Malaria: This is a leading consideration due to the combination of fever, headache, and hepatomegaly following travel to a tropical region. Malaria, caused by Plasmodium species, is prevalent in many tropical areas and can present with these symptoms.

Typhoid Fever: Caused by Salmonella Typhi, this illness is common in tropical regions with poor sanitation. Symptoms include fever, headache, diarrhea, and hepatomegaly, making it a plausible diagnosis.
Dengue Fever: A viral illness transmitted by mosquitoes, dengue fever is common in tropical and subtropical climates. It presents with fever, headache, and can include gastrointestinal symptoms and hepatomegaly.
Hepatitis A: Although primarily causing jaundice and liver dysfunction, hepatitis A can present with non-specific symptoms such as fever, diarrhea, and headache, especially in the prodromal phase.

Yellow Fever: Despite being less common due to vaccination efforts, yellow fever is a critical diagnosis not to miss due to its high mortality rate if untreated. It presents with fever, headache, and can progress to include liver dysfunction and hemorrhagic symptoms.
Leptospirosis: This bacterial infection, contracted through water contaminated with the urine of infected animals, can cause a wide range of symptoms including fever, headache, diarrhea, and liver involvement. Its severity and potential for renal and liver failure make it a diagnosis not to be missed.
Viral Hemorrhagic Fevers (VHFs): Including diseases like Lassa fever and Ebola, VHFs are rare but can be deadly. They present with non-specific symptoms initially, such as fever and headache, and can progress to severe hemorrhagic manifestations.

Schistosomiasis (Bilharzia): Caused by parasitic flatworms, schistosomiasis can lead to liver and intestinal symptoms, including hepatomegaly and diarrhea, but is less likely to present with the acute symptoms described.
Amoebic Liver Abscess: While more commonly causing liver abscesses without systemic symptoms, amoebic infections can occasionally present with fever, diarrhea, and hepatomegaly, especially in travelers to endemic areas.
Rickettsial Infections: Such as those caused by Rickettsia and Orientia species, these can present with fever, headache, and gastrointestinal symptoms but are less commonly associated with hepatomegaly and specific travel history.