The yellow fever virus is mosquito-transmitted and endemic to Africa and Latin America. The disease doesn’t always show symptoms, which can make diagnosing and preventing outbreaks difficult. When severe symptoms do appear, it is estimated to cause between 20,000 and 180,000 deaths per year in Africa alone.
The majority of the global burden of the disease is carried by Africa, which means that the countries in Africa most affected by yellow fever have the highest risk factors and mortality rates.
Measuring yellow fever burden depends on climate, most notably rainfall and temperature which are crucial to mosquito life cycles and population numbers. Previously, models of yellow fever risk areas were based on annual climate averages.
In a new study, researchers from Imperial College London and the World Health Organization examined the burden of yellow fever and past quantifiers that measured impact, severity, and risk of yellow fever outbreaks.
The results were published in the journal PLOS Neglected Tropical Diseases.
Rather than rely on past measurements of annual climate averages, the researchers were able to develop a new model that more accurately pinpointed risk areas and burden based on seasonal climate dynamics.
The model included variations in rainfall, temperature, and vegetation on a month to month basis throughout the year in Africa.
Temperature and rainfall can dictate mosquito infestations, and examining monthly climate variations can show which areas are at the highest risk of yellow fever at any given time.
The researchers found that even in areas known for being high risk of yellow fever transmission, the risk varies throughout the year depending on seasonal climate conditions.
“This finding, in conjunction with forecasted data, could highlight areas of increased transmission and provide insights into the occurrence of large outbreaks, such as those seen in Angola, the Democratic Republic of Congo and Brazil,” said the researchers.
Considering seasonal variation could help prevent future outbreaks of yellow fever and give a better understanding of which areas are most at risk during different times of the year.