**Core Concept**
International surveillance is a global monitoring system for infectious diseases, aiming to detect and respond to public health threats. The World Health Organization (WHO) and other health authorities maintain a list of diseases under international surveillance, requiring rapid reporting and investigation of outbreaks.

**Why the Correct Answer is Right**
Salmonellosis, caused by Salmonella bacteria, is a major public health concern due to its potential to cause outbreaks and severe illness. The WHO includes salmonellosis in its list of diseases under international surveillance, emphasizing the need for prompt reporting and control measures. This is because Salmonella outbreaks can be spread through contaminated food and water, affecting large populations and causing significant morbidity and mortality. The surveillance of salmonellosis helps in identifying the source of outbreaks, implementing control measures, and preventing further transmission.

**Why Each Wrong Option is Incorrect**
**Option A:** Typhoid fever, although a significant public health concern, is not typically included in international surveillance lists due to its relatively lower incidence and more localized outbreaks compared to salmonellosis.

**Option C:** Chikungunya fever, a viral disease, is not under international surveillance as it is generally not considered a high-risk disease for global spread or severe public health impact.

**Option D:** Hepatitis B, a viral liver disease, is not under international surveillance in the same way as salmonellosis, as it is more commonly managed through vaccination and individual treatment rather than outbreak control.

**Clinical Pearl / High-Yield Fact**
The WHO's International Health Regulations (IHR) require countries to report certain diseases, including salmonellosis, within 24 hours of detection, facilitating global coordination and response to public health emergencies.

**✓ Correct Answer: B. Salmonellosis**