Yellow fever Technical Working Group Lead at the Nigeria Centre for Disease Control, Dr William Nwachukwu, speaks to DAYO OJERINDE on the recent outbreak of the disease in some parts of the country
To a lay man, how will you describe Yellow fever?
Yellow fever is caused by an infectious agent called the yellow fever virus. It causes a systemic illness characterised by increased amount of virus in the blood, hepatic, renal, and myocardial injury, haemorrhage and high death. It is caused through the bite of a species of mosquitoes called Aedes spp. It presents with yellowish discolouration of the eyes, skin, urine and stool. The ‘yellow’ in the name refers to the jaundice that affects some patients.
Yellow fever is not a new disease in Nigeria. Outbreaks of yellow fever have been occurring in Nigeria since the 19th century. Most ethnic groups in Nigeria have vernacular names that are being used to identify the disease like in Igbo, Orianchananya; Hausa, Shawara; Yoruba, Iba aponju; and Ikwerre, Iba Ochananya, etc. Outbreaks had been occurring till 1986, but between 1986 and 2017, there was no yellow fever outbreak observed in Nigeria. This led to low surveillance activities on yellow fever and low index of suspicion among health care workers, low coverage of yellow fever immunisation among the under-five age group, and there was low herd immunity, leading to accumulation of a high number of susceptible individuals for yellow fever in Nigeria.
Is it a disease or an infection?
A disease is a disorder of structure or function in a living cell (human, animal, or plant), especially one that produces specific symptoms or that affects a specific location and is not simply a direct result of physical injury. Yellow fever is a disease. An infection is the invasion of an organism’s body tissues by disease-causing agents, their multiplication, and the reaction of host tissues to the infectious agents and the toxin they produce. An infectious disease, also known as a transmissible disease or communicable disease, is the illness resulting from an infection, which makes yellow fever an infection. From the above definition of disease and infection, yellow fever is both a disease and an infection.
How do people contract yellow fever?
Yellow fever is introduced into the body through mosquito bites into the skin. This spreads through the local lymph nodes where it multiplies. From the lymph nodes, the virus enters the circulating blood and is localised in some of the body organs like the liver, spleen, kidney, bone marrow, lymph glands and heart, and this may persist for some days. The lesions caused by yellow fever virus are due to the localisation and propagation of the virus in these organs.
The cells (hepatocytes) in the liver, nephrons in the kidneys, stem cells in the bone marrow and macrophages in the spleen in the organs are affected, leading to degeneration of these organs. The consequence of this degeneration is the formation of necrotic (dead) tissues. There is loss of functions of these organs. There will be jaundice due to liver damage, acute renal failure due to kidney damage, bleeding into the body orifices due to low platelets and interference in the clotting system, and shock due heart failure etc.
Why is yellow fever always described as a strange disease whenever there is an outbreak?
Since 2017 when we started having yellow fever outbreaks in Nigeria, we alerted the public and hence the surveillance system has a history of ‘strange disease’, ‘mysterious deaths’, ‘unknown disease/illness’. After investigation, we realised that most of affected the communities/individuals were those with low level of yellow fever immunity, i.e. communities where yellow fever vaccination and other routine immunisation uptake is very poor, access to health care is low and reporting of symptoms to the health authority is also low. The only signal for the public and health system is strange disease’, ‘mysterious deaths’, ‘unknown disease/illness’.
What could be responsible for the recent outbreak in some parts of the country?
High susceptible number of individuals in the communities with low herd immunity; and poor reporting of ill health to facilities for early detection and treatment.
Is there a possibility of the outbreak spreading to other parts of the country?
From experience, when a yellow fever outbreak occurs in one locality, it spreads to nearby localities (LGAs or states). In 2017, when we had the first outbreak, which started from Kwara State, other states were affected such as Kogi, Zamfara, Kebbi, Katsina and Niger; it also led to outbreaks in the FCT and Nasarawa.
In 2018, we had an outbreak in Edo; other contiguous LGAs/states were affected (Delta and Ondo). In 2019, we had clusters of outbreaks in Bauchi, other states were also involved, including Kano, Gombe, Plateau, Katsina, Borno etc. Similarly, there is the tendency that this present outbreak may spread to other LGAs/states beyond what we have now. However, in 2017, only three states – Nasarawa, Cross River and Akwa Ibom – had state-wide mass vaccination. But now, more states have been covered with yellow fever mass vaccination campaigns, meaning that the spread may only be limited.
Is it true that there is no cure for yellow fever?
Yellow fever is a viral disease and most viral diseases do not have a cure. So also yellow fever; it has no specific drug for its treatment. There is currently no specific antiviral drug for yellow fever; however, yellow fever is treated when the patient reports early to health facilities. Good and early supportive treatment in hospitals improves survival rates. Specific care to treat fever, dehydration, liver and kidney failure improves outcomes. Associated bacterial infections can be treated with antibiotics.
What are the symptoms of the disease?
The initial symptoms of yellow fever may include sudden onset of fever, flu-like symptoms, chills, nausea, vomiting, headache, back pain, generalised body pain and fatigue. Most persons recover from the phase. At the late stage of yellow fever infection, approximately 15 per cent of cases develop a more severe disease characterised by high fever, jaundice (yellowness of the eyes, skin or both), haemorrhage (bleeding) from multiple body sites, circulatory shock, and multi-organ failure (especially the liver and kidneys). About 25 to 50 per cent of those who developed severe diseases may die of yellow fever
Since it is caused by mosquito bites, why is the disease so deadly?
The major reason why it seems to be deadly is because most individuals affected have low immunity for yellow fever and report very late to health facilities and some do not report all until death.
How can the disease be prevented?
Through vaccination. A single dose of yellow fever vaccine is sufficient to confer sustained immunity and life-long protection against yellow fever disease. This is through improved yellow fever vaccination (routine immunisation, reactive and preventive mass vaccination campaign). It can also be prevented through good environmental sanitation by removing mosquitoes breeding sites; protection against mosquito bites; use of mosquito repellent; wearing of light-coloured, long-sleeved clothes when outdoors; avoidance of wearing perfume or cologne (some of these can attract mosquitoes); preventing mosquitoes from entering your accommodation; use of a mosquito net (LLINs) at night-time if mosquitoes are likely to be present; protection of travellers by ensuring every potential international traveller has a valid yellow fever vaccination certificate; good vector control; and early reporting of cases to health facilities.
In some situations, the infection may be so mild as to go unrecognised by the individual, while in some severe cases, it may lead to death. The outcome in this case may be either death or living. For those who survive the infection, there is sequelae or complication, meaning that the individual recovers completely.
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