Malaria – A Disease Caused by a Parasite

But what is a parasite? Examples of parasites? A parasite is an organism that lives IN or ON another organism (the host) and causes damage to that organism

What we need to know… Malaria is not CAUSED by mosquitoes. A mosquito is the vector which carries Malaria. Vectors don’t cause the disease they just transmit it. The parasite which causes Malaria is the eukaryotic, single-celled organism Plasmodium.

The symptoms of Malaria are caused by the lifecycle that the Plasmodium go through. There are 4 types of Plasmodium that can infect humans. They are: P. falciparum – Most dangerous P. vivax P. ovale P. malariae Malaria is only transmitted through the female mosquito. The type of mosquito that acts as the vector is the Anopheles mosquito.

Mosquitoes bite humans to get a blood meal Mosquitoes bite humans to get a blood meal. The Plasmodium parasite resides in the salivary glands of the mosquito. The immature parasites enter the blood stream. Within minutes the parasites infect the hepatocytes (liver cells). The parasites replicate asexually for between 8-30 days. No symptoms. After this time, the parasites burst out of the hepatocytes and enter the blood stream, invading RBC’s.

Once inside the RBC’s, the parasites can multiply, again asexually Once inside the RBC’s, the parasites can multiply, again asexually. Periodically, they break out of the RBC’s, infect new ones and cause symptoms.

Stage 1 Malaria parasites are single-celled organisms that cause malaria in humans. The organism has different forms. Each form is specialised for living in a different place in the host: gametocytes that infect mosquitoes and reproduce sexually. When the mosquito has sucked blood containing gametocytes, these pass into the salivary glands, where they develop into a new form, the sporozoite

Symptoms The symptoms of Malaria correspond to the stage that the parasite is in. Fever Shivering Joint pain Vomiting Anaemia Cyclical occurrence of sudden coldness followed by fever and sweating lasting for 3-4 hours every 2-3 days. Symptoms often occur 14 days after infection and affect many organs

Spleen – Enlarged spleen. Infected RBC’s are destroyed by the spleen. Liver – Enlarged liver due to becoming massively infected and damaged by invading parasites. Renal failure Blood clots

Diagnosis Physical symptoms Blood smears – to visualise the parasites. Antigen tests

Prevention Prophylaxis – Anti-malarials – disrupt the life cycle of the parasite. Effective? Mosquito nets – Effective? Affordable? Mosquito eradication: DDT? Effective?

Stats WHO state that Malaria causes 250 million cases of fever and 1 million deaths annually. Why is the exact number of cases not known?

Malaria is found in parts of the Americas, Asia and many parts of Africa, however Malaria free areas are often found next to areas where Malaria is endemic. In dry areas, outbreaks of malaria can be predicted by mapping rainfall?

Selective Pressure? Malaria is thought to have been the greatest selective pressure on the human genome in recent history

List the impact of Malaria on the economy and society More inpatients in hospital Days lost from work Slower economic development Lower levels of tourism

For You to Do Produce a life cycle diagram similar to the one seen earlier in the lesson describing how Malaria develops. Link the stages of development to the onset of illness.