By Abbas Nazil
Nigeria and other West African countries may experience increasing Lassa fever outbreaks in the coming years as climate change alters rainfall patterns and influences the movement of disease-carrying rodents into human settlements, a new report has warned.
A 2025 systematic review by Cochrane Nigeria revealed that changing seasonal rainfall patterns are becoming a major factor shaping the spread of Lassa fever, with human infections often rising during dry seasons when multimammate rats leave farms and move into homes in search of food and shelter.
The report noted that rainfall does not directly transmit the Lassa virus but affects the behaviour, population growth and movement patterns of rodents that serve as carriers of the disease.
“Seasonal rain patterns are a leading driver of Lassa fever outbreaks in humans. Human cases often peak during the dry season because that is when rodents move into human settlements,” the review stated.
An associate of Cochrane Nigeria from the Paediatric Department of the University of Uyo Teaching Hospital, Dr. Ekong Udoh, explained that Lassa fever is a viral haemorrhagic disease caused by the Lassa virus and transmitted through contact with the urine, faeces, saliva or blood of infected rats, particularly the multimammate rat, Mastomys natalensis.
Udoh said the disease remains endemic in several parts of Nigeria, with Edo, Ebonyi and Ondo states among the areas considered highly vulnerable.
He identified weak disease surveillance systems, limited diagnostic capacity and shortages of healthcare workers as some of the challenges affecting efforts to control Lassa fever outbreaks in the country.
Another Cochrane Nigeria associate from the University of Calabar Teaching Hospital, Dr. Ekpereone Esu, said about 37.7 million people across 14 West African countries live in areas with environmental conditions suitable for rodents that transmit the virus.
According to him, thousands of deaths occur annually from Lassa fever, yet the disease remains one of the region’s neglected health challenges.
The review analysed studies conducted between 1969 and 2023 and found that climate factors, agricultural expansion and poor housing conditions are increasing human exposure to infected rodents.
Scientists explained that during rainy seasons, rodent populations increase in farmlands, but cases among humans usually rise during dry periods when the animals migrate into communities where food storage practices and housing conditions allow easier contact.
The researchers also warned that biodiversity loss may worsen the situation by reducing natural predators of disease-carrying rodents, allowing their populations to expand.
With climate change expected to continue affecting temperature and rainfall patterns, experts predict that areas suitable for the spread of Lassa fever could expand across Nigeria and other parts of West Africa.
The report stressed the need for a One Health approach involving health authorities, agricultural institutions and environmental agencies to address the growing threat and protect vulnerable populations from future outbreaks.