Question

The definitive host for Toxoplasma gondii is ___________.

Short answer

The definitive host for Toxoplasma gondii is the domestic cat or other feline species.

Step-by-step solution

Identify the Organism

First, identify the organism mentioned in the exercise, Toxoplasma gondii, which is a parasitic protozoan.

Understanding the Life Cycle

Understand that Toxoplasma gondii has a complex life cycle involving two hosts: an intermediate host where asexual reproduction occurs, and a definitive host where sexual reproduction takes place.

Identifying the Definitive Host

The definitive host for Toxoplasma gondii is where sexual reproduction occurs. This is the only organism in which the parasite can complete its life cycle and form oocysts. For Toxoplasma gondii, this host is the domestic cat or other members of the feline family.

Key concepts

Parasitic Protozoan

Protozoans are single-celled organisms that can cause a variety of diseases, and among them are parasitic types which live at the expense of a host. Toxoplasma gondii is one such parasitic protozoan that has garnered attention due to its ability to infect a wide range of hosts, including humans. It belongs to the group of organisms known as Apicomplexa, which are characterized by their unique cell structures used for invading host cells.

Humans typically encounter Toxoplasma gondii through contaminated food or soil, or by handling cat feces as cats are the definitive hosts where the parasite can sexually reproduce. Understanding the roles of parasitic protozoans in diseases is crucial for both treatment and prevention strategies. Due to their complex life cycles and various survival strategies, these parasites are often difficult to eliminate completely from affected populations.

Complex Life Cycle

The life cycle of Toxoplasma gondii is quite intricate and involves multiple stages of development that occur within different hosts. Breaking down this complex cycle: during the asexual phase, the protozoan can infect virtually any warm-blooded animal, including birds, rodents, and even humans. In this phase, known as the intermediate host phase, the protozoan undergoes rapid multiplication.

Asexual Reproduction in Intermediate Hosts

In these hosts, Toxoplasma gondii forms structures known as 'tachyzoites' during acute infection and 'bradyzoites' within tissue cysts when in a latent phase. These stages are crucial for spreading within and between intermediate hosts. However, the final stage of the life cycle, which is essential for propagation of the species, occurs only within the definitive host.

Sexual Reproduction in Parasites

Regarding the sexual reproduction phase of Toxoplasma gondii, it occurs exclusively in the definitive host.

Role of the Definitive Host

The definitive host for this parasite is the feline family, including domestic cats, where the protozoan undergoes sexual reproduction. Within the intestines of these feline hosts, Toxoplasma gondii forms gametes that ultimately fuse to form oocysts, which are then shed in the feces of the host. The oocysts are very resistant to environmental pressures and can survive for long periods outside a host.

Once another host, such as a rodent or even a human, ingests these oocysts, the cycle continues as the oocysts transform into tachyzoites and begin the asexual reproduction phase anew. Understanding the sexual reproduction phase is vital as it is the only stage where genetic recombination occurs, which can result in genetic diversity and adaptability of the parasite.