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Germs that infect humans

Plasmodium falciparum

Plasmodium falciparum

© Dennis Kunkel Microscopy, Inc.

Microorganism: the parasites Plasmodium falciparum, Plasmodium vivax

Disease: malaria, paludism

Occurrence of the disease

History: malaria is the infectious disease that has had the most impact on humans, notably contributing to the fall of the Greek and Roman empires. Ancient Chinese and Hindi texts mention this disease, describing the fever and chills that are typical of malaria. Several researchers, from Hippocrates at the end of the Vth century BC to Ronald Ross in 1902, studied malaria to finally demonstrate that this disease is transmitted by mosquitoes. This explained why people exposed to swampy environments were often affected. In 1955, the Word Health Organization began a malaria eradication program, which was largely unsuccessful: the mosquitoes became increasingly resistant to the insecticides and the parasites became increasingly resistant to medication.

Current situation: In most temperate zones as well as in several sub-tropical regions, malaria has either never existed or has been eradicated. However, it remains one of the most important diseases in nearly all tropical countries. Worldwide, more than 100 million individuals are infected annually and nearly one million of them die.

Mechanism of action of the microorganism: the bite of a Plasmodium-infected mosquito allows the parasite to get into the bloodstream. It travels to the liver to reproduce and then invades the oxygen-carrying blood cells. When the parasite is in the bloodstream, it can be picked up by another mosquito, which can spread the disease to new individuals by biting them.

Symptoms of the disease: fever, cough, chills, sweating, diarrhea, and headaches. Furthermore, the disease can evolve toward renal, pulmonary, or cerebral problems and can even lead to coma and death.

Incubation period: seven to 14 days

Contagious period: a mosquito can transmit malaria during its entire life. In humans, the parasite can be transmitted to mosquitoes for about a year.

Hosts: humans and mosquitoes

Transmission: transmission occurs through the bite of a mosquito of the genus Anopheles. The bite allows the insect to ingest contaminated blood. When the mosquito bites another human, it liberates the parasite into the individual’s blood.

Certain populations of west Africa are resistant to malaria. The hemoglobin of these individuals has a mutation that makes it impossible for the malaria-causing parasite to reproduce. Unfortunately, this mutation is responsible for a disease called falciform anemia, which is accompanied by chronic fatigue. Not an interesting choice to make!

Discoverer or the microorganism: Laveran in 1880

Treatment: chloroquine, if the diagnosis is rapid.

Geographical distribution of the microorganism: the forests of South America, southeast Asia and the southern Sahara in Africa.

Prevention: eliminate the breeding grounds of anopheles mosquitoes when they are near human populations. Administer chloroquine or mefloquine preventively. It is also recommended to use insecticides, to install mosquito nets around the bed and to close the windows in the evening and at night.

Vaccine: not available