null A new model, developed for Lassa fever that is spread by rats, will be able to predict how animal diseases can be carried over into humans.

With the help of the model, the scientists have predicted that there would be twice as many human cases of the disease in Africa by 2070.

Like the Ebola virus, the Lassa virus causes haemorrhagic fever and can be fatal. It is an acute viral disease occurring chiefly in West Africa. It is usually acquired from infected Mastomys rat, which is found in parts of Africa.

Lassa fever virus currently affects between 100,000 and one million people a year in western sub-Saharan Africa.

For the study, Prof Kate Jones of the Centre for Biodiversity and Environment Research at UCL and his team looked at about 400 known outbreaks of Lassa fever between 1967 and 2012.

Model of Lassa fever

The Lassa virus is passed to people through direct contact with infected rats by catching and eating the rats, or by food or household items that have been contaminated with rat droppings or urine.

The researchers developed a model to calculate how often people are likely to come into contact with the disease-carrying animals and the risk of the virus spilling over to humans.

“Our model suggests that in future, it is likely to become a greater burden on local communities spreading to more areas with approximately twice as many spill-over events predicted by 2070,” Dr Jones and colleagues from the University of Cambridge and the Zoological Society London report in the journal, Methods in Ecology and Evolution.

The model of the virus shows that more areas of West Africa are at risk from Lassa fever spillover events than previously thought.

Symptoms of the virus include fever, fatigue, nausea, vomiting, diarrhoea, headaches, abdominal pains, sore throat and facial swelling.

The model

The researchers developed the model by taking into account environmental changes and the way human populations are expected to grow.

“This model is a major improvement in our understanding of the spread of diseases from animals to people,” explained Prof Jones.

“We hope it can be used to help communities prepare and respond to disease outbreaks, as well as to make decisions about environmental change factors that may be within their control.

The projected increase in Lassa fever is attributed largely to climate change, with the rat that passes it to people (M. natalensis) thriving in hot and wet conditions.

Also, increase in human populations in certain areas will mean more people coming into contact with the rodent.

“Our new approach successfully predicts outbreaks of individual diseases by pairing the changes in the host’s distribution as the environment changes with the mechanics of how that disease spreads from animals to people, which hasn’t been done before, ” said co-researcher Dr David Redding of UCL.

The researchers say the model could be refined further to include diseases such as Ebola and Zika.

Prof Jonathan Ball of the University of Nottingham, who was not involved in the research, said,

“The threat of emerging and neglected diseases will not go away and we need to invest in research and global healthcare systems to ensure that we are ready to deal with these threats and their consequences.”

He said that future climate change and population growth would significantly increase the number of Lassa fever outbreaks.