This study provides evidence of a strong geospatial association in endemic villages between pigs with a heavy-burden of T. solium cysts and humans with taeniasis. The prevalence of taeniasis was 8 times higher among residents living within 100 meters of a tongue-positive pig compared to residents living outside this range (adjusted PR 8.1; 95% CI 1.4–47.0). This finding suggests that tongue-positive pigs in endemic communities can indicate geospatial foci in which the risk for human taeniasis is increased. Targeted screening or presumptive treatment for taeniasis within these high-risk foci may be an effective and practical control intervention in rural endemic areas.
Other findings in our study support our conclusion. We observed a similar geospatial association between tongue-positive pigs and humans with serum antibodies against T. solium taeniasis (adjusted PR 3.1; 95% CI 1.2–8.3). The slightly weaker observed association is likely due to antibody persistence after cleared infection in some rES33 antibody-positive individuals, as any tongue-positive pigs resulting from the cleared infection would likely have been slaughtered prior to our study. We also observed a weak geospatial association between tongue-positive pigs and human serum antibodies against T. solium cysticercosis (adjusted PR 1.3, 95% CI 0.9–1.7), suggesting some concentration of human exposure to T. solium eggs within the high-risk foci. However, seropositive pigs and people were widely distributed across the village suggesting that egg exposure is pervasive.
Few other studies have examined geospatial patterns of T. solium
infection. A previous study in Peru demonstrated that seroprevalence and seroincidence of antibodies against T. solium
cysticercosis in pigs increases as the distance to a house with taeniasis decreases 
. However, targeted interventions for taeniasis around seropositive pigs would be impractical as the majority of pigs in an endemic area have been exposed. There was no attempt to verify the true infection status of pigs by tongue examination or necroscopy in that study. Another community study in Peru in which pigs were necroscopied found that nearly half of infected pigs with viable cysts were raised in a house where someone had active taeniasis, while 94% were within 500 meters of a household with taeniasis [unpublished, Cysticercosis Working Group in Peru 2012]. A study of a small village in Mexico reported that none of the 4 taenia carriers found by stool microscopy resided in the same house as a tongue-positive pig 
. However, actual distances were not reported so geospatial relationships cannot be further assessed. Two other studies in Mexico and Tanzania have shown conflicting results regarding the clustering of infected pigs 
. However, neither of these studies examined geographic association between porcine cysticercosis and human taeniasis, which our results suggest could provide the basis for a targeted intervention.
While we observed a strong geospatial association between taeniasis and tongue-positive pigs, the relationship was not absolute. There were two people with taeniasis in the community who were not associated with a nearby tongue-positive pig. There are several possible explanations. Recently acquired taeniasis may not be associated with visibly infected pigs, as the latent period between exposure to eggs and development of viable cysts is about 2 months 
. It is also possible that any heavily-infected pigs associated with these cases of taeniasis were sold or slaughtered prior to our intervention. Finally, it is possible that some cases of taeniasis will simply not lead to heavy infection in a pig due to mitigating host or environmental conditions. Regardless of the explanation, a single cross-sectional approach to targeted screening for taeniasis around tongue-positive pigs would have missed these two individuals. This has important implications for control as an adult tapeworm sheds countless infective eggs into the environment over the course of their lifespan. A single case of persistent taeniasis could potentially maintain transmission in a community. While an alternate strategy of screening around pigs with more than 4 reactive bands on EITB LLGP identified one additional case of taeniasis, this strategy appears less efficient due to the increased number of rings generated and the additional people requiring screening.
It is also important to note that we did not identify any cases of taeniasis occurring within the same household as a tongue-positive pig. This suggests that geographically-targeted screening for taeniasis should not be limited to the source household of the infected pig. Unrestrained pigs will roam beyond their immediate home to forage and may be exposed to T. solium eggs in other locales. It is also important to note that the results of the coproantigen test do not provide definitive speciation, and some of the taeniasis we detected could be T. saginata rather than T. solium. However, we employed a more stringent cutoff for positivity using the coproantigen ELISA in order to reduce the likelihood of detection of T. saginata. Our experience in Peru (>100,000 samples processed) has demonstrated that T. solium taeniasis produces higher optical density readings than T. saginata taeniasis.
Although taeniasis/cysticercosis is considered a potentially eradicable disease, there has been relatively little data published on the effectiveness and sustainability of applied interventions. The TSOL 18 vaccine has been shown to be highly effective in protecting pigs from infection in community settings, but a commercial formulation is not yet available and there are lingering questions about villager uptake in a programmatic setting due to the requirement of multiple doses 
. Mass human chemotherapy has been attempted in multiple countries using either niclosamide or praziquantel 
, and in combination with mass treatment of pigs with oxfendazole 
. With any of these interventions, a longitudinal approach is important in order to preserve control gains, as demonstrated in Peru where combined human and pig mass chemotherapy showed a return to baseline within 18 months 
. Persistence of underlying conditions for transmission, decreased herd immunity among pigs, and migration of adult tapeworm carriers into treated areas can promote renewed transmission 
. Interventions addressing underlying risk factors, including improving animal husbandry practices and sanitary infrastructure, should occur in parallel 
As T. solium is endemic across several continents, a variety of alternative approaches will likely be required to implement regionally-appropriate control and elimination programs. Studies reporting the effectiveness, practicality and acceptability of candidate control interventions in a variety of settings are urgently needed. The Cysticercosis Working Group in Peru is currently conducting a pilot evaluation of targeting screening for taeniasis around tongue-positive pigs in northern Peru, with initial results expected within a year.
Our study was conducted in a small rural village in northern Peru, a region in which T. solium is known to be highly endemic. Our results may not be generalizable to other endemic regions in which the underlying composition of risk factors may not be the same. We chose to analyze a 100-meter radius for targeted screening for taeniasis as this is a practical and easily-replicated distance for implementation purposes. However, housing density, agricultural practices, sanitation, topography and climatic factors may all influence geospatial associations between infected pigs and humans with taeniasis. The factors which promote T. solium endemic stability are not fully understood, and it is possible that the foci-centered intervention we propose may not be effective enough to counteract these forces. For example, decreasing pig herd immunity due to reduced exposure to T. solium eggs could potentially promote a higher rate of successful infection and ongoing transmission. Finally, this is a small study and analysis is therefore limited to a low number of tongue-positive pigs and taeniasis cases. Our results and conclusions should be validated in a larger endemic population and in areas with higher prevalence of taeniasis.