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Intermediate Host vs. Definitive Host — What's the Difference?

By Tayyaba Rehman — Published on November 8, 2023
An Intermediate Host temporarily houses a pathogen's juvenile or non-reproductive stages, while a Definitive Host harbors its mature or reproductive stages. Both are essential for the pathogen's life cycle.
Intermediate Host vs. Definitive Host — What's the Difference?

Difference Between Intermediate Host and Definitive Host


Key Differences

The terms Intermediate Host and Definitive Host arise when discussing the life cycles of parasites. An Intermediate Host is an organism that houses a parasite during its developmental or non-reproductive phases. This is a temporary phase, and the parasite does not reach maturity within this host. In contrast, the Definitive Host is the organism where the parasite completes its life cycle, often involving reproduction.
Intermediate Hosts can be seen as a transitional phase in the life cycle of certain parasites. For instance, certain parasites may need to pass through an Intermediate Host to undergo necessary developmental changes before reaching their mature stage. Definitive Hosts, on the other hand, are where these parasites find their permanent residence, often utilizing the host's resources to reproduce and spread.
It's important to note that not all parasites require both types of hosts. Some may directly infect their Definitive Host without needing an Intermediate Host. However, when both types are involved, the Intermediate Host usually becomes infected when consuming the parasite, and the Definitive Host gets infected when consuming the Intermediate Host.
In essence, both Intermediate and Definitive Hosts play crucial roles in the life cycles of many parasites. The Intermediate Host provides a necessary step in the development of the parasite, while the Definitive Host allows for its eventual reproduction.

Comparison Chart

Role in Parasite Life Cycle

Houses developmental or non-reproductive stages
Houses mature or reproductive stages

Duration of Parasite Stay

Permanent (for that stage)


Essential for parasite development
Essential for parasite reproduction


Snail in the life cycle of certain flukes
Human in the life cycle of malaria parasite

Reproduction of Parasite

Does not occur

Compare with Definitions

Intermediate Host

An Intermediate Host shelters a parasite's developmental stages.
The mosquito acts as an Intermediate Host for the heartworm parasite in dogs.

Definitive Host

Parasites complete their life cycles in the Definitive Host.
For tapeworms, humans often act as the Definitive Host.

Intermediate Host

Intermediate Hosts facilitate certain changes in the parasite.
Certain flukes require a snail as an Intermediate Host to mature.

Definitive Host

The Definitive Host often becomes infected by consuming an Intermediate Host.
By eating undercooked fish, humans can become the Definitive Host for certain fish tapeworms.

Intermediate Host

Intermediate Hosts can get infected in various ways, often by ingesting the parasite.
Fish become Intermediate Hosts for certain parasites when they feed on infected water plants.

Definitive Host

A Definitive Host provides the environment for the mature stages of a parasite.
Dogs are the Definitive Host for heartworms, where the worms reproduce.

Intermediate Host

Parasites in Intermediate Hosts don't typically reproduce.
The liver fluke, while in the snail Intermediate Host, does not reproduce.

Definitive Host

Definitive Hosts are essential for the reproduction of many parasites.
Cats are the Definitive Host for the Toxoplasma gondii parasite.

Intermediate Host

An Intermediate Host plays a transitional role in a parasite's life.
For tapeworms, cows can serve as the Intermediate Host.

Definitive Host

A Definitive Host is where a parasite reaches maturity.
Humans are the Definitive Host for the malaria parasite.

Common Curiosities

How does a parasite move from an Intermediate Host to a Definitive Host?

Often, the Definitive Host becomes infected by consuming the infected Intermediate Host.

Do parasites reproduce in the Intermediate Host?

Typically, no. Reproduction usually occurs in the Definitive Host.

Why do some parasites need an Intermediate Host?

To undergo essential developmental changes before reaching maturity.

Is a human always a Definitive Host for parasites?

No, humans can act as either Intermediate or Definitive Hosts, depending on the parasite.

How does a Definitive Host differ from an Intermediate Host?

A Definitive Host harbors the mature or reproductive stages of a parasite, completing its life cycle.

Can an organism be both an Intermediate and Definitive Host for different parasites?

Yes, an organism's role can vary depending on the specific parasite's life cycle.

What is an Intermediate Host?

It's an organism that temporarily houses a parasite during its developmental or non-reproductive stages.

Do all parasites need both an Intermediate and Definitive Host?

No, some parasites may directly infect their Definitive Host without an Intermediate stage.

Is the presence of an Intermediate Host always harmful to the Definitive Host?

Not necessarily, but the parasites they carry can cause diseases in the Definitive Host.

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Written by
Tayyaba Rehman
Tayyaba Rehman is a distinguished writer, currently serving as a primary contributor to As a researcher in semantics and etymology, Tayyaba's passion for the complexity of languages and their distinctions has found a perfect home on the platform. Tayyaba delves into the intricacies of language, distinguishing between commonly confused words and phrases, thereby providing clarity for readers worldwide.

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