What is yellow fever? Yellow fever is a serious viral infection, similar to influenza, normally transmitted by the Aedes aegypti mosquito. It is characterized by high fever and jaundice (yellowing in the body), which is why the disease is called that way. It is considered a zoonosis, since it affects humans and some other primates. Not always those infected by the virus develop the disease, and may have weak symptoms that pass in a few days. However, those who develop the condition may suddenly have symptoms such as high fever, chills, tiredness, headache, muscle pain, nausea and vomiting. When transmitted to humans, the yellow fever virus can damage the liver and other internal organs, as well as being potentially fatal. The disease occurs mainly in areas of southern Africa and South America, affecting travelers and residents. Some studies have shown that the disease is more common in the months of December to May. As this is the rainy season, there is an increase in mosquito populations, which favors the circulation of the virus. . Yellow Fever Types Yellow fever can be divided into four types, according to the transmitting mosquito, transmission area and symptoms. In the urban area, the main transmitter of yellow fever is Aedes aegypti, the vector responsible for several other endemic diseases, such as dengue, chikungunya and zika. . 2 - Wild Yellow Fever: (FAS) In rural areas, yellow fever is transmitted by mosquitoes of the Haemagogus and Sabethes species, which are present in the forests and river borders. It is believed that cases recorded in other primates come from these mosquitoes, but humans may also be stung by them. . Acute yellow fever: At the beginning of the infection, there is the so-called acute yellow fever, whose main symptoms are fever, pain, dizziness, nausea and vomiting. This is the initial stage of the illness, which lasts for a few days. 2 - Toxic yellow fever: After passing through acute yellow fever, a small percentage of infected people develop toxic yellow fever, a type that puts the patient's life at risk. It is this stage that gives the name of the disease, as it is characterized by yellowing of the skin, renal failure and bleeding. Causes: Yellow fever is caused by a virus of the Flavivirus family, which is transmitted through the bite of mosquitoes Aedes aegypti (the same that transmits diseases like dengue, chikungunya and zika), Sabethes and those belonging to the species Haemagogus, such as Haemagogus janthinomys and the Haemagogus leucocelaenus. There is no evidence that Aedes albopictus is capable of transmitting the yellow fever virus and, to date, no representative of this species has yet been found to have been infected by the virus in the wild. However, the mosquito was susceptible to infection in the laboratory. Therefore, the proliferation of this type of mosquito is worrying, even more because of its capacity to adapt to different environments (urban, rural, among others), which can transform it into a bridge between the wild and urban transmission cycles. The incubation period of the virus is 3 to 7 days after the bite. .Transmission: The transmission of yellow fever is by the bite of an infected female mosquito.The virus can infect humans, some primates (monkeys) and several species of mosquitoes, but transmission can only be done from the bite. Transmission can be done via monkey-mosquito-person or person-mosquito-person, but never between two people or directly from monkeys to humans. .Cycle: When a mosquito bites a human or an infected monkey, the virus enters your bloodstream and circulates through it before settling in the salivary glands. By biting another monkey or human, the mosquito transmits the virus, which enters the bloodstream of the host, infecting it. Mosquitoes breed more in tropical forests, moist and semi-moist environments, as well as around standing waters. Contact between potential hosts and infected mosquitoes, particularly in areas where people do not take fever vaccines, can create small-scale epidemics. From the Wild Cycle to the Urban Cycle: Since the main mosquito that transmits wild yellow fever can not fly away and arrive in cities, the disease can only start the urban cycle when a human being goes to a forest, is bitten and infected and, when returning to the city, is stung by the Aedes aegypti, which acquires the virus and transmits it to other people. .Vector and etiological agent: The name given to the causative agent of an illness is "etiological agent". In the case of yellow fever, the etiologic agent is an arbovirus (virus transmitted by arthropods) from the same dengue virus group. It belongs to the genus Flavivirus of the Flaviviridae family. In Brazil, the main vectors of the disease are Aedes aegypti, Sabethes and those belonging to the Haemagogus species. What is the role of apes in combating yellow fever? Because it is a zoonosis, that is, a disease that affects humans and other animals, many people believe that the transmission of yellow fever occurs directly between monkeys and humans. However, this is not the truth. In March 2017, the Ministry of Health launched the campaign "The Guilt is not the Monkey", warning the population not to mistreat or kill these animals. This is because they have a very important role in fighting the disease: they are the ones that alert us when the virus is being transmitted somewhere. This is what happened in São Paulo, with the death of monkeys in the parks of the state capital. Knowing that these deaths were yellow fever, the authorities were able to take preventive measures, closing the parks to prevent anyone from being bitten by an infected mosquito. Taking into account that the transmission of yellow fever among the monkeys occurs mainly by the Haemagogus, it is unlikely that the disease will arrive in the whole city, because this species has a reduced autonomy of flight. Still, it is best to prevent mosquitoes of the species Aedes aegypti from being infected. In short, monkeys are like sentinels for this disease, since the infection of these animals near urban areas is a sign that the disease is arriving in the city. Risk groups: Some people are more likely to be infected and develop yellow fever. They are: 1 - People without a vaccine: People who have never been vaccinated or who have never come into contact with the disease may be at risk of becoming infected with the virus if they live or travel to regions where the disease is potentially active, such as South Africa or South America. Elderly people 60 years of age or older who have never taken the vaccine should consult a specialist before, as it is necessary to evaluate the cost-benefit of the medication. 2 - People with weakened immune systems Patients who are seropositive (HIV) and immunocompromised should avoid travel to places where the disease is potentially active. If there is even a need, you should consult an infectious disease doctor to evaluate the situation. Risk Factors: Some other potential factors should be considered regarding the reurbanization of yellow fever in Brazil, such as: 1 - Territorial expansion of vectors One of the major risk factors is the territorial expansion of Aedes aegypti infestation, already detected in all Brazilian states. There are many areas infested by Aedes aegypti and Aedes albopictus and are close to the circulation areas of the yellow fever virus. Many urban areas are infested by mosquitoes and are close to areas at risk for wild yellow fever, increasing the chances of spreading the disease even more. 2 - Migration: Another important factor is the intense process of migration in the rural-urban environment, leading to the possibility of importing the disease virus from wild to urban environments. 3 - Low Vaccine Coverage: There is a greater chance of being infected in areas where vaccination coverage is low and there is a large circulation of the virus.
Areas of risk: Most likely to be infected with the yellow fever virus are located in Africa, South and Central America: 1 - Africa: Most cases of yellow fever occur in sub-Saharan Africa . Some countries where the disease is most likely to be contracted are Angola, Cameroon, Congo, Côte d'Ivoire, Ethiopia, Nigeria, Kenya, Central African Republic, Democratic Republic of Congo, Rwanda, Sudan, Uganda, among others. 2 - Central America: In Central America, the island of Trinidad in Trinidad and Tobago has a high risk of yellow fever transmission. 3 - South America: In South America, the yellow fever virus is present in Bolivia, Brazil, Colombia, Ecuador, Guyana, French Guiana, Panama, Paraguay, Peru, Suriname and Venezuela. In Brazil: Not all Brazilian states have a high risk of contracting the disease. So much so that vaccination is only routinely offered in 19 states, and not all cities are immunized. The states are: 1-Acre; 2-Amazons; 3-Amapá; 4-Pará; 5-Rondônia; 6-Roraima; 7-Tocantins; 8-Federal District; 9-Goiás; 10-Mato Grosso do Sul; 11-Mato Grosso; 12-Bahia; 13-Maranhão; 14-Piauí; 15-Minas Gerais; 16-São Paulo; 17-Paraná; 18-Rio Grande do Sul; 19-Santa Catarina. Symptoms of yellow fever: The symptoms of yellow fever may take between 3 to 7 days to appear, due to the incubation period of the virus. After that, symptoms can occur in two phases: acute phase and toxic phase. Acute phase: Once the infection is in the acute stage, you may present the following symptoms: 1-Fever; 2-Headache; 3-Muscle pains, especially in the region of the back and in the knees; 4-Sensitivity to light; 5-Nausea, vomiting or both; 6-Loss of appetite; 7-Dizziness; 8-Red face, eyes or tongue. 9-Most people recover within 3 to 4 days, but some of them develop more severe symptoms. Toxic Phase: After about 2 days of remission of acute phase symptoms, about 15% of people develop the toxic phase of the disease. Thereafter, the patient's life is at risk because the mortality rate is relatively high. The symptoms of the toxic phase are: 1-Recurrent fever; 2-Abdominal pain; 3-Vomiting; 4-Jaundice (yellowing of the skin caused by damage to the liver); 5-Renal failure; 6-Bleeding from the nose, eyes or mouth; 7-Dark urine; 8-Slow heart rate; 9-Cerebral dysfunction, including delusions, seizures, and coma.
How is yellow fever diagnosed? Diagnosing yellow fever based on the initial symptoms can be difficult because it can easily be confused with other diseases such as malaria, hemorrhagic dengue, hepatitis and leptospirosis. However, in the midst of outbreaks or when there are warning signs such as the death of monkeys in the parks of São Paulo, the suspicion is quickly raised and, with this, the diagnosis is faster. To diagnose the condition, the doctor (who may be a general practitioner, travel physician, emergency physician or infectious) may inquire about travel history and ask for a blood sample. The blood test may show a reduction in the number of white blood cells that fight the infection and is a sign of the disease because the yellow fever virus affects the bone marrow. Other tests performed for the diagnosis of yellow fever are: 1-Serology by ELISA: In serology by ELISA, blood serum is analyzed for antibodies and antigens. When a person is infected with a virus, his body begins to produce antibodies specific for that virus. With this, doctors can detect the antibody specific for the virus of yellow fever, making possible the diagnosis. 2-Polymerase Chain Reaction: (PCR) Polymerase chain reaction is an assay done to identify the disease-causing microorganism. To do this, it uses the patient's blood sample and copies the DNA of the microorganism, which is multiplied several times until the virus can be identified. Yellow fever has a cure? Yes, yellow fever has a cure. A few days after the infection, the immune system itself is in charge of expelling the virus. In some cases, the disease progresses to the toxic phase, which also has a cure, but its mortality rate is high. As the immune system has a "memory", the individual who has had the disease gets immunized for the rest of their lives, because the body already has antibodies against this virus, ensuring lifetime protection. Treatment of yellow fever: There are no drugs available to destroy the virus. Therefore, the treatment consists mainly of exclusive care of a hospital. This includes fluid and oxygen supply, maintaining blood pressure, replacing blood loss, providing dialysis for kidney failure, and proper treatment for any other infections that may develop. Blood transfusion: One of the procedures to treat yellow fever is blood transfusion, especially in cases where there is excessive blood loss. Some people may receive plasma transfusions to replace blood proteins that improve coagulation. Fluids: In order to avoid dehydration, the patient should ingest plenty of fluids. However, when this is not possible because of vomiting, an intravenous solution may be given to maintain hydration. Dialysis: When the patient has renal failure, dialysis becomes necessary. This procedure consists in filtering the blood through machines, preventing toxins from accumulating in the bloodstream of the individual. Natural Remedies: Along with clinical treatment, there are some natural remedies (herbal medicine) used to relieve the symptoms of yellow fever. They are: 1-Angelicó (Aristolochia trilobata L): Helps in the control of gastric symptoms of yellow fever; 2-Passionflower (Passiflora edulis Sims): Improves symptoms by reducing fever; 3-Alfavaca, lemongrass, stone break and nettle: Considered diuretic herbs, these four help in the treatment of anuria (decreased urine production); 4-Pau bitter and Pau lieutenant: They are indicated for the disorder of the stomach, intestinal fevers, diarrhea and gases caused by the disease. Medications for yellow fever: To relieve the symptoms of yellow fever, your doctor may indicate the following medicines: 1-Paracetamol, to reduce fever and headaches; 2-Ibuprofen and nimesulide, to relieve muscle pain; 3-Cimetidine and omeprazole, to protect the stomach, avoiding gastrites, ulcers and reducing the risk of bleeding; 4-Metoclopramide, to control vomiting; 5-Aspirin (acetylsalicylic acid) should not be taken, as this medicine dissolves the blood, increasing the risk of bleeding.Attention! NEVER self-medicate or stop using a medicine without first consulting a doctor. Only he can tell which medication, dosage and duration of treatment is most appropriate for your specific case. The information contained on this site is for informational purposes only and is not intended to replace a specialist's advice or to serve as a recommendation for any type of treatment. Always follow the directions on the package leaflet and, if symptoms persist, seek medical or pharmaceutical advice. Complications: 1-Internal hemorrhages and scattered clots: As the disease progresses, various organs can bleed (bleeding). At this stage, the patient may have nosebleeds and gums. In addition, it can develop clots spread throughout the body, causing blue or green spots under the skin. 2-Multiple organ failure: Clots and lack of blood impede blood circulation, leading to multiple organ failure. The main organs affected are the kidneys, liver and heart. 3-Blood in vomit and stool: Gastrointestinal bleeding leads to blood release in vomit and feces. 4-Hepatic and renal insufficiency: With hemorrhages and clots, irrigation of blood to the liver and kidneys is impaired, which can lead to insufficiency in these two organs. 5-Hypovolemic shock: When there is a lack of blood circulating in the veins and arteries - as in the case of bleeding - the body can suffer a hypovolemic shock, ie a shock caused by the low volume of blood circulating through the blood vessels. This can cause the heart to beat faster, which causes an overload. Therefore, hypovolemic shock is a highly deadly condition that should be treated as soon as possible. 6-Jaundice: Injury to the liver can cause an increase in bilirubin levels in the blood, giving a yellowish color to the skin and the sclera (whites of the eye) of the patient. This symptom is called jaundice. Bilirubin is a pigment of biliary juice, a liver substance that helps in the digestion of fats. 7-Delusions and convulsions: When the disease causes brain damage, the patient may present with symptoms such as convulsions and delusions. 8-Coma: Due to brain damage and lack of blood supply to this organ, the patient may lose consciousness and go into a coma: a state in which he can not return to alertness, but is not yet considered a brain death. 9-Death: The mortality rate in the toxic phase is quite high. It is estimated that between 20% and 40% of the patients end up not resisting, being, for the most part, children and the elderly. How to prevent yellow fever? The prevention of yellow fever is carried out through vaccination and mosquito control. Some tips for this are: 1-Do not leave tires or containers that could accumulate water exposed to rain; 2-Put sand in the pots of plants and use water treated with bleach to water the plants; 3-Leave the roof rails uncovered so that there is no water accumulation; 4-Maintain water tanks, cisterns, barrels and capped filters; 5-Leave the bottle nozzles down; 6-Put disinfectant in the drains; 7-If you have a swimming pool in your home, clean it frequently; 8-Put your household trash in sealed plastic bags and cans with lids; 9-Use mosquito nets and screens to prevent mosquitoes from entering the house; 10-Use repellents, especially on trips or in places where the amount of mosquitoes is high; 11- If you need to travel to a place with a high incidence of the disease, take the vaccine at least 10 days before. If you are already vaccinated, there is no need for a second dose; 12-Apply sunscreen always before repellent. Otherwise, it may lose its effectiveness; 13-Avoid perfumes in areas of forest, because the sweet scent of fragrances attracts mosquitoes; 14-Do not use repellent in children under 2 months; 15-Wear long and clear clothes, avoiding to leave much exposed skin; 16-Do not apply repellent under clothing. Vaccination for yellow fever: According to the World Health Organization (WHO), vaccination is considered the main and most effective way to combat yellow fever. The yellow fever vaccine is made up of the attenuated virus and, according to the WHO, immunity is acquired within 30 days in 99% of people vaccinated.
In May 2013, WHO announced that a single dose of the vaccine warrants lifelong immunity. Therefore, the application of the booster dose is not considered necessary. However, in Brazil, the Ministry of Health chose to keep the scheme of applying two doses of the vaccine until the beginning of 2017. In April of that year, the country decided to adopt the WHO single dose recommendation. It is worth remembering that the vaccine itself has not changed. That is why anyone who has already taken the vaccine and is waiting to take the second dose, no need to worry, because it is already immunized. The vaccine is administered subcutaneously and is distributed free of charge at health clinics. Currently, in several Brazilian states, this vaccine is already part of the National Vaccination Calendar. Who should take the vaccine? Children in areas at risk from 9 months of age should receive the first dose of the yellow fever vaccine. The booster dose should be given at the age of 4. The vaccine is also indicated for all persons, whether adults or children, who live in the vicinity of areas that may have an outbreak of the disease or who wish to travel to these places, inside or outside Brazil. If you intend to travel, the first dose of the vaccine should be given 10 days in advance so that the body has time to produce the antibodies needed to fight the virus. Who should not take the vaccine? Babies younger than 6 months should not take the vaccine because they are more vulnerable to possible dose complications, including viral encephalitis. Pregnant and lactating women also should not take the vaccine as there is no evidence that the infection passes into the fetus or that the attenuated virus passes into breast milk. Immunocompromised people with HIV, malignant tumors (including leukemia and lymphomas), who use cortisone-derived drugs, are on chemo or radiotherapy, or are carriers of diseases that alter the functioning of the thymus immune system). Allergic to some vaccine substance, such as egg protein, gelatin or the antibiotic erythromycin, should avoid the vaccine. Who depends on medical advice? Adults 60 years of age or older can only take the vaccine after consulting a specialist, who will evaluate the cost-effectiveness of the medication. In this age range, the risks of adverse reactions increase. People with HIV or immunocompromised people generally should avoid travel to places where the risk of yellow fever exists, but if there is an absolute need, such patients should seek medical advice. Adverse reactions of the vaccine: The vaccine is considered to be extremely safe. A single dose provides lifetime protection, however, some adverse reactions may appear. They are: 1-Light headache; 2-Muscle pain; 3-Pain at the injection site; 4-Fatigue; 5-Low grade fever. 6-If you take the vaccine and have adverse reactions, consult your doctor. Vaccine Exemption Letters: In cases where the yellow fever vaccine is not advisable, the doctor may send a letter of exemption. The letter should be written on letterhead and contain all the practical details of why the vaccine is not recommended to that person. This letter may be accepted by some authorities responsible for immigration. Yellow fever is known to be a highly dangerous disease and, if not treated properly, can be fatal! This article will help you understand the risks of the disease and how to prevent it. Share with your friends so they also understand! Source: FM-USP
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