Malaria

Malaria has been in the limelight ever since about 90 years ago when Sir Ronald Ross  showed how it was transmitted. Malaria, you might be aware is an infectious disease caused by the presence of a parasitic protozoa of the genus plasmodium within the red blood cells. The disease is transmitted by a type of female mosquito called Anopheles. The disease is mainly confined to tropical and subtropical areas. 

In India, concerted attempts have been made since 1950 to control the problem of malaria. There have been  major setback to the early success achieved in the sixties in the control of malaria. In India the number of cases of malaria dropped down  from about 75 million to about 2 million  in 1958. However, in the year 1976. 6.5 million cases of malaria were detected in the country. In  view of this upsurge in the disease malaria is receiving the attention of the health administrators and policy  makers. 

The Disease-What  Causes it? Who gets it? How and when does it spread? 

The disease is caused by the plasmodium parasite and is transmitted by the anopheles mosquito. 

Who gets the disease? 

The discussion below (under different headings) prevent a clear picture of who are susceptible to malaria. 

Age : Malaria affects all ages, though new born infants have considerable resistance to infection with malaria. 

Sex : Males are more affected than  females mainly because they lead more outdoor life and are likely to frequent areas where infected mosquitoes thrive. Also females in India are better covered with clothes. 

Socio-economic conditions : Where economic conditions are poor, malaria is more prevalent. Houses which are ill-ventilated and poorly lighted provide ideal resting places for mosquitoes. Malaria is commonly acquired by mosquito bites within the house. Malaria is widely prevalent in tribal areas. This is because the conditions in tribal areas, usually  surrounded by forests, provide favorable grounds for  mosquito breeding. In addition, in view of their inaccessibility, malaria control in these areas is often difficult. 

Migrant labourers working on dams : Engineering sites and migrant agricultural labour may import malaria  and reintroduce malaria into areas where it has been  under control. 

Environmental factors : Discussed below are environmental factors. 

Season - In India, malaria is most prevalent during the months of July to November. High Temperatures are detrimental to parasite development. 

Rainfall - Rain in  general increases mosquito breeding. However, heavy rains may flush out breeding places. 

Man-made Malaria - Man-made alterations to the environment like extensive irrigation  systems can introduce malaria into areas where mosquito activity would have reduced during dry season. Garden pools and stagnant pools of water and sewage can increase mosquito breeding and lead to malaria. 

How does it spread? 

Malaria is transmitted by the bites of certain  species of infected female anopheles mosquitoes. In India, the mosquito vectors of importance are Anopheles culicifacies and Anopheles fluviatilis. Anopheles stephensi is considered an important vector (carrier of infective agent from one host  to another) of malaria in the urban areas. 

These female anopheles mosquitoes ingest human blood containing malarial parasites. The male and female unite in  the stomach of the mosquito and  multiply and then invade the salivary glands. When the mosquito bites the man and takes blood meals the parasites are injected into the blood stream and migrate to the liver and other organs where  they multiply. (In the liver the parasites penetrate into a liver cell and after considerable development the original single infective form sub-divides into as many as several thousands of new individual forms). The liver cell ruptures liberating the new individuals into the blood stream. Some of these enter cells and  undergo a process of multiplication and development. Rapid multiplication of the parasite results in destruction of  the red cell and the new forms are free in the blood stream and enter fresh red cells. Red cell destruction results in anaemia and at this stage of the life cycle of parasite the patient experiences periodic bouts of shivering, fever and sweating. From this stage, sexual forms (gametocytes) of the parasite develop which on ingestion in a blood  feed by an anopheles mosquito to carry on the life cycle of the parasite in that insect. 

In the susceptible individuals, after undergoing cycle, parasites usually appear in blood within 3 to 14 days after onset of symptoms. 

Malaria is also transmitted by blood transfusion. 

Incubation period : The length of time between the bite of an infected mosquito and the first attack of fever is usually  not less than 10 days. 

There are four types of plasmodium species. The incubation period varies according to the species. In the case of P. falciparwn it is  12 days  and in P. vivax and P. ovale 14 to 15 days. It is about one month in the case of P. malariae. 

Period of communicability : As long as the parasite are present in the blood of patients mosquitos can be infected.

Susceptibility : Susceptibility is 'universal'. In those who were frequently infected, the degree of susceptibility is sometimes lessened. In  highly endemic areas, adults may be more tolerant to developing malaria. Individuals with sickle cell trait are relatively immune to malaria.