What is Yellow Fever?
Yellow fever (fievre jaune, fiebre amarilla, vomito negro, febris flava) is an acute obligate-transmissible disease with natural foci from the group of viral hemorrhagic fevers. Treats especially dangerous infections. Characterized by a severe course with high fever, damage to the liver and kidneys, jaundice, bleeding from the gastrointestinal tract. For the first time the clinical picture of yellow fever was described during an outbreak in America in 1648. In the XVII-XIX centuries, numerous epidemics were recorded in Africa and South America, and outbreaks of the disease in southern Europe. The transmissible route of infection through mosquitoes Aedes aegypti was established by C. Finlay (1881), its viral etiology by W. Reed and D. Carroll (1901). The natural foci of the disease, the role of monkeys in the circulation of the pathogen in the foci has been established by studies of Stokes (1928) and Souper et al. (1933). In 1936, Lloyd et al. have developed an effective yellow fever vaccine.
Causes of Yellow Fever
The causative agent of yellow fever is the RNA-genomic virus Viscerophilus tropicus of the genus Flavivirus of the Flaviviridae family. The diameter of the virus particles – 17-25 nm. It is antigenically related to Japanese encephalitis and dengue viruses. Pathogenic for monkeys, white mice and guinea pigs. It is cultivated in the developing chicken embryo and tissue cultures. For a long time (more than a year) it is kept frozen and when dried, but at 60 ° C it is inactivated for 10 minutes. Dies quickly under the influence of ultraviolet rays, ether, chlorine-containing drugs in normal concentrations. Low pH values affect him destructively.
Populations at risk of yellow fever
A population of 45 endemic countries in Africa and Latin America, totaling more than 900 million people, is at risk. In Africa, an estimated 508 million people live in 32 countries at risk. The remaining population at risk resides in 13 countries in Latin America, of which Bolivia, Brazil, Colombia, Peru and Ecuador are most at risk. An estimated 200,000 cases of yellow fever occur annually in the world (30,000 of which are fatal). A small number of imported cases occur in countries free of yellow fever. Although this disease has never been imported into Asia, this region is at risk, as there are conditions necessary for the transmission of infection. The reservoir and sources of infection are various animals (monkeys, marsupials, hedgehogs, possibly rodents, etc.). In the absence of a carrier, a sick person is not dangerous to others. The transmission mechanism is transmissive. Mosquito vectors of the genera Naetagogus (in the Americas) and Aedes, especially A. aegypti (in Africa), which are closely related to human habitation. Carriers multiply in ornamental reservoirs, barrels of water, and other temporary reservoirs of water. Often attack a person. Mosquitoes become infectious after 9–12 days after blood sucking at ambient temperatures of up to 25 ° C and after 4 days at 37 ° C. At temperatures below 18 ° C, the mosquito loses its ability to transmit the virus. If contaminated blood gets on damaged skin and mucous membrane, a contact route of infection is possible. The natural susceptibility of people is high, long-term post-infectious immunity.
Major epidemiological signs.
Yellow fever is classified as a quarantine disease (a particularly dangerous disease) subject to international registration. The greatest incidence is recorded in tropical areas, but outbreaks of this disease are noted almost everywhere where there are carriers of the virus. The spread of the virus from endemic areas can be realized both through sick persons and with mosquitoes during the transportation of goods. There are two types of foci: natural (jungle) and urban (anthropurgic). The latter are more often manifested in the form of epidemics; while the sources of infection are patients during the period of viremia. In recent years, yellow fever becomes more urban disease and acquires the features of anthroponosis (transmission is carried out along the chain “man – mosquito – man”). If there are conditions for the spread of the pathogen (virus carriers, a large number of carriers and susceptible persons), yellow fever can take on an epidemic character.
Pathogenesis during Yellow Fever
Reproduction of a virus that has entered the body through a mosquito bite occurs in the regional lymph nodes during the incubation period. During the first few days of illness, the virus with the bloodstream disseminates throughout the body, causing damage to the vascular apparatus of the liver, kidney, spleen, bone marrow, myocardium, brain and other organs. They develop pronounced dystrophic, necrobiotic, hemorrhagic and inflammatory changes. Characterized by multiple hemorrhages in the digestive tract organs, pleura and lungs, as well as perivascular infiltrates in the brain.
Yellow Fever Symptoms
There are three options for yellow fever in humans. These are jungle fever (rural type), urban fever and intermediate type.
Rural variant (yellow jungle fever). In tropical forests (jungle), yellow fever occurs in monkeys infected with wild mosquito bites. Infected monkeys can spread the infection by transmitting it to healthy mosquitoes. Infected “wild” mosquitoes with a bite transmit the virus to people in the forest. This chain leads to isolated cases of infection mainly in young people working in logging, without leading to epidemics and major outbreaks. Infection can also spread between infected people.
Intermediate infection occurs in humid or semi-humid African savannas, is the dominant form of infection in the continent. There are limited epidemics that are different from the urban variant of the infection. “Semi-domestic” mosquitoes infect both animals and humans. With such epidemics, several villages can be affected at the same time, however, the mortality rate in this variant of yellow fever is lower than in urban areas.
The urban variant of the infection is accompanied by large-scale epidemics that are caused by the influx of migrants into urbanized regions characterized by high population density. “Domestic mosquitoes” (Aedes aegypti species) carry the virus from person to person, monkeys do not participate in the epidemic chain of disease transmission.
The incubation period lasts about a week, occasionally up to 10 days. In typical cases, the disease goes through several stages.
Phase hyperemia. Acute onset of the disease is manifested by a rapid increase in body temperature of more than 38 ° C with chills, headache, myalgia, pain in the back muscles, nausea and vomiting, agitation and delusions. In the dynamics of this phase of the disease, these symptoms persist and increase. On examination, patients noted hyperemia and puffiness of the face, neck, shoulder girdle, vivid hyperemia of the vessels of the sclera and conjunctiva, photophobia, lacrimation. Very characteristic hyperemia of the tongue and oral mucosa. Severe tachycardia persists in severe disease or is quickly replaced by bradycardia, initial hypertension – hypotension. Slightly increase the size of the liver, less spleen. There oliguria, albuminuria, leukopenia. Appear cyanosis, petechiae, develop symptoms of bleeding. At the end of the phase, icteric sclera can be noted. The duration of the phase of hyperemia is 3-4 days.
Short-term remission. Lasts from several hours to 1-2 days. At this time, the body temperature usually decreases (up to normal values), the state of health and the condition of patients somewhat improve. In some cases, with light and abortive forms, further recovery gradually occurs. However, more often after a short-term remission, high fever reappears, which can last up to 8–10 days, counting from the onset of the disease. In severe cases, remission is replaced by a period of venous stasis. During this period, viremia is absent, however, fever persists, pallor and cyanosis of the skin, jaundice staining of sclera, conjunctiva and soft palate are noted. The patient’s condition worsens, cyanosis, like jaundice, progresses rapidly. There are common petechiae, purpura, ecchymosis. Hepatolienal syndrome is expressed. Characterized by vomiting blood, melena, bleeding gums, organ bleeding. Develop oliguria or anuria, azotemia. Infectious and toxic shock, encephalitis are possible. Infectious-toxic shock, kidney and liver failure lead to the death of patients on the 7-9th day of illness.
Complications of infection can be pneumonia, myocarditis, soft tissue or limb gangrene, sepsis as a result of the layering of secondary bacterial infection. In cases of recovery, a long period of recovery occurs. Post-infectious immunity for life.
Diagnosing Yellow Fever
In Ukraine, yellow fever can occur only in the form of imported cases. In clinical differential diagnosis, attention is paid to the successive change of the main two phases in the development of the disease — hyperemia and venous stasis — with a possible short remission period between them.
In the initial stage of the disease, leukopenia with a sharp left shift, neutropenia, thrombocytopenia, leukocytosis in the midst, progressive thrombocytopenia, and elevated hematocrit, nitrogen and potassium are characteristic. The amount of protein in the urine increases, erythrocytes, cylinders appear. Note hyperbilirubinemia, high activity of aminotransferases (mainly ACT). In the conditions of specialized laboratories, the virus can be released from the blood in the initial period, using biological diagnostic methods (infection of the newborn mice). Antibodies to the virus is determined using the phaemogram, RSK, RNIF, the reaction of inhibition of indirect hemagglutination, ELISA.
Yellow Fever Treatment
Treatment of yellow fever is carried out according to the same principles as hemorrhagic fever with renal syndrome, in conditions of infectious diseases for work with especially dangerous infections. Etiotropic therapy is not developed. The blood plasma of convalescents, used in the first days of the disease, gives a weak therapeutic effect. Forecast: the mortality rate of the disease ranges from 5% -10% to 15-20%, and during epidemic outbreaks – up to 50-60%.
Prevention of Yellow Fever
Preventive measures are aimed at preventing the introduction of the pathogen from abroad and are based on compliance with the International Health Regulations and Rules for the sanitary protection of the territory. They carry out the destruction of mosquitoes and their breeding sites, the protection of the premises from them and the use of personal protective equipment. In the foci of infection, specific immunization is carried out with live attenuated vaccine. It is administered to individuals of all ages subcutaneously in a volume of 0.5 ml. Immunity develops within one week in 95% of the vaccinated. Immunity develops in 7-10 days and lasts for at least 10 years. Vaccinations of children and adults are carried out before going to endemic areas (South Africa), where the disease in the new arrivals is very difficult and high mortality.
Immunization against yellow fever is recommended:
- to persons traveling on a business or leisure trip (even for a short time), or living in a region endemic for this disease,
- to unvaccinated persons departing from an endemic to a non-endemic region. In accordance with the established rules, a mark of vaccination against yellow fever must be affixed to the International Certificate, as well as signed and approved by the accredited center for the prevention of yellow fever. This vaccination certificate is valid for 10 years, starting from the 10th day after the date of vaccination.
- to persons at risk of infection due to their professional duties, to HIV-infected persons in the asymptomatic stage. In accordance with established rules, a yellow fever vaccination mark must be affixed to the International Certificate, and signed and approved at an accredited yellow fever vaccine prevention center. This vaccination certificate is valid for 10 years, starting from the 10th day after the date of vaccination.
Contraindications to yellow fever vaccination
General contraindications to yellow fever vaccine prevention are similar to those of any vaccination: – infectious diseases in the active stage, – progressive malignant diseases, – current immunosuppressive therapy. Specific contraindications: – documented allergy to egg proteins, – acquired or congenital immunodeficiency. Pregnant women and children under 6 months of age are not recommended to vaccinate. However, in case of an epidemic, pregnant women and babies, from the age of 4 months, can be vaccinated. In difficult cases, you should consult with your doctor.
Cautions for yellow fever vaccination
In individuals with allergic diseases, a test is shown to assess the sensitivity to the drug by intradermal administration of 0.1 ml of the vaccine. In the absence of reactions within 10 to 15 minutes, the remaining 0.4 ml of the vaccine should be injected subcutaneously. – In special cases, it may be decided to vaccinate patients receiving immunosuppressive therapy. It is most correct not to carry out vaccination before the expiration of 1 month after the end of such therapy and, in any case, one should make sure that biological indicators are within the normal range. – In difficult cases, you should consult a doctor.
Sometimes, 4-7 days after vaccination, there may be general reactions – headache, malaise, a slight increase in body temperature.
Activities in the epidemic focus
Patients are hospitalized in the infectious disease ward. If a patient is identified on a ship during a voyage, he is isolated in a separate cabin. Disinfection in the outbreak is not carried out. Any vehicle arriving from countries unfavorable for yellow fever should be aware of the disinsection carried out. Unvaccinated persons who come from endemic areas are subject to isolation with medical supervision for 9 days. When an outbreak of yellow fever occurs, immediately begin a mass immunization of the population.
List of countries requiring an international certificate of vaccination against yellow fever. 1. Benin 2. Burkina Faso 3. Gabon 4. Ghana 5. Democratic Republic of the Congo 6. Cameroon 7. Congo 8. Côte d’Ivoire 9. Liberia 10. Mauritania 11. Mali 12. Niger 13. Peru (only when visiting jungle areas) 14. Rwanda 15. Sao Tome and Principe 16. Togo 17. French Guiana 18. Central African Republic 19. Bolivia
The list of countries with endemic areas for this infection, upon entry into which it is recommended to have an international certificate of vaccination against yellow fever: South American countries 1. Venezuela 2. Bolivia 3. Brazil 4. Guyana 5. Colombia 6. Panama 7. Suriname 8. Ecuador African countries 1. Angola 2. Burundi 3. Gambia 4. Guinea 5. Guinea-Bissau 6. Zambia 7. Kenya 8. Nigeria 9. Senegal 10. Somalia 11. Sudan 12. Sierra Leone 13. Tanzania 14. Uganda 15 Chad 16. Equatorial Guinea 17. Ethiopia