Nigeria is a high-risk country for yellow fever (YF). The re-emergence of yellow fever in September 2017 in Nigeria has been marked by outbreaks over a wide geographical area. The yellow fever outbreaks reported in Bauchi, Benue, and Katsina states from August to November 2019, with spread to multiple other states showed an expansion of YF transmission, and an elevated risk for YF outbreaks to rapidly spread and amplify, impacting areas without prior reported cases since 2017 and in areas with large under-immunized populations.

This year, suspected YF cases have been reported from all 36 states and the Federal Capital Territory (FCT) and confirmed YF cases across 9 states (Delta, Enugu, Bauchi, Benue, Kogi, Oyo, Edo Kwara and Katsina)

What is Yellow Fever?

Yellow fever is a serious, potentially deadly flu-like disease spread by mosquitoes. It is characterized by a high fever and jaundice. Jaundice is the yellowing of the skin and eyes, which is why this disease is called yellow fever

Causes

Yellow fever is caused by the Flavivirus and transmitted when a person is bitten by an infected mosquito. Mosquitoes become infected with the virus when they bite an infected human or monkey. The disease cannot be spread from one person to another.

Signs & Symptoms

Once contracted, the initial symptoms of the infection include fever, muscle pain with prominent backache, headache, loss of appetite, and nausea or vomiting. In most cases, symptoms disappear after 3 to 4 days.

However, a small percentage of patients, enter a second, more toxic phase within 24 hours of recovering from initial symptoms. This stage is characterized by decreased urination, abdominal pain, vomiting (sometimes with blood), heart rhythm problems, seizures, delirium, bleeding from the nose, mouth, and eyes. Half of the patients who enter the toxic phase die within 7 – 10 days.

Treatment

There is no specific treatment, although the disease is preventable using a single dose of yellow fever vaccine which provides immunity for life. Supportive care to treat dehydration, respiratory failure and fever and antibiotic treatment for associated bacterial infections can reduce mortality.

Diagnosis

Polymerase chain reaction (PCR) testing in blood and urine can sometimes detect the virus in early stages of the disease. In later stages, testing to identify antibodies is needed (ELISA and PRNT).

Prevention

1. Vaccination: Vaccination is the most important means of preventing yellow fever.

The yellow fever vaccine is safe, affordable and a single dose provides life-long protection against yellow fever disease. People who are usually excluded from vaccination include:

  • infants aged less than 9 months;
  • pregnant women – except during a yellow fever outbreak when the risk of infection is high;
  • people with severe allergies to egg protein; and
  • people with severe immunodeficiency due to symptomatic HIV/AIDS or other causes, or who have a thymus disorder.

2. Vector control: The risk of yellow fever transmission in urban areas can be reduced by eliminating potential mosquito breeding sites. This can be done by applying larvicides to water storage containers and other places where standing water collects.

Personal preventive measures such as minimizing skin exposure and repellents are recommended to avoid mosquito bites. The use of insecticide-treated bed nets is limited by the fact that Aedes mosquitos bite during the daytime.

3. Epidemic preparedness and response: Prompt detection of yellow fever and rapid response through emergency vaccination campaigns are essential for controlling outbreaks. 

Yellow fever is endemic in Nigeria. The WHO recommends vaccination against yellow fever for all international travellers from 9 months of age going to Nigeria.

Sources: Healthline, WHO

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