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Biology / Protozoa

Parasitic Protozoans of Protista Kingdom

Kingdom Protista includes eukaryotic, unicellular micro organisms like Protozoan protists, Slime Moulds and Protistian Algae. Protista is a link between Monera kingdom and Fungi, Plantae and Animalia kingdoms. Protozoan protists were previously included in the Animal kingdom. Many of the Protozoan protists are free living and few are parasitic Protozoans. Many of them live in water, damp soils and inside the body other animals. Examples of free living protozoans are Amoeba, Paramecium (appears in the form of slippers), Euglena (it is considered plant animal and is having chlorophyll), etc.

Parasitic Protozoans

The Protozoans are classified mainly into four groups, namely Amoeboid protozoans (e.g. Amoeba), Ciliated protozoans (E.g. Paramecium), Flagellated protozoans (e.g. Euglena) and Sporozoans (e.g. Plasmodium). In these 4 groups, some protozoans are parasitic in nature. Some examples of the parasitic protozoans are given below,

  • Entamoeba histolytica - It lives in the colon of large intestine of man and cause Amoebiasis or Amoebic dysentery (Blood + Mucus + Loose stool).

  • Plasmodium - It causes Malaria. It is spread by female Anopheles mosquito.

  • Balantidium coli - It causes Balantidiasis (in colon).

  • Leishmania tropica - It affects the skin and causes ulcers (Delhi boils / cutaneous leishmaniasis / oriental sores).

  • Leishmania donovani - It develops in White Blood Corpuscles (WBC) and internal body organs, causes Kala Azar / Dum Dum fever / Visceral Leishmaniasis. It is spread by the bite of sand fly. It is more prevalent in North India and East India. `

Life Cycle of Malarial Parasite

Malaria is caused by Plasmodium, which belongs the Sporozoan kind of Protozoa. These organisms are so-called because their life cycle has a spore-like stage.

  • In 1881, Charles Laveran discovered that Plasmodium is the causative agent of Malaria. In 1897, Ronald Ross identified Plasmodium in the stomache wall of female Anopheles mosquito.

  • Plasmodium is a digenetic parasite, which requires two hosts (human beings and female Anopheles mosquito) for completing its life cycle.

  • The stage of the parasite that enters the host is the infective stage. The way the parasite enters the host is the mode of infection. Infective stage of Plasmodium is the uninucleate, lancet-shaped Sporozoite.

  • The time period between the entry of the parasite and the appearance of symptoms is called incubation period.

  • Plasmodium enters the human body in the form of Sporozoites and multiplies in the liver and then finally infect the Red Blood Corpuscles (RBC). In the RBC, they feed on the Globin part of the Haemoglobin, multiply themselves and convert Haem part into a poison called Haemozoin.

  • The bursting of RBCs releases Haemozoin into the blood and the body starts to show the malarial symptoms.

  • Symptoms of Malaria - Recurrent chill fever, headache, body ache, nausea, pain in the muscles, decrease in fever with sweating.

  • If any female Anopheles mosquito bites a malarial patient, all the stages of Plasmodium enter into it. Many of them die in its stomach and those which survive reproduce sexually and produce Sporozoites again. These Sporozoites settle in the salivary glands of the mosquito. When it bites a healthy person, it will be transferred to that person.

  • 4 species of Plasmodium cause Malaria -

    • Plasmodium vivax - It causes Benign tertian Malaria (most common Malaria)

    • Plasmodium falciparum (Africa) – It causes Malignant tertian Malaria (fatal Malaria)

    • Plasmodium ovale – It causes Mild tertian Malaria

    • Plasmodium malariae – It causes Quartan Malaria (moderate fever)

  • Treatment of Malaria -

    • Quinine - It is the traditional medicine obtained from the bark of Cinchona officinalis plant.

    • Daraprim - It is effective against all the four diseases.

    • Larvicidal fish like Gambusia, Minnows, Trouts, etc. can be introduced into water to eat Larvae of the Mosquito.

    • Water should not be stagnated so that mosquitoes cannot breed.