Yellow fever pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Pathophysiology

The female Aedes aegypti mosquito on a human host, about to obtain a blood meal

• Yellow fever is caused by an arbovirus of the family Flaviviridae, a positive single-stranded RNA virus.
• Human infection begins after deposition of viral particles through the skin in infected arthropod saliva.
• The mosquitos involved are Aedes simpsaloni, A. africanus, and A. aegypti in Africa, the Haemagogus genus in South America, and the Sasbethes genera in France.
• Yellow fever is frequently severe but more moderate cases may occur as the result of previous infection by another flavivirus.
• After infection the virus first replicates locally, followed by transportation to the rest of the body via the lymphatic system.
• Following systemic lymphatic infection the virus proceeds to establish itself throughout organ systems, including the heart, kidneys, adrenal glands, and the parenchyma of the liver; high viral loads are also present in the blood.
• Necrotic masses (Councilman bodies) appear in the cytoplasm of hepatocytes.^,
• There is a difference between disease outbreaks in rural or forest areas and in towns. Disease outbreaks in towns and non-native people are usually more serious.

Transmission

Transmission of Yellow Fever Virus Image obtained from CDC

• Yellow fever virus is an RNA virus that belongs to the genus Flavivirus.

• It is related to West Nile, St. Louis encephalitis, and Japanese encephalitis viruses.

• Yellow fever virus is transmitted to humans primarily through the bite of infected Aedes or Haemagogus species mosquitoes.

• Mosquitoes acquire the virus by feeding on infected primates (human or non-human) and then can transmit the virus to other primates (human or non-human).

• Humans infected with yellow fever virus are infectious to mosquitoes shortly before the onset of fever and for 3–5 days after onset.

• Yellow fever virus has three transmission cycles: jungle (sylvatic), inter­mediate (savannah), and urban.

Jungle Cycle

• The jungle (sylvatic) cycle involves transmission of the virus between nonhuman primates (e.g., monkeys) and mosquito species found in the forest canopy.
• The virus is transmitted by mosquitoes from monkeys to humans when humans are visiting or working in the jungle.

Intermediate Cycle

• In Africa, an intermediate (savannah) cycle exists that involves transmission of virus from mosquitoes to humans living or working in jungle border areas.
• In this cycle, the virus can be transmitted from monkey to human or from human to human via mosquitoes.

Urban Cycle

• The urban cycle involves transmission of the virus between humans and urban mosquitoes, primarily Aedes aegypti.
• The virus is usually brought to the urban setting by a viremic human who was infected in the jungle or savannah.

References

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