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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

Impact of super-spreaders I.A: Distribution of all individual  for both nosocomial outbreaks, based on the  permutations of the duration of illness. Mean value of the joint data: , median: , maximum: , proportion of cases when : , proportion of cases when : . B: Distribution of the effective reproduction number for cases of hospitalized patients in KGH for different values of the contribution of human-to-human transmission, , the corresponding data for the extra-nosocomial ( permutation based on , , , ,  cases in Jos) and all nosocomial outbreaks (based on all Jos and Zorzor cases) are also shown. C: Distribution of the total effective reproduction number, i.e. the average number of cases during the entire duration of the epidemic for different values the contribution of human-to-human transmission, .
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pntd-0003398-g005: Impact of super-spreaders I.A: Distribution of all individual for both nosocomial outbreaks, based on the permutations of the duration of illness. Mean value of the joint data: , median: , maximum: , proportion of cases when : , proportion of cases when : . B: Distribution of the effective reproduction number for cases of hospitalized patients in KGH for different values of the contribution of human-to-human transmission, , the corresponding data for the extra-nosocomial ( permutation based on , , , , cases in Jos) and all nosocomial outbreaks (based on all Jos and Zorzor cases) are also shown. C: Distribution of the total effective reproduction number, i.e. the average number of cases during the entire duration of the epidemic for different values the contribution of human-to-human transmission, .

Mentions: Super-spreaders are individuals who can infect a disproportionately large pool of susceptibles [45]. Here, super-spreading events are identified and quantified by analyzing how the effective reproduction number is distributed. The distribution of the individual effective reproduction numbers for the Jos and Zorzor outbreaks, based on the permutations of the duration of illness, is shown in Fig. 5.A. Although of the predictions for individual , there is a fat tailed distribution, with extreme values of . Similar patterns are observed for KGH cases for the individual effective reproduction number . As shown in Fig. 5.B and 5.C, the distribution of the individual and total, effective reproduction numbers, and appears to have a fat-tailed distribution, especially for larger values of .


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)

Impact of super-spreaders I.A: Distribution of all individual  for both nosocomial outbreaks, based on the  permutations of the duration of illness. Mean value of the joint data: , median: , maximum: , proportion of cases when : , proportion of cases when : . B: Distribution of the effective reproduction number for cases of hospitalized patients in KGH for different values of the contribution of human-to-human transmission, , the corresponding data for the extra-nosocomial ( permutation based on , , , ,  cases in Jos) and all nosocomial outbreaks (based on all Jos and Zorzor cases) are also shown. C: Distribution of the total effective reproduction number, i.e. the average number of cases during the entire duration of the epidemic for different values the contribution of human-to-human transmission, .
© Copyright Policy
Related In: Results  -  Collection

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

pntd-0003398-g005: Impact of super-spreaders I.A: Distribution of all individual for both nosocomial outbreaks, based on the permutations of the duration of illness. Mean value of the joint data: , median: , maximum: , proportion of cases when : , proportion of cases when : . B: Distribution of the effective reproduction number for cases of hospitalized patients in KGH for different values of the contribution of human-to-human transmission, , the corresponding data for the extra-nosocomial ( permutation based on , , , , cases in Jos) and all nosocomial outbreaks (based on all Jos and Zorzor cases) are also shown. C: Distribution of the total effective reproduction number, i.e. the average number of cases during the entire duration of the epidemic for different values the contribution of human-to-human transmission, .
Mentions: Super-spreaders are individuals who can infect a disproportionately large pool of susceptibles [45]. Here, super-spreading events are identified and quantified by analyzing how the effective reproduction number is distributed. The distribution of the individual effective reproduction numbers for the Jos and Zorzor outbreaks, based on the permutations of the duration of illness, is shown in Fig. 5.A. Although of the predictions for individual , there is a fat tailed distribution, with extreme values of . Similar patterns are observed for KGH cases for the individual effective reproduction number . As shown in Fig. 5.B and 5.C, the distribution of the individual and total, effective reproduction numbers, and appears to have a fat-tailed distribution, especially for larger values of .

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