[Biology Class Notes] on Common Diseases in Humans – Malaria Pdf

Malaria is a life-threatening disease that is transmitted through the bite of an infected female Anopheles mosquito. Infected mosquitoes carry the Plasmodium parasite (the malarial parasite/ the causative agent of malaria). When this mosquito bites a human being, the parasite is released into its bloodstream.

Once the parasites are inside the human body, they travel to the liver, where they mature. After several days, the mature parasites enter the bloodstream and begin to infect red blood corpuscles or RBCs

How Malaria Enters the Body?

Within 48-72 hours, the parasites inside the red blood cells multiply, which causes the infected cells to burst open. The parasites continue to infect red blood cells, leading to symptoms that occur in cycles that last two to three days at a time.

Malaria is generally found in tropical and subtropical climates where the parasites can survive and thrive. The World Health Organization (WHO) Trusted Source reports state that in 2016, there were an estimated 216 million cases of malaria across 91 countries.

 

What Causes Malaria?

Malaria is caused by the female anopheles mosquito, which carries the plasmodium protozoa responsible for the disease.

There are four types of the malarial parasite that can infect humans: 

1. Plasmodium Vivax

2. P. Ovale

3. P. Malaria

4. P. Falciparum.

P. falciparum causes a severe form of the disease and those who contract this form of malaria have a higher risk of death. An infected mother can also pass the disease to the fetus in the womb. This condition is known as congenital malaria.

What are the Symptoms of Malaria? / Malaria Symptoms

In the uncomplicated forms, which last 6-10 hours and recur every second day the general malaria disease symptoms are: 

• A sensation of cold with shivering

• Fever, headaches and vomiting

• Seizures can be observed in younger people with the disease

• Sweats and then a return to normal temperature with fatigue

In the Severe form of Malaria, the Symptoms are: 

Stages of Malaria Fever

Malaria fever has the following characteristics; chills, fever, rigor followed by sweating, called as the cold stage, the hot stage and sweating stage respectively. 

• The first cold stage lasts 15-60 minutes and is characterised by a feeling of cold and shivering. 

• The cold stage is followed by the hot stage, with fever from 39-41.5°C, lasting 2-6 hours, also associated with flushed and dry skin, headaches, nausea and vomiting. 

• At the end of the cold stage, the fever drops rapidly and the patient sweats profusely over a period of 2-4 hours.

Malaria Mode of Infection

The mode of infection in malaria occurs through the following cycle:

• A female anopheles mosquito becomes infected by feeding on a person who has malaria.

• The mosquito becomes the carrier of the parasite and it then transmits into a human body when the carrier mosquito bites a human

• The parasite enters the body and travels to the liver, where it matures. (it can lie dormant up to a year)

• When the parasites mature, they leave the liver and infect the RBCs of the bloodstream. (the symptoms start showing at this stage)

• The cycle continues when an uninfected mosquito bites an infected person.

Other Modes of Transmission are:

• From mother to the unborn child.

• Through blood transfusion

• Usage of shared syringes or needles

Malaria Life Cycle (Life Cycle of Malarial Parasite)

The complete development of the malarial parasite takes place in two different hosts; humans and mosquitoes.

The malarial parasite, plasmodium, exists in the form of a motile sporozoite. The female Anopheles mosquito, which is the vector of malaria, transmits the sporozoites into the hosts. 

It is inside the mosquito’s body that the actual development and maturing of the plasmodium parasite takes place. The parasitic cells that are produced in the human body reach the intestine of the mosquito. Here, the male and female cells of the parasite fertilise each other to lead to the formation of a sporozoite.

After maturing, the sporozoite breaks out of the mosquito’s intestine and migrates to the salivary glands. When an infected mosquito bites a human, the sporozoites are transmitted into the bloodstream through the mosquito’s saliva. 

Then they travel via the blood and accumulate in the liver. These parasites multiply within the liver and mature by damaging the liver and rupturing the blood cells in the body.

The parasites reproduce asexually in the RBCs, causing lysis of the cells and releasing more parasites to infect more cells. The rupture of red blood cells by the malaria parasite releases a toxin called haemozoin which causes the infected to experience a condition known as the chills and eventually one of the causes of malaria fever.

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Prevention of Malaria

• Vector Control: Vector control is an effective way of preventing and reducing malaria transmission. There are two forms of vector control:

• Insecticide Treated Mosquito Nets: Sleeping under/inside an insecticide-treated net can reduce contact wit
  h mosquitos. It acts as a physical barrier and the insecticide also keeps other harmful insects away.

• Indoor Spraying With Residual Insecticides: This method can rapidly reduce malaria transmission. A particular insecticide is sprayed within a housing structure once or twice a year. This results in a significant increase in protection from the disease for the community. 

• Antimalarial Drugs: Antimalarial drugs can also be used to prevent malaria. For travellers, the disease can be prevented through chemoprophylaxis, which acts by suppressing the blood stage of malaria infections, thereby preventing malaria disease.

For women who are pregnant and are living in moderate-to-high transmission areas, WHO recommends intermittent preventive treatment with sulfadoxine-pyrimethamine at each scheduled antenatal visit after the first trimester. 

For infants who live in high-transmission areas of Africa, 3 doses of intermittent preventive treatment with sulfadoxine-pyrimethamine are recommended, delivered alongside routine vaccinations.