The common and fatal disease of poultry is Ranikhet.

Answer

**Step-by-Step Solution:**

1. **Identify the Disease**: The question states that Ranikhet is a common and fatal disease of poultry.

2. **Understand the Nature of the Disease**: Ranikhet is classified as an acute viral disease, which means it is caused by a virus and can lead to severe health issues in affected birds.

3. **Determine the Causative Agent**: The specific virus responsible for Ranikhet is known as Paramyxovirus. This is crucial for understanding the disease's origin and potential treatment or prevention methods.

4. **Recognize Symptoms**: Key symptoms of Ranikhet include a sudden decrease in respiratory rate and a significant drop in egg production. These symptoms indicate that the disease severely impacts the health and productivity of poultry.

5. **Assess the Severity**: The disease can lead to a gradual decline in the lifespan of affected birds, ultimately resulting in a high mortality rate, with chances of 100% death in severe cases.

6. **Conclude the Statement**: Based on the understanding of Ranikhet as a fatal disease caused by Paramyxovirus, characterized by specific symptoms and high mortality, we can confirm that the statement regarding Ranikhet being a common and fatal disease of poultry is true.

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