Yellow fever

Doris Obinna

In the past few weeks, Nigeria has witnessed mysterious deaths from strange disease where scores died. The disease, which hit Delta, Enugu and Bauchi states was followed by a laboratory confirmation by the Nigeria Centre of Disease Control (NCDC), which disclosed that it is a re-emergency of Yellow fever (YF).

Yellow fever is an acute viral haemorrhagic disease transmitted by infected mosquitoes. The “yellow” in the name refers to the jaundice that affects some patients. The World Health Organisation WHO) said yellow fever has the potential to spread rapidly and cause serious public health impact:

“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 is required to treat dehydration, respiratory failure, and fever; and antibiotics are recommended to treat associated bacterial infections.”

WHO further disclosed that a four-year (2018-2021) national yellow fever preventive mass vaccination campaign (PMVC) plan, supported by the global alliance for vaccines and immunization (GAVI) and partners, is being implemented to cover all states in the country: “By 2025, it is anticipated that all states in Nigeria will have conducted PMVC activities to protect at-risk populations against yellow fever.

“This year’s phased preventive campaigns will target the following states, Anambra, Ekiti, Katsina and Rivers, with specialised activities in Borno. Bauchi has not yet been covered by the phased PMVCs, and the states planned for the next phase are undergoing through a review process to consider the evolving epidemiology.”

Dr Olaekan Sunday said, the yellow fever virus is an arbovirus of the flavivirus genus and is transmitted by mosquitoes, belonging to the Aedes and Haemogogus species: “The different mosquito species live in different habitats – some breed around houses (domestic), others in the jungle (wild) and some in both habitats (semi-domestic).

“The three types of transmission cycles includes; sylvatic (or jungle) yellow fever, intermediate yellow fever and the urban yellow fever”.

Signs, symptoms and diagnosis

Sunday said yellow fever virus incubates in the body for three to six days: “Many people do not experience symptoms, but when these do occur, the most common are fever, muscle pain with prominent backache, headache, loss of appetite, and nausea or vomiting. In most cases, symptoms disappear after three to four days.

“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 the toxic phase die within seven to 10 days.

“Yellow fever is difficult to diagnose, especially during the early stages. A more 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.

“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.”

Prevention

Another authority, Dr Gabriel Omonaiye, said government should ensure that the citizens are given the yellow fever vaccine, a shot of which lasts for 10 years: “The political will, policies and the provision of the financial, material and human resources to ensure that the vaccination is done widely and free of charge. Individuals can reduce their exposure to mosquitoes by wearing long sleeves dresses and long trousers.

“Houses should have mosquito nets. The use of repellents can reduce mosquitoes’ bites. Living in air-conditioned and well-screened houses is a good method to reduce exposure to mosquitoes

“Research also shows that occasionally travellers who visit yellow fever endemic countries may bring the disease to countries free from yellow fever. To prevent such importation of the disease, many countries require proof of vaccination against yellow fever before they will issue a visa, particularly if travellers come from, or have visited yellow fever endemic areas.”

Measures taken by Nigerian authorities

The NCDC is currently responding to clusters of yellow fever outbreaks in Delta, Enugu, Bauchi and Benue States. Twenty new confirmed cases were reported in Enugu 14, Benue three, Delta two and Ebonyi one.

Four new local governments in three states reported confirmed cases: Benue one; Enugu two and Ebonyi one. Two new deaths among confirmed cases were reported and 39 confirmed cases were reported from seven LGAs in five states. Also, six deaths were recorded among the confirmed cases with a case fatality rate (CFR) of 15 per cent.

The NCDC and National Primary Health Care Development Agency (NPHCDA) are coordinating response activities through the national YF emergency operation centre (EOC), in collaboration with states and partners.  There are on-going reactive mass vaccination campaigns in Bauchi, Delta and Enugu states with Benue, which started a preventive mass vaccination campaign (PMVC) on November 20, 2020.

Cumulatively, in 2020, 1,558 suspected cases and 46 confirmed cases were reported from 481 (62 per cent) LGAs in all states and the Federal Capital Territory (FCT), Abuja.  Laboratory results confirmed 37  (PCR); 30 presumptive positive; 11 inconclusive; 1,481 negative; 31 pending testing.

Laboratory results from IP Dakar, Senegal, shows of the 41 samples sent, eight (19.5 per cent) were confirmed, two (4.9 per cent) discarded and 31 (75.6 per cent) pending.  The 46 confirmed cases were reported from 14 LGAs in Bauchi eight; Benue three; Delta eight; Ebonyi one; Edo five; Ekiti one; Enugu 19 and Oyo one.

WHO said: “Nigeria is a high priority country for the Eliminate Yellow Fever Epidemic (EYE) strategy. Vaccination is the primary intervention for prevention and control of yellow fever. The early detection and investigation of yellow fever cases through strong surveillance are keys to control the risk of yellow fever outbreaks.

“Prevention of mosquito bites (repellents, wearing long clothes) is an additional measure that limits the risk of yellow fever transmission. In urban centres, targeted vector control measures are also helpful to interrupt transmission.”

WHO recommends vaccination against yellow fever for all international travellers more than nine months of age going to Nigeria, as “there is evidence of persistent or periodic yellow fever virus transmission.”