Overview

Parasites grow and reproduce by taking advantage of a host for their habitat and nutrition. Vectors transmit parasites into suitable hosts. Malaria is caused by the Plasmodium species of protozoan parasites, and the parasites are transmitted by the Anopheles mosquito. Once inside humans, the parasites multiply, causing the destruction of red blood cells which are essential for life. Diagnosis of malaria is done by seeing the parasites inside the blood cells through a microscope. For a few dollars a day, malaria can be stopped from causing over 250 million new infections each year.

Parasites

A parasite is an organism that lives at the expense of another organism. Classic examples of parasites in humans include viruses, fungi, tapeworms, roundworms, and lice. Parasites tend to be smaller than the host, and they use the host for protection, nutrition, and to aid in reproduction. In fact, some parasites cannot reproduce without a host.

Vectors

A vector is an organism that transmits a parasite from a source to a host. For parasites that affect humans, the most common vectors are insects. Other vectors include inanimate objects like door knobs, which transmit viral infections like the flu, and foods, like swine that may transmit tapeworms. Vectors are not necessary for the parasite to grow and reproduce, yet it helps parasites reach new hosts and new environments.

Anopheles mosquito having a meal

 

Malaria

Malaria is a disease caused by protozoan parasites of any one of four Plasmodium species (falciparum, ovale, vivax, and malariae). The females of the Anopheles species mosquitoes serve as vectors for malarial parasites. The mosquito delivers the parasites into a person’s blood through a bite. Once inside the body, the parasites travel to the liver and begin multiplying. They then move into the red blood cells, multiplying further. New generations of parasites then invade other red blood cells, destroying the red blood cells. This causes anemia, the main complication of malaria.

Diagnosis of Malaria

The diagnosis of malaria is done by seeing the parasites in blood cells through a microscope by a hematologist. Experience in doing this is key since the parasites in the red blood cells may not be identified as such because of their size. The parasites exist in four development stages within red blood cells: ring, trophozoite, schizont, and gametocyte. Knowing the shape and size of each stage for each of the four species of parasite is essential since this has implication in the treatment and prognosis. For example, the Plasmodium falciparum and vivax species have drug resistance in certain parts of the world, and P. falciparum causes the worst disease of all species.

Malaria by the Numbers

According to the World Health Organization, about one half of the people in the world are at risk for contracting malaria. Each year, there are about 250 million new infections and almost one million deaths. One fifth of the deaths in children in Africa occur because of malaria. Yet, according to the Nothing But Nets Foundation, it takes only a few dollars to treat malaria, prevent mosquito bites, and eliminate sources of mosquitoes.

References

Centers for Disease Control, “Malaria” http://www.cdc.gov/Malaria/

World Health Organization, “Malaria” http://www.who.int/topics/malaria/en/

Nothing But Nets Foundation, “Malaria Kills” http://www.nothingbutnets.net/malaria-kills/