Class 12th Biology Unit 8 – COMMON HUMAN DISEASES CAUSED BY PROTOZOA
- Malaria: It is caused by Plasmodium parasites. The parasites are spread to people through the bites of infected female Anopheles mosquitoes, called “malaria vectors.” There are 5 parasite species that cause malaria in humans, and 2 of these species – P. falciparum and P. vivax – pose the greatest threat. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases, it can cause yellow skin, seizures, coma, or death. Symptoms usually begin ten to fifteen days after being bitten. If not properly treated, people may have recurrences of the disease months later.
The disease is most commonly transmitted by an infected female Anopheles mosquito. The mosquito bite introduces the parasites from the mosquito’s saliva into a person’s blood. The parasites travel to the liver where they mature and reproduce. The parasites initially multiply in liver but later they enter Red Blood Celle (RBC) causing the rupture of cells. Ruptured RBC releases a toxic substance called hemozoin, which causes chill and fever after every 3-4 days. When the female Anopheles mosquito bites the infected person, these parasites enter the body of the mosquito and undergo further development. They multiply to form sporozoites which are stored in the mosquito’s salivary glands. When this mosquito bites another healthy person, the sporozoites are released into his or her body and again the life cycle begins causing the disease. Most deaths are caused by P. falciparum. P. vivax, P. ovale, and P. malariae generally cause a milder form of malaria. The species P. knowlesi rarely causes disease in humans.
The life cycle of Plasmodium sp.
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Malaria is typically diagnosed by the microscopic examination of blood using blood films, or with antigen-based rapid diagnostic tests.
The risk of disease can be reduced by preventing mosquito bites through the use of mosquito nets and insect repellents or with mosquito control measures such as spraying insecticides and draining standing water. Antimalarial drugs like, quinine and chloroquine are used to treat malaria.
- Amoebiasis: Amoebiasis or amoebic dysentery is caused by an intestinal endo-parasite Entamoeba histolytica which is found in the large intestine of humans. This parasite is carried by houseflies, when the house flies sit on the faeces of infected persons they carry the parasites to the uncovered food or water thereby contaminating it. Through the contaminated food and water, this disease is transmitted to a healthy person. Cysts of Entamoeba can survive for up to a month in soil or for up to 45 minutes under fingernails. Invasion of the intestinal lining can cause bloody diarrhea. The symptoms of the disease are abdominal pains, constipation, cramps, and faeces with excess mucous and blood clots. If the parasite reaches the bloodstream it can spread through the body, most frequently ending up in the liver where it can cause amoebic liver abscesses.
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Diagnosis is typical by stool examination using a microscope. An increased white blood cell count may be present in severe cases.
Prevention of amoebiasis is by improved sanitation, including separating food and water from faeces. There are two treatment options depending on the location of the infection. Amoebiasis in tissues is treated with either metronidazole, tinidazole, nitazoxanide, dehydroemetine or chloroquine, while the luminal infection is treated with diloxanide furoate or iodoquinoline. Effective treatment against all stages of the disease may require a combination of medications.
The life cycle of Entamoeba histolytica
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