In an era in which Ebola, West Nile Virus, and Dengue fever make frequent headlines, we often forget that there are other viruses that have been causing illness for a longer period of time. A prime example of this is yellow fever, a serious mosquito-transmitted illness that is endemic to Sub-Saharan Africa and South America. Yellow fever can attack multiple organs and is associated with a high mortality rate. Official reports state that approximately 78,000 people succumb to yellow fever every year; but this is thought to be a sharp underestimate as many of these cases occur in remote areas where clinical data reporting remains sparse. Since we live in a time in which international travel is commonplace, those who do visit applicable countries should be aware of this disease. Luckily, a vaccine is available, and given the viral species has not changed drastically, the original vaccine continues to be as effective for all known genetic types of yellow fever virus.
The yellow fever virus belongs to the flaviviridae family – the same group to which West Nile and Dengue belong. The transmission of disease occurs when an infected mosquito feeds on human skin. The mosquito introduces disease particles and replication ensues at whatever the location. It subsequently makes its way to the lymph nodes and bloodstream; routes through which it can access any organ system. Yellow fever has a predilection for the liver and spleen but can also attack the kidneys, heart, and central nervous system. The virus induces cell death which leads to a shock state in which there is a dangerous drop in blood flow. The clinical manifestations occur within 3-6 days of the mosquito bite and there are three recognized stages. The first is characterized by an acute infection, in which patients develop fevers, headache, fatigue, vomiting, dizziness, back pain, and muscle aches (unfortunately, these symptoms are not dissimilar to those seen in other common viral illnesses). During the second stage, patients undergo remission and they may remain symptom-free for 48 hours. The third phase is known as the intoxication period, in which patients will demonstrate fevers, vomiting, abdominal pain, jaundice (yellow discoloration of the skin from which the name derives), and gastrointestinal bleeding. The diagnosis of yellow fever is made via specialized blood tests and the treatment is mostly supportive; it typically includes intravenous fluids, blood transfusions, and dialysis if there is evidence of kidney failure.
The outcome of disease is determined during the second week, where up to 50% of patients may die. There is no antiviral treatment that can cure yellow fever, but there is a vaccine that can prevent disease. It confers nearly 100% immunity within a few short weeks after the injection. Furthermore, the vaccine is extremely safe and adverse events are rare. Still, there are some simple recommendations that should be followed by those at risk, which include: wearing long sleeve shirts and pants, limiting the time you spend outdoors during high mosquito activity, using screens to protect your lodging, and applying mosquito repellent at all times. Practicing these measures will protect you from yellow fever as well as any other serious mosquito-borne illnesses.