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Why do the symptoms of malaria not appear immediately after the entry of sporozoites into the human body when bitten by female Anopheles? Explain.

Answer
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Hint: Malaria is caused by Plasmodium sp. The mosquito picks up the parasites along with the blood when it bites an infected person. When the infected mosquito(vector- transmitting agent) bites a healthy person, parasites migrate into his blood with the saliva, which the mosquito injects before sucking up blood to prevent its clotting.

Complete answer:
The toxins produced in the human body by the malarial parasites, Plasmodium cause malaria. There are four different kinds of human malaria: P.vivax, P.ovale, P.malarie, P.falciparum. The incubation time for malaria induced by Plasmodium vivax is about 10-14 days. This species is widespread in the tropical and temperate regions including India. Plasmodium completes its lifecycle in two phases and two hosts: asexual phase in the human host and sexual phase in the female Anopheles mosquito host. Man and mosquitoes are regarded as secondary(intermediate) host and primary (final) host respectively. It enters in man as sporozoites through the bite of infected female Anopheles mosquito. In the liver cells, they multiply and then attack the RBCs resulting in their rupture. A release of toxic substance hemoxin is responsible for the rupture of RBCs. This results in a chill and high fever recurring every three to four days. When a female Anopheles mosquito bites an infected person the parasites are transferred to the body of the mosquito and undergo a series of development processes. These parasites are stored in the salivary gland of the mosquito. Now the parasites find their way into the blood of a healthy man along with the salivary (anticoagulant) secretion of an infected female Anopheles mosquito, which bites for getting a blood meal and the cycle continues.

Note:
The attack of malaria is preceded by yawning, tiredness, headache, and muscular pain. During the five, the patient feels chilly and shivers and has an acute headache, nausea, and high temperature. In chronic cases, there are general weaknesses and anemia (paleness) due to large-scale destruction of the red blood corpuscles. This is also accompanied by the engagement of the spleen and liver.