Geographic correlation between tapeworm carriers and heavily infected cysticercotic pigs

Abstract

Background: Neurocysticercosis is a leading cause of preventable epilepsy in the developing world. Sustainable community-based interventions are urgently needed to control transmission of the causative parasite, Taenia solium. We examined the geospatial relationship between live pigs with visible cysticercotic cysts on their tongues and humans with adult intestinal tapeworm infection (taeniasis) in a rural village in northern Peru. The objective was to determine whether tongue-positive pigs could indicate high-risk geographic foci for taeniasis to guide targeted screening efforts. This approach could offer significant benefit compared to mass intervention.

Methods: We recorded geographic coordinates of all village houses, collected stool samples from all consenting villagers, and collected blood and examined tongues of all village pigs. Stool samples were processed by enzyme-linked immunosorbent assay (ELISA) for presence of Taenia sp. coproantigens indicative of active taeniasis; serum was processed by enzyme-linked immunoelectrotransfer blot for antibodies against T. solium cysticercosis (EITB LLGP) and T. solium taeniasis (EITB rES33).

Findings: Of 548 pigs, 256 (46.7%) were positive for antibodies against cysticercosis on EITB LLGP. Of 402 fecal samples, 6 (1.5%) were positive for the presence of Taenia sp. coproantigens. The proportion of coproantigen-positive individuals differed significantly between residents living within 100-meters of a tongue-positive pig (4/79, 5.1%) and residents living >100 meters from a tongue-positive pig (2/323, 0.6%) (p = 0.02). 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).

Conclusions: Tongue-positive pigs in endemic communities can indicate geospatial foci in which the risk for taeniasis is increased. Targeted screening or presumptive treatment for taeniasis within these high-risk foci may be an effective and practical control intervention for rural endemic areas.

Figure 1. Relationship between age category and positive laboratory results for Taenia solium infection in humans, Rica Playa, Tumbes, Peru.

Figure 2. Maps of Rica Playa, Tumbes, Peru, showing the geographic locations of people with taeniasis and heavily-infected cysticercotic pigs.

Green stars indicate the 5 households in which 6 coproantigen-positive individuals resided. A. Red circles indicate 100-meter ring radius around households where a tongue-positive pig was raised. There were 11 tongue-positive pigs raised in 7 different households (2 overlap on map). B. Blue circles indicate 100-meter ring radius around households where a seropositive pig with more than 4 reactive bands on EITB LLGP was raised. There were 8 pigs with 4+ reactive bands in 8 separate households.