In this interview, Dr Joseph Okoeguale, Director, Institute of Viral and Emergent Pathogens, Control and Research, Irrua Specialist Teaching Hospital (ISTH), Edo State, a leading centre for Lassa fever treatment and research in this interview with Sade Oguntola, speaks on the trends driving this infection, the challenges in diagnosis and treatment, and what Nigeria must do to curb the disease. Excerpts:

Currently, the threat of Lassa fever remains significant in Nigeria, with rising cases reported across the country. How do you view the spike in cases and the geographical spread in recent years?

Lassa fever is a major public health emergency in Nigeria. The disease has been with us for about 57 years since it was first reported in Lassa town in 1959. Unfortunately, there has hardly been any month or year since then without reported cases or deaths.

Almost every state in Nigeria has recorded at least one case, although the disease is more common in certain regions. States such as Edo and Ondo have long been hotspots, while in recent years, many northern states have begun reporting increasing numbers of cases. Areas such as Bauchi, Borno, Taraba and Benue are now seeing significant outbreaks.

Lassa fever cases usually follow a seasonal pattern. There is a surge period during the dry season, typically from November or December through March. During this period, cases can rise sharply, sometimes reaching up to 20 cases per week. Outside the surge period, the numbers decline and may drop to only a few cases per week or month.

This seasonal increase is linked to several factors. Lassa fever is a rodent-borne disease, primarily transmitted by a species of rat known as Mastomys natalensis. These rats are peridomestic, meaning they live both in bushes and around human homes. During the dry season, activities such as bush burning and deforestation force rodents out of their natural habitats and into homes.

At the same time, people often dry food items such as grains and garri along roadsides because there is no rainfall. Rodents may contaminate these foods with urine or feces carrying the virus. When people consume contaminated food or handle contaminated items, infection can occur.

Climate patterns may also be contributing to current trends. This year, for example, the northern part of Nigeria experienced a prolonged dry season, while the southern region had less intense dry conditions. Consequently, more than 60% of reported cases have come from northern states. In some areas, including Taraba and Benue, outbreaks have been severe, even affecting healthcare workers.

What is the trend and what factors are associated with Lassa fever in Nigeria?

Since 2018, Lassa fever has been designated a priority disease for research and development, which has increased interest in understanding its epidemiology and transmission.

We already know that transmission occurs mainly from rodents to humans, although human-to-human transmission can also occur, particularly in healthcare settings. However, sequencing studies conducted in 2018 showed that over 98% of infections originate from rodent-to-human transmission, meaning that rats remain the primary source of infection.

Nigeria carries the largest burden of Lassa fever globally. Although cases occur in other West African countries such as Liberia and Sierra Leone, more than 80% of reported cases each year occur in Nigeria.

The disease is also associated with specific socio-economic and environmental conditions. It is more common in rural or impoverished communities where sanitation is poor and rodents easily access homes and food supplies.

Another challenge is that the early symptoms of Lassa fever resemble other common illnesses, such as malaria and typhoid. Symptoms like fever, weakness and fatigue are often misdiagnosed. Many patients initially self-medicate with malaria drugs or antibiotics, delaying proper diagnosis. By the time they arrive at the hospital, complications such as renal failure or organ damage may already have developed.

Limited diagnostic facilities also contribute to delays. In many areas, samples must be transported to specialized laboratories for confirmation. Expanding diagnostic capacity across the country would greatly improve early detection and survival rates.

Can it be inferred that the Lassa fever belt is expanding in Nigeria, and is climate change influencing this trend?

Data from the Nigerian Centre for Disease Control (NCDC) indicates that the geographical spread of Lassa fever is increasing. Earlier records from around 2010 showed relatively low numbers of cases. Between 2012 and 2017, cases increased gradually. Then in 2018 Nigeria recorded the largest outbreak, prompting the World Health Organization to send special teams to assist.

Since then, the number of states reporting cases has grown. What was once referred to as the “Lassa fever belt” now appears to be only part of the picture. Cases are being reported in areas that previously had little or no history of the disease.

Some experts attribute this spread to rodent migration, while others point to climate change. Regions experiencing prolonged drought often report higher numbers of cases, likely because rodents are driven into human environments in search of food and shelter.

Despite improvements in case management, fatality rates remain significant. In the past, case fatality rates exceeded 30%. Recent reports suggest a decline to around 15–20%, but deaths still occur every year, particularly where diagnosis and treatment are delayed.

Are there indications that the Lassa fever virus is mutating like the COVID-19 virus?

No. Lassa fever and COVID-19 are caused by completely different viruses. Lassa fever belongs to the group of viral hemorrhagic fevers, while COVID-19 is caused by a coronavirus. One of the major challenges with Lassa fever is that it has long been considered a neglected tropical disease. Unlike COVID-19, which triggered massive global investment in vaccine and drug development, Lassa fever receives less international attention because it is largely confined to West Africa.

Currently, there are no fully approved drugs or vaccines specifically developed for Lassa fever, although several research efforts are underway to develop both treatments and vaccines.

What about the drug Ribavirin?

Ribavirin is widely used in the treatment of Lassa fever, but it is important to understand that it was not originally developed for this disease. Its use is largely based on clinical experience and expert opinion, rather than extensive clinical trials specifically designed for Lassa fever.

While the drug has helped many patients recover, it also has side effects and has not been fully validated as the definitive treatment. For this reason, researchers are currently re-evaluating Ribavirin through clinical trials and comparing it with other potential therapies. These studies aim to determine the most effective drugs and appropriate dosages for treating Lassa fever.

Are there common socio-economic or geographical predictors of the disease in Nigeria?

Yes. Lassa fever is more common in economically disadvantaged communities, especially rural areas with poor housing, sanitation and waste management. Rodents thrive in environments where food is poorly stored and homes are not well protected against infestation. People living in such conditions are therefore at greater risk of exposure. Limited access to healthcare also increases the risk of complications and death, as many patients cannot afford hospital care or diagnostic tests.

How can Nigeria curb the rising cases of Lassa fever?

Efforts to control Lassa fever must follow the standard public health approach of primary and secondary prevention.

First, public awareness and health education are essential. Many people still believe every fever is malaria or typhoid. Communities must be educated about Lassa fever symptoms and the importance of seeking medical care early.

Second, early diagnosis must be strengthened by expanding laboratory capacity and improving sample transport systems.

Third, communities must adopt preventive practices such as keeping homes and surroundings clean; storing food in rodent-proof containers; blocking holes in houses where rodents can enter; using traps or other rodent control measures and avoiding drying food along roadsides where rodents can contaminate it.

Early treatment is also critical. Patients who present early and receive supportive care have a much higher chance of survival.

It is often said that Lassa fever is deadlier than COVID-19. How accurate is this comparison?

In terms of case fatality rate, Lassa fever can indeed be more deadly than COVID-19. While COVID-19 infected millions of people worldwide, its mortality rate was relatively lower for most cases.

Lassa fever, however, can have very high fatality rates, particularly when diagnosis and treatment are delayed or when complications such as organ failure develop.However, Lassa fever is not as easily transmitted as COVID-19. COVID-19 spreads through the air, whereas Lassa fever is mainly transmitted through contact with infected rodents or contaminated materials. This is why far fewer people contract Lassa fever compared to COVID-19.

What community-level strategies can reduce rodent populations and human-rodent contact?

Completely eliminating rodents is extremely difficult because they reproduce rapidly. A single rat can give birth to more than 18 offspring, and they breed throughout the year.

However, communities can reduce risk through several practical measures, including keeping homes and surroundings clean; storing food properly in sealed containers; avoiding drying food by the roadside and blocking holes and entry points in houses. Also, using traps or rodent control methods and reheating foods such as garri before consumption if contamination is suspected. The virus is relatively weak and can be destroyed at temperatures above 55°C, so proper cooking or reheating can reduce risk.

From your experience, are there myths or misconceptions about Lassa fever that should be addressed?

One major concern is that after more than five decades since the discovery of Lassa fever, Nigeria still lacks a definitive treatment or vaccine. This highlights the need for greater investment in research and development.

Although the government and international partners support diagnosis and treatment, managing Lassa fever can be expensive. Diagnostic tests such as PCR are costly and supportive care, including dialysis for patients with kidney complications, can cost hundreds of thousands of naira.

Given that the disease mostly affects poor and rural populations, sustained support from government and international partners is essential. Ultimately, the most effective long-term strategy will likely be the development of an effective vaccine, alongside improved diagnostics, treatment and community awareness. (Tribune)

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