GPS Tracking of Free-Ranging Pigs to Evaluate Ring Strategies for the Control of Cysticercosis/Taeniasis in Peru

Abstract

BackgroundTaenia solium, a parasitic cestode that affects humans and pigs, is the leading cause of preventable epilepsy in the developing world. T. solium eggs are released into the environment through the stool of humans infected with an adult intestinal tapeworm (a condition called taeniasis), and cause cysticercosis when ingested by pigs or other humans. A control strategy to intervene within high-risk foci in endemic communities has been proposed as an alternative to mass antihelminthic treatment. In this ring strategy, antihelminthic treatment is targeted to humans and pigs residing within a 100 meter radius of a pig heavily-infected with cysticercosis. Our aim was to describe the roaming ranges of pigs in this region, and to evaluate whether the 100 meter radius rings encompass areas where risk factors for T. solium transmission, such as open human defecation and dense pig activity, are concentrated.Methodology/Principal FindingsIn this study, we used Global Positioning System (GPS) devices to track pig roaming ranges in two rural villages of northern Peru. We selected 41 pigs from two villages to participate in a 48-hour tracking period. Additionally, we surveyed all households to record the locations of open human defecation areas. We found that pigs spent a median of 82.8% (IQR: 73.5, 94.4) of their time roaming within 100 meters of their homes. The size of home ranges varied significantly by pig age, and 93% of the total time spent interacting with open human defecation areas occurred within 100 meters of pig residences.Conclusions/SignificanceThese results indicate that 100 meter radius rings around heavily-infected pigs adequately capture the average pig’s roaming area (i.e., home range) and represent an area where the great majority of exposure to human feces occurs.

Clustering of Necropsy-Confirmed Porcine Cysticercosis Surrounding Taenia solium Tapeworm Carriers in Peru

“…This mechanism of within-household transmission of T. solium from human carriers to their pig herd is consistent with a GPS tracking study previously conducted by our group in this region. 23 In that study, we found that both pig roaming patterns and reported human defecation locations were concentrated in the immediate vicinity of households, highlighting the potential for focal transmission through exposure to T. solium eggs in cases where the pig owner has taeniasis.…”

Understanding transmission and control of the pork tapeworm with CystiAgent: a spatially explicit agent-based model

“…Despite this strength, CystiAgent only begins to account for the complex heterogeneities that likely occur in real-world systems. Age-related differences in pig roaming patterns [23], seasonal and climate-related variations in transmission [44], acquired immunity and resistance among pigs [45], vector-borne transmission of T. solium eggs to pigs [46,47], and black-market distribution of infected pork [48] are only a few of the many additional factors that may impact transmission patterns and are not explicitly defined in CystiAgent. Additional data from experimental or field studies and will be needed in order to incorporate these features into future versions of the model and evaluate their impact on transmission.…”

“…Local variations in pig-raising practices, sanitation, diet, and migration all interact to create locally specific transmission patterns that differ from one endemic village to the next [20]. Even within villages, spatial heterogeneities caused by pig-roaming patterns and open defecation cause clustering that is important for a model to capture [21][22][23]. Importantly, incorporating underlying spatial and biological processes of T. solium transmission was highlighted in a recent report on the WHO 2030 goals [13], and there is evidence that models that fail to account for these heterogeneities are susceptible to overestimating the effect of control interventions [24] and yielding unrealistic predictions for achieving control and elimination targets [25].…”

Understanding transmission and control of the pork tapeworm with CystiAgent: a spatially explicit agent-based model

“…Despite this strength, CystiAgent only begins to account for the complex heterogeneities that likely occur in real-world systems. Age-related differences in pig roaming patterns [20], seasonal and climate-related variations in transmission [41], acquired immunity and resistance among pigs [42], vector-borne transmission of T. solium eggs to pigs [43,44], and black-market distribution of infected pork [45] are only a few of the many additional factors that may impact transmission patterns and are not explicitly de ned in CystiAgent. Additional data from experimental or eld studies and will be needed in order to incorporate these features into future versions of the model and evaluate their impact on transmission.…”

“…Local variations in pig-raising practices, sanitation, diet, and migration all interact to create locally speci c transmission patterns that differ from one endemic village to the next [17]. Even within villages, spatial heterogeneities caused by pig-roaming patterns and open defecation cause clustering that is important for a model to capture [18][19][20]. Importantly, incorporating underlying spatial and biological processes of T. solium transmission was highlighted in a recent report on the WHO 2030 goals [11], and there is evidence that models that fail to account for these heterogeneities are susceptible to overestimating the effect of control interventions [21] and yielding unrealistic predictions for achieving control and elimination targets [22].…”