Question

Q. Compare and contrast the life cycles of Plasmodium falciparum, Schistosoma spp., Taenia spp. and Ascaris lumbricoides.

Answer 1

Plasmodium falciparum

1. It causes malaria.

2.Life cycle

*The intermediate host is a man and the definitive host is female anopheles mosquito.

*This disease is spread by the female anopheles mosquito.

*Infected mosquito bites human, then sporozoites lodged in the salivary gland of mosquito-spread to human blood.

*Then they migrate to the liver and undergo a developmental phase inside the liver, this stage is called pre-erythrocytic schizogony. They undergo multiple division and develop into schizont. This schizont contains merozoites.

*The merozoites released due to rupture of hepatocytes. These merozoites enter into RBC. The parasite uses haemoglobin for its energy requirements. When merozoites are produced in large number, RBC ruptures merozoites released which are ready to attack other RBC. Hemozoin is released from ruptured RBC which leads to chills and high-grade fever.

* Some merozoites develop into both male and female gametocytes.

* When a mosquito bites these gametocytes enter to mosquito and fertilisation of these gametocytes happen in the midgut of mosquito.

*Zygote formed develop into ookinete and then this ookinete matures into an oocyst. This oocyst matures and releases sporozoites and they began to concentrate in the salivary gland of mosquito.

Schistosoma

1.The causative agent of schistosomiasis

2.   Lifecycle​

*Definitive host is a man and the intermediate host is a snail.

*​​​Adult worm live in pelvic venous plexuses, inferior mesenteric vein and superior mesenteric vein. Adult male worm carries a female worm in a canal.

*Female worm deposit egg in venules. These eggs are discharged in urine and faeces.

*Embryonated eggs reach freshwater and hatches out and releases miracidium larve.

* Intermediate host snail is infected by miracidium

*Miracidium develop into the first-generation sporocyst and then to second-generation sporocyst.

* Fork-tailed cercaria larvae produced from sporocyst.

*Man get the infection by penetration of cercaria. In human they become schistosomulae.

*In intrahepatic portal veins, the schistosomulae grow and become sexually mature. The male and female worm is formed.

Taenia

1. Their larval forms cause cysticercus cellulose and cysticercus Bovis

2.Lifecycle

*Man is definitive host and pig or cattle is the intermediate host.

*Adult lives in the small intestine of man and egg or gravid proglottids pass through faeces.

*Ingested by the intermediate host and oncosphere hatches out and releases into the systemic circulation.

* Get deposited muscles and are transformed into cysticercus stage.

*Meat of this intermediate host eaten by man and cysticercus cellulose evaginates and attaches to gut wall. They grow here attains sexual maturity.

Ascaris lumbricoides

1. It causes Ascariasis

2.​​​​​Lifecycle

*Man is the definitive host and no intermediate host.

*Adult wives live in the jejunum of man.

*Fertilised eggs pass through stools. A rhabditiform larve developed in the egg.

* Man eats food containing eggs containing larvae. This large released at the duodenum. They penetrate the intestinal wall and reaches the liver through the portal circulation.

*Then they migrate into lungs. In the lungs, they grow and break capillaries and reach lung alveoli

*From alveoli they crawl up to trachea and pharynx and are again swallowed.