title: Using modelling to disentangle the relative contributions of zoonotic and anthroponotic transmission: the case of lassa fever.
abstract: BACKGROUND
  Zoonotic infections, which transmit from animals to humans, form the majority of new human pathogens. Following zoonotic transmission, the pathogen may already have, or may acquire, the ability to transmit from human to human. With infections such as Lassa fever (LF), an often fatal, rodent-borne, hemorrhagic fever common in areas of West Africa, rodent-to-rodent, rodent-to-human, human-to-human and even human-to-rodent transmission patterns are possible. Indeed, large hospital-related outbreaks have been reported. Estimating the proportion of transmission due to human-to-human routes and related patterns (e.g. existence of super-spreaders), in these scenarios is challenging, but essential for planned interventions.
  
  
  RESULTS
  Here, we make use of an innovative modeling approach to analyze data from published outbreaks and the number of LF hospitalized patients to Kenema Government Hospital in Sierra Leone to estimate the likely contribution of human-to-human transmission. The analyses show that almost [Formula: see text] of the cases at KGH are secondary cases arising from human-to-human transmission. However, we found much of this transmission is associated with a disproportionally large impact of a few individuals ('super-spreaders'), as we found only [Formula: see text] of human cases result in an effective reproduction number (i.e. the average number of secondary cases per infectious case) [Formula: see text], with a maximum value up to [Formula: see text].
  
  
  CONCLUSIONS
  This work explains the discrepancy between the sizes of reported LF outbreaks and a clinical perception that human-to-human transmission is low. Future assessment of risks of LF and infection control guidelines should take into account the potentially large impact of super-spreaders in human-to-human transmission. Our work highlights several neglected topics in LF research, the occurrence and nature of super-spreading events and aspects of social behavior in transmission and detection.
authors.affiliation: Department of Veterinary Medicine, Disease Dynamics Unit, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Lo Iacono
authors.affiliation: Institute of Zoology, Zoological Society of London, London, United Kingdom.
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Cunningham
authors.affiliation: Bernhard-Nocht Institute of Tropical Medicine, Hamburg, Germany.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Fichet-Calvet
authors.affiliation: Department of Microbiology and Immunology, Tulane University, New Orleans, Louisiana, United States of America; Broad Institute, Cambridge, Massachusetts, United States of America; Zalgen Labs, LLC, Germantown, Maryland, United States of America.
authors.forename: Robert F
authors.initials: RF
authors.lastname: Garry
authors.affiliation: Lassa Fever Program, Kenema Government Hospital, Kenema, Sierra Leone.
authors.forename: Donald S
authors.initials: DS
authors.lastname: Grant
authors.affiliation: Lassa Fever Program, Kenema Government Hospital, Kenema, Sierra Leone.
authors.forename: Sheik Humarr
authors.initials: SH
authors.lastname: Khan
authors.affiliation: Institute of Development Studies, University of Sussex. Brighton, United Kingdom.
authors.forename: Melissa
authors.initials: M
authors.lastname: Leach
authors.affiliation: Department of Microbiology and Immunology, Tulane University, New Orleans, Louisiana, United States of America.
authors.forename: Lina M
authors.initials: LM
authors.lastname: Moses
authors.affiliation: Sections of Infectious Disease, Departments of Pediatrics and Internal Medicine, School of Medicine, Tulane University, New Orleans, Louisiana, United States of America.
authors.forename: John S
authors.initials: JS
authors.lastname: Schieffelin
authors.affiliation: Department of Biostatistics and Bioinformatics, Tulane School of Public Health and Tropical Medicine, New Orleans, Louisiana, United States of America.
authors.forename: Jeffrey G
authors.initials: JG
authors.lastname: Shaffer
authors.affiliation: Department of Biology, Colorado State University, Fort Collins, Colorado, United States of America.
authors.forename: Colleen T
authors.initials: CT
authors.lastname: Webb
authors.affiliation: Department of Veterinary Medicine, Disease Dynamics Unit, University of Cambridge, Cambridge, United Kingdom.
authors.forename: James L N
authors.initials: JL
authors.lastname: Wood
mesh_terms: D000818:Animals; D003428:Cross Infection / Q000635:transmission; D006801:Humans; D007835:Lassa Fever / Q000453:epidemiology / Q000635:transmission*; D008954:Models, Biological; D012807:Sierra Leone / Q000453:epidemiology; D015047:Zoonoses