An acute and sometimes sever haemorrhagic illness endemic in West Africa, Lassa fever was first recognised in Nigeria in 1969. The virus (LASV) is contacted by humans primarily through the contaminated excreta of the rodent Mastomys natalensis. There have been various reports on the yearly case burden of the disease in Nigeria from the Federal Ministry of Health, through the Nigeria Centre for Disease Control. Nigeria has been the epicentre of the disease which has also unfortunately been exported to neighbouring and distant countries.
A review of the prevalence of the disease in Nigeria, from 2015 to 2021, shows that the most affected age group was 21-40 years, with a male to female ratio of 1:0.8. With a total of 3311 laboratory-confirmed cases, out of the 20,588 suspected cases from 29 Nigerian states, there have been yearly outbreaks in Edo, Ondo, Taraba, Ebonyi, Bauchi, Plateau and Nasarawa over the aforementioned time frame. Over 33,802 persons underwent contact tracing, with about 90 per cent completing follow-up.
There was a case-fertility rate that ranged from 9.3 per cent to 29.2 per cent within the period. The epidemiological trend of the disease has witnessed a sharp decline in the yearly seasonal peaks from weeks 1 to 13, with about 75 per cent reduction in incidence between 2020 and 2021.
Being a yearly outbreak in West Africa, Lassa fever has been reported more in Nigeria. The disease usually records seasonal peaks during the dry season, from November to April, and is common in Sierra Leone, Ghana, Mali, Nigeria, Benin, Togo, Guinea and Liberia.
One of the reasons for delay in Lassa fever diagnosis is its non-specific symptoms, such as fever and the assumption that the febrile illness is caused by other factors, such as malaria, which is very endemic in sub-Saharan Africa. Another challenge with the management of the disease is the difficulty in identifying its onset, due to the generalised symptoms and clinical presentation, such as fever, vomiting, fatigue, abdominal pain, sore throat, chest pain and myalgia. The disease may also progress to serious complications, such as encephalitis, respiratory difficulty, haemorrhage, neurological problems and hearing loss.
The incubation period for the Lassa fever virus is one to three weeks. This long incubation period makes it easier for an infected person living in an endemic region to travel both locally and internationally, spreading the disease. The ease of human movement, coupled with the interconnectedness of countries in West Africa escalates the risk of international spread of the disease.
There is an urgent need for disease surveillance systems as well as a comprehensive outbreak response. This should serve as a public health procedure in cross-border migration.
The World Health (WHO) Organisation has said that Nigeria’s failure to fully implement disease surveillance mechanisms to handle Lassa fever has led to the repeated outbreaks of the disease at state and national levels. The negligent and lackadaisical attitude of the Nigerian government towards healthcare also contributes significantly to the high mortality rate recorded yearly.
However, in recent years, the provision and use of personal protective equipment (PPE) for healthcare workers has led to the substantial reduction in confirmed cases among Nigerian healthcare workers. Cumulatively, from week 1 to week 24, 2022, 158 deaths have been reported, with a case fatality rate (CFR) of 19.8 per cent, which is lower than the CFR for the same period in 2021 (20.5 per cent).
In total for 2022, 24 States have recorded at least one confirmed case across 99 Local Government Areas. Of all confirmed cases, 68 are from Ondo (29 per cent), Edo (25 per cent) and Bauchi (14 per cent).
The prevention of Lassa fever outbreak depends on many factors but most importantly, there should be a deliberate and focused effort on the promotion of community hygiene, to make it difficult or impossible for rodents to infest homes. Effective measures in this regard include: storing grains and other foodstuff in rodent-proof containers, disposing of garbage far from home, maintaining clean households and, if possible, keeping cats.
Lassa fever causes approximately 5000 to 10,000 deaths annually in West Africa and cases have been exported to Europe and the Americas, challenging public health. Although the Lassa virus was first identified over five decades ago in 1969, no treatments or vaccines have been approved to treat or prevent infection.
Notwithstanding, ribavirin, an antiviral drug, has been used with success in most patients. It has been shown to be most effective when given early in the course of the illness.