Yellow Fever
Yellow fever is an acute viral hemorrhagic disease transmitted by infected mosquitoes. The term "yellow" refers to the jaundice presented by some patients.
Symptoms include fever, headache, jaundice, jaundice, myalgia, nausea, vomiting and fatigue.
In a small proportion of cases, patients who contract the disease develop severe symptoms and about half of them die within 7 to 10 days.
The virus is endemic in the tropical regions of Africa, Central and South America.
Large epidemics of yellow fever occur when infected individuals introduce the virus into densely populated areas with high mosquito densities and where most people have little or no immunity due to inadequate vaccination. Under these conditions, infected mosquitoes spread the virus from person to person.
Prevention of yellow fever is possible with an extremely effective, safe and inexpensive vaccine. A single dose of the vaccine provides long-lasting immunity and lifelong protection against the disease, without the need for a booster dose. The vaccine confers effective immunity within 30 days for 99% of those vaccinated.
Good symptomatic treatment in the hospital setting improves survival rates. There are currently no specific antiviral drugs available for yellow fever.
The "Eliminate Yellow fever Epidemics" (EYE) strategy launched in 2017 is an unprecedented initiative. With the participation of more than 50 partners, the EYE partnership assists 40 at-risk countries in Africa and the Americas in the prevention, diagnosis and response to suspected cases and outbreaks of yellow fever. By 2026, more than one billion people are expected to be protected against the disease.
Signs and symptoms
Once infected with the yellow fever virus, the incubation period in the body lasts from 3 to 6 days. Infection remains asymptomatic in many people, but when symptoms do appear, the most common are fever, myalgia, with back pain, headache, loss of appetite, nausea or vomiting being the most common. In most cases, symptoms disappear after 3 to 4 days.
In a small proportion of cases, however, patients enter a second, more toxic phase within 24 hours of the initial remission. A high fever returns and several organ systems are affected, usually the liver and kidneys.
In this phase, jaundice often appears (yellowing of the skin and eyes, hence the name "yellow fever"), with dark urine and abdominal pain accompanied by vomiting. Bleeding may occur in the mouth, nose, eyes or stomach. Half of the patients with this toxic phase die within 7 to 10 days.
Diagnosis
Yellow fever is difficult to diagnose, especially in the early stages. In its more severe form, it can be confused with severe malaria, leptospirosis, viral hepatitis (especially the fulminant forms), other hemorrhagic fevers, other flavivirus diseases (such as hemorrhagic dengue fever) or intoxication.
Blood tests (RT-PCR) can sometimes detect the virus at an early stage of the disease. At later stages, tests to identify antibodies (ELISA and PRNT) are required.
Populations at risk
Yellow fever is endemic throughout or in parts of 47 countries in Africa (34 countries) and Latin America (13 countries). Modeling based on African data sources has estimated the burden of disease attributable to this disease in 2013: there were 84,000-170,000 severe cases and 29,000-60,000 deaths.
Occasional travelers to endemic countries may report the disease to countries where yellow fever does not occur. To avoid such importations, many countries require a certificate of yellow fever vaccination before issuing visas, particularly if travelers come from or have visited endemic areas.
In past centuries (17th to 19th centuries), yellow fever was brought to North America and Europe and caused major epidemics that disrupted economies, development and, in some cases, decimated populations.
Transmission
Yellow fever virus is an arbovirus belonging to the genus Flavivirus and is transmitted by certain species of mosquitoes of the genera Aedes and Haemogogus. These species live in different habitats, some breed around houses (domestic), some in the jungle (wild) and some in both types of habitats (semi-domestic). There are 3 types of transmission cycles:
Selvatic yellow fever (in the jungle): in tropical rainforests, monkeys, the main reservoir of the disease, are bitten by wild mosquitoes of the genera Aedes and Haemogogus, which transmit the virus to other monkeys. Occasionally, humans working or traveling in the forest are bitten by the infected mosquitoes and develop yellow fever.
Intermediate (or rural) yellow fever: in this type of transmission, semi-domestic mosquitoes (those that breed both in the wild and around homes) infect monkeys and humans. The increased contact between humans and infected mosquitoes leads to increased transmission, and many isolated villages in the same area may experience simultaneous outbreaks. This is the most common type of outbreak in Africa.
Urban Yellow Fever: Large epidemics occur when infected individuals introduce the virus into densely populated areas with high densities of Aedes Egypti mosquitoes where most people have little or no immunity due to inadequate vaccination or have not been exposed to yellow fever. Under these conditions, infected mosquitoes transmit the virus from person to person.
0 Commentaires