Which of the following diseases is transmitted by the bite of an infected phlebotomine sandfly, characterised by irregular fever, weight loss and enlargement of the spleen and liver?
Visceral leishmaniasis
Understanding Sandfly Transmitted Diseases and Symptoms
This question asks us to identify a specific disease based on its transmission method and characteristic symptoms. The key clues are: transmitted by the bite of an infected phlebotomine sandfly and symptoms including irregular fever, weight loss, and enlargement of the spleen and liver.
Analyzing the Transmission Vector: Phlebotomine Sandfly
The question specifically mentions transmission by an infected phlebotomine sandfly. This is a crucial piece of information as different diseases are transmitted by different vectors (like mosquitoes, ticks, flies, etc.). We need to consider which of the given diseases is known to be transmitted by this particular insect.
Examining the Characteristic Symptoms
The symptoms described are irregular fever, weight loss, and enlargement of the spleen and liver (known as hepatosplenomegaly). These are clinical signs that point towards a specific type of systemic disease.
Evaluating the Options
Let's look at each option in the context of sandfly transmission and the described symptoms:
- Anaplasmosis: This is a tick-borne disease caused by the bacterium Anaplasma phagocytophilum. It is transmitted by certain species of ticks, not sandflies. Symptoms typically include fever, headache, muscle aches, and fatigue. It does not usually cause significant enlargement of the spleen and liver in the way described.
- Japanese encephalitis: This is a viral disease transmitted by mosquitoes (specifically Culex species). It affects the brain and spinal cord, causing symptoms like fever, headache, vomiting, confusion, seizures, and paralysis. It is not transmitted by sandflies and its primary symptoms are neurological.
- Diarrhoea: Diarrhoea is a symptom, not a single disease entity caused by sandflies. It is typically caused by infections (bacterial, viral, parasitic) or other issues related to the digestive system, often acquired through contaminated food or water.
- Visceral leishmaniasis: Also known as Kala-azar, this is a serious parasitic disease caused by protozoa of the genus Leishmania. It is transmitted to humans through the bite of infected female phlebotomine sandflies. The parasite attacks the internal organs (viscera), including the spleen, liver, and bone marrow. Characteristic symptoms include long-lasting, irregular fever, significant weight loss, anaemia, and pronounced enlargement of the spleen and liver. This description perfectly matches the details provided in the question.
Conclusion on the Sandfly-Transmitted Disease
Based on the transmission vector (phlebotomine sandfly) and the specific symptoms (irregular fever, weight loss, enlarged spleen and liver), Visceral leishmaniasis is the disease that fits the description precisely.
| Disease | Primary Transmission Vector | Key Symptoms |
|---|---|---|
| Anaplasmosis | Ticks | Fever, headache, muscle aches, fatigue |
| Japanese encephalitis | Mosquitoes | Fever, headache, vomiting, neurological issues (confusion, seizures) |
| Diarrhoea | N/A (Symptom, often from contaminated food/water) | Loose, watery stools |
| Visceral leishmaniasis (Kala-azar) | Phlebotomine Sandflies | Irregular fever, weight loss, enlarged spleen & liver, anaemia |
Therefore, the disease transmitted by the bite of an infected phlebotomine sandfly, characterised by irregular fever, weight loss and enlargement of the spleen and liver is Visceral leishmaniasis.
Revision Table: Sandfly Disease Characteristics
| Feature | Visceral Leishmaniasis |
|---|---|
| Transmission | Bite of infected phlebotomine sandfly |
| Pathogen Type | Parasite (Leishmania) |
| Key Symptoms | Irregular fever, weight loss, hepatosplenomegaly (enlarged spleen & liver), anaemia |
| Other Names | Kala-azar |
Additional Information: Sandflies and Leishmaniasis
Phlebotomine sandflies are small, blood-feeding insects found in tropical and subtropical regions. Only the female sandflies bite mammals (including humans) because they need blood meals to produce eggs. They transmit the Leishmania parasites from an infected host (like humans or animals) to another person during the biting process. There are different forms of leishmaniasis depending on the species of Leishmania parasite involved:
- Visceral leishmaniasis: Affects internal organs; caused by species like L. donovani, L. infantum, L. chagasi. It is the most severe form.
- Cutaneous leishmaniasis: Causes skin sores; common worldwide.
- Mucocutaneous leishmaniasis: Affects skin and mucosal tissues (nose, mouth, throat); primarily in the Americas.
The symptoms of Visceral leishmaniasis develop gradually, often weeks or months after the sandfly bite. If left untreated, it is usually fatal.
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