Yellow fever

Tourists planning a trip to Africa often experience anxiety regarding yellow fever. What are the causes and the severity of this disease? Is there a vaccine, and how can it be prevented? Additionally, is yellow fever present only in Africa or other parts of the world too? This article provides you with all the essential information regarding yellow fever.

Yellow fever is an acute viral illness prevalent in some African and South American countries. The yellow fever virus is transmitted through the bites of a specific species of mosquito that has been infected with the virus. The disease is named yellow fever because it can lead to jaundice, which causes yellowing of the skin, but this is rare. While yellow fever can be frightening, it is uncommon for travelers to contract the illness. Yellow fever mainly affects people in countries where it is endemic, with 90% of cases occurring in West and Central Africa, south of the Sahara. According to the World Health Organization (WHO), there are 47 countries where yellow fever is endemic. The regional distribution of the disease is attributed to the source of the virus, which is carried by mosquitoes. Specifically, the Aedes aegypti species, known as yellow-fever mosquitoes due to their white dots and stripes, is a primary carrier of the virus. These mosquitoes transmit over 50 types of viruses and several parasites that are harmful to animals. In South and Central America, the Haemagogus genus of mosquitoes can also transmit yellow fever.

Yellow-fever mosquitoes, originally from Africa, were introduced to South and Central America during the slave trade period. Although there is a similar mosquito species in Asia, it is not a transmitter of yellow fever. Concerningly, due to global warming, vector mosquitoes are expanding their habitats, and these insects have already been sighted in the United States, Turkey, and the south of France. This is yet another negative consequence of climate change. Since 2017, the "Eliminate Yellow Fever Epidemics (EYE) Strategy" has been implemented worldwide. This effort is coordinated by the World Health Organization, the United Nations Children's Fund (UNICEF), and the Global Alliance for Vaccines and Immunization. The EYE Strategy involves forty countries that monitor yellow fever cases and respond to outbreaks promptly to prevent the disease from spreading globally.

To detect yellow fever promptly, early diagnosis is crucial. However, diagnosing this disease is not straightforward. The majority of people who are bitten by infected mosquitoes do not experience any noticeable symptoms and recover quickly without complications. It is worth noting that individuals who have previously contracted yellow fever acquire lifelong immunity to the disease. Yellow fever can also present with more noticeable symptoms, although it typically starts with mild manifestations, which complicates diagnosis.

When symptoms appear, it typically happens within three to six days after contact with the virus. The initial symptoms of yellow fever include fever, headache, back pain, general muscle pain throughout the body, weakness, rapid fatigue, loss of appetite, and in some cases, nausea and vomiting may appear. The general nature of these symptoms makes it difficult to determine the cause. Occasionally, a blood test can identify yellow fever, but in most cases, it is unnecessary because the disease subsides on its own. Typically, a person completely recovers within a week or even faster, within 3-4 days. However, in some cases, the process can drag on, and a feeling of fatigue may persist for several more months before the body ultimately triumphs over the virus. Yellow fever is deceptive because a small proportion of infected individuals feel like they are recovering on the first day, and all initial symptoms appear to be improving. However, a sharp deterioration may follow.

Yellow fever is a disease that can strike suddenly and severely. In approximately 15% of cases, patients experience mild symptoms that disappear, only to be replaced by a full-blown attack. Symptoms of the severe stage include a sharp rise in temperature, abdominal pain, and jaundice, which causes the skin and whites of the eyes to turn yellow. The liver and kidneys are often affected, as evidenced by darkened urine. However, the most alarming consequence of the disease is internal bleeding. This is indicated by bleeding from the head orifices, such as the mouth, nose, eyes, or ears, as well as the presence of blood in the feces. The body's organ systems go into shock, and many patients are unable to recover. According to the U.S. Centers for Disease Control and Prevention, 30% to 60% of individuals who progress to the severe stage of yellow fever do not survive.

Viscerophilus tropicus is a virus that causes a tropical disease. It belongs to a group of 53 flaviviruses that affect birds and mammals, including humans. All flaviviruses are spread by either mosquitoes or ticks. Despite causing a variety of diseases worldwide, flaviviruses were named after yellow fever due to its prominent yellowing symptom - flavus, a Latin word, means "yellow." The virus is present in primate populations, including humans. To transmit the virus from one human to another, mosquitoes act as vectors. Aedes aegypti is the most common species that carries the virus, but other species, such as Aedes africanus and several species indigenous to South America, such as Haemagogus and Sabethes, also play a role in transmission. These species pose a danger to non-human primates.

The yellow fever virus is primarily carried by the female Aedes aegypti mosquito. When they bite an infected person or monkey, they contract the virus and pass it on to their next host through their saliva. The virus can also be transmitted to the mosquito larvae, causing them to become carriers from birth. It is important to note that the virus cannot be directly transmitted from person to person or between monkeys and humans. Therefore, there is no need to fear individuals carrying the disease. The yellow fever virus has three transmission cycles, classified as jungle (sylvatic), intermediate (savannah), and urban based on the type of environment in which it spreads. In the jungle cycle, the virus is transmitted between monkeys living in humid rainforests. People can become infected while working in the jungle. This mode of transmission is the only one in South America, which accounts for only 10% of yellow fever cases worldwide.

Yellow fever cases have been recently recorded in the Atlantic Forest ecoregion of Brazil in South America. Urban yellow fever begins when individuals who have been infected in the jungle area travel to cities with high population densities. Mosquitoes of the Aedes and Haemagogus genera can quickly transmit the virus from infected humans to other people, resulting in yellow fever outbreaks in Africa. Savannah yellow fever, also known as intermediate yellow fever, is the most common cycle found on the same continent. People and monkeys in rural areas often come into contact with infected mosquitoes that breed in the wild and near homes. Interestingly, people inadvertently contribute to the breeding of mosquitoes near their homes, increasing the risk of pathogen transmission. Mosquitoes prefer stagnant water, where female mosquitoes lay their larvae. To minimize the risk of mosquito breeding, water should either be flowing or periodically changed. Any bodies of stagnant water, natural or artificial, can be dangerous, including water containers and objects such as cans, tires, and other household waste where rainwater can accumulate.

West and Central Africa are the regions primarily at risk for yellow fever, and due to a lack of high-quality statistics in some countries, there is no accurate data on the prevalence of the disease. WHO staff use simulations to estimate the number of people affected, and in 2013, it was estimated that 84,000-170,000 Africans could have been diagnosed with severe yellow fever, with 29,000-60,000 deaths. Countries at high risk of infection include Cape Verde, Senegal, Guinea-Bissau, Gambia, Guinea, Sierra Leone, Liberia, Ivory Coast, Burkina Faso, Ghana, Togo, Benin, Nigeria, Cameroon, Equatorial Guinea, Gabon, Republic of Congo, Democratic Republic of Congo, Sao Tome and Principe, Angola, Central African Republic, South Sudan, Uganda, and Burundi. Some countries have areas with a risk of infection, including Mauritania, Mali, Niger, Chad, Sudan, Ethiopia, and Kenya. The U.S. CDC recommends getting vaccinated against yellow fever before traveling to any of these countries.

There are several neighboring countries in which yellow fever is not present, and their health ministries are taking measures to prevent the occurrence of the disease. These measures include requiring vaccination certificates at entry from citizens of endemic countries and tourists who have transited through them for an extended period. If you are flying directly into these countries, there is no recommendation for vaccination. The countries that fall under this category are Eritrea, Djibouti, Somalia, Rwanda, Tanzania, and Zambia. In South America and its surrounding regions, the risk group includes residents of Panama, Colombia, Ecuador, Peru, Bolivia, Paraguay, Argentina, Brazil, Venezuela, Trinidad and Tobago, Guyana, Suriname, and French Guiana. Vaccination is recommended for travelers visiting any of these countries. However, it is essential to note that not all regions of these countries are infested with infectious mosquitoes. For instance, in Argentina, the risk of infection is only present in a small region in the north of the country.

Regrettably, there are currently no known remedies for illnesses stemming from flaviviruses, including yellow fever, tick-borne encephalitis, Japanese encephalitis, dengue fever, and West Nile fever. Medical treatments or drugs against the virus do not exist. In the event of disease progression, patients may be admitted to the hospital. Physicians will provide symptomatic care to assist the body in combatting the virus. Interventions can be beneficial in managing symptoms such as fever, dehydration, liver and kidney damage, and severe pain. Those affected by yellow fever are advised to rest and drink ample fluids. Prevention is considered the most effective way to avoid yellow fever.

Getting vaccinated against yellow fever is the most effective method to ensure your safety. The vaccine, developed in 1937 from a weakened strain of the virus, is regarded as safe, causing only minor side effects. Additionally, it is widely available and affordable.

Both the WHO and the U.S. CDC consider preventative measures to be very effective Taking measures against mosquito-borne illnesses is straightforward for individuals traveling to areas where there is a risk of infection. Prevention measures include:

• Use of insect repellents.
• Wearing pants and clothing with long sleeves.
• Staying in hotels with nets on windows or with air conditioning.
• Using mosquito nets over the bed while sleeping

In summary, here are the top 10 key points to know about this tropical disease.

• Yellow fever is caused by a virus that is transmitted by infected female mosquitoes of certain species. This disease can affect humans and other primates, but it cannot be transmitted from person to person.
• The yellow fever vaccine is a single shot that provides lifelong protection. It is administered in the shoulder, and immunity develops within 10 days.
• Yellow fever is primarily found in certain countries in Africa and South America.
• Most people infected with yellow fever do not experience serious complications, and they typically recover within a few days.
• The initial symptoms of yellow fever include fever, headache, muscle pain, loss of appetite, vomiting, and weakness. These symptoms usually appear 3 to 6 days after infection.
• Serious symptoms of yellow fever include jaundice, bleeding from the nose, mouth, eyes, or ears, vomiting blood, and blood in the stool. These symptoms occur in about 15% of cases, and up to half of those with severe symptoms die within a week.
• Prevention measures for yellow fever include vaccination, vector control (eliminating dangerous mosquito species through government programs), and self-protection (using repellents, nets on windows, mosquito nets over beds, and wearing clothing that covers the arms and legs).
• Residents of 47 countries in Africa, South America, and Central America are at risk for yellow fever.
• If you are traveling to a country with yellow fever, neighboring countries may require a certificate of vaccination.
• Travelers from non-endemic countries are at low risk for contracting yellow fever.