Malaria used to be endemic in the United States. (a) What is the causative agent

Question

Malaria used to be endemic in the United States.
(a) What is the causative agent of malaria? Describe the unique way this organism reproduces. (5 pts.)
(b) How is malaria transmitted? Why do some people have some resistance to malaria infections? (10 pts.)
(c) Explain how occurrence of the following situations could lead to the reemergence of malaria in the United States: (i) increased travel or immigration of individuals from endemic regions to the United States, (ii) regulations against the use of insecticides, and (iii) laws protecting wetlands.

Explanation / Answer

a.

1. There are mainly four members of Plasmodium that cause malaria. Those are P. falciparum, P. vivax, P. ovale and P. malariae belongs to protozoan group. The species P. knowlesi rarely causes disease in humans

2. The disease is transmitted most commonly by Plasmodium infected female Anopheles mosquito (Primary host). The mosquito bite introduces the parasites (Plamodium spp.,) from the mosquito's saliva into a person's blood (secondary host). So, Plasmodium completes its lifecycle in two hosts. In primary host it completes its sexual life cycle and in secondary host it completes its asexual life cycle.

Sexual cycle of Plasmodium (in mosquito)

When a female Anopheles sucks the blood of a malaria patient, the gametocytes reach the stomach of mosquito and formation of male and female gametes take place by gametogenesis. The gametes fertilize and forms Zygote. The zygote remains inactive for some time and then elongates into a worm like Ookinete which is motile. The Ookinete penetrates the stomach wall and comes to lie below its outer epithelial layer. The Ookinete gets enclosed in a cyst. The encysted zygote is called Oocyst The Oocyet bursts and sporozoites are liberated into the haemolymph of the mosquito

Asexual cycle of plasmodium (in man)

Disease causing form of Plasmodium is known as sporozoites. Sporozoites are 11-12µ long slender, uni-nucleated, Sickle-shaped structure present in the salivary glands of infected mosquito. When an infected female Anopheles mosquito bites a healthy man, a large number of sporozoites enter into the blood stream of man. Within half an hour, sporozoites enter the liver cells and undergo asexual multiplication called schizogony (asexual reproduction by multiple fission). The cycle is repeated.

b.

1. Only female Anopheles mosquitoes can transmit malaria and they must have been infected through a previous blood meal taken from an infected person. When a mosquito bites an infected person, a small amount of blood is taken in which contains microscopic malaria parasites. About one week later, when the mosquito takes its next blood meal, these parasites mix with the mosquito's saliva and are injected into the person being bitten.

Because the malaria parasite is found in red blood cells of an infected person, malaria can also be transmitted through blood transfusion, organ transplant, or the shared use of needles or syringes contaminated with blood. Malaria may also be transmitted from a mother to her unborn infant before or during delivery.

2. Some people have resistance to malaria due to their genetic resistance. The genetic resistance in man is due to alteration of the hemoglobin molecule or cellular proteins or enzymes of erythrocytes that inhibits invasion by or replication of Plasmodia. So the organism cannot grow and reproduce.

c.

(i) Certain regions of the world are known as malaria-endemic or malaria-risk areas. If people are travelling more from these regions to America, this could lead to the reemergence of malaria through transmittance.

(ii) Some insecticides like DTT is completely banned in USA and many other countries. World Health Organization (WHO) has banned some insecticides which are having impact on environment. So banning of some insecticides could also lead to the reemergence of malaria

(iii) Mosquitoes need standing water to breed, and because of this on a global scale wherever there are wetlands there are mosquitoes. So, the laws which are protecting wet lands could also lead to the reemergence of malaria.

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