#HEALTHTALK 27: Yellow fever pandemic in Nigeria - What you need to know

Fever is characterized by a rise in the body temperature commonly caused by infections. When anopheles female mosquitoes bite a person, he/she may develop malaria, but when mosquitoes of the Aedes and Haemogogus species that are infected with the yellow fever virus bite a person, it can lead to yellow fever. The virus is an arbovirus of the flavivirus genus.

The mosquitoes become infected with the virus when they bite an infected human or monkey. And the disease cannot be spread from one person to another without a mosquito bite. 

Yellow fever is a preventable, deadly, flu-like disease that is mostly common in Africa and South America where mosquitoes of the Aedes and Homogogus species are mainly found. Common symptoms include high body temperature, headache, fatigue, nausea, vomiting, yellowing of the eyes and skin (known as jaundice), and muscle pain. 

Modes of Transmission

According to the World Health Organization (WHO), there are three (3) main transmission cycles:

• Sylvatic (or jungle) yellow fever: In tropical rainforests, monkeys, which are the primary reservoir of yellow fever, are bitten by wild mosquitoes of the Aedes and Haemogogus species, which pass the virus on to other monkeys. Occasionally humans working or travelling in the forest are bitten by infected mosquitoes and develop yellow fever.
• Intermediate yellow fever: In this type of transmission, semi-domestic mosquitoes (those that breed both in the wild and around households) infect both monkeys and people. Increased contact between people and infected mosquitoes leads to increased transmission and many separate villages in an area can develop outbreaks at the same time. This is the most common type of outbreak in Africa.
• Urban yellow fever: Large epidemics occur when infected people introduce the virus into heavily populated areas with high density of Aedes aegypti mosquitoes and where most people have little or no immunity, due to lack of vaccination or prior exposure to yellow fever. In these conditions, infected mosquitoes transmit the virus from person to person. 

Signs and Symptoms

According to the WHO, there are two phases.

In the first phase, the virus is contracted, and it incubates within the body for 3 to 6 days. The most common symptoms experienced during this period are fever, muscle pain with prominent backache, headache, loss of appetite, and nausea or vomiting. But many people have been known to be asymptomatic during this phase. In symptomatic cases, however, symptoms mostly disappear after 3 to 4 days.

Source: NCDC

A small percentage of patients, however, enter a second, more toxic phase within 24 hours of recovering from initial symptoms. High fever returns and several body systems are affected, usually the liver and the kidneys. In this phase, people are likely to develop jaundice (yellowing of the skin and eyes, hence the name ‘yellow fever’), dark urine and abdominal pain with vomiting. Bleeding can occur from the mouth, nose, eyes or stomach. Half of the patients who enter this toxic second phase die within 7 - 10 days, says WHO.

Who Does Yellow fever affect?

According to WHO data, 34 African countries and 13 Central and South American countries "are either endemic for, or have regions that are endemic for, yellow fever". The six (6) most recent outbreaks occurred in 2020 in Senegal, Guinea, Nigeria, France, Gabon, and Togo. In 2018 and 2019, outbreaks were also recorded in Netherlands, Brazil, and Venezuela, among other countries as well.

Since the yellow fever virus is transmitted mainly through the bite of an infected mosquito of the Aedes and Homogogus species, the people at most risk of contracting yellow fever are people living in densely-populated areas with a high density of those species of mosquitoes. When the mosquito bites an infected person, and then proceeds to bite another person who isn't infected, the virus can be transmitted in that process. 

Secondly, people who go to work or who travel through a forest are at risk of becoming infected with the sylvatic yellow fever if they get bitten by mosquitoes that have bitten infected monkeys or other animals or infected persons.

Fourthly, foreigners travelling to endemic areas with high density of mosquitoes, without vaccination, and people living in those areas but not vaccinated, are all at risk of becoming infected.

Also, travelers who have been to an endemic area can transport the virus by visiting another area or country that is free from the virus. In the 17th and 19th centuries, large outbreaks occurred in North America and Europe as a result of this. In order to prevent such importation of the disease, many countries require visa applicants to show proof of vaccination against yellow fever before they can be issued a visa, particularly if travelers come from, or have visited yellow fever endemic areas.

Individuals display their 'yellow cards' after vaccination

In Nigeria, the Nigeria Center for Disease Control (NCDC) advises on the importance of getting "vaccinated against yellow fever at least 10 days before traveling to or from a yellow fever endemic country". Travelers leaving the country are advised to get vaccinated at least 10 days before departure at any Ports Health Service (PHS) office nationwide and obtain a valid vaccination card (also known as 'yellow card') as evidence. View the most recent NCDC travel guidelines here.

How is Yellow fever diagnosed?

Yellow fever is difficult to diagnose, especially during the early stages. According to WHO, a severe case can be confused with severe malaria, leptospirosis, viral hepatitis (especially fulminant forms), other haemorrhagic fevers, infection with other flaviviruses (such as dengue haemorrhagic fever), and poisoning. 

During the early stages, Polymerase chain reaction (PCR) testing in blood and urine can sometimes detect the virus. But in latter stages, testing to identify antibodies is needed (ELISA and PRNT). 

Prevention and Control

The best and most effective way to prevent yellow fever is through vaccination. According to the WHO, the vaccine is safe, affordable, and a single dose provides life-long protection against yellow fever disease. A booster dose of yellow fever vaccine is not needed. 

"There have been rare reports of serious side-effects from the yellow fever vaccine. The rates for these severe ‘adverse events following immunization’ (AEFI), when the vaccine provokes an attack on the liver, the kidneys or on the nervous system are between 0 and 0.21 cases per 10 000 doses in regions where yellow fever is endemic, and from 0.09 to 0.4 cases per 10 000 doses in populations not exposed to the virus."

However, according to the NCDC, reactions to yellow fever vaccine are possible and generally mild. They can include: mild headaches, muscle aches, and low- grade fevers.

People who have a thymus disorder, severe immunodeficiency due to symptomatic HIV/AIDS or other causes, or anyone who is above 60 years of age, stand a higher risk of AEFI. Hence, a careful risk-benefit assessment should be made before administering the vaccine in such cases by the patient's healthcare provider.

According to current guidelines by the Nigeria Center for Disease Control (NCDC), the vaccine is free for children from 9 months old, as part of routine childhood immunization schedule in government-owned/public health facilities across the country. All individuals aged 9 months to 59 years are encouraged to get vaccinated. However, adults are required to pay for it, except during mass vaccination campaigns when it is often administered free of charge.

The NCDC also says that the following groups should not get the vaccine:

• Infants younger than 9 months of age
• Adults above 60 years
• Anyone with a severe allergy to any part of the vaccine, including eggs, chicken proteins, or gelatin should not get the vaccine

In addition, if you have any of the following conditions, your healthcare provider can help you decide whether you can safely receive the vaccine:

• HIV/AIDS or other disease that affects the immune system
• Weakened immune system as a result of cancer or other medical conditions, transplant, or drug treatment (such as steroids, chemotherapy, or others that affect immune function)
• Pregnant women and nursing mothers

Apart from vaccination, other preventive measures include: elimination of potential mosquito breeding sites, the use of insect repellants, wearing protective clothing while sleeping at night to avoid mosquito bites, staying in rooms with screens or air conditioners, and epidemic preparedness and response through swift emergency vaccination campaigns upon detection of the virus. 

Treatment

There is no specific treatment for yellow fever. However, supportive treatment can be provided; medicines can be used to relieve the symptoms and may improve the outcome for seriously ill patients if presented early at health facility.

Yellow Fever Updates in Nigeria

In an October 2020 press release, the World Health Organization announced that it was partnering with the Nigerian government to resume mass yellow fever vaccinations in the country, stating that "With support from WHO, UNICEF, Gavi, and other partners, Nigeria has updated its strategic elimination plan with the accelerated EYE strategic plan 2020-2023, aimed at completing nationwide vaccination by 2023 (instead of 2025 as initially planned), improve yellow fever diagnosis capacity, routine childhood immunization coverage and overall population immunity in all states. Over the duration of the strategy, it is expected that almost 180 million Nigerians will be protected against yellow fever through accelerated phased preventive mass vaccination campaigns."

Subsequently, on the 1st of November, "a cluster of deaths from an undiagnosed disease were notified on 1 November 2020 through Event Based Surveillance in two states, Delta and Enugu, located in southern Nigeria", according to the WHO. And a November 12 press report by The Guardian said, "More than 70 people are feared to have died of yellow fever in Nigeria since September, as health authorities warn of a resurgence of the disease".

NCDC says: If you notice symptoms such as fever, headache, vomiting and yellowness of the eyes, report immediately to the nearest health facility for treatment and close observation by health care workers. The NCDC toll-free call centre is also available to manage public enquiries and concerns. Toll free number: 0800 9700 0010, Whatsapp: +234 708 711 0839, SMS: +234 809 955 5577

Source: WHO, NCDC