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Yellow fever virus
Last reviewed: 04.07.2025
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Yellow fever is an acute severe infectious disease characterized by severe intoxication, two-wave fever, severe hemorrhagic syndrome, and kidney and liver damage. Due to its high mortality rate (40-90%) and severe course, it is classified as a group of especially dangerous conventional (included in international agreements) diseases.
The causative agent of yellow fever is a virus discovered in 1901 by W. Reed, belongs to the Flaviviridae family and has properties typical of flaviviruses.
In the external environment, the yellow fever virus is unstable; it quickly dies under the influence of conventional disinfectants, in a liquid medium at a temperature of 60 °C it dies within 10 minutes, but in a dried state it is preserved at 100-110 °C for 5 hours, in a frozen state - for several years. In infected dead mosquitoes it is preserved for up to 4 weeks. The virus reproduces well in chicken embryos and in various cell cultures. Of the laboratory animals, white mice and monkeys (Macacus rhesus) are susceptible to it. It is antigenically homogeneous.
Epidemiology of yellow fever
Yellow fever is a disease with endemic natural foci located in the tropical belt of Central and West Africa, South and Central America. Epidemiologically, two variants of yellow fever are distinguished.
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Yellow fever of the jungle
Primates are the main reservoir of the virus, although some species of other animals (opossums, anteaters, armadillos, etc.) are sensitive to the virus. Infection of monkeys (and other hosts) occurs through mosquito bites: in America, the genus Haemagogus, and in Africa, the genus Aedes. Epizootics among monkeys recur every 3-4 years, after which the entire primate population either dies or acquires immunity.
Urban (classical) form of yellow fever
This form of the disease is the main danger, since the main source of the virus is an infected person. Urban yellow fever occurs when a person enters a natural focus of yellow fever in the jungle. The virus multiplies in the human body, circulates in the blood and is not released into the environment. A person becomes contagious from the end of the incubation period (it lasts 3-6 days, in some cases up to 10-12 days) and in the first 3-4 days of the disease (viremia stage). Infection occurs mainly through the bites of the female Aedes aegypti mosquito. The virus multiplies and accumulates in the salivary glands of the mosquito, remains in it until the end of the mosquito's life (1-2 months), but is not transmitted to the mosquito's offspring. The mosquito usually attacks a person during the day, rarely at night; after feeding, it becomes contagious at a temperature of 36-37 ° C after 4-5 days, at 24 ° C - after 11, at 21 ° C - after 18 days. At a temperature of 18 °C, the reproduction of the virus in the mosquito's body stops; at temperatures below 15 °C, the mosquito becomes inactive and therefore is unable to transmit the virus. Due to these biological characteristics of the mosquito, yellow fever epidemics occur in high humidity and heat, which promote mass reproduction of mosquitoes.
Unlike jungle yellow fever, which is a zoonotic infection, urban yellow fever is an anthroponotic disease with a single, transmissible route of transmission. All people are susceptible to yellow fever. Only children of the first six months, if they have received passive immunity from their mother, rarely get sick.
Symptoms of Yellow Fever
The following main stages are distinguished in the development of the disease:
- I - infection (the virus enters the body);
- II - the virus penetrates the regional lymph nodes via the lymphatic system, where it multiplies;
- III - viremia, the virus is carried by the blood throughout the body and circulates in it for five days. The onset of viremia corresponds to the onset of the disease;
- IV - the virus, due to its pantropic nature, penetrates the cells of various organs and systems and affects them, especially the endothelium of capillaries, as a result of which the blood coagulation system is disrupted and hemorrhagic diathesis develops, with the liver and kidneys particularly affected, which leads to hepatorenal failure;
- V - formation of immunity and gradual recovery.
Yellow fever is characterized by cyclicity: an incubation period, an initial (general toxic) period, a period of pronounced damage to the functions of individual organs, and a recovery period. However, the disease can proceed in a mild form or be fatal. The fatality rate in severe forms of the disease reaches 85-90%.
Laboratory diagnostics of yellow fever
Diagnostics of yellow fever includes the use of virological, biological and serological methods. The virus can be isolated from blood by infecting chicken embryos or cell cultures. A neutralization reaction is used to identify the virus. The biological test involves infecting suckling mice with the blood of patients intracerebrally, in which the virus causes fatal encephalitis. To detect virus-specific antibodies in paired sera, which are taken 7-8 days later, the RSC, RTGA, RN and other serological reactions are used.
Specific prophylaxis of yellow fever
The main method of combating yellow fever is vaccination against yellow fever - active immunization in epidemic foci using a live vaccine obtained by M. Taylor in 1936 (strain 17D). Children from the first year of life and adults are vaccinated in a dose of 0.5 ml subcutaneously. Post-vaccination immunity develops 10 days after vaccination and lasts for 10 years. All persons traveling to and from epidemic foci are subject to mandatory vaccination. In accordance with the decision of WHO (1989), vaccinations against yellow fever are included in the expanded immunization program. According to WHO, in 1998-2000, 446 of 1202 people who fell ill with yellow fever died.