**Question:** Not true regarding Hydatid cyst of lung

A. Hydatid cyst is caused by a single parasite infection.
B. Hydatid cyst is rare in developed countries.
C. Hydatid cyst is always associated with liver and kidney involvement.
D. Hydatid cyst is always treated with surgery alone.

**Correct Answer: B. Hydatid cyst is rare in developed countries.**

**Core Concept:**
Hydatid disease, also known as echinococcosis, is a zoonotic infection caused by the larval stage of the tapeworms of the genus Echinococcus. There are two main types:

1. **Human-infective**: Echinococcus granulosus (cystic form) and Echinococcus multilocularis (alveolar form).
2. **Canine-infective**: Echinococcus canicola and Echinococcus oligarthus.

**Why the Correct Answer is Right:**

Hydatid disease is primarily found in areas where dogs and other canines are kept as farm animals, such as Australia, South America, Africa, and parts of Asia. In developed countries like the UK, USA, and Western Europe, the prevalence is much lower due to better hygiene practices and control of canine populations. In these regions, the infection is more commonly seen in immigrants from endemic areas or in those who consume contaminated food products.

**Why Each Wrong Option is Incorrect:**

A. Although single-stage infections are more common overall, there can be co-infections with other stages (e.g., adult worms or multi-locular forms) in certain cases.
C. Although liver and kidney are commonly involved, other organs like lungs, spleen, and bones can also be affected.
D. Surgery alone is often not sufficient for complete eradication of the disease. Medical treatment with antiparasitic drugs (e.g., albendazole or praziquantel) is often required alongside surgery, especially for pulmonary hydatidosis to prevent recurrence.

**Clinical Pearl:**

Hydatid disease requires a high index of suspicion in non-endemic areas, especially in patients with a history of travel or immigration from endemic regions. Thorough clinical examination, imaging studies (e.g., CT scan), and serological tests (e.g., ELISA, IFA) are essential for diagnosis. Treatment involves a combination of surgery and antiparasitic drugs, as mentioned above.

**Why the Correct Answer is Right:**

The prevalence of hydatid disease is lower in developed countries due to better hygiene practices and control of dog populations. Infections are often acquired through ingestion of contaminated food products or direct contact with infected dogs.

**Why Each Wrong Option is Incorrect:**

A. The core concept is that the disease is less common in developed countries. However, it can still occur in certain cases.
B. While liver and kidney are commonly involved, other organs can also be affected, including lungs, spleen, and bones.
C. Surgery alone is not sufficient for complete eradication