Pilot Field Trial of the EG95 Vaccine Against Ovine Cystic Echinococcosis in Rio Negro, Argentina: Second Study of Impact.

BACKGROUND: Cystic echinococcosis (CE) is an important zoonotic disease caused by the cestode parasite Echinococcus granulosus. It occurs in many parts of the world where pastoral activities predominate, including the Rio Negro province of Argentina. Although CE control activities have been undertaken in the western regions of Rio Negro for more than two decades, the disease continues to remain prevalent in both the human and livestock animal populations. Vaccination of animal intermediate hosts of CE with the EG95 vaccine may provide a new opportunity to improve the effectiveness of CE control measures, although data are lacking about field application of the vaccine. AIMS: Evaluate the impact of EG95 vaccination in sheep on the transmission of Echinococcus granulosus in a field environment. METHODOLOGY: Two trial sites were established in western Rio Negro province within indigenous communities. Vaccination of lambs born into one trial site was introduced and continued for 6 years. Prior to initiation of the trial, and at the end of the trial, the prevalence of CE in sheep was determined by necropsy. Weaned lambs received two injections of EG95 vaccine, approximately one month apart, and a single booster injection one year later. Vaccination was not implemented at the second trial site. A total of 2725 animals were vaccinated in the first year. Animals from this cohort as well as age-matched sheep from the control area were evaluated by necropsy. KEY RESULTS: Introduction of the vaccine led to a statistically significant in the number and size of hydatid cysts in comparison to the situation prior to the introduction of the vaccine, or compared to CE prevalence in the control area where the vaccine was not applied. The prevalence of infection in the vaccinated area was also significantly reduced by 62% compared to the re-intervention level, being lower than the prevalence seen in the control area, although the difference from the control area after the intervention was not significant possibly due to limitations in the numbers of animals available for necropsy. CONCLUSIONS: Vaccination of sheep with the EG95 vaccine provides a valuable new tool which improves the effectiveness of CE control activities. Vaccination was effective even in a difficult, remote environment where only approximately half the lambs born into the communities were fully vaccinated.

Humoral response and evolution of Echinococcus infection in experimentally infected sheep.

There is little information on the humoral response of sheep experimentally infected with Echinococcus granulosus. Thus, the objective of this study was to evaluate this response and measure its evolution. Doses of 10, 100, 1000 and 10000 E. granulosus eggs were prepared and inoculated via intraruminal puncture. Blood samples were obtained before inoculation and every 48 h after inoculation, until they became seropositive. Thereafter, they were taken monthly for the first year and then every three months until 1700 days of observation had been completed. An ELISA test, with total hydatid fluid antigen, was used for immunodiagnosis. The average optical density of the 12 inoculated sheep was found to be above the mean cutoff value 10 days after inoculation, went on increasing until 180 days after inoculation and remained above the cutoff level until the end of the observation period. This confirms that the antibody response of sheep to E. granulosus infection occurs before production of hydatid fluid and that activation, mobilization and establishment of oncospheres in the tissues generates a persistent response from the host's immune system.

Humoral response and evolution of Echinococcus infection in experimentally infected sheep / Resposta humoral e evolução à infecção por Echinococcus em ovinos experimentalmente infectados

There is little information on the humoral response of sheep experimentally infected with Echinococcus granulosus. Thus, the objective of this study was to evaluate this response and measure its evolution. Doses of 10, 100, 1000 and 10000 E. granulosus eggs were prepared and inoculated via intraruminal puncture. Blood samples were obtained before inoculation and every 48 h after inoculation, until they became seropositive. Thereafter, they were taken monthly for the first year and then every three months until 1700 days of observation had been completed. An ELISA test, with total hydatid fluid antigen, was used for immunodiagnosis. The average optical density of the 12 inoculated sheep was found to be above the mean cutoff value 10 days after inoculation, went on increasing until 180 days after inoculation and remained above the cutoff level until the end of the observation period. This confirms that the antibody response of sheep to E. granulosus infection occurs before production of hydatid fluid and that activation, mobilization and establishment of oncospheres in the tissues generates a persistent response from the host's immune system.

Existe pouca informação sobre a resposta imune humoral de ovinos experimentalmente infectados por Echinococcus granulosus. O objetivo deste estudo é avaliar a resposta imune por anticorpos em ovinos infectados. Os ovinos receberam doses de 10, 100, 1.000 e 10.000 ovos de E. granulosus por via intrarruminal. Amostras de sangue foram colhidas antes e após infecção, a cada 48 horas, até a detecção de anticorpos anti-E. granulosus e após, colheram-se amostras mensal e trimestralmente, no primeiro ano até 1.700 dias de infecção. No imunodiagnóstico, utilizou-se o ensaio imunoenzimático indireto (ELISA-teste) e como antígeno total, líquido hidático. Na detecção de anticorpos anti-E. granulosus no soro das 12 ovelhas, a densidade ótica esteve acima do ponto de corte, após 10 dias de infecção, aumentando até 180 dias pós-infecção, e permanecendo acima desses dias até o final do experimento. Isso confirma que a resposta por anticorpos em ovinos infectados por E. granulosus antecede a produção de líquido hidático, e que a ativação, mobilidade e permanência das oncosferas nos tecidos possibilita a resposta imune dos hospedeiros.

Pilot field trial of the EG95 vaccine against ovine cystic echinococcosis in Rio Negro, Argentina: early impact and preliminary data.

Cystic echinococcosis is endemic in the Rio Negro province of Argentina. After 30 years of control using praziquantel in dogs the transmission rate to humans and sheep has decreased significantly, however transmission persists. The objective of the study is to assess the impact of the inclusion of the EG95 vaccine for sheep in the control programme, including analysis of the vaccine's operative feasibility in field conditions. The vaccine was applied in an area comprising four communities of native people including 79 farms with 3146 lambs and 311 dogs in total. Seventy one farms were designated as control areas where no vaccinations were undertaken while vaccinations of lambs undertaken on 91 farms. Lambs received two vaccinations with the EG95 vaccine followed by a single booster injection when the animals were 1-1.5 years of age. Farm locations were defined using GPS coordinates for the houses. Evidence for Echinococcus granulosus transmission was monitored by coproantigen ELISA on samples of dog faeces, by E. granulosus-specific PCR using soil samples, and anti-E. granulosus antibody assessments in sera from 2 to 4 teeth lambs, purgation of dogs to detect E. granulosus worms and necropsy on adult sheep. Before the vaccine was introduced, 26.2% of sheep with 2-4 teeth were positive using ELISA/WB, the prevalence decreased to 7.8% at the third year following use of the vaccine. Necropsy of animals older than 6 years (not vaccinated) showed that 66.1% of animals were infected with E. granulosus. In dogs, 4% was found positive for E. granulosus using arecoline purgation and 24.7% of the farms were infected using coproELISA/WB. During the first year of vaccination 2721 lambs received the first vaccine dose and 2448 received a booster. In the second year 2138 lambs were initially vaccinated and 1745 received a booster, and 1308 animals received the third dose. During the third year 1110 lambs received the first dose from which 539 received a booster and 723 animals received the third dose. An analysis of advantages and limitations of the diagnostic techniques used and the ability of the geospatial analysis to detect risk area are included. Based in the immunodiagnostic techniques, the EG95 vaccine has been able to prevent the infection in animals up to 3 years old. Also, the difficulties in the field for the correct vaccine administration and the social features and habits that may impact on echinococcosis control are included in the analysis.

Hydatidosis in the province of La Pampa, Argentina, 1998

Echinococcus granulosus es el agente causal de la hidatidosis clásica o equinococcosis quística. En América del Sur el ciclo más extendido es el que involucra al perro y la oveja al existir condiciones ideales para la existencia del parásito. En la Provincia de la La Pampa mantiene una presencia endémica con notificación de casos de infección humana y perros infectados con E. granulosus. En el presente trabajo se evalúa la prevalencia y distribución en el Departamento Maracó, Provincia de La Pampa. Perros de 36 establecimientos ganaderos fueron evaluados con bromhidrato de arecolina a la dosis de 3,5 mg/kg. En 27 establecimientos se detectó Taenia sp. y en tres E. granulosus. Se tomaron muestras de sangre de todos los habitantes de los establecimientos ganaderos las que fueron procesadas por enzmoinmunoensayo (ELISA). Asimismo, se efectuó un estudio retrospectivo sobre casos de hidatidosis tratados en el hospital General Pico y dos clínicas privadas. Once casos humanos fueron tratados en período 96/97 (tasa de incidencia 6,79 x 100000). La Provincia de La Pampa parece mantener una presencia endémica con notificación de casos y perros infectados. A consecuencia de ello es de interés sanitario ampliar las investigaciones a otros departamentos provinciales a los efectos de delimitar el área endémica de distribución y organizar sistemas de vigilancia epidemiológica de la enfermedad

Hidatidosis/equinococosis en el área de General Acha, provincia de La Pampa de Argentina / Hydatidosis/echinococosis in General Acha area, La Pampa province, Argentina

Hydatidosis situation in the General Acha area (La Pampa province) is described herein. The work comprises a retrospective compilacion of new hydatidosis in human population, and investigation on dog echinococosis granulosus infection prevalence carried out on the basis of arecoline bromhydrate application. Sicteen human cases were detected during 1994 (incidence rate: 26,7/100,000) founding a serological prevalence of 1,3 percent. Studies on dog echinococosis have shown a prevalence rate of 2,3 percent. The epidemiological situation of hydatidosis is analyzed by comparison with values from other endemic areas. These results suggest the necessity of completing surveys in the whole provincial territory, and the implementation of educational and sanitary measures aimed to controlling this zoonosis.