5 marks)

d- Cysticercoid larva is the infective stage in case of Hymenolepis spp. (1.5 marks)