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Yellow fever virus
Last reviewed: 23.04.2024
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Yellow fever is an acute serious infectious disease characterized by severe intoxication, a two-wave fever, severe hemorrhagic syndrome, and kidney and liver damage. Due to high mortality (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 family Flaviviridae and possesses the properties typical for flaviviruses.
In the external environment, the yellow fever virus is not very resistant; quickly dies under the influence of conventional disinfectants, it dies in a liquid medium at a temperature of 60 ° C for 10 minutes, but remains in the dried state at 100-110 ° C for 5 hours, frozen for several years. In infected dead mosquitoes persists up to 4 weeks. The virus multiplies well in a chicken embryo and in various cell cultures. From laboratory animals, white mice and monkeys (Macacus rhesus) are susceptible to it. Antigenically, it is 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, there are two variants of yellow fever.
[Yellow jungle fever
The main reservoir of the virus is the primates, although some species of other animals (possums, 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 are repeated after 3-4 years, after them the entire population of primates either perishes, or acquires immunity.
The urban (classical) form of yellow fever
This form of the disease is the main danger, since the infected person becomes the main source of the virus. Urban yellow fever occurs when a person enters the natural focus of yellow jungle fever. The virus multiplies in the human body, circulates in its blood and is not released into the external environment. The person becomes infectious 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 (stage of viremia). Infection occurs mainly through the bites of the female mosquito Aedes aegypti. The virus multiplies and accumulates in the salivary glands of the mosquito, it remains in it until the end of the mosquito's life (1-2 months), but the progeny of the mosquito is not transmitted. The mosquito attacks a person usually during the day, at night - rarely; it becomes infectious at a temperature of 36-37 ° C in 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 is suspended, at temperatures below 15 ° C the mosquito becomes inactive and therefore is unable to transmit the virus. In connection with these biological characteristics of the mosquito, epidemics of yellow fever occur at high humidity and heat, contributing to the mass reproduction of mosquitoes.
Unlike the yellow jungle fever, which is a zoonotic infection, urban yellow fever is anthropogenous disease with a single, transmissible transmission route. All people are susceptible to yellow fever. Only children of the first six months, if they received passive immunity from the mother, are rarely ill.
Symptoms of yellow fever
In the development of the disease, the following main stages are distinguished:
- I - infection (the virus penetrates the body);
- II - the virus lymphogenically penetrates the regional lymph nodes, where it multiplies;
- III - virusemia, the virus carries blood throughout the body and circulates in it for five days. The onset of virusemia corresponds to the onset of the disease;
- IV - the virus, by virtue of its pantropy, penetrates into cells of various organs and systems and affects them, especially the endothelium of the capillaries, as a result of which the blood clotting system is broken and hemorrhagic diathesis develops, especially the liver and kidneys, which leads to hepatic renal insufficiency;
- V - formation of immunity and gradual recovery.
Yellow fever is characterized by cyclicity: the incubation period, the initial (general toxic) period, the period of pronounced defeat of the functions of individual organs and the period of recovery. However, the disease can occur in both mild form and lightning-fast with a fatal outcome. Mortality with a severe form of the disease reaches 85-90%.
Laboratory diagnosis of yellow fever
Diagnosis of yellow fever includes the use of virological, biological and serological methods. A virus from the blood can be isolated by infecting chick embryos or cell cultures. The neutralization reaction is used to identify the virus. The biological test consists in infecting the patients with intracerebral blood by suckling mice, in which the virus causes fatal encephalitis. To detect virus-specific antibodies in paired sera, which are taken after 7-8 days, use of RSK, RTGA, PH and other serological reactions.
Specific prevention of yellow fever
The main method of combating yellow fever is vaccination against yellow fever - active immunization in epidemic outbreaks with the help of live vaccine, obtained by M. Taylor in 1936 (strain 17D). Vaccinate children from the first year of life and adults in a dose of 0.5 ml subcutaneously. Postvaccinal immunity develops 10 days after vaccination and persists for 10 years. All persons who go to and out of epidemic outbreaks are subject to mandatory vaccination. In accordance with the decision of the WHO (1989), vaccinations against yellow fever are included in the expanded program of immunization. According to WHO, in 1998-2000. Of the 1202 who fell ill with yellow fever, 446 died.