The key difference between tachyzoite and bradyzoite stages is that tachyzoite stage is a rapidly dividing stage of the life cycle of parasite Toxoplasma gondii while bradyzoite stage is a slow dividing stage of the life cycle of parasite T. gondii.
Toxoplasma gondii is an obligate intracellular parasitic protozoan that causes toxoplasmosis disease in humans. It is found worldwide. T. gondii is capable of infecting warm-blooded animals, including humans. It shows both sexual and asexual reproduction. This parasite completes sexual reproduction inside definitive hosts like cats. Asexual reproduction takes place in intermediate hosts such as humans, chickens, pigs, sheep, and goats. During the life cycle of this parasite, it undergoes several cellular stages. Therefore, tachyzoite and bradyzoite stages are two cellular stages of the life cycle of the parasite T. gondii.
CONTENTS
1. Overview and Key Difference
2. What are Tachyzoite Stages
3. What are Bradyzoite Stages
4. Similarities – Tachyzoite and Bradyzoite Stages
5. Tachyzoite vs Bradyzoite Stages in Tabular Form
6. Summary – Tachyzoite vs Bradyzoite Stages
What are Tachyzoite Stages?
Tachyzoite stage is a rapidly dividing stage of the life cycle of the parasite T. gondii. This stage is seen in the asexual reproduction of T. gondii, which normally takes place in warm-blooded animals such as humans. Sporozoites are generated in the sexual reproduction of this parasite in the definitive host. Sporozoites are the stage of the parasite residing within oocysts. When an intermediate host like a human or other warm-blooded animal consumes an oocyst, sporozoites are released from it. These sporozoites infect the epithelial cells of the intermediate host before converting to the proliferative tachyzoite stage of asexual reproduction. Moreover, when a host consumes a tissue cyst containing bradyzoites, the bradyzoites can also convert into the tachyzoites upon infecting the epithelium of the host.
Figure 01: Tachyzoite
Tachyzoites are motile and quickly multiplying. They are responsible for expanding the population of the parasite in the host. During the initial period of the infection, tachyzoite spreads throughout the body via the bloodstream. Furthermore, during the later stages of infection, tachyzoites convert back to bradyzoites to form tissue cysts.
What are Bradyzoite Stages?
Bradyzoite stage is the slow dividing stage of the life cycle of parasite T. gondii. The Bradyzoite stage contains bradyzoites, which make up the tissue cysts of the parasite. Tissue cysts vary in size. The younger tissue cysts may be as small as 5 μm in diameter and contain only two bradyzoites. The older tissue cysts may contain hundreds of bradyzoites. Bradyzoites are also known as cystozoites.
Figure 02: Bradyzoite Stage
When an uninfected host consumes a tissue cyst containing bradyzoites, bradyzoites come out from the cyst and infect intestinal epithelial cells before converting to the proliferative tachyzoite stage. Following the initial period of proliferation throughout the host body, the tachyzoites convert back to bradyzoites that reproduce inside host cells to form tissue cysts again in the new host.
What are the Similarities Between Tachyzoite and Bradyzoite Stages?
- Tachyzoite and bradyzoite stages are two cellular stages of the life cycle of the parasite gondii.
- Both stages are seen in the asexual reproduction of the gondii.
- They can be identified in intermediate hosts like humans and other warm-blooded animals.
- Both stages are extremely important for the survival and spread of the parasite gondii.
What is the Difference Between Tachyzoite and Bradyzoite Stages?
Tachyzoite stage is the rapidly dividing stage of T. gondii, while bradyzoite stage is the slow dividing stage of T. gondii. Thus, this is the key difference between tachyzoite and bradyzoite stages. Furthermore, tachyzoite stage contains tachyzoites, which are also known as tachyzoic merozoites, while bradyzoite stage contains bradyzoites, which are also known as bradyzoic merozoites.
The below infographic presents the differences between tachyzoite and bradyzoite stages in tabular form for side-by-side comparison.
Summary – Tachyzoite vs Bradyzoite Stages
Tachyzoite and bradyzoite stages are two cellular stages of the life cycle of T. gondii. Tachyzoite stage is the rapidly dividing stage of the life cycle of the parasite Toxoplasma gondii while bradyzoite stage is the slow dividing stage. So, this is the key difference between tachyzoite and bradyzoite stages. Both stages are seen during the asexual reproduction of this parasite.
Reference:
1. Dubey, J P, et al. “Structures of Toxoplasma Gondii Tachyzoites, Bradyzoites, and Sporozoites and Biology and Development of Tissue Cysts.” Clinical Microbiology Reviews, American Society for Microbiology.
2. “Bradyzoite.” An Overview | ScienceDirect Topics.
Image Courtesy:
1. “T. gondii traquizoito Conoide” By Koreny L., Zeeshan M., Barylyuk K., Tromer E.C., van Hooff J.J.E., Brady D., WallerHuiling Ke R.F., Chelaghma S., Ferguson D.JP, Eme L., Tewari R. (2021) – Molecular characterization of the conoid complex in Toxoplasma reveals its conservation in all apicomplexans, including Plasmodium species. PLoS Biol 19(3): e3001081. doi:10.1371/journal.pbio.3001081 (CC BY 4.0) via Commons Wikimedia
2. “Toxoplasma gondii bradyzoite” By Servier Medical Art – (CC BY 2.0) via Commons Wikimedia