Evaluating the Role of Corrals and Insects in the Transmission of Porcine Cysticercosis: A Cohort Study.

The widespread dispersion of pigs infected with cysticercosis across endemic villages, low cyst burden among infected pigs, and low prevalence of taeniasis all suggest that pig ingestion of human feces is not the only mode of transmission for Taenia solium. Our objective was to evaluate the risk of porcine cysticercosis associated with exposure to human feces, dung beetles, and flies in an endemic community setting. We used a cluster-randomized cohort design to compare the risk of developing antibodies and infection among 120 piglets raised in either free-roaming (FR), standard corral (SC), or netted corral environments (NC). We collected monthly blood samples to detect serum antibodies and necropsied all pigs after 10 months to identify cysts. A total of 66 piglets developed antibodies with the relative risk of seropositivity in FR vs. all corralled pigs increasing significantly after 18 weeks. Of 108 necropsied pigs, 15 had T. solium cysts, all belonging to the FR group. Corrals were protective against infection but less so against seropositivity. NC, which did not completely exclude insects, did not provide added protection against seropositivity as compared to SC. The results of this study suggest that dung beetles and flies do not play an important role in infection.

Geographically Targeted Interventions versus Mass Drug Administration to Control Taenia solium Cysticercosis, Peru.

Optimal control strategies for Taenia solium taeniasis and cysticercosis have not been determined. We conducted a 2-year cluster randomized trial in Peru by assigning 23 villages to 1 of 3 geographically targeted intervention approaches. For ring screening (RS), participants living near pigs with cysticercosis were screened for taeniasis; identified cases were treated with niclosamide. In ring treatment (RT), participants living near pigs with cysticercosis received presumptive treatment with niclosamide. In mass treatment (MT), participants received niclosamide treatment every 6 months regardless of location. In each approach, half the villages received targeted or mass oxfendazole for pigs (6 total study arms). We noted significant reductions in seroincidence among pigs in all approaches (67.1% decrease in RS, 69.3% in RT, 64.7% in MT; p<0.001), despite a smaller proportion of population treated by targeted approaches (RS 1.4%, RT 19.3%, MT 88.5%). Our findings suggest multiple approaches can achieve rapid control of T. solium transmission.

Seroprevalence of Toxoplasma gondii in free-range pigs in northern Peru.

Toxoplasma gondii is an important foodborne pathogen worldwide, with undercooked meat as the main source of human transmission. In this study, we determined the seroprevalence of T. gondii in free-range pigs from two adjacent villages in the Tumbes region of northern Peru, El Tutumo and Nuevo Progreso. We randomly selected 100 pig serum samples collected during a prior study and processed these using Western Blot to detect IgG anti-T. gondii antibodies. Results indicated a prevalence of 32% (32/100) to T. gondii in pigs. Free-ranging pigs from northern Peru represent a substantial risk for transmission of T. gondii to humans.

Population Screening for Urine Antigens to Detect Asymptomatic Subarachnoid Neurocysticercosis: A Pilot Study in Northern Peru.

Subarachnoid neurocysticercosis (SANCC) is a severe and progressive brain infection with Taenia solium. We performed a pilot study of noninvasive screening for SANCC in two endemic villages in northern Peru using a urine antigen screen followed by brain magnetic resonance imaging for participants with elevated levels of antigen. Among the 978 participants screened, we identified eight individuals with SANCC, many of whom were asymptomatic. This represents a minimum prevalence of 0.8% of SANCC, a level higher than expected based on prior studies, and a positive predictive value of 62% for our novel urine screening test. Future studies should confirm whether early detection and management improve clinical outcomes.

Seasonal patterns in risk factors for Taenia solium transmission: a GPS tracking study of pigs and open human defecation in northern Peru.

BACKGROUND: Taenia solium (cysticercosis) is a parasitic cestode that is endemic in rural populations where open defecation is common and free-roaming pigs have access to human feces. The purpose of this study was to examine the roaming patterns of free-range pigs, and identify areas where T. solium transmission could occur via contact with human feces. We did this by using GPS trackers to log the movement of 108 pigs in three villages of northern Peru. Pigs were tracked for approximately six days each and tracking was repeated in the rainy and dry seasons. Maps of pig ranges were analyzed for size, distance from home, land type and contact with human defecation sites, which were assessed in a community-wide defecation survey. RESULTS: Consistent with prior GPS studies and spatial analyses, we found that the majority of pigs remained close to home during the tracking period and had contact with human feces in their home areas: pigs spent a median of 79% (IQR: 61-90%) of their active roaming time within 50 m of their homes and a median of 60% of their contact with open defecation within 100 m of home. Extended away-from-home roaming was predominately observed during the rainy season; overall, home range areas were 61% larger during the rainy season compared to the dry season (95% CI: 41-73%). Both home range size and contact with open defecation sites showed substantial variation between villages, and contact with open defecation sites was more frequent among pigs with larger home ranges and pigs living in higher density areas of their village. CONCLUSIONS: Our study builds upon prior work showing that pigs predominately roam and have contact with human feces within 50-100 m of the home, and that T. solium transmission is most likely to occur in these concentrated areas of contact. This finding, therefore, supports control strategies that target treatment resources to these areas of increased transmission. Our finding of a seasonal trend in roaming ranges may be useful for control programs relying on pig interventions, and in the field of transmission modeling, which require precise estimates of pig behavior and risk.

Evaluating Urban Taeniasis as a Threat to Cysticercosis Elimination in Northern Peru.

Reintroduction of Taenia solium into a region in Peru where it had been eliminated prompted evaluation of the possibility of reintroduction from an urban reservoir of taeniasis. In a cross-sectional study of an adjacent urban area, we found low prevalence of taeniasis (4/1,621; 0.25%), suggesting minimal risk of parasite reintroduction into rural areas through this route.

Barriers to Participation in a Community-Based Program to Control Transmission of Taenia solium in Peru.

Infection of the brain with Taenia solium larvae (neurocysticercosis) is a leading cause of preventable epilepsy worldwide. Effective and sustainable strategies to control parasite transmission in rural endemic communities are needed to prevent the disease. Surveillance and targeted intervention around infected pigs (ring control strategy) have been shown to be effective when carried out by research teams. However, this strategy has not been implemented or tested as a community-based program. In this small trial in northern Peru, eight villages were randomly assigned to community-led surveillance and treatment (five villages, 997 residents) or control (three villages, 1,192 residents). In intervention villages, community-led surveillance and reporting were promoted by community health workers, radio advertisement, and school and household education. Each suspected pig infection was verified, with confirmed cases resulting in treatment with niclosamide for taeniasis and oxfendazole for pigs in clusters of homes nearby. No incentives beyond human and pig treatment were offered. Control villages received basic disease education but no treatment intervention in response to reports. Despite 14 case reports, community-based replication of ring control strategy did not replicate prior results. After 12 months, there was no change in seroincidence in intervention villages between the baseline and study end, and no difference compared with control villages. There was no difference in prevalence of taeniasis or porcine cysticercosis at study end. Community members described lack of knowledge as the main reason for not reporting infected pigs. Further exploration of methods to transfer ring strategy and other control interventions for cysticercosis to the community is needed.

Porcine Cysticercosis: Possible Cross-Reactivity of Taenia hydatigena to GP50 Antigen in the Enzyme-Linked Immunoelectrotransfer Blot Assay.

The lentil lectin glycoprotein enzyme-linked immunoelectrotransfer blot (LLGP EITB, reported sensitivity 99% and specificity 100%) is used as a serologic marker of exposure to Taenia solium in pigs. However, only a limited number of parasites have been evaluated for cross reactivity. Pigs may host other related cestode infections, including Taenia hydatigena, which have not been formally evaluated for cross-reactions. We investigated a corral in Tumbes, Peru, a region where a cysticercosis elimination demonstration project was completed in 2012. In this corral, 14/19 (73.7%) 6-8-week-old piglets were reactive to GP50 on LLGP EITB, and all had circulating Taenia sp. antigens. From eight necropsied piglets; four were infected with T. hydatigena metacestodes whereas none had evidence of T. solium infection. Two resident dogs were subsequently confirmed to have T. hydatigena taeniasis. These results suggest GP50 cross-reactivity in T. hydatigena-infected pigs, although controlled experimental infection is needed to confirm this hypothesis.

Prevalence, Age Profile, and Associated Risk Factors for Hymenolepis nana Infection in a Large Population-Based Study in Northern Peru.

Hymenolepis nana, the dwarf tapeworm, is a common intestinal infection of children worldwide. We evaluated infection and risk factor data that were previously collected from 14,761 children aged 2-15 years during a large-scale program in northern Peru. We found that 1,124 of 14,761 children (7.61%) had H. nana infection, a likely underestimate given that only a single stool sample was examined by microscopy for diagnosis. The strongest association with infection was lack of adequate water (adjusted prevalence ratio [aPR] 2.22, 95% confidence interval [CI] 1.82-2.48) and sanitation infrastructure in the house (aPR 1.94, 95% CI 1.64-2.29). One quarter of those tested did not have a bathroom or latrine at home, which doubled their likelihood of infection. Similarly, one quarter did not have piped public water to the house, which also increased the likelihood of infection. Continued efforts to improve access to basic water and sanitation services will likely reduce the burden of infection in children for this and other intestinal infections.

Spatial relationship between Taenia solium tapeworm carriers and necropsy cyst burden in pigs.

BACKGROUND: Taenia solium, a parasite that affects humans and pigs, is the leading cause of preventable epilepsy in the developing world. Geographic hotspots of pigs testing positive for serologic markers of T. solium exposure have been observed surrounding the locations of human tapeworm carriers. This clustered pattern of seropositivity in endemic areas formed the basis for geographically targeted control interventions, which have been effective at reducing transmission. In this study, we further explore the spatial relationship between human tapeworm carriers and infected pigs using necroscopic examination as a quantitative gold-standard diagnostic to detect viable T. solium cyst infection in pigs. METHODOLOGY/PRINCIPAL FINDINGS: We performed necroscopic examinations on pigs from 7 villages in northern Peru to determine the number of viable T. solium cysts in each pig. Participating humans in the study villages were tested for T. solium tapeworm infection (i.e., taeniasis) with an ELISA coproantigen assay, and the distances from each pig to its nearest human tapeworm carrier were calculated. We assessed the relationship between proximity to a tapeworm carrier and the prevalence of light, moderate, and heavy cyst burden in pigs. The prevalence of pig infection was greatest within 50 meters of a tapeworm carrier and decreased monotonically as distance increased. Pigs living less than 50 meters from a human tapeworm carrier were 4.6 times more likely to be infected with at least one cyst than more distant pigs. Heavier cyst burdens, however, were not more strongly associated with proximity to tapeworm carriers than light cyst burdens. CONCLUSION/SIGNIFICANCE: Our study shows that human tapeworm carriers and pigs with viable T. solium cyst infection are geographically correlated in endemic areas. This finding supports control strategies that treat humans and pigs based on their proximity to other infected individuals. We did not, however, find sufficient evidence that heavier cyst burdens in pigs would serve as improved targets for geographically focused control interventions.

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

BACKGROUND: Taenia 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 FINDINGS: In 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/SIGNIFICANCE: These 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.