Mode of transmission of malaria SlideShare

The malaria parasite develops both in humans and in the female Anopheles mosquitoes. The size and genetic complexity of the parasite mean that each infection presents thousands of antigens (proteins) to the human immune system.

The parasite also changes through several life stages even while in the human host, presenting different antigens at different stages of its life cycle. Understanding which of these can be a useful target for vaccine development has been complicated. In addition, the parasite has developed a series of strategies that allow it to confuse, hide, and misdirect the human immune system.

1. Malaria infection begins when an infected female Anopheles mosquito bites a person, injecting Plasmodium parasites, in the form of sporozoites, into the bloodstream.
    
2. The sporozoites pass quickly into the human liver.
    
3. The sporozoites multiply asexually in the liver cells over the next 7 to 10 days, causing no symptoms.
    
4. In an animal model, the parasites, in the form of merozoites, are released from the liver cells in vesicles, journey through the heart, and arrive in the lungs, where they settle within lung capillaries. The vesicles eventually disintegrate, freeing the merozoites to enter the blood phase of their development.*
    
5. In the bloodstream, the merozoites invade red blood cells (erythrocytes) and multiply again until the cells burst. Then they invade more erythrocytes. This cycle is repeated, causing fever each time parasites break free and invade blood cells.
    
6. Some of the infected blood cells leave the cycle of asexual multiplication. Instead of replicating, the merozoites in these cells develop into sexual forms of the parasite, called gametocytes, that circulate in the blood stream.
    
7. When a mosquito bites an infected human, it ingests the gametocytes, which develop further into mature sex cells called gametes.
    
8. The fertilized female gametes develop into actively moving ookinetes that burrow through the mosquito's midgut wall and form oocysts on the exterior surface.
    
9. Inside the oocyst, thousands of active sporozoites develop. The oocyst eventually bursts, releasing sporozoites into the body cavity that travel to the mosquito's salivary glands.
    
10. The cycle of human infection begins again when the mosquito bites another person.

* Baer K, Klotz C, Kappe SH, et al. Release of hepatic Plasmodium yoelii merozoites into the pulmonary microvasculature. PLoS Pathogens. 2007;(11):e171.

Malaria is a life-threatening disease caused by parasites that are transmitted to people through the bites of infected female Anopheles mosquitoes. It is preventable and curable. There are 5 parasite species that cause malaria in humans, and 2 of these species – Plasmodium falciparum and Plasmodium vivax – pose the greatest threat. 

In 2020, nearly half of the world's population was at risk of malaria. Most cases and deaths occur in sub-Saharan Africa. However, the WHO regions of South-East Asia, Eastern Mediterranean, Western Pacific, and the Americas also report significant numbers of cases and deaths.

There were an estimated 247 million cases of malaria in 2021, and the estimated number of malaria deaths stood at 619 000. The WHO African Region carries a disproportionately high share of the global malaria burden. In 2020, the region was home to 95% and 96% of malaria cases and deaths, respectively. 

Children under 5 years of age are the most vulnerable group affected by malaria; in 2021, they accounted for nearly 80% of all malaria deaths in the WHO African Region.

Symptoms

Malaria is an acute febrile illness. In a non-immune individual, symptoms usually appear 10–15 days after the infective mosquito bite. The first symptoms – fever, headache, and chills – may be mild and difficult to recognize as malaria. If not treated within 24 hours, Plasmodium falciparum malaria can progress to severe illness, and lead to death.

Children with severe malaria frequently develop one or more of the following symptoms: severe anaemia, respiratory distress in relation to metabolic acidosis, or cerebral malaria. In adults, multi-organ failure is also frequent. In malaria endemic areas, people may develop partial immunity, allowing asymptomatic infections to occur.

Some population groups are at considerably higher risk of contracting malaria, and developing severe disease, than others. These include infants, children under 5 years of age, pregnant women and patients with HIV/AIDS, as well as non-immune migrants, mobile populations and travellers. National malaria control programmes need to take special measures to protect these population groups from malaria infection, taking into consideration their specific circumstances.

Treatment

Malaria is a preventable and treatable disease. Early diagnosis and treatment of malaria reduces disease and prevents deaths, and also contributes to reducing transmission. The best available treatment, particularly for Plasmodium falciparum malaria, is artemisinin-based combination therapy (ACT). Antimalarial medicines can also be used to prevent malaria. 

For travellers, malaria can be prevented through chemoprophylaxis, which suppresses the blood stage of malaria infections, thereby preventing malaria disease. Prior to their travel to malaria-endemic countries or regions, individuals should consult their national disease control centres, or other institutions offering travel advice, for information regarding the preventive measures that should be taken.

What is the mode of transmission malaria?

What are the methods of transmission and control of malaria?

What are the mode of transmission of malaria in pregnancy?

What is the mode of transmission of malaria write its vector name?