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Lassa fever controls need to consider human to human transmission and the role of ‘super spreaders’, say researchers

last modified May 25, 2016 11:25 AM
One in five cases of Lassa fever – a disease that kills around 5,000 people a year in West Africa – could be due to human-to-human transmission, with a large proportion of these cases caused by ‘super-spreaders’, according to research published today in the journal PLOS Neglected Tropical Diseases.
Lassa fever is an acute viral haemorrhagic illness caused by Lassa virus. First identified in the village of Lassa, Nigeria, in 1969, the disease is thought to be transmitted to humans from contact with food or household items contaminated with rat urine or faeces. There have also been recorded cases of human-to-human transmission within hospital settings, but until now the risk – or mode – of transmission has not been clear. Understanding the different modes of transmission and how they are affected by factors such as people’s interaction with their environment is crucial for understanding the link between Lassa and changes in the ecosystem, and has important implications for public health strategies.

“Given the many competing health priorities in West Africa – exacerbated by the current Ebola epidemic – it is essential that we know the relative risk of human-to-human transmission of other potentially deadly diseases, such as Lassa fever,” says first author Dr Gianni Lo Iacono from the Department of Veterinary Medicine at the University of Cambridge. “That way, public health officials can decide where to focus their public health campaigns and how to prevent or respond to potential outbreaks.”

The researchers, part of the Dynamic Drivers of Disease in Africa Consortium, used mathematical modelling to analyse data from outbreaks known to be due to human-to-human chains of transmission, and calculated the ‘effective reproductive number’. This number represents the number of secondary infections from a typical infected individual – for an outbreak to take hold, this number needs to be greater than one.  They compared data from hundreds of Lassa infected patients from Kenema Government Hospital, in Sierra Leone, who could have been infected either by rodents or humans, with the data from human-to-human chains. By considering the effective reproductive numbers, they inferred the proportion of patients infected by humans rather than rodents. Read more..