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Using modelling to disentangle the relative contributions of zoonotic and anthroponotic transmission: the case of lassa fever.

Lo Iacono G, Cunningham AA, Fichet-Calvet E, Garry RF, Grant DS, Khan SH, Leach M, Moses LM, Schieffelin JS, Shaffer JG, Webb CT, Wood JL - PLoS Negl Trop Dis (2015)

Bottom Line: Zoonotic infections, which transmit from animals to humans, form the majority of new human pathogens.Indeed, large hospital-related outbreaks have been reported.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].

View Article: PubMed Central - PubMed

Affiliation: Department of Veterinary Medicine, Disease Dynamics Unit, University of Cambridge, Cambridge, United Kingdom.

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.

Methodology/principal findings: 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/significance: 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.

No MeSH data available.


Related in: MedlinePlus

Contribution of human-to-human transmission.Mean value of the total effective reproduction number,  and its daily mean, , for the KGH epidemic curve vs the proportion  of cases due to human-to-human transmission (blue line). The shaded grey area covers the range between the  and  percentiles in  and/or ; the dashed red line represents the mean, nosocomial, effective reproduction number. A and B:  and  based on the full networks (in Jos and in Zorzor) of nosocomial cases;  days. C and D:  and  based on the extra-nosocomial cases in Jos;  days.
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pntd-0003398-g004: Contribution of human-to-human transmission.Mean value of the total effective reproduction number, and its daily mean, , for the KGH epidemic curve vs the proportion of cases due to human-to-human transmission (blue line). The shaded grey area covers the range between the and percentiles in and/or ; the dashed red line represents the mean, nosocomial, effective reproduction number. A and B: and based on the full networks (in Jos and in Zorzor) of nosocomial cases; days. C and D: and based on the extra-nosocomial cases in Jos; days.

Mentions: Fig. 4 shows the total effective reproduction number and its daily mean for the cases in KGH, vs the estimated proportion of cases due to human-to-human transmission. The shaded grey area covers the range between and percentiles arising from the simulations for each value of . The predictions were then compared with the total effective reproduction number (or with the equivalent daily mean), in the nosocomial outbreaks (or ) based on the full network of cases and with the extra-nosocomial cases in Jos alone (or ). For the full network of cases, the mean nosocomial reproduction number was higher than the mean KGH one, implying that the severe hospital outbreaks ought to be seen as exceptional circumstances. In contrast, the daily mean effective reproduction number arising from the Jos extra-hospital cases (due only to human-to-human transmission) was entirely compatible with the daily mean KGH effective reproduction number if we allow a proportion of cases to be due to human-to-human transmission . Based on the and percentiles in the predictions for the reproduction number , the lower and upper estimates for the proportion of human-to-human transmission are and respectively.


Using modelling to disentangle the relative contributions of zoonotic and anthroponotic transmission: the case of lassa fever.

Lo Iacono G, Cunningham AA, Fichet-Calvet E, Garry RF, Grant DS, Khan SH, Leach M, Moses LM, Schieffelin JS, Shaffer JG, Webb CT, Wood JL - PLoS Negl Trop Dis (2015)

Contribution of human-to-human transmission.Mean value of the total effective reproduction number,  and its daily mean, , for the KGH epidemic curve vs the proportion  of cases due to human-to-human transmission (blue line). The shaded grey area covers the range between the  and  percentiles in  and/or ; the dashed red line represents the mean, nosocomial, effective reproduction number. A and B:  and  based on the full networks (in Jos and in Zorzor) of nosocomial cases;  days. C and D:  and  based on the extra-nosocomial cases in Jos;  days.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4288732&req=5

pntd-0003398-g004: Contribution of human-to-human transmission.Mean value of the total effective reproduction number, and its daily mean, , for the KGH epidemic curve vs the proportion of cases due to human-to-human transmission (blue line). The shaded grey area covers the range between the and percentiles in and/or ; the dashed red line represents the mean, nosocomial, effective reproduction number. A and B: and based on the full networks (in Jos and in Zorzor) of nosocomial cases; days. C and D: and based on the extra-nosocomial cases in Jos; days.
Mentions: Fig. 4 shows the total effective reproduction number and its daily mean for the cases in KGH, vs the estimated proportion of cases due to human-to-human transmission. The shaded grey area covers the range between and percentiles arising from the simulations for each value of . The predictions were then compared with the total effective reproduction number (or with the equivalent daily mean), in the nosocomial outbreaks (or ) based on the full network of cases and with the extra-nosocomial cases in Jos alone (or ). For the full network of cases, the mean nosocomial reproduction number was higher than the mean KGH one, implying that the severe hospital outbreaks ought to be seen as exceptional circumstances. In contrast, the daily mean effective reproduction number arising from the Jos extra-hospital cases (due only to human-to-human transmission) was entirely compatible with the daily mean KGH effective reproduction number if we allow a proportion of cases to be due to human-to-human transmission . Based on the and percentiles in the predictions for the reproduction number , the lower and upper estimates for the proportion of human-to-human transmission are and respectively.

Bottom Line: Zoonotic infections, which transmit from animals to humans, form the majority of new human pathogens.Indeed, large hospital-related outbreaks have been reported.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].

View Article: PubMed Central - PubMed

Affiliation: Department of Veterinary Medicine, Disease Dynamics Unit, University of Cambridge, Cambridge, United Kingdom.

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.

Methodology/principal findings: 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/significance: 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.

No MeSH data available.


Related in: MedlinePlus