Final answer:
Cysts act as a resistant stage in the life cycle of Giardia intestinalis, allowing it to survive in cold temperatures and chlorination treatment in drinking water. Consuming contaminated food or water with cysts leads to the development of the parasite and the onset of giardiasis. Filtering municipal water is crucial to prevent the spread of Giardia.
Step-by-step explanation:
The importance of cysts to the spread of Giardia intestinalis is that they act as a resistant stage in the parasite's life cycle. These cysts can survive cold temperatures and chlorination treatment in drinking water, allowing them to spread easily.
When contaminated food or water containing cysts is consumed by a host, the cysts are ingested and the parasite develops into the active tropozoite, causing giardiasis.
In order to prevent the spread of Giardia, municipal water must be filtered to remove these cysts and ensure safe drinking water.