What causes Yellow Fever?
The yellow fever virus named Flavivirus is an RNA positive virus that belongs to the family Flaviviridae. The first epidemic was reported in 1648; however, scientists believed then that the virus was not transmitted between humans. By the end of the 19th century, advances in research by Walter Reed and his team demonstrated this virus was able to spread between humans through the vector Aedes mosquitos. Since then, there have been multiple outbreaks of the yellow virus that has caused severe infections and deaths on a global scale but also in endemic areas such as South America and Africa.
The yellow fever virus is spread by Aedes or Haemagogus mosquito bites. Mosquitoes obtain the virus by feeding on primates or humans. Once the virus reaches the mosquito, it infects the cells and replicates in the salivary gland. This is then transmitted to humans once the mosquito bites and sucks the blood of the individual the virus travels in the blood.
Transmission of Yellow fever Virus
There are various ways that the virus was known to spread through mosquitos. These transmissions modes include:
- Jungle yellow fever virus: Monkeys are the primary source of the yellow fever virus, and they are bitten by mosquitoes and transmit the virus to other monkeys.
- Intermediate yellow fever virus: Mosquitoes in the wild and around living areas infect both monkeys and humans. The transmission dramatically increases due to the contact between people and mosquitoes. This type of cycle is mostly attributed to the outbreaks of yellow fever in Africa.
- Urban yellow fever virus: This cycle can cause epidemics as individuals spread the virus to other individuals in areas with a high volume of mosquitos and with little immunity and no vaccination.
Symptoms and Presentation of Yellow fever
Symptoms and clinical presentation of yellow fever are generally mild, take a minimum of 3 days to manifest after infection, and lasts between 3-5 days. These symptoms include:
- Nausea and Vomiting
Symptoms resolve within a week, and if the patient does not feel better, they should seek immediate help.
Complications from Yellow fever
The patient can enter a toxic phase that involves high fever, abdominal pain, bleeding, and liver failure.
The mortality rate for the yellow virus is around 5%, while in more severe cases, the mortality rate can increase to more than 50%. Therefore, patients should seek medical help if any of the above symptoms or complications start to manifest.
Prevention of Yellow fever
There are a few preventative measures that can be taken to reduce the risk of developing Yellow fever. These measures include:
- Use of mosquito repellent
- Get vaccinated
- Wear long-sleeved clothing to cover skin
- Avoid travel to high-risk areas
- Stay indoors
Diagnosis of Yellow fever
The diagnosis of yellow fever is commonly made based on medical and travel history. Patients need to provide physicians with a detailed history of their symptomology and whereabouts in the last two weeks.
Verification of the diagnosis cannot be made until more than six days have passed after the illness. If mild symptoms are detected, this confirmation can be made by RT-PCR or isolation of the virus and growth in culture. Moreover, another method for verification used is the detection of immunoglobins M and G, but this is not used as frequently due to the cross-reaction with other viruses from the Flavidadae family.
If severe symptoms are detected, verification can be made through a liver biopsy to detect any necrosis or inflammation.
Similar to other viruses in the family, there is no definitive cure for the yellow virus. The treatment has revolved mostly around rest, plenty of fluids, and medications such as analgesics and antipyretics to relieve symptoms. In cases of severe symptoms, patients will need to be hospitalized and admitted to the intensive care unit and monitored closely.
Fortunately, a vaccine exists against the Yellow virus since the late 1930s, and in some cases, it might be mandatory before traveling to high-risk areas. In 2006, there were more than 100 million people in West Africa who were vaccinated. However, the utilization of this vaccination is still incomplete in many areas, and many outbreaks still occur. According to the World Health Organization, one dose of the vaccine can help patients develop long-lasting immunity against the Yellow virus.
Yellow fever is a mosquito-borne illness that can manifest into a severe phase in more than 15% of the patients. Currently, there is vaccination, and patients infected should drink plenty of fluids and rest. If symptoms become severe, patients should seek immediate medical help. Mortality rates in patients with severe symptoms are over 50%. Therefore, preventive measures are vital to reduce the risk factors of developing Yellow fever. There was a strategy developed in 2017 that aims at vaccinating over 1 billion people by 2026.