New Nigerian Lassa Fever Outbreak Underway – and Expanding its Range  
lassa fever
Nigeria has set up an emergency response centre to deal with outbreaks of the deadly Lassa fever in parts of the country.

Following reports of an unusually large number of cases in January 2022 across some 12 states, Nigeria is stepping up its surveillance of Lassa fever, the deadly viral hemorrhagic illness transmitted by infected rodents, or through other infected people or tainted food. 

This year marks the fourth year in a row in which large outbreaks of the  disease are being reported by Africa’s most populous state..   

According to the Nigeria Center for Disease Control (NCDC), there have been a total of 759 suspected cases, 170 confirmed cases and 32 confirmed deaths in January – following the emergence of the first cluster of new LF cases in December.

In a worrisome trend,  January’s cases were reported from 37 local government areas (LGAs) spread across 12 states. 

That is about twice the number of LGAs and states where cases of Lassa fever were reported within the same period in 2021 (17 and 6 respectively).

While the number of cases and states so far affected by the 2022 Lassa fever outbreak are higher, the case fatality rate of 18.8% remains lower than that of the  2021 outbreak where one out of four confirmed cases resulted in death (CFR — 25%).

Notably, is also about 16 times higher than the CFR for COVID-19 in Nigeria (1.2%), Nigerian health authorities underline.

Although cases have been reported from 12 states, three states (Edo, Ondo and Bauchi) are the epicenters for the outbreak, accounting for 74% of all confirmed cases.

Expanding range nationally and global health threats

This year mark’s the fourth in a row when large clusters of cases have been reported in Nigeria, “raising concerns about an ongoing, systematic emergence of LF nationally,” according to a recent Nature Communications review of the disease’s gradual expansion country-wide.

In 2019, there were 833 confirmed cases of Lassa fever in Nigeria with 174 deaths (CFR — 20.9%). In 2020, Nigeria recorded a total of 1181 confirmed cases of Lassa fever and 244 deaths (a CFR of 20.7%) but the following year (2021), the number of confirmed cases reduced to 510 with 102 deaths among confirmed cases (CFR - 20%). 

In addition to the national and regional risks, Lassa Fever is a “WHO-listed priority pathogen and a major focus of international vaccine development funding3 and, although often framed as a global health threat.”

Lassa fever is an acute viral illness and a viral haemorrhagic fever that is associated with high morbidity and mortality, and it thus has both economic and health security consequences.

Some cases, however, can be mild and thus go undetected or be confused with other common febrile conditions, like malaria - underlining the need for surveillance and vigilance to stop its spread. 

First reported in Nigeria’s state of Borno in 1969 when two missionary nurses died from an unusual febrile illness, Lassa fever cases and outbreaks continue to be reported in Nigeria and the diseases is increasingly recognised to be endemic in many parts of West Africa, including Nigeria, Benin, Ghana, Mali and the Mano River region (Sierra Leone, Liberia and Guinea).

The disease has typically been characterised as having two main endemic foci in West Africa, one centered around Sierra Leone and Liberia, and the other in Nigeria, but in recent years, Nigeria, in particular, has continued to record a trend of increasing numbers of cases - although most countries in the region have reported regular or sporadic cases, researchers report.

Response measures

In a statement this week, NCDC said it has activated the country’s national multi-sectoral and multi-disciplinary Lassa fever Emergency Operations Centre (EOC) in response to the Lassa fever outbreak in some parts of the country. 

“This became necessary given the increase in the number of confirmed Lassa fever cases across the country and a joint risk assessment with partners and sister agencies,” the center said in the statement.

It described the reports in weeks 1 and 2 as the highest number of confirmed cases recorded in Nigeria in the last four years for the same period. It however reassured Nigerians of its preparedness which hinged on the center’s experience in responding to Lassa fever outbreaks. 

“Since 2016, NCDC has worked hard to improve diagnostic capacity for the disease. Currently, seven laboratories can conduct confirmatory tests for Lassa fever in Nigeria and are coordinated by the NCDC National Reference Laboratory (NRL). This has improved active case detection for the disease,” NCDC stated. 

In the same vein, care for affected individuals has improved. NCDC said it is providing support to states including the provision of emergency medical and laboratory supplies as well as oral and intravenous Ribavirin for preventive and curative treatment to treatment centres across the country. 

“In addition, Nigeria through NCDC is participating in the largest-ever Lassa fever study that aims to provide an accurate assessment of the incidence of the disease in West Africa. This will also accelerate the development of vaccines and therapeutics for Lassa fever,” NCDC added.

It has also commenced training for healthcare workers in Nigeria’s tertiary health institutions on Lassa fever case management and infection prevention control.

Risk factors for exposure 

Contact with the rodent Mastomys natalensis is thought to be the reason for Lassa fever.

According to a research report published in Nature Communications in October, 2021, the significant majority of observed LF cases—including those from recent years in Nigeria—are thought to arise directly from contact with the rodent rodent Mastomys natalensis, the main viral reservoir host and a common agricultural pest. Other cases have occured, however, via hospital-acquired infections and potentially, in other small clusters of human-to-human transmission.

Risk factors for spillover of the virus, while not well understood, are thought to include factors that increase direct and indirect contact between rodents and people through poor food storage and housing quality, as well as certain crop processing practices.

Correlations between human case surges and seasonal rainfall patterns “suggests that LF is a climate-sensitive disease whose incidence may be increasing with regional climatic change,” according to the Nature Communications study, led by David Redding of University College London and and Chikwe Ihekweazu, of the Nigerian Centre for Disease Control (NCDC). 

Image Credits: Channel Africa/Twitter, Sahara Reporters/Nigeria.

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