Introduction

Malaria is an infectious disease caused by a protozoa which infects red blood cells(erythrocytes), Plasmodium sp. transmitted by an infective female Anopheles mosquito vector. It is commonly characterized by typical features such as febrile paroxysms, anaemia and splenomegaly. Historical records suggest malaria has infected humans since the beginning of mankind. The name "mala aria" (meaning "bad air" in Italian) was first used in English in 1740 by H. Walpole when describing the disease. The term was shortened to "malaria" in the 20th century. C. Laveran in 1880 was the first to identify the parasites in human blood. In 1889, R. Ross discovered that mosquitoes transmitted malaria.

Female Anopheles mosquito

The 4 Plasmodium species known to cause malaria :

i)                    Plasmodium falciparum

ii)                  Plasmodium vivax

iii)                Plasmodium ovale

iv)                Plasmodium malariae.

*A fifth species, Plasmodium knowlesi, has recently been identified as a clinically    significant pathogen in humans.

Most of the malaria cases reported are due to single infection (infection by a single species) while some individuals may be infected with multiple Plasmodium species. P. falciparum is the most common cause of infection and is responsible for about 80% of all malaria cases, and is also responsible for about 90% of the deaths from malaria. Parasitic Plasmodium species also infect birds, reptiles, monkeys, chimpanzees and rodents.

Life Cycle of Malarial Parasites

Life Cycle of Malarial Parasites

• Sporozoites are injected into human dermis through the bite of infected Anopheles mosquito.
• After inoculation, sporozoites migrate to liver cells to establish the first intracellular replicative stage.
• Merozoites generated from this exoerythrocytic phase then invade erythrocytes (RBCs), and it is during this erythrocytic stage that severe conditions of malaria occur.
• The life cycle is completed when sexual stages (gametocytes) are ingested by a mosquito.
• Sporozoites deposited in the skin migrate rapidly through the region of the bite. Some eventually penetrate capillaries or lymph vessels.
• Those entering the lymph vessels will penetrate lymph vascular endothelial cells in lymph nodes to establish a lymph node form, which appears not to continue the life cycle—but may be significant in priming an immune response.