Mosquito Borne Diseases

A broad category of viral, parasitic and, less commonly, bacterial infections transmitted by mosquito vectors.

It encompasses malaria, the arboviral infections dengue, Zika, yellow fever and Japanese encephalitis, together with other mosquito transmitted infections including chikungunya, West Nile virus and lymphatic filariasis.

The shared epidemiological principle is that risk correlates with the specific mosquito vector distribution: Aedes species for dengue, Zika, yellow fever and chikungunya, versus Anopheles for malaria, versus Culex for West Nile virus and Japanese encephalitis. This informs both geographical risk assessment and preventive strategy.

Classification by vector and pathogen

• Aedes aegypti and Aedes albopictus transmitted infections (dengue, Zika, yellow fever, chikungunya) share overlapping geographical distribution across much of the tropics and subtropics. These day biting mosquitoes favour urban and peri urban breeding sites in stagnant water. Co-infection or diagnostic confusion between these arboviruses is a genuine clinical consideration given overlapping presentation.
• Anopheles mosquitoes, predominantly night biting, transmit malaria specifically.
• Culex mosquitoes transmit West Nile virus and Japanese encephalitis. Lymphatic filariasis (caused by Wuchereria bancrofti and Brugia species) is transmitted by various mosquito genera depending on the specific endemic region.

• A non specific febrile illness with headache, myalgia, arthralgia and, in a proportion, rash characterises the common presenting pattern across most arboviral infections in this group. Clinical distinction between individual pathogens based on symptoms alone is frequently unreliable and specific laboratory testing guided by the travel and exposure history is required.
• Chikungunya characteristically produces severe, often debilitating polyarthralgia, sometimes persisting for months following the acute illness, a feature that helps distinguish it clinically from dengue and Zika, though considerable symptom overlap exists in the acute phase.
• West Nile virus infection is asymptomatic or mild in the majority, with a small proportion developing neuroinvasive disease (meningitis, encephalitis, or a poliomyelitis like acute flaccid paralysis), particularly in older or immunocompromised patients.
• Lymphatic filariasis presents with recurrent episodes of acute lymphangitis and, over years of repeated infection, progressive lymphoedema, most classically affecting the lower limbs and, in men, the scrotum (hydrocele), reflecting chronic lymphatic obstruction by adult filarial worms.

• A detailed travel history specifying the exact countries and regions visited, together with the timing of travel relative to symptom onset, is the essential starting point given the differing and sometimes overlapping geographical distribution of the relevant vectors and pathogens.
• Malaria must always be actively excluded first with blood film examination in any returning traveller with fever, given its potential for rapid deterioration, before other arboviral causes are pursued.
• Specific serological and polymerase chain reaction testing, directed by the travel history and clinical picture, confirms the specific arboviral diagnosis, with the individual approach depending on the specific condition (dengue, Zika, yellow fever).
• Microfilariae can be identified on blood film examination for suspected lymphatic filariasis, with sample timing coordinated to the specific nocturnal or diurnal periodicity of circulating microfilariae relevant to the endemic region and likely infecting species.

• Management is predominantly supportive across the great majority of mosquito borne viral infections in this group, given the absence of specific antiviral treatment for most. Paracetamol is preferred over nonsteroidal anti inflammatory drugs and aspirin for symptomatic fever and pain relief until dengue has been reasonably excluded, given the bleeding risk associated with these agents in that specific condition.
• Chikungunya associated arthralgia may require more prolonged analgesic and, in some cases, disease modifying antirheumatic drug therapy for persistent symptoms, managed following principles similar to inflammatory arthritis where chronic joint symptoms persist beyond the acute viral illness.
• Neuroinvasive West Nile virus disease is managed supportively, following the general principles of viral encephalitis management, given the absence of a specific licensed antiviral treatment.
• Lymphatic filariasis is treated with diethylcarbamazine (6 mg per kg daily in divided doses for twelve days, standard adult regimen) or, in regions with coexisting onchocerciasis or loiasis where diethylcarbamazine carries specific risk, alternative regimens under specialist guidance. Established lymphoedema is managed through meticulous skin hygiene, compression and, where indicated, surgical intervention for significant hydrocele.
• Mosquito bite avoidance (repellent containing DEET, permethrin treated clothing and bed nets, elimination of standing water breeding sites) remains the cornerstone preventive strategy shared across this entire group of infections. Specific vaccination is available and recommended for yellow fever and, in some jurisdictions, dengue and Japanese encephalitis according to destination specific risk.