In this article we will discuss about the life cycle of plasmodium vivax.
Malaria is associated with a mosquito vector, Anopheles. The life cycle of Plasmodium is very complex. The mosquito carries the inocula of P. vivax where it multiplies and produces the sporozoites.
After mosquito bite, the sporozoites present in sahva are dehvered in the blood of human. Thirty minutes after bite, the sporozoites enter in liver cells and undergo reproductive schizogamy through a series of intermediate stages.
At the last stage of schizogamy, a large number of merozoites are released in the blood stream. The merozoites are infectious which in turn infect the red blood corpuscles and undergo reproductive schizogamy. A large number of merozoites are released upon rupture of RBCs. The merozoites infect the other RBCs and renew the cycle.
The infected RBCs are disintegrated which release the toxic substances. The toxic substances induce the characteristic symptoms of malaria i.e. chills and fever. After reaching the body temperature upto 40°C, fever subsides. However, due to break down of RBCs, the patient suffers from anaemia, and liver and spleen enlargement.
As per estimate 1% infected RBCs contain about 10,000 millions of parasite at a time in the blood of malaria patients. Rest of merozoites act as male or female gametocytes. Again the merozoites enter in the digestive tract of new mosquitoes when they bite the infected person. The merozoites multiply in digestive tract of mosquito, pass through reproductive cycle and form infective sporozoites (Fig. 24.3).
Laboratory diagnosis of Plasmodium can be made by taking out blood samples, preparation of smear and microscopic observations for the presence of parasite. However, no effective immunity against Plasmodium develops besides some resistance in endemic areas.
Much researches have been done on chemotherapy of malaria. Quinine and derivatives of quinine e.g. chloroquine, primaquine, etc. have been used for several years. Choloroquine inhibits DNA replication at merozoite stage. Now-a-days, resistance to these drugs have been reported.
Therefore, in recent years drug combinations have been recommended e.g. Fansidar which is a combination of pyrimethamine and sulfadoxine. The combinations of drug act synergistically. However, effective control of malaria is not known except chemotherapy.
In recent years, much effort has been made for the preparation of effective vaccine through gene mapping, preparation of monoclonal antibodies, and protein synthesis. In 1975, Rath and Victor at New York University, Medical Care Centre, identified a surface antigen of the sporozoites known as circumsporozoite (CS). The CS antigen was used to produce the monoclonal antibodies against Plasmodium.
In 1983, the CS gene was cloned to produce the CS protein in large quantities and to analyse and prepare antibodies. In 1987, for the first time human test for vaccine was done at the University of Maryland, School of Medical Science (U.S.A.) and the effectiveness of vaccine was determined in 1989. But much research work is needed on the preparation of vaccine for its use at several stages of the parasite.
Several times malaria eradication movement was launched by the government organizations to eradicate mosquitoes by spraying DDT, but the mosquitoes developed resistance. However, no significant control measure has been reported so far.