The key difference between merozoites and sporozoites is that merozoites are the form of malaria parasite that infects red blood cells, while sporozoites are the form of malaria parasite that infects liver cells.
Plasmodium is a parasitic protozoan. It is the causative agent of malaria. This parasite uses two hosts: Anopheles mosquitoes and humans, in order to complete its life cycle. Three invasive forms of Plasmodium can be observed. They are sporozoites, merozoites, and ookinetes. Anopheles mosquito inoculates sporozoites to the human host. Then the sporozoites go with the bloodstream and infect liver cells. Sporozoites mature into schizonts and rupture in order to release merozoites. Merozoites infect red blood cells. They grow inside the red blood cells and destroy them.
CONTENTS
1. Overview and Key Difference
2. What are Merozoites
3. What are Sporozoites
4. Similarities Between Merozoites and Sporozoites
5. Side by Side Comparison – Merozoites vs Sporozoites in Tabular Form
6. Summary
What are Merozoites?
Merozoites are a form of malaria parasites within the human host. Mature schizonts rupture and release meroziotes. Liberated merozoites come into the bloodstream and infect red blood cells. Merozoites resemble sporozoites. They are motile ovoid forms. They grow inside the red blood cells. Then they transform into trophozoites.
Figure 01: Life Cycle of Malaria Parasite
Trophozoites develop into schizonts containing 6-12 daughter merozoites that can infect more red blood cells and continue the cycle by invading other red blood cells. The onset of malaria is due to the invasion of red blood cells by merozoites and the rupture of infected red blood cells.
What are Sporozoites?
Sporozoites are the form of parasite inoculated into the human host through a female Anopheles mosquito bite. Sporozoites are crescent-shaped and motile. The oocysts grow, rupture, and release sporozoites. Sporozoites migrate to the salivary gland of the mosquito.
Figure 02: Sporozoites
During a blood meal, the mosquito injects anticoagulant saliva together with sporozoites. This inoculation of sporozoites into a new human host perpetuates the malaria life cycle. Sporozoites enter the bloodstream to be transported to the liver. Once they reach the liver, they infect liver cells. Then they mature into schizonts containing merozoites. Schizonts rupture and release merozoites.
What are the Similarities Between Merozoites and Sporozoites?
- They are two forms of the malaria parasite.
- Both forms are motile.
- Mature sporozoites release merozoites.
- Generally, each sporozoite becomes a schizont that matures to yield up to 40 000 merozoites over a period of one to several weeks.
- Merozoites closely resemble sporozoites.
- Both show ovoid shape.
What is the Difference Between Merozoites and Sporozoites?
Merozoites are an invasive form of malaria parasite that infects red blood cells, while Sporozoites are an invasive form of malaria parasite that infects liver cells. So, this is the key difference between merozoites and sporozoites. Moreover, the mature schizonts release merozoites, while mature oocysts release sporozoites. The clinical onset of malaria is due to the rupture of infected red blood cells. It is not due to the rupture of liver cells. This is another difference between merozoites and sporozoites.
The below infographic tabulates the differences between merozoites and sporozoites for side by side comparison.
Summary – Merozoites vs Sporozoites
Merozoites and sporozoites are two forms of the malaria parasite. They resemble each other. Both forms are motile forms. Merozoites infect human red blood cells and destroy them. On the other hand, sporozoites infect liver cells and destroy them. Thus, this is the key difference between merozoites and sporozoites. Mature schizonts rupture and release merozoites, while mature oocysts rupture and release sporozoites.
Reference:
1. Frischknecht, Friedrich, and Kai Matuschewski. “Plasmodium Sporozoite Biology.” Cold Spring Harbor Perspectives in Medicine, Cold Spring Harbor Laboratory Press, 1 May 2017, Available here.
2. “Apicomplexan Life Cycle.” Wikipedia, Wikimedia Foundation, 8 Feb. 2021, Available here.
Image Courtesy:
1. “Life Cycle of the Malaria Parasite” By Bbkkk – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Malaria Sporozoites” By NIAID (CC BY 2.0) via Flickr