Yellow fever

Definition

An acute viral hemorrhagic disease caused by the yellow fever virus (genus Flavivirus, family Flaviviridae), transmitted to humans and non-human primates primarily through the bite of infected mosquitoes. The virus undergoes extrinsic incubation in the vector, replicating in the mosquito midgut, disseminating to the haemocoel, and ultimately invading the salivary glands, from which it is injected into subsequent hosts during blood-feeding. The disease manifests in two clinical forms: an acute, self-limiting infection with fever and myalgia, and a severe, potentially fatal form characterized by hepatic necrosis, jaundice (the eponymous 'yellow' appearance), and hemorrhagic diathesis. Sylvatic (jungle) cycles involve non-human primates and tree-hole-breeding mosquitoes (Haemagogus, Sabethes), while urban cycles depend on human-mosquito-human transmission mediated by Aedes aegypti.

Etymology

From the characteristic jaundice (yellowing of skin and sclera) caused by liver damage in severe cases; 'fever' from the acute febrile onset.

Example

In the Amazon basin, sylvatic yellow fever maintains an enzootic cycle between howler monkeys (Alouatta spp.) and canopy-dwelling Haemagogus mosquitoes; when humans enter forest habitats for logging or agriculture, they become incidental dead-end hosts, whereas urban epidemics emerge when viremic travelers introduce the virus into Aedes aegypti-infested cities.

Synonyms

• American plague

Related Terms

• Vector
• Aedes aegypti
• Flaviviridae
• haemocoel
• extrinsic incubation period
• sylvatic cycle
• urban cycle
• dengue fever
• Epizootic
• viral hemorrhagic fever

Usage Notes

Distinguished from 'yellow fever' in a horticultural context (plant disease). In entomological literature, emphasizes vector competence, extrinsic incubation temperature thresholds, and the distinction between sylvatic (jungle) and urban transmission cycles. The term 'American plague' is archaic and potentially confusing with plague (Yersinia pestis); prefer 'yellow fever' in scientific contexts. Vaccination provides lifelong immunity, but vector control remains critical for outbreak prevention in entomological practice.