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From Aniekan Aniekan, Calabar
Nigeria and other West African countries could see more Lassa fever cases in the coming years as climate change alters rainfall patterns and pushes disease-carrying rats closer to humans.
A 2025 systematic review by Cochrane Nigeria warns that shifting rains are already dictating when and where outbreaks occur, with infections spiking every dry season as multimammate rats abandon farms and invade homes in search of food.
“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 report disclosed.”
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 hemorrhagic disease caused by the Lassa virus. “It spreads when people come into contact with the urine, faeces, saliva or blood of infected rats, especially the common multimammate rat, Mastomys natalensis,” he stated.
He said the disease remains endemic in many parts of Nigeria, with Edo, Ebonyi and Ondo identified as high-risk states. He also cited challenges including limited surveillance, insufficient diagnostic capabilities, and healthcare workforce shortages that worsen the burden.
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Another associate of Cochrane Nigeria from the University of Calabar Teaching Hospital, Dr. Ekpereone Esu, added that an estimated 37.7 million people across 14 West African countries live in areas with highly suitable conditions for the rodents that carry the virus. “18,000 deaths occur each year, yet the disease remains severely neglected,” he said.
The review analysed research from 1969 to 2023 and found that rainfall does not spread the virus directly. Instead, it controls rodent behaviour. The review also identified seasonal rain patterns as a leading driver of Lassa fever outbreaks in humans as it dictates the movement and population cycles of the rodents.
During the rainy season, rats thrive in fields. But human cases peak during dry season as rodents move into homes in search of food. Two other factors are worsening the risk: the expansion of agriculture and poor housing with open food storage, which give rats easy access to people.
Scientists also noted that loss of biodiversity may be removing natural competitors to the rodents that carry the virus, allowing the primary reservoir rat to multiply. The most alarming finding concerns the future. As climate change continues to shift temperatures and rainfall, the ecological zone suitable for the Lassa virus is projected to expand, putting more communities across Nigeria and West Africa at risk.
“The link between environment and Lassa fever is clear,” the review concluded and also emphasized that “A One Health approach that unites health, agriculture and environmental agencies is urgently needed to protect vulnerable populations.”
