Yellow fever is an acute hemorrhagic transmissible disease of viral etiology. This disease has much in common with malaria. This similarity includes not only the fact that the diseases get involved in the history of human society and are similar in the area of epidemiology, but also some clinical signs. Christian Nordqvist (2009) states that “yellow fever originated in Africa and was introduced to South America via the slave trade in the 16th century. Several major yellow fever epidemics have taken place in Europe, the Americas and Africa since the 17th century. It was deemed one of the most dangerous infectious diseases in the 19th century”.
In 1881, Carlos J. Finlay presented his hypothesis that the yellow fever is transmitted by particular species of mosquitoes. Two decades later, fighting the epidemic of this disease in Havana in 1900, Walter Reed and James Carroll gave their life to confirm that yellow fever is transmitted by mosquito species Aedes. William Crawford Gorgas led a squad that destroyed outbreaks of mosquito and achieved a significant reduction in morbidity. In 1937, the American virologist Max Theiler created the yellow fever vaccine.
It was believed that the first victims of yellow fever were Europeans, who were among sailors of Christopher Columbus, who arrived in America in 1492. In subsequent years, many major yellow fever epidemics occurred in Central America, and, in 1778, the first major epidemic of this disease was registered in Africa, among British troops in Senegal.
The epidemics of yellow fever were accompanied by a large scale and high fatality. In 1802, the French colonial army in North America, numbering 32 thousand people, has lost 20 generals and 22 thousand soldiers because of yellow fever for only 2 months. A few years later, 30 thousand Spanish soldiers died because of this disease in Cuba. Until 1900, a few thousand people died of yellow fever in Cuba annually.
Yellow fever was commonplace companion of colonial wars and the slave trade. It was repeatedly fumbled in the port cities of the USA and the Mediterranean basin from the tropical regions. In 1741, in Cadiz (Spain), 10 thousand people died of yellow fever. 25 thousand people died because of this epidemic in Barcelona in 1824.
Over the past decades, the number of cases of infection of the yellow fever has increased as a result of declining of people’s immunity to disease, deforestation, urbanization, migration and changes of climate. The citizens of forty-five countries in Latin America and Africa are at the highest risk. According to Yellow Fever (2014), “the remaining population at risk are in 13 countries in Latin America, with Bolivia, Brazil, Colombia, Ecuador and Peru at greatest risk”.
There is also particular population that is at the highest risk of infection. Mark D. Gershman, and J. Erin Staples (n.d.) state that “in South America, yellow fever occurs most frequently in unimmunized young men who are exposed to mosquito vectors through their work in forested areas”. Moreover, the susceptibility to yellow fever is universal. It has long been observed that the yellow fever victims are often not locals, but those, who come from other countries. It is caused by the presence of life-long immunity in individuals, who have had yellow fever. Children are not immune and suffer much more often than adults. A passive immunity in newborn is stored for 6 months. The possibility of the disease in mild or even asymptomatic form that leads to the development of immunity occurs more frequently in children and explains significantly less morbidity and mortality from yellow fever among the locals compared to foreigners.
It was believed that Columbia would not deal with the existence of yellow fever. This part of South America was not included in the campaign for the elimination yellow fever from the world. However, in March 1923, the illness has appeared in Bucaramanga (Hanson, 1925:393).
Recently, in Colombia, the government announced the start of the epidemic of yellow fever. According to Country Information (n.d.), “there is a risk of yellow fever transmission in areas below 2,300m in the departments of: Amazonas, Antioquia, Arauca, Atlántico, Bolivar, Boyacá, Caldas, Caquetá, Casanare, Cauca, Cesar, Córdoba, Cundinamarca, Guainía, Guaviare, Huila, Magdalena, Meta, Norte de Santander, Putumayo, Quindio, Riasaralda, Santander, Sucre, Tolima, Vaupés, and Vichada”. Now, the country is carrying out mass vaccination. Vaccines are given not only locals, but also to all tourists, who arrive in the country. The World Health Organization recorded the first victims. Four people died in the clinic of Colombian capital Bogota.
The yellow fever’s main vectors are mosquitoes. They carry viruses between hosts, mainly among monkeys: monkeys transfer it to humans. Then, it spreads between people. The virus is transferred by several different species of mosquitoes of Aedes and Haemogogus. Mosquitoes breed near dwellings (domestic) in the wild jungle, or in both peri-domestic habitats. There are three types of transmission cycles:
- Forest yellow fever. Monkeys become infected with wild mosquitoes. The infected monkeys transfer the virus to mosquitoes that are feeding on their blood. Infected mosquitoes bite people, who come into the woods that lead to individual cases of yellow fever. Most infections occur among young people working in the forest.
- Intermediate yellow fever. Peri-domestic mosquitoes infect both humans and monkeys. An increased contact between infected mosquitoes and people leads to further transmission. The outbreak of the disease can take the form of more severe epidemic, when the infection gets into the area inhabited by both unimmunized people and domestic mosquitoes.
- Urban yellow fever. The largest epidemics begin, when infected people submit the virus into populated areas, which have a large number of non-immunized people and Aedes mosquitoes. Then infected mosquitoes are transmitting the virus from one person to another.
Temperature factor can change the properties of the yellow fever virus in the body of its carrier. The virus in mosquitoes at 16 ° loses its ability to cause fatal disease in experimental animals and ensures the development immunity to infection with active virus.
After the infection of yellow fever, the incubation period of the virus begins, lasting from three to six days. Thereafter, disease manifests. It may occur in several stages. At first, acute stage, the temperature rises; muscle pain appears, particularly strong in the lumbar region; headache, loss of appetite, chills, nausea or vomiting occur. In most patients, the condition improves and symptoms disappear within 3-4 days. 15% of patients experience more toxic stage. The temperature rises again, resulting in affecting body systems. The jaundice begins to develop rapidly. There may be bleeding from the nose, mouth, eyes or stomach. The renal functioning is deteriorating. There is a high possibility of mortality.
It is very difficult to diagnose yellow fever, especially in the early stage of the disease. The disease can be confused with other infections: leptospirosis, dengue hemorrhagic fever, severe malaria, viral hepatitis (especially fulminant form of hepatitis D and B), etc. The antibodies to yellow fever can be detected with the help of blood tests.
With the discovering of the pathogen of the yellow fever and its vectors and after the development of an effective vaccine, medicine has effective means to combat yellow fever. However, it is impossible to handle the morbidity. Yellow fever epidemic continues to be observed in a number of countries.
A special treat for yellow fever does not exist. Only symptomatic treatment can be carried out in order to prevent dehydration and reduce the temperature. Symptomatic therapy can improve outcomes for critically ill patients. However, in poor areas, such treatment is rarely available.
The pathogenesis of the disease shows that during the first three days of disease, the virus manages to infiltrate the cells of the internal organs and begins to damage them. It is very difficult to intercept and destroy viruses on their way to the cells in such a short time. As the virus has already penetrated into the cells, the antibodies are not able to act. Therefore, the use of immune serum does not give the desired effect. The chemotherapeutic agents and antibiotics that suppress the essential activity of yellow fever virus do not exist. The process of cell’s protection of non-immune body occurs due to the development of interferon. Therefore, the treatment of the patients with yellow fever is focused on pathogenic treatment. It includes the detoxification therapy performed by intravenous administration of gemodeza, glucose, alkaline solution of sodium hydrogen carbonate. The anti-bleeding drugs, vitamins C and E, transfusion of small amounts of blood can be applied too. An easily digestible diet with restriction of salt, protein and excess fat due to the exception of the liver and kidneys is assigned. The cardiovascular drugs are used in the acute phase. In the acute stage, patients require especially careful monitoring and care.
Vaccination is the important measure for providing the prevention of the disease. To prevent epidemics in areas, which are at the risk, with low vaccination coverage, vaccinations are necessary for rapid detection and providing control of outbreaks. To prevent disease’s outbreaks in the affected areas, the coverage of vaccination should be at least 60 % -80 % of the population at risk. Vaccination can be offered as part of routine immunization of children and disposable campaigns of mass vaccination in order to expand people’s coverage in countries at high risk and immunizing persons, who are traveling to these areas.
Yellow fever vaccine is affordable and safe. For 95% of vaccinated people, it ensures effective immunity in a week. One dose of the vaccine gives protection against the disease for 30-35 years or more, and possibly for life. There is a little possibility of serious side effects. Risk of death from this infection is much higher than risks, which are associated with its vaccination. However, some groups should not be vaccinated. They include children under the age of nine months, pregnant women, people with severe immunodeficiency, etc.
Persons, who travel to Latin America countries, must have a certificate of vaccination against yellow fever. Under the International Health Regulations, exemption from vaccination on medical indications must be certified by the relevant authorities.
In some cases, until the vaccine will not start acting, it is necessary to provide mosquito control. The risk of transmission of yellow fever in populated urban areas can be reduced by providing of elimination of potential sites of mosquito breeding. The Latin American experience showed that the yellow fever was managed to be completely eliminated in seven countries in 15 years. However, this struggle must be conducted for many years
A rapid detection of the yellow fever and quick response to it through campaigns of emergency vaccination has a significant importance for dealing with outbreaks of the disease.