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Spatial Dynamics and High Risk Transmission Pathways of Poliovirus in Nigeria 2001-2013

View Article: PubMed Central - PubMed

ABSTRACT

The polio eradication programme in Nigeria has been successful in reducing incidence to just six confirmed cases in 2014 and zero to date in 2015, but prediction and management of future outbreaks remains a concern. A Poisson mixed effects model was used to describe poliovirus spread between January 2001 and November 2013, incorporating the strength of connectivity between districts (local government areas, LGAs) as estimated by three models of human mobility: simple distance, gravity and radiation models. Potential explanatory variables associated with the case numbers in each LGA were investigated and the model fit was tested by simulation. Spatial connectivity, the number of non-immune children under five years old, and season were associated with the incidence of poliomyelitis in an LGA (all P < 0.001). The best-fitting spatial model was the radiation model, outperforming the simple distance and gravity models (likelihood ratio test P < 0.05), under which the number of people estimated to move from an infected LGA to an uninfected LGA was strongly associated with the incidence of poliomyelitis in that LGA. We inferred transmission networks between LGAs based on this model and found these to be highly local, largely restricted to neighbouring LGAs (e.g. 67.7% of secondary spread from Kano was expected to occur within 10 km). The remaining secondary spread occurred along routes of high population movement. Poliovirus transmission in Nigeria is predominantly localised, occurring between spatially contiguous areas. Outbreak response should be guided by knowledge of high-probability pathways to ensure vulnerable children are protected.

No MeSH data available.


Related in: MedlinePlus

The most probable infection pathways for the northern states of Nigeria (arrows) based on estimated population movement during 2002–2007 (A) and 2008–2013 (B). The expected number of susceptible children (aged under 15 years) during April-September 2012 based on reported vaccination records and vaccine efficacy (C). Arrows indicating the direction of the infection pathway originate from the centrepoints of infected LGAs to the most highly connected LGAs and are colour-coded by the strength of the force of infection (A-B). The force of infection is estimated by the incidence within LGA i and the spatial coupling between LGAs i and j, following the radiation model. Incidence of poliomyelitis is aggregated over the time-periods (fill colours) and refers to confirmed, symptomatic cases caused by wild-type 1 poliovirus only. Inset: Kano Municipal Area and surrounding LGAs.
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pone.0163065.g002: The most probable infection pathways for the northern states of Nigeria (arrows) based on estimated population movement during 2002–2007 (A) and 2008–2013 (B). The expected number of susceptible children (aged under 15 years) during April-September 2012 based on reported vaccination records and vaccine efficacy (C). Arrows indicating the direction of the infection pathway originate from the centrepoints of infected LGAs to the most highly connected LGAs and are colour-coded by the strength of the force of infection (A-B). The force of infection is estimated by the incidence within LGA i and the spatial coupling between LGAs i and j, following the radiation model. Incidence of poliomyelitis is aggregated over the time-periods (fill colours) and refers to confirmed, symptomatic cases caused by wild-type 1 poliovirus only. Inset: Kano Municipal Area and surrounding LGAs.

Mentions: Population movement predicted by the radiation model for Kano Municipal Area in Kano state is illustrated in Fig 1. The predicted pathways of high transmission show highly localised spread, dominated by short-range infection paths (Fig 2, S2–S4 Figs). We present here only the transmission pathways linking LGAs in northern states of Nigeria as incidence of poliomyelitis in the southern states is relatively rare (123 cases in southern states and 3414 cases in northern states during the study period). The inset maps in Fig 2A and 2B show that transmission between Kano Municipal Area and the surrounding LGAs is highly probable and the strong inter-connectivity of these areas is likely to support continued poliovirus transmission in the absence of high population immunity.


Spatial Dynamics and High Risk Transmission Pathways of Poliovirus in Nigeria 2001-2013
The most probable infection pathways for the northern states of Nigeria (arrows) based on estimated population movement during 2002–2007 (A) and 2008–2013 (B). The expected number of susceptible children (aged under 15 years) during April-September 2012 based on reported vaccination records and vaccine efficacy (C). Arrows indicating the direction of the infection pathway originate from the centrepoints of infected LGAs to the most highly connected LGAs and are colour-coded by the strength of the force of infection (A-B). The force of infection is estimated by the incidence within LGA i and the spatial coupling between LGAs i and j, following the radiation model. Incidence of poliomyelitis is aggregated over the time-periods (fill colours) and refers to confirmed, symptomatic cases caused by wild-type 1 poliovirus only. Inset: Kano Municipal Area and surrounding LGAs.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5036822&req=5

pone.0163065.g002: The most probable infection pathways for the northern states of Nigeria (arrows) based on estimated population movement during 2002–2007 (A) and 2008–2013 (B). The expected number of susceptible children (aged under 15 years) during April-September 2012 based on reported vaccination records and vaccine efficacy (C). Arrows indicating the direction of the infection pathway originate from the centrepoints of infected LGAs to the most highly connected LGAs and are colour-coded by the strength of the force of infection (A-B). The force of infection is estimated by the incidence within LGA i and the spatial coupling between LGAs i and j, following the radiation model. Incidence of poliomyelitis is aggregated over the time-periods (fill colours) and refers to confirmed, symptomatic cases caused by wild-type 1 poliovirus only. Inset: Kano Municipal Area and surrounding LGAs.
Mentions: Population movement predicted by the radiation model for Kano Municipal Area in Kano state is illustrated in Fig 1. The predicted pathways of high transmission show highly localised spread, dominated by short-range infection paths (Fig 2, S2–S4 Figs). We present here only the transmission pathways linking LGAs in northern states of Nigeria as incidence of poliomyelitis in the southern states is relatively rare (123 cases in southern states and 3414 cases in northern states during the study period). The inset maps in Fig 2A and 2B show that transmission between Kano Municipal Area and the surrounding LGAs is highly probable and the strong inter-connectivity of these areas is likely to support continued poliovirus transmission in the absence of high population immunity.

View Article: PubMed Central - PubMed

ABSTRACT

The polio eradication programme in Nigeria has been successful in reducing incidence to just six confirmed cases in 2014 and zero to date in 2015, but prediction and management of future outbreaks remains a concern. A Poisson mixed effects model was used to describe poliovirus spread between January 2001 and November 2013, incorporating the strength of connectivity between districts (local government areas, LGAs) as estimated by three models of human mobility: simple distance, gravity and radiation models. Potential explanatory variables associated with the case numbers in each LGA were investigated and the model fit was tested by simulation. Spatial connectivity, the number of non-immune children under five years old, and season were associated with the incidence of poliomyelitis in an LGA (all P < 0.001). The best-fitting spatial model was the radiation model, outperforming the simple distance and gravity models (likelihood ratio test P < 0.05), under which the number of people estimated to move from an infected LGA to an uninfected LGA was strongly associated with the incidence of poliomyelitis in that LGA. We inferred transmission networks between LGAs based on this model and found these to be highly local, largely restricted to neighbouring LGAs (e.g. 67.7% of secondary spread from Kano was expected to occur within 10 km). The remaining secondary spread occurred along routes of high population movement. Poliovirus transmission in Nigeria is predominantly localised, occurring between spatially contiguous areas. Outbreak response should be guided by knowledge of high-probability pathways to ensure vulnerable children are protected.

No MeSH data available.


Related in: MedlinePlus