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Raccoon social networks and the potential for disease transmission.

Hirsch BT, Prange S, Hauver SA, Gehrt SD - PLoS ONE (2013)

Bottom Line: Most studies of raccoon sociality have found patterns consistent with low levels of social connectivity within populations, thus the likelihood of direct pathogen transmission between raccoons is theoretically low.As this time criteria for censoring the social networks increased from one to thirty minutes, corresponding measures of network connectivity declined.These findings demonstrate that raccoon populations are much more tightly connected than would have been predicted based on previous studies, but also point out that additional research is needed to calculate more precise transmission probabilities by infected individuals, and determine how disease infection changes normal social behaviors.

View Article: PubMed Central - PubMed

Affiliation: School of Environment and Natural Resources, The Ohio State University, Columbus, Ohio, United States of America ; Smithsonian Tropical Research Institute (STRI), Balboa, Panama.

ABSTRACT
Raccoons are an important vector of rabies and other pathogens. The degree to which these pathogens can spread through a raccoon population should be closely linked to association rates between individual raccoons. Most studies of raccoon sociality have found patterns consistent with low levels of social connectivity within populations, thus the likelihood of direct pathogen transmission between raccoons is theoretically low. We used proximity detecting collars and social network metrics to calculate the degree of social connectivity in an urban raccoon population for purposes of estimating potential pathogen spread. In contrast to previous assumptions, raccoon social association networks were highly connected, and all individuals were connected to one large social network during 15 out of 18 months of study. However, these metrics may overestimate the potential for a pathogen to spread through a population, as many of the social connections were based on relatively short contact periods. To more closely reflect varying probabilities of pathogen spread, we censored the raccoon social networks based on the total amount of time spent in close proximity between two individuals per month. As this time criteria for censoring the social networks increased from one to thirty minutes, corresponding measures of network connectivity declined. These findings demonstrate that raccoon populations are much more tightly connected than would have been predicted based on previous studies, but also point out that additional research is needed to calculate more precise transmission probabilities by infected individuals, and determine how disease infection changes normal social behaviors.

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Average normalized degree (blue triangles), and two-step reach (green circles) in relation to network size.Average normalized degree values were not significantly correlated (R2 = 0.106, F1,18 = 1.893, P = 0.188), while two-step reach values were significantly higher (R2 = 0.225, F1,18 = 4.655, P = 0.047).
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pone-0075830-g001: Average normalized degree (blue triangles), and two-step reach (green circles) in relation to network size.Average normalized degree values were not significantly correlated (R2 = 0.106, F1,18 = 1.893, P = 0.188), while two-step reach values were significantly higher (R2 = 0.225, F1,18 = 4.655, P = 0.047).

Mentions: Monthly social association networks were highly connected (Table 1). The average number of individuals per network was 16.22±3.44 SD, and raccoon individuals associated with an average of 7.07±2.24 SD other individuals per month, resulting in an average normalized degree of 0.46±0.08 SD. The two-step reach values were notably higher, averaging 0.88±0.14 SD. Overall levels of connectedness in the social networks were remarkably high (monthly average  = 0.95±0.12 SD), and 15 of the 18 monthly social networks had connectedness values equal to 1 (i.e. every individual in the population was connected to one large social network). In general, our social network measures were not closely correlated to social network size (logistic regression p values >0.05). Average normalized degree values were slightly higher during months with larger social network size (R2 = 0.106, F1,18 = 1.893, p = 0.188), and two step reach values were significantly higher (R2 = 0.225, F1,18 = 4.655, p = 0.047) indicating the removal of individuals from the population does lead to some decrease in network connectivity (Figure 1). Even though individuals spend more time in close proximity and contacted each other more frequently during the winter [5], which overlaps with the December-March mating season, social networks during these months were not more compact (average compactness April-November  = 0.721, range  = 0.624–0.805; December-March  = 0.616, range  = 0.444–0.771).


Raccoon social networks and the potential for disease transmission.

Hirsch BT, Prange S, Hauver SA, Gehrt SD - PLoS ONE (2013)

Average normalized degree (blue triangles), and two-step reach (green circles) in relation to network size.Average normalized degree values were not significantly correlated (R2 = 0.106, F1,18 = 1.893, P = 0.188), while two-step reach values were significantly higher (R2 = 0.225, F1,18 = 4.655, P = 0.047).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3794951&req=5

pone-0075830-g001: Average normalized degree (blue triangles), and two-step reach (green circles) in relation to network size.Average normalized degree values were not significantly correlated (R2 = 0.106, F1,18 = 1.893, P = 0.188), while two-step reach values were significantly higher (R2 = 0.225, F1,18 = 4.655, P = 0.047).
Mentions: Monthly social association networks were highly connected (Table 1). The average number of individuals per network was 16.22±3.44 SD, and raccoon individuals associated with an average of 7.07±2.24 SD other individuals per month, resulting in an average normalized degree of 0.46±0.08 SD. The two-step reach values were notably higher, averaging 0.88±0.14 SD. Overall levels of connectedness in the social networks were remarkably high (monthly average  = 0.95±0.12 SD), and 15 of the 18 monthly social networks had connectedness values equal to 1 (i.e. every individual in the population was connected to one large social network). In general, our social network measures were not closely correlated to social network size (logistic regression p values >0.05). Average normalized degree values were slightly higher during months with larger social network size (R2 = 0.106, F1,18 = 1.893, p = 0.188), and two step reach values were significantly higher (R2 = 0.225, F1,18 = 4.655, p = 0.047) indicating the removal of individuals from the population does lead to some decrease in network connectivity (Figure 1). Even though individuals spend more time in close proximity and contacted each other more frequently during the winter [5], which overlaps with the December-March mating season, social networks during these months were not more compact (average compactness April-November  = 0.721, range  = 0.624–0.805; December-March  = 0.616, range  = 0.444–0.771).

Bottom Line: Most studies of raccoon sociality have found patterns consistent with low levels of social connectivity within populations, thus the likelihood of direct pathogen transmission between raccoons is theoretically low.As this time criteria for censoring the social networks increased from one to thirty minutes, corresponding measures of network connectivity declined.These findings demonstrate that raccoon populations are much more tightly connected than would have been predicted based on previous studies, but also point out that additional research is needed to calculate more precise transmission probabilities by infected individuals, and determine how disease infection changes normal social behaviors.

View Article: PubMed Central - PubMed

Affiliation: School of Environment and Natural Resources, The Ohio State University, Columbus, Ohio, United States of America ; Smithsonian Tropical Research Institute (STRI), Balboa, Panama.

ABSTRACT
Raccoons are an important vector of rabies and other pathogens. The degree to which these pathogens can spread through a raccoon population should be closely linked to association rates between individual raccoons. Most studies of raccoon sociality have found patterns consistent with low levels of social connectivity within populations, thus the likelihood of direct pathogen transmission between raccoons is theoretically low. We used proximity detecting collars and social network metrics to calculate the degree of social connectivity in an urban raccoon population for purposes of estimating potential pathogen spread. In contrast to previous assumptions, raccoon social association networks were highly connected, and all individuals were connected to one large social network during 15 out of 18 months of study. However, these metrics may overestimate the potential for a pathogen to spread through a population, as many of the social connections were based on relatively short contact periods. To more closely reflect varying probabilities of pathogen spread, we censored the raccoon social networks based on the total amount of time spent in close proximity between two individuals per month. As this time criteria for censoring the social networks increased from one to thirty minutes, corresponding measures of network connectivity declined. These findings demonstrate that raccoon populations are much more tightly connected than would have been predicted based on previous studies, but also point out that additional research is needed to calculate more precise transmission probabilities by infected individuals, and determine how disease infection changes normal social behaviors.

Show MeSH
Related in: MedlinePlus