MOSQUITOS transmit yellow fever, a hemorrhagic and potentially lethal RNA virus that's caused an outbreak in Angola, Democratic Republic of Congo, and Uganda for the first time in 30 years.1 This vector-borne disease is spread by the Aedes and Haemagogus species of mosquito. Yellow fever has also been identified in Kenya (2 confirmed cases), and China (11 confirmed cases).2 Due to this spread to border nations through nonimmunized travelers, more than 30 million people were vaccinated.3

Angola announced the end of the outbreak at the end of 2016, and Democratic Republic of Congo followed in February 2017.2 Today, a new outbreak of the virus has begun in Brazil with over 1,300 cases and 249 confirmed deaths.4 At the peak of the outbreak in summer 2016, 47 countries declared the virus as endemic. Today, the number of countries identified as at risk for transmission has been reduced to 42; 29 of these are in Africa.5-7

Transmission and infection of yellow fever occur in largely unvaccinated populations of the tropical and subtropical areas of sub-Saharan Africa and Central and South America.8 Vaccines are recommended for those living in or traveling to countries bordering Angola, certain areas of Brazil, Bolivia, Ecuador, Peru, and many more, including Cameroon and other countries in sub-Saharan Africa.9 Angola requires all travelers over age 9 months to have proof of vaccination upon entering the country; many countries are also requiring proof of vaccination if a traveler has come from Angola, and, in some cases, the Democratic Republic of the Congo and Uganda.7 The United States doesn't require the vaccination from travelers, nor does WHO recommend it.7

Epidemiology

Spread by mosquitoes, yellow fever is related to other Flaviviridae (viruses using mammals as hosts), such as the West Nile and Zika viruses.10 Monkeys and humans serve as the primary hosts for the virus.

The female Aedes and Haemagogus mosquitoes transmit the virus via saliva entering a bite wound. In the first 3 to 4 days following an infectious bite, the virus can be spread to other mosquitoes that bite the infected host. From there, the cycle of infection continues. Yellow fever isn't directly passed from person to person.11

Clinical manifestations

Signs and symptoms of illness appear abruptly 3 to 6 days after the bite of an infected mosquito.12 Yellow fever is characterized by the following three stages: period of infection, period of remission, and period of intoxication.

First, during the period of infection, which lasts 3 to 4 days, the patient is febrile and presents with malaise, headaches, photophobia, lumbosacral pain, pain in the lower extremities, myalgia, anorexia, nausea, vomiting, restlessness, irritability, and dizziness.12

The next phase, the period of remission, can last up to 48 hours. Here, fever and other signs and symptoms typically subside. Although many patients recover after this stage, about 15% will progress to the third stage.12

Beginning on day 3 to 6 after the onset of infection, the period of intoxication is characterized by returning signs and symptoms, including fever, prostration, nausea, vomiting, epigastric pain, jaundice, oliguria, hemorrhagic diathesis, and possibly organ failure. Between 20% and 50% of patients who enter this stage die of the disease.12

Diagnosis

Yellow fever is diagnosed based on signs and symptoms, lab findings, and travel history, including possible exposure to infected mosquitoes.13

The disease can be detected using serology, viral genome by polymerase chain reaction in serum, virus isolation, or histopathology and immunocytochemistry.12 However, these diagnostic studies require highly trained lab staff and specialized equipment that aren't always available in developing countries such as Angola.14

Treatment

Care for the patient with yellow fever is mainly supportive because no specific antiviral therapy is currently available.12 Rest, fluids, analgesics, and antipyretics as early interventions may improve the patient's prognosis.15 However, medications that increase the risk of bleeding, such as aspirin and nonsteroidal anti-inflammatory drugs, should always be avoided as they may compound the disease's hemorrhagic effects.13 Additional treatment options can include supplemental oxygen, endotracheal intubation, enteral or parenteral nutrition, vasoactive medications, fresh frozen plasma, dialysis, and treatment for secondary infections if necessary.16

As patients wait for the disease to take its course, healthcare providers should attempt to isolate infected patients to prevent the spread through further mosquito bites. This will limit the number of vector-borne mosquitoes and may allow time to vaccinate the rest of the population.13

Prevention

Vaccination, given to patients age 9 months and older, is safe, affordable, and the most effective way to prevent yellow fever.5 In the United States, the yellow fever vaccine is a live, attenuated vaccine given subcutaneously.17 It provides effective immunity within 30 days for 99% of patients.5,8 Worldwide, six manufacturers of yellow fever vaccines produce about 70 to 90 million doses annually.12,18

WHO recommends a single dose for most travelers, but those who were pregnant during vaccination, had a stem cell transplant, plan to spend an extended period in endemic areas, or work regularly in labs with yellow fever samples may consider a booster immunization.12

Because the vaccine is a live attenuated virus, it's contraindicated in breastfeeding women due to the potential for transmission of vaccine virus via breastmilk. It's also contraindicated in infants under age 9 months because of the increased risk for encephalitis.17,19 Patients with a severe, life-threatening allergy to eggs, chicken protein, gelatin, or previous yellow fever vaccines shouldn't get the vaccine. Extreme caution should be taken before administering the vaccine to patients on chemotherapy, with HIV infection, or any other condition that compromises the immune system.20

The Yellow Fever Initiative in 2007 marked a global campaign aimed at eradicating the deadly disease. This joint coalition of WHO, UNICEF, and the Global Alliance for Vaccines and Immunization managed to greatly reduce the rate of infections by increasing the vaccine's stockpile.21

Nursing considerations

To prevent transmission of yellow fever via mosquito bite, teach patients that the CDC recommends using insect repellent, wearing protective clothing, and vaccination.13 Remind patients of the importance of heeding vaccination alerts when traveling. Assess patients with a history of travel or recent immigration for signs and symptoms of yellow fever such as fever, headache, myalgia, nausea, vomiting, and fatigue.

Nurses should be prepared to intervene quickly and know when further intervention is warranted for patients who may have yellow fever. Communicate assessment findings to the healthcare provider and be ready to support the patient and family, provide information, and help them cope with a potentially life-threatening situation.

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