Lassa Fever: Nigeria’s silent threat demands urgent action
By Franca Ofili
When Amina Peter’s fever persisted for days, her family initially assumed it was malaria. They bought over-the-counter medication and waited for her to recover.
It was only when her weakness became severe that they finally took her to a hospital for testing.
Her experience reflects a dangerous reality confronting Nigerians as Lassa fever continues to spread quietly, often beginning with symptoms that resemble familiar illnesses. This can lead people to delay treatment until severe complications emerge.
The Nigeria Centre for Disease Control and Prevention (NCDC) reported 14 new confirmed cases during epidemiological week 33, bringing cumulative infections in 2026 to 1,035 nationwide, with deaths reaching 252 in Nigeria.
The latest infections, recorded between Aug. 10 and Aug. 16, occurred in Ondo, Bauchi, Edo and Benue States, reinforcing the concentration of transmission in several repeatedly affected states and communities nationwide.
More worrying is the rising case fatality rate, which reached 24.4 per cent by week 33, compared with 18.6 per cent during the corresponding period in 2025.
Behind those statistics are households, patients, health workers and communities confronting a disease that can move silently from rodents into homes and potentially from infected people to others.
Lassa fever is a viral haemorrhagic disease caused by the Lassa virus, with multimammate rats serving as the principal reservoir. The virus can be transmitted through urine, droppings, saliva and contaminated materials.
For many families, however, the greatest danger may not initially appear to be rodents. It can begin with an ordinary fever, headache, weakness or stomach discomfort that is mistaken for malaria.
Dr Eno Onen, a Community Physician at University College Hospital, Ibadan, said early Lassa fever symptoms were often mild and easily mistaken for malaria, requiring heightened clinical suspicion across affected areas.
He said people should become concerned when fever persists beyond 48 hours without responding to malaria treatment, particularly where rodent exposure or contact with suspected patients has occurred.
“My advice is this: if you experience fever lasting more than 48 hours that does not respond to malaria treatment, don’t manage it at home.”
Such advice is crucial because delayed diagnosis can allow the disease to progress from nonspecific symptoms to bleeding, facial swelling, breathing difficulty, confusion, seizures and potentially fatal complications.
Onen explained that transmission occurred primarily through contact with infected multimammate rats, contaminated food and water, household surfaces, or airborne particles generated while cleaning contaminated environments.
“Together, these rodent-to-human routes account for an estimated 90 percent to 95 per cent of human Lassa infections,” Onen said.
The remaining infections can occur through contact with the blood, urine, saliva and other body fluids of infected people, creating particular risks in healthcare settings where infection prevention is inadequate.
Yet the disease does not exist independently of Nigeria’s changing environment.
Dr Ekpereonne Esu, Associate Director of Cochrane Nigeria, linked increasing transmission partly to ecological disruption across Nigeria’s affected states.
Esu said deforestation, biodiversity loss and changing rainfall patterns could alter rodent behaviour and populations, increasing opportunities for infected animals to enter homes and encounter people.
Seasonal rainfall, he explained, could influence the movement of multimammate rats, driving them towards human dwellings when environmental conditions make surrounding habitats less suitable for their survival.
“Deforestation adds another dimension because expanding farmland into forested areas can create favourable conditions for rodents while simultaneously reducing natural habitats and disrupting ecological balance.
“Biodiversity loss, caused by human activities, reduces natural predators that ordinarily control rat populations, allowing the rodents to multiply and spread infections more easily,” Esu said.
Poor housing can magnify the danger. Cracks, gaps, leaking roofs, poorly fitted doors and inadequate waste management provide rodents with opportunities to enter homes and contaminate living spaces.
Dr. Jide Idris, NCDC boss
The TETFund-sponsored Mega Research Project on Lassa fever similarly identified poor housing, rodent infestation, food contamination, leaking roofs and poorly fitted doors as important environmental risk factors.
Researchers therefore increasingly view Lassa fever through a One Health lens, recognising that human health, animal populations, environmental conditions, agriculture, housing and sanitation are interconnected in disease transmission.
This approach matters because controlling Lassa fever cannot depend solely on hospitals. Communities must reduce exposure before infection occurs, while laboratories and health facilities must detect cases rapidly.
By week 33, NCDC reported confirmed infections in 23 states and 117 local government areas, demonstrating that although transmission is concentrated, the national risk remains substantial.
Bauchi, Ondo, Taraba, Benue and Edo States accounted for 87 per cent of cumulative confirmed cases by week 33, making sustained interventions in these states especially important.
The pattern has fluctuated rather than followed a straight upward trajectory. Week 32 recorded four new cases, down from 17 in week 31, before rising again during week 33.
Earlier figures tell a similar story. In week 30, 17 new cases were recorded after 20 cases in week 29, while week 28 registered 25 following 14 cases during week 27.
These fluctuations can create a false sense of reassurance if declining weekly numbers are interpreted as the disappearance of the disease. Lassa fever remains active whenever new infections continue to occur.
The persistently high fatality rate also deserves attention because it indicates that diagnosis and treatment challenges remain significant despite improvements in surveillance, clinical awareness and outbreak response.
People aged between 21 and 30 years remain the predominant affected group in recent NCDC reports, while research findings suggest adults between 20 and 40 face substantial exposure.
The research team attributed this exposure partly to farming and outdoor activities, where people may encounter rodents, contaminated environments or food stored under conditions that encourage infestation.
At Abubakar Tafawa Balewa University Teaching Hospital in Bauchi, researchers are examining survivors to understand why some people recover while others develop severe disease or die.
Prof. Alash’le Abimiku, Executive Director of the International Research Centre of Excellence and Institute of Human Virology Nigeria, said the work could support the development of an effective vaccine.
“We want to study survivors and understand what made them survive,” Abimiku said, explaining that researchers were examining immune responses and different Lassa virus lineages circulating in Nigeria.
The project also includes community engagement, clinician training, improved diagnosis and laboratory investigation, recognising that scientific discoveries become valuable only when translated into practical public health action.
Abimiku noted that Lassa fever was no longer strictly seasonal, with infections now recorded throughout the year, strengthening the case for continuous surveillance and prevention activities.
“What is the shortest route toward developing a vaccine? How can we ensure that the burden on our people is reduced?” Echono asked during the presentation of research findings.
He said TETFund would escalate validated findings to relevant authorities, including NCDC and the Federal Ministry of Health, potentially strengthening the case for a vaccine development centre in Nigeria.
The Federal University of Health Sciences, Otukpo, received a N250 million Mega Research Grant for the project, generating evidence on the epidemiology, diagnosis, management and control of Lassa fever.
Principal Investigator Joseph Okopi said Nigeria bore the highest global burden, estimating that between 5,000 and 10,000 people die annually and underscoring the urgency of stronger interventions.
The study investigated antibody prevalence, rodent vectors, transmission patterns and associated risks across five states, with Benue recording the highest prevalence of Lassa fever antibodies among surveyed populations.
Clinical findings from 1,266 participants and 392 suspected cases investigated in Benue and Kogi produced 43 PCR-confirmed infections, including 25 in Benue and 18 in Kogi.
Audu Onyemocho, Professor of Community Medicine and a Consultant in Public Health, said bleeding, older age and seizures emerged as strong predictors of mortality, providing useful evidence for clinicians identifying patients requiring urgent and intensive management.
Defeating Lassa fever, experts say, will require science matched with everyday action: stronger laboratories, better housing, cleaner environments, informed communities, protected health workers and sustained investment in vaccine development.
The message is clear: Lassa fever may often begin quietly, but Nigeria cannot afford to respond quietly. Early testing, prompt treatment, better surveillance and stronger prevention must become part of the country’s sustained response to a disease that continues to claim lives. (NAN)