Elimination of Taenia solium Transmission in Northern Peru / Eliminación de la transmisión de Taenia solium en el norte del Perú

Background: Taeniasis and cysticercosis are major causes of seizures and epilepsy. Infection by the causative parasite Taenia solium requires transmission between humans and pigs. The disease is considered to be eradicable, but data on attempts at regional elimination are lacking. We conducted a three-phase control program in Tumbes, Peru, to determine whether regional elimination would be feasible. Methods: We systematically tested and compared elimination strategies to show the feasibility of interrupting the transmission of T. solium infection in a region of highly endemic disease in Peru. In phase 1, we assessed the effectiveness and feasibility of six intervention strategies that involved screening of humans and pigs, antiparasitic treatment, prevention education, and pig replacement in 42 villages. In phase 2, we compared mass treatment with mass screening (each either with or without vaccination of pigs) in 17 villages. In phase 3, we implemented the final strategy of mass treatment of humans along with the mass treatment and vaccination of pigs in the entire rural region of Tumbes (107 villages comprising 81,170 people and 55,638 pigs). The effect of the intervention was measured after phases 2 and 3 with the use of detailed necropsy to detect pigs with live, nondegenerated cysts capable of causing new infection. The necropsy sampling was weighted in that we preferentially included more samples from seropositive pigs than from seronegative pigs. Results: Only two of the strategies implemented in phase 1 resulted in limited control over the transmission of T. solium infection, which highlighted the need to intensify the subsequent strategies. After the strategies in phase 2 were implemented, no cyst that was capable of further transmission of T. solium infection was found among 658 sampled pigs. One year later, without further intervention, 7 of 310 sampled pigs had live, nondegenerated cysts, but no infected pig was found in 11 of 17 villages, including all the villages in which mass antiparasitic treatment plus vaccination was implemented. After the final strategy was implemented in phase 3, a total of 3 of 342 pigs had live, nondegenerated cysts, but no infected pig was found in 105 of 107 villages. Conclusions: We showed that the transmission of T. solium infection was interrupted on a regional scale in a highly endemic region in Peru. (Funded by the Bill and Melinda Gates Foundation and others).

Introducción: La teniasis y la cisticercosis son causas importantes de convulsiones y epilepsia. La infección por el parásito causal Taenia solium requiere la transmisión entre humanos y cerdos. La enfermedad se considera erradicable, pero faltan datos sobre los intentos de eliminación regional. Llevamos a cabo un programa de control de tres fases en Tumbes, Perú, para determinar si sería factible la eliminación regional. Métodos: Probamos y comparamos sistemáticamente las estrategias de eliminación para demostrar la viabilidad de interrumpir la transmisión de la infección por T. solium en una región de enfermedad altamente endémica en Perú. En la fase 1, evaluamos la eficacia y viabilidad de seis estrategias de intervención que incluyeron detección de humanos y cerdos, tratamiento antiparasitario, educación preventiva y reemplazo de cerdos en 42 aldeas. En la fase 2, comparamos el tratamiento masivo con la detección masiva (cada una con o sin vacunación de cerdos) en 17 aldeas. En la fase 3, implementamos la estrategia final de tratamiento masivo de humanos junto con el tratamiento masivo y vacunación de cerdos en toda la región rural de Tumbes (107 aldeas que comprenden 81.170 personas y 55.638 cerdos). El efecto de la intervención se midió después de las fases 2 y 3 con el uso de necropsia detallada para detectar cerdos con quistes vivos, no degenerados capaces de causar una nueva infección. El muestreo de necropsia fue ponderado de manera que incluimos preferentemente más muestras de cerdos seropositivos que de cerdos seronegativos. Resultados: Sólo dos de las estrategias implementadas en la fase 1 dieron como resultado un control limitado sobre la transmisión de la infección por T. solium, lo que destacó la necesidad de intensificar las estrategias posteriores. Después de que se implementaron las estrategias en la fase 2, no se encontró ningún quiste capaz de transmitir más la infección por T. solium entre los 658 cerdos muestreados. Un año después, sin más intervenciones, 7 de los 310 cerdos muestreados tenían quistes vivos, no degenerados, pero no se encontró ningún cerdo infectado en 11 de las 17 aldeas, incluidas todas las aldeas en las que se implementó el tratamiento antiparasitario masivo más la vacunación. Después de que se implementó la estrategia final en la fase 3, un total de 3 de 342 cerdos tenían quistes vivos, no degenerados, pero no se encontró ningún cerdo infectado en 105 de las 107 aldeas. Conclusiones: Demostramos que la transmisión de la infección por T. solium se interrumpió a escala regional en una región altamente endémica del Perú. (Financiado por la Fundación Bill y Melinda Gates y otros).

Cysticercosis/taeniasis: recent advances in serological and molecular diagnoses.

Serodiagnosis by immunoblot, using recombinant chimeric T. solium antigen and native glycoprotein antigens, has been applied for neurocysticercosis cases. Specific antibodies against both antigens were detected in serum samples from NCC patients involving multiple cysts in the brain, whereas it was not always easy to detect specific antibodies in NCC cases with a solitary cyst or calcified lesion(s). On the other hand, the diagnosis for human taeniasis or worm carriers has been routinely performed by stool examination. In this study, multiplex PCR has been established to differentiate taeniasis using Taenia mitochondrial DNA in fecal samples from worm carriers. Furthermore, the molecular identification of human taeniid cestodes by base excision sequence scanning thymine-base analysis has also been introduced. This method provides four thymine-base peak profiles unique for Asian and American/African genotypes of T. solium, T. saginata and T. asiatica. By comparing thymine base peak profiles, it is possible to differentiate human taeniid cestodes without DNA sequencing. The approaches are powerful tools for the routine diagnosis of taeniasis and the molecular identification of taeniid cestodes.

Recent advances in basic and applied science for the control of taeniasis/cysticercosis in Asia.

Detection of seven specific bands by immunoblot (IB) using glycoproteins (GPs) purified by lentil-lectin affinity chromatography has been the gold-standard for neurocysticercosis (NCC) serodiagnosis since 1989. However, due to the presence of contaminants, it was impossible to apply the GPs to ELISA. Our group at Asahikawa Medical College (AMC) succeeded in purifying the GPs by preparative isoelectric focusing; these higher quality GPs were suitable for ELISA. Based on the results of both IB and ELISA testing, developed at AMC for a field survey in Irian Jaya, it became evident that that area had pandemic NCC. We found many NCC patients, pigs full of cysts, and one dog infected with two cysts: these findings were based on serology. Recently, we conducted another survey to detect of the worm carriers of T. solium. Three of the 38 local people were positive by copro-antigen specific to Taenia species; these three patients expelled segments of Taenia spp and these were confirmed as those of T. solium by mitochondrial DNA analysis. When viable eggs of any taeniid species could be obtained, they can be developed into metacestodes in NOD-scid mice; it then becomes possible to analyze morphological dynamics, metacestode antigenicity, the efficacy of new metacestocidal drugs, and mitochondrial DNA. Mitochondrial DNA analysis of the specimens obtained in Irian Jaya was compared with that of other isolates worldwide. T. solium is now divided into two genotypes: the Asian type, and the Africa-American type. Some aspects of the pathological differences between the Asian and Africa-American types and the antigenic components of these two types are discussed.