What is yellow fever, specifically, in terms of its cause (virus type and family), symptoms, and potential complications? Beyond that, how is yellow fever contracted, detailing the vector(s) involved, the geographic distribution of the disease and its vectors, and whether there are any other known transmission routes besides mosquito bites? What are the risk factors that increase susceptibility to yellow fever infection or severe disease outcomes?
Answer
Yellow fever is an acute viral hemorrhagic disease transmitted by infected mosquitoes. It is found in tropical and subtropical areas of Africa and South America.
How it is Contracted:
The yellow fever virus is primarily transmitted to humans through the bite of infected Aedes and Haemagogus mosquitoes. These mosquitoes acquire the virus by feeding on infected primates (humans or monkeys).
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Mosquito Vectors: Aedes aegypti is the primary urban vector, meaning it thrives in and around human settlements and is responsible for outbreaks in cities. Other Aedes species and Haemagogus species are involved in jungle (sylvatic) transmission.
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Transmission Cycle: The transmission cycle involves the mosquito biting an infected person or monkey, acquiring the virus, and then biting another person, transmitting the virus. The virus incubates within the mosquito for a period (8-12 days depending on the temperature) before it can be transmitted.
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Humans as Hosts: Humans become infected when bitten by an infected mosquito. The virus then replicates in the body. Humans are infectious to mosquitoes shortly before the onset of fever and remain so for 3-5 days.
- Risk Factors: Risk factors for contracting yellow fever include living in or traveling to areas where the disease is endemic, not being vaccinated against yellow fever, and exposure to mosquitoes.